U.S. patent number RE42,865 [Application Number 11/802,914] was granted by the patent office on 2011-10-25 for image forming system employing effective optical scan-line control device.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Taku Amada, Satoru Itoh, Naoki Miyatake, Kazuyuki Shimada, Mitsuo Suzuki, Seizo Suzuki.
United States Patent |
RE42,865 |
Suzuki , et al. |
October 25, 2011 |
Image forming system employing effective optical scan-line control
device
Abstract
An optical scanning characteristic control method is applied to
an optical scanning system in which a beam is deflected, and the
deflected beam is converged and directed toward a scanning surface,
so that optical scanning of the scanning surface is performed by an
optical spot formed thereon by the deflected beam. The method
comprising the steps of a) disposing a beam deflection control
device on the light path of the beam before it is incident on the
scanning surface; and b) controlling a beam deflection amount of
the beam deflecting device provide to an incident beam so as to
control a scanning characteristic of the optical scanning.
Inventors: |
Suzuki; Mitsuo (Kanagawa,
JP), Miyatake; Naoki (Kanagawa, JP), Amada;
Taku (Kanagawa, JP), Suzuki; Seizo (Kanagawa,
JP), Shimada; Kazuyuki (Tokyo, JP), Itoh;
Satoru (Kanagawa, JP) |
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
|
Family
ID: |
27739413 |
Appl.
No.: |
11/802,914 |
Filed: |
May 25, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
10347746 |
Jan 22, 2003 |
7050082 |
May 23, 2006 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Jan 23, 2002 [JP] |
|
|
2002-014255 |
Jan 24, 2002 [JP] |
|
|
2002-015647 |
Feb 14, 2002 [JP] |
|
|
2002-036825 |
Apr 30, 2002 [JP] |
|
|
2002-128011 |
Dec 2, 2002 [JP] |
|
|
2002-350285 |
|
Current U.S.
Class: |
347/241; 347/256;
349/2 |
Current CPC
Class: |
G02B
26/127 (20130101); B41J 2/473 (20130101) |
Current International
Class: |
B41J
15/14 (20060101); B41J 27/00 (20060101); G02F
1/13 (20060101) |
Field of
Search: |
;347/118,129,116,229,248-250,233-235,241-244,256-261,239,255
;349/1-4,16,66,193-197 ;359/226.3,254-259,272 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
63-240533 |
|
Oct 1988 |
|
JP |
|
01-105905 |
|
Apr 1989 |
|
JP |
|
01-232322 |
|
Sep 1989 |
|
JP |
|
01-284871 |
|
Nov 1989 |
|
JP |
|
3-42116 |
|
Apr 1991 |
|
JP |
|
04-196869 |
|
Jul 1992 |
|
JP |
|
07-128603 |
|
May 1995 |
|
JP |
|
07-181441 |
|
Jul 1995 |
|
JP |
|
7-218856 |
|
Aug 1995 |
|
JP |
|
7-234612 |
|
Sep 1995 |
|
JP |
|
07-261204 |
|
Oct 1995 |
|
JP |
|
8-313941 |
|
Nov 1996 |
|
JP |
|
09-033846 |
|
Feb 1997 |
|
JP |
|
10-213940 |
|
Aug 1998 |
|
JP |
|
10-268217 |
|
Oct 1998 |
|
JP |
|
11-002766 |
|
Jan 1999 |
|
JP |
|
2000-003110 |
|
Jan 2000 |
|
JP |
|
2000003110 |
|
Jan 2000 |
|
JP |
|
2001-030537 |
|
Feb 2001 |
|
JP |
|
2001-091879 |
|
Apr 2001 |
|
JP |
|
2001-133718 |
|
May 2001 |
|
JP |
|
2001-183592 |
|
Jul 2001 |
|
JP |
|
2001-194613 |
|
Jul 2001 |
|
JP |
|
2001-328294 |
|
Nov 2001 |
|
JP |
|
2001-356314 |
|
Dec 2001 |
|
JP |
|
2001356314 |
|
Dec 2001 |
|
JP |
|
3262490 |
|
Mar 2002 |
|
JP |
|
Other References
US. Appl. No. 10/347,746, filed Jan. 2003, Suzuki, et al. cited by
other .
U.S. Appl. No. 10/735,690, filed Dec. 2003, Suhara. cited by other
.
U.S. Appl. No. 12/051,404, filed Mar. 19, 2008, Amada, et al. cited
by other .
U.S. Appl. No. 90/008,383, filed Dec. 19, 2006, Suzuki, et al.
cited by other .
U.S. Appl. No. 11/612,750, filed Dec. 19, 2006, Imai, et al. cited
by other .
U.S. Appl. No. 09/955,181, filed Sep. 19, 2001, Suzuki et al.,
Pending. cited by other .
U.S. Appl. No. 09/633,867, filed Aug. 7, 2000, Suzuki et al. cited
by other .
U.S. Appl. No. 09/678,611, filed Oct. 4, 2000, Sakai et al.,
Pending. cited by other .
U.S. Appl. No. 09/716,949, filed Nov. 22, 2000, Atsuumi et al.,
Pending. cited by other .
U.S. Appl. No. 09/788,415, filed Feb. 21, 2001, Sakai et al., U.S.
6,596,985. cited by other .
U.S. Appl. No. 09/816,378, filed Mar. 26, 2001, Suzuki et al., U.S.
6,657,761. cited by other .
U.S. Appl. No. 09/833,821, filed Apr. 13, 2001, Nakajima et al.,
U.S. 6,621,512. cited by other .
U.S. Appl. No. 09/984,236, filed Oct. 29, 2001, Masuda et al., U.S.
6,686,946. cited by other .
U.S. Appl. No. 09/982,831, filed Oct. 22, 2001, Hayashi et al.,
Pending. cited by other .
U.S. Appl. No. 10/047,698, filed Jan. 18, 2002, Suzuki, Pending.
cited by other .
U.S. Appl. No. 10/090,824, filed Mar. 6, 2002, Amada et al.,
Pending. cited by other .
U.S. Appl. No. 10/096,250, filed Mar. 13, 2002, Itami et al.,
Pending. cited by other .
U.S. Appl. No. 10/143,013, filed May 13, 2002, Suhara et al.,
Pending. cited by other .
U.S. Appl. No. 10/161,659, filed Jun. 5, 2002, Suzuki et al.,
Pending. cited by other .
U.S. Appl. No. 10/161,756, filed Jun. 5, 2002, Atsuumi et al.,
Pending. cited by other .
U.S. Appl. No. 10/139,325, filed May 7, 2002, Miyatake, Pending.
cited by other .
U.S. Appl. No. 10/207,241, filed Jul. 30, 2002, Suzuki et al.,
Pending. cited by other .
U.S. Appl. No. 10/200,778, filed Jul. 24, 2002, Amada et al.,
Pending. cited by other .
U.S. Appl. No. 10/226,344, filed Aug. 23, 2002, Suzuki et al.,
Pending. cited by other .
U.S. Appl. No. 10/665,287, filed Sep. 22, 2003, Kubo, Pending.
cited by other .
U.S. Appl. No. 10/635,520, filed Aug. 7, 2003, Sakai et al.,
Pending. cited by other .
U.S. Appl. No. 10/347,746, filed Jan. 22, 2003, Suzuki et al. cited
by other .
U.S. Appl. No. 10/852,183, filed May 25, 2004, Miyatake et al.
cited by other .
U.S. Appl. No. 10/804,369, filed May 7, 2004, Itabashi et al. cited
by other .
U.S. Appl. No. 10/820,733, filed Apr. 9, 2004, Suhara et al. cited
by other .
U.S. Appl. No. 10/892,191, filed Jul. 16, 2004, Suzuki et al. cited
by other .
U.S. Appl. No. 10/942,907, filed Sep 17, 2004, Miyatake et al.
cited by other .
U.S. Appl. No. 11/032,257, filed Jan. 11, 2005, Amada et al. cited
by other.
|
Primary Examiner: Pham; Hai C
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, L.L.P.
Claims
What is claimed is:
.[.1. An optical scanning characteristic control method applied to
an optical scanning system in which a beam is deflected, and the
deflected beam is converged and directed toward a scanning surface,
so that optical scanning of the scanning surface is performed by an
optical spot formed thereon by the deflected beam, said method
comprising the steps: a) disposing a beam deflection control device
on the light path of the beam before it is incident on the scanning
surface, said beam deflection control device configured to cause an
electric field distribution in a liquid crystal by applying
electricity to an electrode formed on a side of a glass substrate;
and b) controlling a beam deflection amount of the beam deflecting
device provided to an incident beam so as to control a scanning
characteristic of the optical scanning, wherein at least one
resinous image-formation optical device is disposed in the optical
scanning system; the beam deflection control device comprises
deflection areas configured by a series of a plurality, of
deflection devices defined in a main scanning direction, and the
control of the scanning characteristic of the optical scanning is
carried out individually for each of a plurality of ranges divided
in the main scanning direction..].
.[.2. The method as claimed in claim 1, wherein: said beam
deflection control device comprises a liquid crystal device by
which refractive index thereof can be controlled electrically, and
thus, the direction of the incident beam can be changed
accordingly, and laser beams corresponding to a plurality of colors
have at least a single scanning image-formation device to pass
through..].
.[.3. The method as claimed in claim 1, wherein: said beam
deflection control device comprises a plurality of beam deflection
control units, arranged in a main scanning direction, each having a
function of providing a deflection amount to the incident beam in a
subscanning direction; said beam deflection control device is
disposed between a beam deflecting device and the scanning surface;
the deflection amount in the subscanning direction of each beam
deflection control unit is controlled for each scanning action so
that scan line bending is corrected, and laser beams corresponding
to a plurality of colors have at least a single scanning
image-formation device to pass through..].
.[.4. The method as claimed in claim 1, wherein: said beam
deflection control device comprises a plurality of beam deflection
control units, arranged in a main scanning direction, each having a
function of providing a deflection amount to the incident beam in
the main scanning direction; said beam deflection control device is
disposed between a beam deflecting device and the scanning surface;
the deflection amount in the main scanning direction of each beam
deflection control unit is controlled for each scanning action so
that a uniform velocity characteristic is corrected, and laser
beams corresponding to a plurality of colors have at east a single
scanning image-formation device to pass through..].
5. An optical scanning device in which a beam is deflected, and the
deflected beam is converged and directed toward a scanning surface,
so that optical scanning of the scanning surface is performed by an
optical spot formed thereon by the deflected beam, said device
comprising: a beam deflection control device disposed on the light
path of the beam before it is incident on the scanning surface,
said beam deflection control device configured to cause an electric
field distribution in a liquid crystal by applying electricity to
an electrode formed on a side of a glass substrate, wherein a beam
deflection amount of the beam .[.deflecting.]. .Iadd.deflection
control .Iaddend.device provided to an incident beam is controlled
so that a scanning characteristic of the optical scanning is
controlled, at least one resinous image-formation optical device is
disposed in the optical scanning system, the beam deflection
control device comprises deflection areas configured by a series of
a plurality of deflection devices defined in a main scanning
direction, and the beam deflection control device has liquid
crystal deflection areas separated in a subscanning direction for
respective laser beams corresponding to a plurality of colors, and
the liquid crystal deflection areas are configured by a single
laser beam transmitting member.
6. The optical scanning device as claimed in claim 5, wherein: said
beam deflection control device comprises a liquid crystal device by
which a refractive index thereof can be controlled electrically,
and thus, the direction of the incident beam can be changed
accordingly.
7. The optical scanning device as claimed in claim 5, wherein: said
beam deflection control device comprises a plurality of beam
deflection control units, arranged in a main scanning direction,
each having a function of providing a deflection amount to the
incident beam in a subscanning direction; said beam deflection
control device is disposed between a beam deflecting device and the
scanning surface; and the deflection amount in the subscanning
direction of each beam deflection control unit is controlled for
each scanning action so that scan line bending is corrected.
8. The optical scanning device as claimed in claim 5, wherein: said
beam deflection control device comprises a plurality of beam
deflection control units, arranged in a main scanning direction,
each having a function of providing a deflection amount to the
incident beam in the main scanning direction; said beam deflection
control device is disposed between a beam deflecting device and the
scanning surface; and the deflection amount in the main scanning
direction of each beam deflection control unit is controlled for
each scanning action so that a uniform velocity characteristic is
corrected.
9. The optical scanning device as claimed in claim 5, further
comprising a beam separating device separating a part of the beam
before it is incident on the scanning surface, wherein: said beam
separating device directs the thus-separated beam part toward a
detection surface which is optically equivalent to the scanning
surface, and then, a scan line bending state on said detection
surface, which is equivalent to the scan line bending occurring on
the scanning surface, is detected.
10. The optical scanning device as claimed in claim 9, wherein:
said beam separating device comprises said beam deflection control
device, wherein: a beam reflected by said beam deflection control
device is directed toward said detection surface.
11. The optical scanning device as claimed in claim 9, further
comprising a scanning position detection device which detects the
position of scanning line on said detection surface, wherein: said
scanning position detection device comprises a number of optical
sensors, which number is the same as the number of the beam
deflection control units included in said beam deflection control
device, said number of optical sensors being disposed at positions
corresponding to the positions of the respective beam deflection
control units and detecting the subscanning-directional positions
of the optical spots.
12. The optical scanning device as claimed in claim 5 comprising a
multi-beam-type optical scanning device in which a light source
device emits a plurality of beams and the scanning surface is
scanned by the plurality of beams simultaneously.
13. The optical scanning device as claimed in claim 5, wherein: a
plurality of light sources are provided; and a scanning optical
system defining a light path from each light source toward the
respective scanning surface is configured so that a scan line drawn
by an optical spot formed by the beam coming from each light source
is substantially parallel to each other.
14. The optical scanning device as claimed in claim 13, wherein:
the beam deflection control device is provided for each light
source.
15. The optical scanning device as claimed in claim 13, wherein:
the number of light sources is 3 or 4, and the beam emitted from
each light source is modulated by image information for forming an
image in a respective one of color components which thus form a
color image in combination.
16. An image formation device which performs image formation by
performing optical scanning of photosensitive bodies, comprising
the optical scanning device claimed in claim 15; wherein: three or
four photoconductive photosensitive bodies which provide the
scanning surfaces to be optically scanned by the beams from the
respective light sources are disposed in mutually parallel.
17. The optical scanning device as claimed in claim 5, wherein: a
plurality of light sources are provided, and scanning optical
systems defining light paths from the respective light sources
toward the respective scanning surfaces are mutually equivalent;
and one of the scanning optical systems is regarded as a reference,
and. the beam deflection control device is provided on the light
path in each of the other scanning optical systems, is used for
correcting the scanning characteristic of each of the other
scanning optical systems for the scanning characteristic of the
reference scanning optical system.
18. The optical scanning device as claimed in claim 17, wherein:
the number of light sources is 3 or 4, and the beam emitted from
each light source is modulated by image information for forming an
image in a respective one of color components which thus form a
color image in combination.
19. An image formation device which performs image formation by
performing optical scanning of photosensitive bodies, comprising
the optical scanning device claimed in claim 18; wherein: three of
four photoconductive photosensitive bodies which provide the
scanning surfaces to be optically scanned by the beams from the
respective light sources are disposed in mutually parallel.
20. An image formation device which performs image formation by
performing optical scanning of a photosensitive medium, comprising
the optical scanning device claimed in claim 5.
21. The image formation device as claimed in claim 20, wherein said
photosensitive medium comprises a photosensitive body having a
photoconductivity.
22. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
said device comprising: a beam deflection control device disposed
on the light path of the beam before it is incident on the scanning
surface, wherein a beam deflection amount of the beam
.[.deflecting.]. .Iadd.deflection control .Iaddend.device provided
to an incident beam is controlled so that a scanning characteristic
of the optical scanning is controlled; a beam separating device
separating a part of the beam before it is incident on the scanning
surface, wherein said beam separating device directs the
thus-separated beam part toward a detection surface which is
optically equivalent to the scanning surface, and then, a scan line
bending state on said detection surface, which is equivalent to the
scan line bending occurring on the scanning surface, is detected; a
scanning position detection device which detects the position of
scanning line on said detection surface, wherein said scanning
position detection device comprises a number of optical sensors,
which number is the same as the number of the beam deflection
control units included in said beam deflection control device, said
number of optical sensors being disposed at positions corresponding
to the positions of the respective beam deflection control units
and detecting the subscanning-directional positions of the optical
spots, wherein a supporting member supporting the number of optical
sensors is made of a material having a thermal expansion
coefficient of not more than 1.0.times.10.sup.-5/.degree. C.
23. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
said device comprising: a beam deflection control device disposed
on the light path of the beam before it is incident on the scanning
surface, wherein a beam deflection amount of the beam
.[.deflecting.]. .Iadd.deflection control .Iaddend.device provided
to an incident beam is controlled so that a scanning characteristic
of the optical scanning is controlled, a plurality of light sources
are provided, and scanning optical systems defining light paths
from the respective light sources toward the respective scanning
surfaces are mutually equivalent; one of the scanning optical
systems is regarded as a reference, and, the beam deflection
control device is provided on the light path in each of the other
scanning optical systems, is used for correcting the scanning
characteristic of each of the other scanning optical systems for
the scanning characteristic of the reference scanning optical
system, and a transparent member is provided on the light path of
the reference scanning optical system for the purpose of correcting
the difference in light path length caused by the existence of the
beam deflection control device provided on the light path of each
of the other scanning optical systems.
.[.24. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
said device comprising: a beam deflection control device disposed
on the light path of the beam before it is incident on the scanning
surface, said beam deflection control device configured to cause an
electric field distribution in a liquid crystal by applying
electricity to an electrode formed on a side of a glass substrate,
wherein a beam deflection amount of the beam deflecting device
provided to an incident beam is controlled so that a scanning
characteristic of the optical scanning is controlled, a plurality
of light sources are provided, and scanning optical systems
defining light paths from the respective light sources toward the
respective scanning surfaces are mutually equivalent; one of the
scanning optical systems is regarded as a reference, and, the beam
deflection control device is provided on the light path in each of
the other scanning optical systems, is used for correcting the
scanning characteristic of each of the other scanning optical
systems for the scanning characteristic of the reference scanning
optical system, and each of the scanning optical systems comprises
a lens system, and the lens system of the reference scanning
optical system is made of a material having a thermal expansion
coefficient of not more than 1.0.times.10.sup.-5/.degree. C..].
.[.25. An optical scanning device in which a plurality of beams for
respective color components for forming a color image in
combination are deflected, are converged by a scanning and
image-formation optical system, are directed to respective scanning
surfaces individually and thus performing optical scanning of the
scanning surfaces respectively, so as to write images of respective
color components, comprising: a scan line correcting device which
corrects a scan line bending, wherein: a scan line bending on the
beam of one color component is regarded as a reference scan line
bending; the scan line correcting device electronically corrects a
scan line bending of the beam of each of the other color components
for the reference scan line bending; at least one resinous
image-formation optical device is disposed in the optical scanning
system; the scan line correcting device comprises deflection areas
configured by a series of a plurality of deflection devices defined
in a main scanning direction, laser beams corresponding to a
plurality of colors have at least a single scanning image-formation
device to pass through; and the control of a scanning
characteristic of the optical scanning is carried out individually
for each of a plurality of ranges divided in the main scanning
direction..].
.[.26. The optical scanning device as claimed in claim 25, wherein:
one of the color components is black; and the scan line bending of
the beam of black is regarded as the reference scan line
bending..].
.[.27. The optical scanning device as claimed in claim 25, wherein:
said scan line correcting device comprises liquid crystal
deflection devices each controllable individually arranged in a
main scanning direction, is disposed on the light path of the
deflected beam for which the scan line bending is to be corrected;
and according to the optical scanning action, a deflection amount
provided to the beam is controlled in a subscanning direction for
each liquid crystal deflection device..].
.[.28. The optical scanning device as claimed in claim 27, wherein:
the scan line correcting device is configured in a manner such that
the liquid crystal deflection devices thereof are combined together
integrally for each deflected beam..].
.[.29. The optical scanning device as claimed in claim 25, wherein:
the plurality of beams corresponding to the respective color
components pass through at least one optical device in common of
the scanning and image-formation optical system..].
.[.30. An image formation device for forming a color image from
respective color-component images formed on respective scanning
surfaces as a result of optical scanning thereof with beams of
respective color components, comprising: the optical scanning
device according to claim 25 which performs optical scanning of the
respective scanning surfaces..].
.[.31. The image formation device as claimed in claim 30, wherein:
after starting a series of image formation processes, the scan line
bending correction is performed by the scan line correcting device
at least once during the thus-started series of processes..].
.[.32. An image formation device for forming a color image from
respective color-component images formed on respective scanning
surfaces as a result of optical scanning thereof with beams of
respective color components, comprising: the optical scanning
device according to claim 25 which performs optical scanning of the
respective scanning surfaces, wherein after starting a series of
image formation processes, the scan line bending correction is
performed by the scan line correcting device at least once during
the thus-started series of processes, the correction operation
performed by the scan line correcting device can be performed
within an interval between successive sheets of paper on which
color images are formed; and the following requirements be
satisfied: T.sub.A<0.8.times.(D/Y) where: T.sub.A denotes a
required control time for the scan line correction operation; D
denotes a distance between adjacent sheets; and V denotes a speed
of each sheet being conveyed during the process..].
.[.33. An image formation device for forming a color image from
respective color-component images formed on respective scanning
surfaces as a result of optical scanning thereof with beams of
respective color components, comprising: the optical scanning
device according to claim 25 which performs optical scanning of the
respective scanning surfaces, wherein a scan line deviation
detecting device is provided for detecting a difference between the
scan lines for the respective color components; the scan line
correcting device performs scan line correction based on the
detection result of the scan line deviation detecting device; and
the following requirements be satisfied: Ts<10.times.(L/V)
where: Ts denotes a time required for the scan line deviation
detection operation by said scan line deviation detecting device; L
denotes a length of sheet-shaped recording medium in a direction in
which it is conveyed in the image formation process on which a
color image is formed; and V denotes a speed of the sheet-shaped
recording medium being conveyed in the image formation
process..].
.[.34. An optical scanning control method applied to an optical
scanning system in which a beam is deflected, and the deflected
beam is converged and directed toward a scanning surface, so that
optical scanning of the scanning surface is performed by an optical
spot formed thereon by the deflected beam, said method comprising
the steps: a) disposing a beam deflection control device on the
light path of the beam before it is incident on the scanning
surface, said beam deflection control device configured to cause an
electric field distribution in a liquid crystal by applying
electricity to an electrode formed on a side of a glass substrate;
b) controlling a beam deflection amount of the beam deflecting
control device provided to an incident beam so as to control a
scanning characteristic of the optical scanning: and c) causing the
incident beam to pass through the beam deflection control device
without application of any beam deflection thereon when no
correction of the current scanning characteristic is needed,
wherein at least one resinous image-formation optical device is
disposed in the optical scanning system; the beam deflection
control device comprises deflection areas configured by a series of
a plurality of deflection devices defined in a main scanning
direction; laser beams corresponding to a plurality of colors have
at least a single scanning image-formation device to pass through;
and the control of the scanning characteristic of the optical
scanning is carried out individually for each of a plurality of
ranges divided in the main scanning direction..].
.[.35. The method as claimed in claim 34, wherein: said beam
deflection control device comprises a liquid crystal device by
which a refractive index thereof can be controlled electrically,
and thus, the direction of the incident beam can be changed
accordingly..].
.[.36. The method as claimed in claim 34, wherein: said beam
deflection control device comprises a plurality of beam deflection
control units, arranged in a main scanning direction, each having a
function of providing a deflection amount to the incident beam in a
subscanning direction; said beam deflection control device is
disposed between a beam deflecting device and the scanning surface;
and the deflection amount in the subscanning direction of each beam
deflection control unit is controlled for each scanning action so
that scan line bending is corrected..].
.[.37. The method as claimed in claim 34, wherein: said beam
deflection control device comprises a plurality of beam deflection
control units, arranged in a main scanning direction, each having a
function of providing a deflection amount to the incident beam in
the main scanning direction; said beam deflection control device is
disposed between a beam deflecting device and the scanning surface;
and the deflection amount in the main scanning direction of each
beam deflection control unit is controlled for each scanning action
so that a uniform velocity characteristic is corrected..].
.[.38. A beam deflection apparatus, comprising: a beam deflection
control device configured for use in an optical scanning device in
which a beam is deflected, and the deflected beam is converged and
directed toward a scanning surface, so that optical scanning of the
scanning surface is performed by an optical spot formed thereon by
the deflected beam, wherein: said beam deflection control device is
disposed on the light path of the beam before it is incident on the
scanning surface, said beam deflection control device configured to
cause an electric field distribution in a liquid crystal by
applying electricity to an electrode formed on a side of a glass
substrate; a beam deflection amount of the beam deflecting device
provided to an incident beam is controlled if necessary so that a
scanning characteristic of the optical scanning is controlled; at
least one resinous image-formation optical device is disposed in
the optical scanning system; the beam deflection control device
comprises deflection areas configured by a series of a plurality of
deflection devices defined in a main scanning direction; laser
beams corresponding to a plurality of colors have at least a single
scanning image-formation device to pass through; and the control of
the scanning characteristic of the optical scanning is carried out
individually for each of a plurality of ranges divided in the main
scanning direction..].
.[.39. The beam deflection control device as claimed in claim 38,
comprising a liquid crystal device by which a refractive index
thereof can be controlled electrically, and thus, the direction of
the incident beam can be changed accordingly..].
.[.40. The beam deflection control device as claimed in claim 38,
wherein: said beam deflection control device comprises a plurality
of beam deflection control units, arranged in a main scanning
direction, each having a function of providing a deflection amount
to the incident beam in a subscanning direction; said beam
deflection control device is disposed between a beam deflecting
device and the scanning surface; and the deflection amount in the
subscanning direction of each beam deflection control unit is
controlled for each scanning action so that scan line bending is
corrected..].
.[.41. An optical scanning device comprising the beam deflection
control device claimed in claim 40..].
.[.42. The beam deflection control device as claimed in claim 38,
wherein: said beam deflection control device comprises a plurality
of beam deflection control units, arranged in a main scanning
direction, each having a function of providing a deflection amount
to the incident beam in the main scanning direction; said beam
deflection control device is disposed between a beam deflecting
device and the scanning surface; and the deflection amount in the
main scanning direction of each beam deflection control unit is
controlled for each scanning action so that a uniform velocity
characteristic is corrected..].
.[.43. An optical scanning device comprising the beam deflection
control device claimed in claim 42..].
.[.44. The beam deflection control device as claimed in claim 38,
comprising: a first array of plurality of beam deflection control
units, arranged in a main scanning direction, each having a
function of providing a deflection amount to the incident beam in a
subscanning direction; a second array of a plurality of beam
deflection control units, arranged in a main scanning direction,
each having a function of providing a deflection amount to the
incident beam in the main scanning direction; said first array and
said second array are disposed in sequence between a beam
deflecting device and the scanning surface; the deflection amount
in the subscanning direction of each beam deflection control unit
of said first array is controlled for each scanning action so that
a scan line bending is corrected; and the deflection amount in the
main scanning direction of each beam deflection control unit of
said second array is controlled for each scanning action so that a
uniform velocity characteristic is corrected..].
.[.45. The beam deflection control device a claimed in claim 44,
wherein: said first array and said second array are configured in
such a manner that these arrays are combined together
integrally..].
.[.46. An optical scanning device comprising the beam deflection
control device claimed in claim 44..].
.[.47. A beam deflection control device, comprising: a beam
deflection device configured for use in an optical scanning device
in which a plurality of beams for respective color components for
forming a color image in combination are deflected, are converged
by a scanning and image-formation optical system, are directed to
respective scanning surfaces individually and thus performing
optical scanning of the scanning surfaces respectively, so as to
write images of respective color components, wherein: said beam
deflection control device acts as a scan line correcting device
which corrects a scan line bending; a scan line bending on the beam
of one color, component is regarded as a reference scan line
bending; the scan line correcting device electronically corrects a
scan line bending of the beam of each of the other color components
for the reference scan line bending; at least one resinous
image-formation optical device is disposed in the optical scanning
system; the beam deflection control device comprises deflection
areas configured by a series of a plurality of deflection devices
defined in a main scanning direction; laser beams corresponding to
a plurality of colors have at least a single scanning
image-formation device to pass through; and the control of a
scanning characteristic of the optical scanning is carried out
individually for each of a plurality of ranges divided in the main
scanning direction..].
.[.48. The beam deflection control device as claimed in claim 47,
comprising: a plurality of individually controllable liquid crystal
deflection devices arranged along the main scanning direction, and
disposed on the light path of the beam to be corrected with respect
to the scan line bending, each individually controllable liquid
crystal deflecting device being controlled with respect to the
deflection amount to be provided to the incident beam in the
subscanning direction according to the optical scanning..].
.[.49. The beam deflection control device claimed in claim 47,
wherein: the beam deflection control device is configured in such a
manner that the respective beam deflection control devices provided
for correcting the scan line bending of the beams for the
respective color components to be corrected for the reference scan
line bending are combined together integrally..].
.[.50. The beam deflection control device claimed in claim 49,
wherein: the beam deflection control device comprising the integral
combination of said respective beam deflection control devices for
the beams for forming the respective color-component images further
comprises, also in an integral combination manner, a portion
through which the beam having said reference scan line bending
passes without having any beam deflection applied thereto..].
.[.51. An optical scanning device in which a plurality of beams for
respective color components for forming a color image in
combination are deflected, are converged by a scanning and
image-formation optical system, are directed to respective scanning
surfaces individually and thus performing optical scanning of the
scanning surfaces respectively, so as to write images of respective
color components, comprising: the beam deflection control device
claimed in claim 47 configured to act as a scan line correcting
device which corrects a scan line bending, wherein a scan line
bending on the beam of one color component is regarded as a
reference scan line bending; and the scan line correcting device
corrects a scan line bending of the beam of each of the other color
components for the reference scan line bending..].
.[.52. An image formation device which performs image formation by
performing optical scanning on a photosensitive medium, comprising
the optical scanning device claimed in claim 51 performing the
optical scanning..].
.[.53. An image formation device forming a color image in which a
plurality of beams for respective color components for forming a
color image in combination are deflected, are converged by a
scanning and image-formation optical system, are directed to
respective scanning surfaces individually and thus performing
optical scanning of the scanning surfaces respectively, so as to
write images of respective color components, the images of the
respective color components being then combined on a sheet-shaped
recording medium so that a color image is formed thereon, said
image formation device comprising the optical scanning device
claimed in claim 51 performing the optical scanning of each
scanning surface..].
.[.54. A beam deflection control device used in an optical scanning
device in which a beam is deflected, and the deflected beam is
converged and directed toward a scanning surface, so that optical
scanning of the scanning surface is performed by an optical spot
formed thereon by the deflected beam, wherein: said beam deflection
control device is used for adjusting the optical spot formed on the
scanning surface: said beam deflection control device comprises a
plurality of beam deflection control units each individually
controllable of a deflection amount provided to an incident beam,
arranged along a main scanning direction, each beam deflection
control unit configured to cause an electric field distribution in
a liquid crystal by applying electricity to an electrode formed on
a side of a glass substrate; the deflection amount of each beam
deflection control unit is controlled according to the optical
scanning; at least one resinous image-formation optical device is
disposed in the optical scanning system; the beam deflection
control device comprises deflection areas configured by a series of
a plurality of deflection devices defined in a main scanning
direction; laser beams corresponding to a plurality of colors have
at least a single scanning image-formation device to pass through;
and the control of a scanning characteristic of the optical
scanning is carried out individually for each of a plurality of
ranges divided in the main scanning direction..].
.[.55. The beam deflection control claim 54, wherein: each beam
deflection control unit comprises a liquid crystal device by which
a refractive index thereof can be controlled electrically, and
thus, the direction of the incident beam can be changed
accordingly..].
.[.56. The beam deflection control device as claimed in claim 54,
wherein: said beam deflection control device comprises a plurality
of beam deflection control units, arranged in a main scanning
direction, each having a function of providing a deflection amount
to the incident beam in a subscanning direction..].
.[.57. The beam deflection control device claimed in claim 56,
wherein: said beam deflection control device is configured so that
the main-directional-length of each beam deflection control unit is
so small that a difference in deflection amount between adjacent
beam deflection control units be regarded as a substantially smooth
variation..].
.[.58. The beam deflection control device as claimed in claim 54,
wherein: said beam deflection control device comprises a plurality
of beam deflection control units, arranged in a main scanning
direction, each having a function of providing a deflection amount
to the incident beam in a main scanning direction..].
.[.59. The beam deflection control device claimed in claim 58,
wherein: said beam deflection control device is configured so that
the main-directional-length of each beam deflection control unit is
so small that a difference in deflection amount between adjacent
beam deflection control units be regarded as a substantially smooth
variation..].
.[.60. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
comprising the beam deflection control device claimed in claim 54
adjusting the optical spot formed on the scanning surface..].
.[.61. The optical scanning device as claimed in claim 60, wherein:
said beam deflection control device is disposed between an optical
scanning device performing the optical scanning of the scanning
surface and the scanning surface..].
.[.62. The optical scanning device as claimed in claim 60
comprising a multi-beam-type optical scanning device in which a
light source device emits a plurality of beams and the scanning
surface is scanned by the plurality of beams simultaneously..].
.[.63. The optical scanning device as claimed in claim 60, wherein:
a plurality of light sources are provided; and a scanning optical
system defining a light path from each light source toward the
respective scanning surface is configured so that a scan line drawn
by an optical spot formed by the beam coming from each light source
is substantially parallel to each other..].
.[.64. The optical scanning device as claimed in claim 63, wherein:
the beam deflection control device is provided for each light
source..].
.[.65. The optical scanning device as claimed in claim 63, wherein:
the number of light sources is 3 or 4, and the beam emitted from
each light source is modulated by image information for forming an
image in a respective one of color components which thus form a
color image in combination..].
.[.66. An image formation device which performs image formation by
performing optical scanning on a photosensitive medium, comprising:
the optical scanning device claimed in claim 60..].
.[.67. The image formation device as claimed in claim 66, wherein:
said photosensitive medium comprises a photoconductive
photosensitive body on which an electrostatic latent image is
formed as a result of the optical scanning performed by said
optical scanning device; and a toner image formed on said
photosensitive body as a result of visualization of the
electrostatic latent image is then transferred onto a sheet-shaped
recording medium..].
.[.68. The image formation device as claimed in claim 67, wherein:
the number of the photoconductive photosensitive bodies is 3 or 4
on which respective color-component images are formed as a result
of optical scanning with beams previously modulated by image
information for forming the respective color-component images from
which a color image is formed in combination; and the respective
photoconductive photosensitive bodies are disposed in mutually
parallel..].
.[.69. An image formation method applied to the image formation
device as claimed in claim 66, comprising: detecting a scanning
position of the optical spot with a scanning position detecting
device; and based on the detection result of the scanning position
detecting device, determining a deflection amount of a respective
beam deflection control unit..].
.[.70. The image formation method as claimed in claim 69, wherein:
said step of determining is performed when a power supply to the
image formation device is started..].
.[.71. The image formation method as claimed in claim 69, further
comprising: said steps of detecting and determining are performed
prior to commencement of a regular image formation process..].
.[.72. The image formation method as claimed in claim 69, further
comprising: when successive image formation processes are performed
in the image formation device in which a photoconductive
photosensitive body is used as the photosensitive medium,
determining whether or not a change of the deflection amount of the
respective beam deflection control unit is needed, within a
recording-medium conveyance time interval on successive conveyance
of sheet-shaped recording media on each of which a toner image is
transferred from the photoconductive photosensitive body..].
.[.73. The image formation method as claimed in claim 72, further
comprising: when a change of the deflection amount on the
respective beam deflection control unit is determined to be needed,
performing an actual change of the deflection amount on the beam
deflection control unit within the recording-medium conveyance
interval same as that in which the optical spot scanning position
detection is performed, or within the subsequent recording-medium
conveyance interval..].
.[.74. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
comprising the beam deflection control device claimed in claim 54
adjusting the optical spot formed on the scanning surface, wherein
said beam deflection control device is disposed in a manner such
that it is inclined with respect to a subscanning direction..].
.[.75. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
comprising: a liquid crystal beam deflection control device
adjusting the optical spot formed on the scanning surface; and a
ghost light removal device blocking a diffracted beam occurring
through said liquid crystal beam deflection control device which
acts as a ghost light from reaching the scanning surface, wherein
said liquid crystal beam deflection control device is disposed
between an optical deflection scanning device which performs the
optical scanning of the scanning surface and the scanning surface,
and said ghost light blocking device comprises a slit opening long
along a main scanning direction through which only a regular
optical scanning beam is passed..].
76. .[.The.]. .Iadd.An .Iaddend.optical scanning device .[.as
claimed in claim 75,.]. .Iadd.in which a beam is deflected, and the
deflected beam is converged and directed toward a scanning surface,
so that optical scanning of the scanning surface is performed by an
optical spot formed thereon by the deflected beam, comprising: a
liquid crystal beam deflection control device adjusting the optical
spot formed on the scanning surface; and a ghost light removal
device blocking a diffracted beam occurring through said liquid
crystal beam deflection control device which acts as a ghost light
from reaching the scanning surface, wherein said liquid crystal
beam deflection control device is disposed between an optical
deflection scanning device which performs the optical scanning of
the scanning surface and the scanning surface, and said ghost light
blocking device comprises a slit opening long along a main scanning
direction through which only a regular optical scanning beam is
passed,.Iaddend. wherein the following requirements be satisfied:
L>(1/2)(b+.DELTA.)/tan .THETA. where: `b` denotes a width in a
subscanning direction of each beam deflected by the liquid crystal
beam deflection control device; .[.`A`.]. .Iadd.`.DELTA.`
.Iaddend.denotes a width in the subscanning direction of the slit
opening of the ghost light removal device; `L` denotes a distance
between the liquid crystal beam deflection control device and the
slit opening of the ghost light removal device; and `.THETA.`
denotes an angle formed in the subscanning direction between the
regular optical scanning beam obtained from the liquid crystal beam
deflection control device and the ghost light which is nearest to
said regular optical scanning beam with respect to the chief rays
thereof.
77. .[.The.]. .Iadd.An .Iaddend.optical scanning device .[.as
claimed in claim 75,.]. .Iadd.in which a beam is deflected, and the
deflected beam is converged and directed toward a scanning surface,
so that optical scanning of the scanning surface is performed by an
optical spot formed thereon by the deflected beam, comprising: a
liquid crystal beam deflection control device adjusting the optical
spot formed on the scanning surface; and a ghost light removal
device blocking a diffracted beam occurring through said liquid
crystal beam deflection control device which acts as a ghost light
from reaching the scanning surface, wherein said liquid crystal
beam deflection control device is disposed between an optical
deflection scanning device which performs the optical scanning of
the scanning surface and the scanning surface, and said ghost light
blocking device comprises a slit opening long along a main scanning
direction through which only a regular optical scanning beam is
passed,.Iaddend. wherein: said ghost light removal device is
provided in such a manner that it is integrally combined with any
one of optical devices disposed between the optical deflection
scanning device and the scanning surface.
.[.78. An image formation device which performs image formation by
performing optical scanning on a photosensitive medium, comprising
the optical scanning device claimed in claim 75 performing the
optical scanning..].
.[.79. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
comprising: a liquid crystal beam deflection control device
adjusting the optical spot formed on the scanning surface; and a
ghost light removal device blocking a diffracted beam occurring
through said liquid crystal beam deflection control device which
acts as a ghost light from reaching the scanning surface, wherein
said ghost light blocking device comprising a slit opening long
along a main scanning direction through which only a regular
optical scanning beam is passed..].
.[.80. A new image formation device which performs image formation
by performing optical scanning on a photosensitive medium,
comprising the optical scanning device claimed in claim 79
performing the optical scanning..].
81. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
comprising: a liquid crystal beam deflection control device
adjusting the optical spot formed on the scanning surface; and a
ghost light removal device blocking a diffracted beam occurring
through said liquid crystal beam deflection control device which
acts as a ghost light from reaching the scanning surface, wherein
said ghost light blocking device comprises a slit opening long
along a main scanning direction through which only a regular
optical scanning beam is passed, and the following requirements by
satisfied: L>(1/2)(b+.DELTA.)/tan .THETA. where: `b` denotes a
width in a subscanning direction of each beam deflected by the
liquid crystal beam deflection control device; `.DELTA.` denotes a
width in the subscanning direction of the slit opening of the ghost
light removal device; `L` denotes a distance between the liquid
crystal beam deflection control device and the slit opening of the
ghost light removal device; and `.THETA.` denotes an angle formed
in the subscanning direction between the regular optical scanning
beam obtained from the liquid crystal beam deflection control
device and the ghost light which is nearest to said regular optical
scanning beam with respect to the chief rays thereof.
82. An optical scanning device in which a beam is deflected, and
the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
comprising: a liquid crystal beam deflection control device
adjusting the optical spot formed on the scanning surface; and a
ghost light removal device blocking a diffracted beam occurring
through said liquid crystal beam deflection control device which
acts as a ghost light from reaching the scanning surface, wherein
said ghost light blocking device comprises a slit opening long
along a main scanning direction through which only a regular
optical scanning beam is passed, and said ghost light removal
device is provided in such a manner that it is integrally combined
with any one of the optical devices disposed between the optical
deflection scanning device and the scanning surface.
.Iadd.83. An optical scanning device in which a beam is deflected,
and the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
said device comprising: a liquid crystal beam deflection control
device disposed on the light path of the beam before it is incident
on the scanning surface, said liquid crystal beam deflection
control device configured to cause an electric field distribution
in a liquid crystal by applying electricity to an electrode formed
on a side of a glass substrate; and a ghost light removal device
configured to block a diffracted beam occurring through said liquid
crystal beam deflection control device which acts as a ghost light
from reaching the scanning surface, and including a slit opening
long along a main scanning direction through which only a regular
optical scanning beam is passed, wherein a beam deflection amount
of the liquid crystal beam deflection control device provided to an
incident beam is controlled so that a scanning characteristic of
the optical scanning is controlled to adjust the optical spot
formed on the scanning surface, at least one resinous
image-formation optical device is disposed in the optical scanning
system, the liquid crystal beam deflection control device comprises
deflection areas configured by a series of a plurality of
deflection devices defined in a main scanning direction, and the
liquid crystal beam deflection control device includes liquid
crystal deflection areas separated in a subscanning direction for
respective laser beams corresponding to a plurality of colors, and
the liquid crystal deflection areas are configured by a single
laser beam transmitting member..Iaddend.
.Iadd.84. An optical scanning device in which a beam is deflected,
and the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
said device comprising: a liquid crystal beam deflection control
device disposed on the light path of the beam before it is incident
on the scanning surface, said liquid crystal beam deflection
control device configured to cause an electric field distribution
in a liquid crystal by applying electricity to an electrode formed
on a side of a glass substrate; and a ghost light removal device
configured to block a diffracted beam occurring through said liquid
crystal beam deflection control device which acts as a ghost light
from reaching the scanning surface, and including a slit opening
long along a main scanning direction through which only a regular
optical scanning beam is passed, wherein a beam deflection amount
of the liquid crystal beam deflection control device provided to an
incident beam is controlled so that a scanning characteristic of
the optical scanning is controlled to adjust the optical spot
formed on the scanning surface, at least one resinous
image-formation optical device is disposed in the optical scanning
system, the liquid crystal beam deflection control device comprises
deflection areas configured by a series of a plurality of
deflection devices defined in a main scanning direction, the liquid
crystal beam deflection control device includes liquid crystal
deflection areas separated in a subscanning direction for
respective laser beams corresponding to a plurality of colors, and
the liquid crystal deflection areas are configured by a single
laser beam transmitting member, and the following conditions are
satisfied: L>(1/2)(b+.DELTA.)/tan .THETA. where: `b` denotes a
width in a subscanning direction of each beam deflected by the
liquid crystal beam deflection control device; `.DELTA.` denotes a
width in the subscanning direction of the slit opening of the ghost
light removal device; `L` denotes a distance between the liquid
crystal beam deflection control device and the slit opening of the
ghost light removal device; and `.THETA.` denotes an angle formed
in the subscanning direction between the regular optical scanning
beam obtained from the liquid crystal beam deflection control
device and the ghost light which is nearest to said regular optical
scanning beam with respect to the chief rays thereof..Iaddend.
.Iadd.85. An optical scanning device in which a beam is deflected,
and the deflected beam is converged and directed toward a scanning
surface, so that optical scanning of the scanning surface is
performed by an optical spot formed thereon by the deflected beam,
said device comprising: a liquid crystal beam deflection control
device disposed on the light path of the beam before it is incident
on the scanning surface, said liquid crystal beam deflection
control device configured to cause an electric field distribution
in a liquid crystal by applying electricity to an electrode formed
on a side of a glass substrate; and a ghost light removal device
configured to block a diffracted beam occurring through said liquid
crystal beam deflection control device which acts as a ghost light
from reaching the scanning surface, and including a slit opening
long along a main scanning direction through which only a regular
optical scanning beam is passed, wherein a beam deflection amount
of the liquid crystal beam deflection control device provided to an
incident beam is controlled so that a scanning characteristic of
the optical scanning is controlled to adjust the optical spot
formed on the scanning surface, at least one resinous
image-formation optical device is disposed in the optical scanning
system, the liquid crystal beam deflection control device comprises
deflection areas configured by a series of a plurality of
deflection devices defined in a main scanning direction, the liquid
crystal beam deflection control device includes liquid crystal
deflection areas separated in a subscanning direction for
respective laser beams corresponding to a plurality of colors, and
the liquid crystal deflection areas are configured by a single
laser beam transmitting member, and the ghost light removal device
is integrally combined with any one of the optical devices disposed
between the optical deflection scanning device and the scanning
surface..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming system employing
an effective optical scan-line control device, in particular, to an
optical scanning control method, optical scanning device, or an
image formation device, which employs an effective optical
scan-line control device.
2. Description of the Related Art
In an image formation device, such as a laser printer, an optical
plotter, a digital copier, or the like, an optical scanning device
is employed. In the optical scanning device, a beam emitted from a
light source is deflected by an optical deflection scanning device
such as a rotation multiple minor such as a polygon mirror or the
like, is focused by a scanning image-formation optical system, such
as an f.theta. lens into an optical spot, onto a scanning
surface.
In the image formation device employing the optical scanning
device, an image formation process is performed in which optical
scanning is performed with the optical scanning device. There, the
quality of the image formed depends on the quality in performance
of the optical scanning. It depends on scanning characteristics on
a main scanning direction and scanning characteristics on a
subscanning direction of the optical scanning device. As one of the
scanning characteristics on the main scanning direction, a uniform
velocity performance is known.
In order to achieve the satisfactory uniform velocity performance
in the optical scanning operation, the deflection of beam is
performed in a uniform angular velocity in case of employing a
rotation multiple mirrors for example. There, a scanning
image-formation optical system having f.theta. characteristics is
used However, the perfect f.theta. characteristics may not be
achieved there, and also, some other performances are also required
from the scanning image-formation optical system.
A scan line bending phenomenon is known as one problem occurring in
regard to the scanning characteristics on the subscanning
direction. A scan line is drawn by an optical spot on the scanning
surface, which should be a straight line ideally. However, due to a
manufacture working error, an assembly error, etc., usually the
scan line inevitably bends on the scanning surface. As one form of
such a scan line bending phenomenon, inclination of scan line is
known in which the scan line does not cross at a right angle with
respect to the subscanning direction.
In case of providing an angle in the subscanning direction between
a direction of a beam incidence onto an image-formation mirror and
a direction of the same reflected thereby in the scanning
image-formation optical system, the scan line bending phenomenon
occurs inherently. In case the scanning image-formation optical
system is formed by a lens system instead, occurrence of scan line
bending is unavoidable in a multi-beam scanning form which carries
out optical scanning with a plurality of optical spots separate
along the subscanning direction.
Distortion along the main scanning direction arises in a resulting
image formed when the above-mentioned uniform velocity performance
of optical scanning is not perfect. When scan line bending occurs
on the other hand, a distortion along the subscanning direction
arises in the resulting image formed.
In case a monochrome image is formed by a single optical scanning
device, imperfection in the uniform velocity performance may not
cause a serious distortion in the resulting image in terms of
visual performance of human eyes as long as the imperfection and
scan line bending phenomenon are controlled to a certain degree.
However, in case a color image is formed by a so-called tandem-type
image formation device in which images of primary color components
first formed are combined so as to provide a full-color image,
serious problems may likely to occur as will now be described.
To form separate color component images of respective three colors
of magenta, cyan and yellow or four colors which also includes
black, and, after that, to produce a full-color image in
combination thereof by piling up these color component images in a
color copying machine, etc. is known. One example of a machine
which performs such a color image forming process is the
tandem-type image formation device mentioned above in which color
component image of each color is formed onto a separate
photoconductor with a separate optical scanning device. In such a
configuration, some abnormality may occur in a resulting image,
when a color deviation due to difference in a manner of scan line
bending occurring on each color component image between the
respective color components. Thereby, image quality in the finally
obtained color image is degraded. The term of color deviation
includes a phenomenon in which colors occurring in the finally
obtained color image are not those which are desired
originally.
Recently, as one trend in manufacture of the optical scanning
device (a lens or so), such a special surface as an aspherical
surface is employed as a surface of an optical system used there.
In this regard, an image-forming optical system made of a resin or
plastic material takes an attention as a method of enabling easy
manufacture of such special surfaces at low costs and thus
advantageous in a recent mass production environment.
As for the image-forming optical system of resin or plastic
material, the optical characteristics tend to change in response to
change in ambient temperature or humidity, which may result in
change in the above-mentioned optical characteristics whereby the
uniform velocity performance may be degraded or the scan line
bending phenomena may likely to occur. As a result, when performing
color image formation of dozens of sheets continuously for example,
the temperature inside the machine rises by the continuation
operation of image formation processing, and the optical
characteristics of the image-forming optical system there may
change. Thereby, the uniform velocity performance or scan line
bending manner on the optical scanning device for each color
component change gradually. As a result, the color tone may
completely differ between a resulting color image obtained at the
beginning of the above-mentioned continuous image forming process
and a resulting color image obtained at the end of the same
process.
The above-mentioned tandem-type image formation device will now be
described in detail. There, four drums of photoconductors for
respective color components are arranged in a recording paper
conveyance direction. Each photoconductor drum is exposed by a
corresponding optical scanning device, and a latent image is formed
on the photoconductor. The thus-obtained latent images are
visualized by toners of the respective color components, i.e.,
yellow, cyan, magenta and black. Then, these visualized images are
transferred onto a recording paper one by one in a piling-up
manner, and, thus, a full-color image is obtained on the recording
paper. Such a configuration of image formation device is put in
practical use as a digital color copying machine or a color laser
printer.
Such an image formation device of a 4-drum tandem type is
advantageous in comparison to another type of color image formation
device in which a (electrostatic) latent image for each color
component is formed on a single common photoconductor one by one
using a single common optical scanning device. In this type of
image formation device, the latent image thus formed is visualized
one by one as a visible image of yellow, magenta, cyan, and black,
and, then, the thus-formed visible image is transferred onto a
recording paper, one by one. In comparison with this type of
machine, the tandem-type machine is advantageous in that full-color
image formation can be archived theoretically at the same rate as
that in case of monochrome image formation. Thus, high-speed color
image formation or printing is achieved by the tandem-type machine.
However, in the tandem-type machine, since a separate scanning
image-formation optical system is provided for each of
photoconductor drums, the above-mentioned color deviation may
likely to occur as mentioned above, when a visible image (toner
image) is transferred on the same recording paper from each
separate photoconductor drum in the piling-up manner.
As causes of the color deviation along the subscanning direction,
the following ones are expected: Rotation speed variation in the
drum-type photoconductors; positional deviation among scan lines
drawn by the optical scanning devices for respective color
components; deviation in manner of scan line bending among the
respective color components; shift of scan lines or change in
manner of scan line bending due to environmental transition or
temperature rise according to progress of the above-mentioned
continuous image formation process, and so forth. Especially, the
temperature rise according to the progress of image formation
process may cause serious optical performance transition in optical
devices made of resin/plastic materials.
As a method of reducing the color deviation, various methods have
been proposed. In one plan, disclosed by Japanese patent No.
3262409, when the temperature in a machine exceeds a threshold, the
amount of toner image transfer registration deviation is detected,
and, based thereon, an actuator is driven so as to correct the
positional deviation. In another plan disclosed by Japanese
laid-open patent application No. 2001-133718, positional adjustment
of an optical scanning device provided for each photoconductor drum
is performed together with a housing thereof with respect to the
photoconductor drum. In another plan, a long lens included in the
optical scanning device is deformed so as to correct the scan line
bending as disclosed so by Japanese laid-open patent application
No. 10-268217.
According to the above-mentioned plan of Japanese patent No.
3262409, it may be difficult to carry out a high-speed drive of the
actuator which drives a long heavy mirror, and, thus, when a
temperature inside the machine changes rapidly at a time of
continuation image formation, it may be difficult to achieve a
timely response thereto.
In the method of Japanese laid-open patent application No.
2001-133718, the cost may increase as the mechanism for the
adjustment tends to become complicated. Moreover, the scan line
bending phenomena occurring gradually due to temperature change or
the like may not be controlled well.
In the method of Japanese laid-open patent application No.
10-268217, it may be effective to well correct the scan line
bending at a time of initial setting state. However, it may be
difficult to deal with a problem occurring gradually due to a
temperature change, or the like, occurring at a late stage.
SUMMARY OF THE INVENTION
The present invention has been devised for the purpose of solving
the above-mentioned problems, and an object of the present
invention is to provide an image forming system or an optical
scanning system in which optical scanning characteristics can be
well controlled along the main and subscanning directions.
Another object of the present invention is to provide an optical
scanning system in which, in case the system is applied to a
tandem-type image formation device for producing a full-color
image, even when a positional deviation of scan lines among
respective color component images, disagreement in manner of scan
line bending thereamong, or the like, occurs due to a rapid
temperature change in the machine, color deviation otherwise
occurring can be well avoided.
An optical scanning characteristic control scheme according to the
present invention is applied to an optical scanning system in which
a beam is deflected, and the deflected beam is converged and
directed toward a scanning surface, so that optical scanning of the
scanning surface is performed by an optical spot formed thereon by
the deflected beam. This scheme comprises the process of:
a) disposing a beam deflection control device on the light path of
the beam before it is incident on the scanning surface; and
b) controlling a beam deflection amount of the beam deflecting
device provided to an incident beam so as to control a scanning
characteristic of the optical scanning.
Thereby, when the beam deflection control device is formed of an
array of liquid crystal deflection devices each of which has a
function of deflecting an incident beam in a subscanning direction
and/or a main scanning direction dynamically according to a control
performed based on a detection result of a current optical scanning
state (scan line bending, scan line inclination, scan line shift
and/or uniform velocity performance), the current scanning
characteristic can be positively corrected dynamically. Thereby, in
particular in a case of full-color image formation system such as a
tandem-type machine in which beams for respective predetermined
color components, i.e., yellow, magenta, cyan and black, or so, are
used for scanning respective photosensitive media (such as
photoconductors) so as to form respective latent images thereon
which are then combined in a predetermined manner such that a
full-color image be thus obtained, and a possible deviation in scan
line characteristics among the respective color components may
degrade the finally obtained full-color image especially with
respect to a color deviation, the above-mentioned scheme according
to the present invention is advantageous in that the scanning
characteristics can be dynamically corrected so that a high-quality
full-color image can be obtained even in a situation in which a
change in the state in the machine such as temperature rise due to
continuous image formation process might otherwise cause a change
in the scanning characteristic resulting in degradation of a color
finally obtained from combination of the respective color
components.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and further features of the present invention will
become more apparent from the following detailed description when
read in conjunction with the accompanying drawings:
FIG. 1 shows a perspective view of an image formation device
according to a first embodiment of the present invention;
FIGS. 2A through 2C illustrate one example of a liquid crystal
deflection device applicable to the present invention;
FIGS. 3A through 3C illustrate another example of a liquid crystal
deflection device applicable to the present invention;
FIGS. 4A and 4B illustrate another example of a liquid crystal
deflection device applicable to the present invention;
FIGS. 5A through 5D illustrate a scheme of scan line bending
correction applicable to the present invention;
FIGS. 6A and 6B illustrate two examples of liquid crystal
deflection device unit configurations applicable to the present
invention;
FIG. 7 shows a perspective view of an image formation device
according to a second embodiment of the present invention;
FIGS. 8A and 8B and 9A through 9C illustrate a scheme of scan line
bending correction applicable to a full-color image formation
apparatus such as that shown in FIG. 7;
FIG. 10A shows a perspective view of an image formation device
according to a third embodiment of the present invention;
FIG. 10B illustrates a scan line correction device used in the
configuration shown in FIG. 10A;
FIG. 11 illustrates an example of a temperature change in an image
formation device during a continuous image formation process
performed therein;
FIGS. 12A and 12B illustrate an optical scanning device according
to a fourth embodiment of the present invention;
FIGS. 13A through 13D illustrate various schemes of scanning
position detection applicable to the present invention;
FIG. 14A illustrates an optical scanning device according to a
fifth embodiment of the present invention;
FIGS. 14B and 14C illustrate an effect obtained due to a difference
in relation between a plurality of beams in a multi-beam type
machine;
FIG. 15 illustrates an image formation device to which the present
invention may be applied;
FIG. 16 illustrates an operation flow chart applicable to an
operation of an image formation device according to the present
invention;
FIGS. 17A and 17B illustrate a variant embodiment of the embodiment
shown in FIGS. 12A and 12B employing a ghost light removal device
according to the present invention;
FIGS. 18A through 18C illustrate requirements concerning an
arrangement of a ghost light removal device according to the
present invention;
FIG. 19 illustrates a second variant embodiment of the embodiment
shown in FIGS. 12A and 12B also employing a ghost light removal
device according to the present invention; and
FIG. 20 illustrates a variant embodiment of the embodiment shown in
FIG. 14A employing a ghost light removal device according to the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will now be
described.
FIG. 1 shows an image formation device in one embodiment of the
present invention. The image formation device shown in FIG. 1 uses
photoconductors having photoconductivity, and forms a full-color
image. The full-color image is formed in combination of yellow,
magenta, cyan, and black color component images which are formed in
a piling-up manner on a common sheet-like recording medium, i.e., a
recording paper, for example.
As a basic configuration of such a type of color image is formation
device is well-known, only parts/components essential to the
present invention are shown in FIG. 1. Light source devices 11Y,
11M, 11C, and 11K employ semiconductor lasers as light sources and
emit laser beams respectively in form of parallel beams, or the
like. In this embodiment, the light source used in each light
source device is a semiconductor laser array, and two semiconductor
laser light-emission parts are arranged at a predetermined interval
(in the subscanning direction) therein. Therefore, two parallel
beams are emitted from each light source device.
The light source device 11Y is used for drawing a yellow component
image. When each light-emission parts of the light source device
11Y is driven by image information signal on a yellow component
image, two parallel beams modulated in intension by the yellow
component image information is emitted. Then, the thus-produced
beam is condensed only in the subscanning direction by a
cylindrical lens 12Y, and is reflected by a reflector 13. Thereby,
these beams form line images long along a main scanning direction
respectively on a deflection reflective surface of a polygon mirror
15B.
The two beams reflected by the deflection reflective surface of the
polygon mirror 15B thus becoming deflected beams pass through
lenses 16A2 and 16B2 which act as an f.theta. lens which is a
scanning image-formation optical system, and then ate reflected by
light path bending minors 18Y and 19Y, in sequence. Thereby, by the
function of the f.theta. lens, they form two optical spots mutually
separated in the subscanning direction on a photoconductor 20Y,
respectively.
These light spots carry out a multi-beam scan (main scan) of the
photoconductor 20Y (scanning surface) so as to draw simultaneously
two scan lines according to a uniform rotation of the polygon minor
15B. A running speed of each optical spot is made uniform by the
function of the f.theta. lens.
The photoconductor 20Y has a shape of a cylinder, and in advance of
the optical scan, uniform electrification thereof is carried out,
and a uniform rotation of a circumferential surface (scanning
surface) in a direction shown by an arrow in the figure is
performed. A subscanning is thus performed by the above-mentioned
uniform rotation of the photoconductor 20Y, and, thereby, a yellow
latent image for a yellow component image is formed on the
photoconductor 20Y in a form of electrostatic latent image.
The light source device 11M is used for drawing a magenta component
image. When each light-emission parts of the light source device
11M is driven by image information signal on a magenta component
image, two parallel beams modulated in intension by the magenta
component image information is emitted. Then, the thus-produced
beam is condensed only in the subscanning direction by a
cylindrical lens 12M. Thereby, these beams form line images long
along the main scanning direction respectively on a deflection
reflective surface of a polygon mirror 15A which has the same
configuration as the polygon mirror 15B, and is rotated integrally
with the polygon mirror 15B by a common shaft of a drive motor (not
shown).
The two beams reflected by the deflection reflective surface of the
polygon mirror 15A thus becoming deflected beams pass through
lenses 16A1 and 16B1 which also act as an f.theta. lens which is a
scanning image-formation optical system, and then are reflected by
light path bending minors 18M and 19M, in sequence. Thereby, by the
function of the f.theta. lens, they form two optical spots mutually
separated in the subscanning direction on a photoconductor 20M,
respectively.
These light spots carry out a multi-beam scan (main scan) of the
photoconductor 20M (scanning surface) so as to draw simultaneously
two scan lines according to a uniform rotation of the polygon
mirror 15A. A running speed of each optical spot is made uniform by
the function of the f.theta. lens.
The photoconductor 20M has a shape of a cylinder, and in advance of
the optical scan, uniform electrification thereof is carried out,
and a uniform rotation of a circumferential surface in a direction
shown by an arrow in the figure is performed. A subscanning is thus
performed by the above-mentioned uniform rotation of the
photoconductor 20M, and, thereby, a magenta latent image for a
magenta component image is formed on the photoconductor 20M as an
electrostatic latent image.
The light source device 11C is used for drawing a cyan component
image. When each light-emission parts of the light source device
11C is driven by an image information signal on a cyan component
image, two parallel beams modulated in intension by the cyan
component image information is emitted. Then, the thus-produced
beam is condensed only in the subscanning direction by a
cylindrical lens 12C. Thereby, these beams form line images long
along the main scanning direction respectively on a deflection
reflective surface of a polygon mirror 15A.
The two beams reflected by the deflection reflective surface of the
polygon mirror 15A thus becoming deflected beams pass through an
optical system (not completely shown, including a lens 17A1 which
acts as a part of an f.theta. lens) disposed approximately
symmetrically with respect to the polygon mirror 15A to the optical
system provided for the magenta component image drawing, which is a
scanning image-formation optical system. Thus, the beams are
directed toward a photoconductor 20C having photoconductivity.
Thereby, by the function of the f.theta. lens, they form two
optical spots mutually separated in the subscanning direction on
the photoconductor 20C, respectively.
These light spots carry out a multi-beam scan (main scan) of the
photoconductor 20C (scanning surface) so as to draw simultaneously
two scan lines according to a uniform rotation of the polygon
mirror 15A. A running speed of each optical spot is made uniform by
the function of the f.theta. lens. The photoconductor 20C has a
shape of a cylinder, and in advance of the optical scan, uniform
electrification thereof is carried out, and a uniform rotation of a
circumferential surface in a direction shown by an arrow in the
figure is performed. A subscanning is thus performed by the
above-mentioned uniform rotation of the photoconductor 20C, and,
thereby, a cyan latent image for a cyan component image is formed
on the photoconductor 20C as an electrostatic latent image.
The light source device 11K is used for drawing a black component
image. When each light-emission parts of the light source device
11K is driven by an image information signal on a black component
image, two parallel beams modulated in intension by the black
component image information is emitted. Then, the thus-produced
beam is condensed only in the subscanning direction by a
cylindrical lens 12K, and reflected by a reflective mirror 14.
Thereby, these beams form line images long along the main scanning
direction respectively on a deflection reflective surface of the
polygon mirror 15B.
The two beams reflected by the deflection reflective surface of the
polygon minor 15B thus becoming deflected beams pass through an
optical system (not completely shown, including a lens 17A2 which
acts as a part of an f.theta. lens) disposed approximately
symmetrically with respect to the polygon mirror 15B to the optical
system provided for the yellow component image drawing, which is a
scanning image-formation optical system. Thus, the beams are
directed toward a photoconductor having photoconductivity, not
shown, which has the same configuration as that of the
above-mentioned photoconductors 20Y, 20M and 20C, and is disposed
in a manner in which the rotation shaft thereof is parallel to
those of the photoconductors 20Y, 20M and 20C. Thereby, by the
function of the f.theta. lens, they form two optical spots mutually
separated in the subscanning direction on the photoconductor,
respectively.
These light spots carry out a multi-beam scan (main scan) of the
photoconductor (scanning surface) so as to draw simultaneously two
scan lines according to a uniform rotation of the polygon mirror
15B. A running speed of each optical spot is made uniform by the
function of the f.theta. lens. The photoconductor has a shape of a
cylinder, and in advance of the optical scan, uniform
electrification thereof is carried out, and a uniform rotation of a
circumferential surface in a direction same as those of the other
photoconductors is performed. A subscanning is thus performed by
the above-mentioned uniform rotation of the photoconductor, and,
thereby, a black latent image for a black component image is formed
on the photoconductor as an electrostatic latent image.
Then, yellow latent image, magenta latent image, cyan latent image,
and black latent image formed on the respective photoconductors are
developed by development devices which are not shown, respectively,
and thus become toner images of yellow, magenta, cyan and black. It
is noted that a configuration is made such that the scan lines
drawn by the beams of the respective color components be mutually
parallel. Furthermore, a configuration is made such that the
optical systems which form the light paths of the beams of the
respective color components be optically equivalent mutually.
On a common sheet-like recording medium (for example, a transfer
paper) which is not shown, alignment of the respective color
component toner images is carried out mutually, they are piled up,
and thus, form a full-color image on the sheet-like recording
medium. After that, the full-color image thus-formed on the
sheet-like recording medium is fixed thereto by a fixing device
which is not shown. The sheet-like recording medium onto which the
full-color image is thus fixed is ejected from the image formation
device.
Transfer to the sheet-like recording medium of each above-mentioned
color component toner image can be performed by one of well-known
various methods. For example, a method disclosed by Japanese
laid-open patent application No. 2001-228416 may be applied. That
is, an endless belt-like intermediate transfer belt is prepared in
a manner such that the respective photoconductors be touched
thereby. Then, in an inner circumferential surface of the
intermediate transfer belt, transfer devices (transfer chargers,
etc.) are prepared at portions corresponding to the respective
photoconductors. Then, fixed-velocity rotation of the intermediate
transfer belt is carried out. Thereby, the color component toner
images are overlapped mutually one by one by the action of the
respective transfer devices, and thus, a full-color image is
obtained on the transfer belt, which is then transferred from on
the transfer belt to the sheet-like recording medium.
Alternatively, instead of the above-mentioned transfer belt, an
endless belt-like conveyance belt may be prepared, thereby, the
photoconductors 20Y through 20K may be touched. Then, a transfer
device, such as a transfer charger, is prepared in a portion
corresponding to each photoconductor, and the sheet-like recording
medium is supported on the conveyance belt. Then, the sheet-like
recording medium is moved by the conveyance belt, and has the
respective color component toner images transferred thereto from
the respective photoconductors in sequence one by one directly by
the functions of the respective transfer devices. The transfer
operation is performed in such a manner that the respective color
component toner images are piled up precisely on the sheet-like
recording medium so that a full-color image be formed finally on
the sheet-like recording medium directly.
In the color image formation device of FIG. 1 described above,
either a line sequential method in which simultaneous optical scan
with two optical spots draws two adjacent scan lines or an
interlaced scanning method in which the same draws two scan lines
not adjacent may be applied in the multi-beam scanning operation.
In the above-mentioned description, the optical scan of two scan
lines is carried out simultaneously. However, other than this
manner, the number of the light-emission sources in each
light-source device may be increased, and thereby, more than two
scan lines may be drawn simultaneously. Other than, this, it is
also possible to apply a single beam scanning method in which
optical scanning is performed by a single beam for each
photoconductor.
In each multi-beam scan, the optical scanning paths on the
photoconductor along which the two optical spots run simultaneously
can be determined as having the substantially same way of scan line
bending.
In the embodiment shown in FIG. 1, each f.theta. lens is formed of
a resin material, and the lenses 16A1 and 16B1 forming the f.theta.
lens for drawing the yellow latent image, and the lenses 16A2 and
16B2 forming the f.theta. lens for drawing the magenta latent image
are formed by an integral molding manner, respectively. By forming
the lenses 16A1 and 16A2 and the lenses 16B1 and 16B2 by the
integral molding manner, cost saving can be achieved in comparison
to a case where these four lenses are formed separately. The same
manner may be applied to form the f.theta. lens for drawing the
cyan latent image drawing, and the f.theta. lens for drawing the
black latent image.
Along with providing these f.theta. lenses from the resin material,
the optical characteristics of the f.theta. lenses may easily
change according to change in temperature and humidity, and
thereby, the way of scan line bending and uniform velocity
performance also may easily change, as mentioned above. According
to this embodiment of the present invention, correction of the scan
line bending is performed by the following manner:
As shown in FIG. 1, a liquid crystal deflection device array 21Y is
provided for this purpose. The liquid crystal deflection device
array 21Y is provided with its longitudinal axis parallel to the
main scanning direction on the optical path between the
optical-path bending mirrors 18Y and 19Y. Further, a scan line
bending detection device 22Y is provided. The scan line bending
detection device 22Y is provided also with its longitudinal axis
parallel to the main scanning direction.
As the liquid crystal deflection device array 21Y is slightly
inclined in the subscanning direction, a part of the deflected beam
incident onto the liquid crystal deflection device array 21Y from
the light-path bending minor 18Y is reflected by a glass substrate
provided on the surface of the liquid crystal deflection device
array 21Y.
The scan line bending detection device 22Y is disposed in such a
manner that a light-receiving part thereof be used as a detection
surface on which an optical spot is formed by the above-mentioned
part LY of the deflected beam reflected by the liquid crystal
deflection device 21Y, and receives the reflected deflected beam
part LY. The above-mentioned detection surface is a surface
approximately optically equivalent to a part of the scanning
surface on the photoconductor 20Y which is optically scanned by the
beam originally same as the beam part LY.
The output of scan line bending detection device 22Y is input into
a controller 23 made of a computer, etc. The controller 23, based
on this input from the scan line bending detection device 22Y,
generates a correction signal indicating the scan line bending
state on the photoconductor 20Y detected, and corrects the
thus-indicated scan line bending state by providing this signal to
the liquid crystal deflection device array 21Y. The scan line
bending state on the photoconductor 20Y is corrected by the liquid
crystal deflection device array 21Y which appropriately controls
the light path of the incident beam by the function of the liquid
crystals according to the given correction signal.
Although not shown in FIG. 1 in order to avoid complication, a pair
of the same liquid crystal deflection device array and scan line
bending detection device as the above-mentioned liquid crystal
deflection device array 21Y and the scan line bending detection
device 22Y are also provided on the light path directed toward each
of the photoconductors 20M, 20C, and 20K. The detection output of
each scan line bending detection device of each pair is also input
to the controller 23, which then controls the corresponding liquid
crystal deflection device array based on the input, and the
controller 23 corrects the scan line bending state on each
photoconductor in the same manner.
The above-mentioned liquid crystal deflection device array will now
be described. Below, the liquid crystal deflection device array is
described assuming that it is driven by an electric signal, while,
in general, a liquid crystal deflection device is driven either by
an electric signal or by a magnetic signal.
In general, a liquid crystal deflection device which deflects a
beam either by controlling a refractive index thereof or by
controlling diffraction effect thereof with an electric signal.
First, a liquid crystal deflection device in a type such that the
refractive index thereof is controlled will now be described. Such
a type of liquid crystal deflection device is disclosed by Japanese
laid-open patent application No. 63-240533. FIGS. 2A and 2B show
one example thereof.
In FIG. 2B, a liquid crystal 1 is a nematic liquid crystal positive
in dielectric anisotropy, and is sealed in a form of thin film
between a pair of transparent orientation films 2A and 2B which has
a predetermined gap maintained by means of spacers 3. The liquid
crystal includes liquid crystal molecules 1A each of which is long
along its molecule axis direction. The orientation film 2A has
undergone orientation processing such that, thereby, the molecule
axis of each liquid crystal molecule 1A becomes perpendicular to
the surfaces of the orientation film 2A, while the orientation film
2B has undergone orientation processing such that, thereby, the
molecule axis of each liquid crystal molecule 1A becomes parallel
to the surfaces of the orientation film 2B.
A transparent resistance film 4 of ZnO etc. is formed outside of
the orientation film 2A. The transparent resistance film 4, the
orientation films 2A and 2B, and liquid crystal 1 are sandwiched by
a pair of transparent glass substrates 5A and 5B, as shown in FIG.
2B. A transparent electrode film 6 of ITO, etc. is formed on one
side of the glass substrate 5B on the side of the orientation film
2B through whole surface thereof.
On the other hand, electrodes 7A and 7B in a pattern shown in FIG.
2A are formed on a side of the glass substrate 5A on the side of
the orientation film 2A, and these electrodes 7A and 7B are in
contact with the resistance film 4, as shown in FIG. 2B. They are
formed of the transparent electrodes of ITO, etc. as mentioned
above, for transmitting an incident beam. However, in case the
electrodes 7A and 7B are disposed in such positions as not blocking
any relevant beam, they may be formed of a material such as metal
films which are not transparent.
In the state of FIG. 2B, the electrode film 6 and the electrode 7B
are grounded, and when a voltage V is applied between terminals A
and B of the electrodes 7A and 7B shown in FIG. 2A, the potential
of the resistance film 4 declines linearly from the electrodes 7A
though the electrode 7B. For this reason, between the resistance
film 4 and transparent electrode film 6, an electric field occurs
along the right-and-left direction of the figure which declines
linearly from the top through the bottom in FIG. 2B.
This electric field drives the liquid crystal 1 in such a manner
that the liquid crystal molecules 1A are rotated so that each
molecule axis may become parallel to the electric field. Since the
rotation angle of the liquid crystal molecule 1A is linearly
proportional to the strength of the electric field given, the
molecule axis of each liquid crystal molecule 1A present near the
electrode 7A tends to become parallel to the direction of electric
field (the right-and-left direction in the figure) while the same
near the electrode 7B has almost no influence by the electric
field, and, as a result, the molecule axis of each liquid crystal
molecule 1A is almost retained as being parallel to the electrode
film 6.
The dielectric constant of each liquid crystal molecule 1A becomes
larger in a direction parallel to its molecule axis, and smaller in
a direction which intersects perpendicularly with its molecule
axis. For this reason, the refractive index becomes larger in a
direction which is nearer to the direction parallel to the molecule
axis of each liquid crystal molecule in the liquid crystal.
Accordingly, according to the variation in direction of molecule
axis mentioned above with reference to FIG. 28, the refractive
index of the liquid crystal 1 becomes larger where the molecule
axis is directed nearer to a direction parallel to the electric
field while the same becomes smaller where the molecule axis is
directed nearer to a direction perpendicular to the electric field.
This decline of the refractive index becomes linear from the side
of the electrode 7A through the electrode 7B, as shows in FIG.
2C.
Therefore, when incidence of a beam is made onto the liquid crystal
deflection device having such a refractive-index distribution from
the right-hand side of FIG. 2B, the beam turns toward the side on
which the refractive index is higher (the side at the top in the
figure) as it is transmitted by the liquid crystal deflection
device.
By altering the electrode to be grounded from the electrode 73 into
the electrode 7A, and, also, inverting the direction of the voltage
applied between the terminals A and B, the refractive-index
distribution which declines from the electrode 7B side toward the
electrode 7A side contrary to the case of FIGS. 2A through 2C
occurs, and a transmitted beam can be deflected downward in the
figure in this case.
Thus, beam deflection can be achieved dynamically by means of
refractive index control in the liquid crystal deflection device.
According to this configuration, the beam deflection amount or beam
deflection angle is saturated by a value inherent to a particular
liquid crystal deflection device. No further beam deflection can be
obtained after the saturation occurs. A direct-current voltage may
be used as an electric signal which drives the liquid crystal
deflection device. However, in terms of the life of the liquid
crystal deflection device, the electric signal to be applied is
preferably such that a pulse-like or sinusoidally modulated signal
and the average of the voltage become approximately 0 volts.
Control of the deflection angle can be made by changing the voltage
of the electric signal applied to the liquid crystal deflecting
device. However, instead, it is also possible to achieve the same
effect by controlling the duty ratio in pulse of the pulse-like
modulated signal.
FIGS. 3A through 3C shows anther example of the liquid crystal
deflection device employing the scheme of controlling the
refractive index with an electric signal. In order to avoid
complexity, the same reference numerals are applied as those in
FIGS. 2A through 2C. This device is a variant of the device shown
in FIGS. 2A through 2C. In the configuration shown in FIGS. 3A
through 3C, on the side of the glass substrate 5A, three
transparent resistance films 4A, 4B and 4C are provided as shown in
FIG. 3A. Patterning of a transparent electrode is made as shown,
and, thus, electrodes 7A1 and 7B1 are provided for the resistance
film 4A, electrode 7A2 and 7B2 are provided for the resistance film
4B, and electrodes 7A3 and 7B3 are provided for the resistance film
4C. When a drive signal is applied between terminals A and B, a
refractive-index distribution as shown in FIG. 3C occurs in this
configuration. In this case, since the rate of change of the
electric field with respect to the voltage V applied between the
terminals A and B can be made larger, as compared with the device
configuration shown in FIGS. 2A through 2C, a larger
refractive-index inclination is acquired more, and thereby, a
larger beam deflection angle (the amount of beam deflection) can be
acquired.
FIGS. 4A and 4B show another example of the liquid crystal
deflection device. This liquid crystal deflection device provides
diffraction controlled according to an electric signal. This type
of liquid crystal deflection device is disclosed by Japanese
laid-open patent application No. 8-313941. Also in this case, in
order to avoid complexity, the same reference numerals are given as
those in the case of FIGS. 2A through 2C.
In FIG. 4A, a nematic liquid crystal negative in dielectric
anisotropy such that the dielectric constant along the direction of
the molecule axis of liquid crystal molecule 1A is smaller than the
dielectric constant of the direction which intersects
perpendicularly with the molecule axis is employed as the liquid
crystal 1. Between a pair of transparent orientation films 2A and
2B maintained by spacers 3 in a predetermined gap, the liquid
crystal 1 in a form of thin layer is sealed.
Orientation films 2A and 2B are sandwiched by a glass substrate 5A
which has a transparent electrode 6A, and a glass substrate 5B
which has a transparent electrode 6B. The transparent electrodes 6A
and 6B are formed in a shape of thin films made of ITO or the like,
and are uniformly provided on the surfaces of the glass substrates
5A and 5B, respectively, with predetermined shapes (for example,
rectangles).
The orientation films 2A and 2B have undergone orientation
processing such that, in the liquid crystal 1, the direction of the
molecule axis of each liquid crystal molecule 1A of the liquid
crystal 1 may turn into a direction which intersects
perpendicularly with the drawing. In such a configuration, when a
direct current or the voltage of a low frequency on the order of
300 Hz or less is applied between the transparent electrode 6A and
6B, a diffraction lattice pattern which has a vertical lattice
arrangement direction (which intersects perpendicularly with the
above-mentioned orientation direction) in the figure is formed in
the liquid crystal 1 (see paragraph [0054] of the above-mentioned
Japanese laid-open patent application No. 8-313941). FIG. 4B shows
a refractive-index distribution in the diffraction lattice pattern
formed in this way.
When a beam is incident onto the liquid crystal deflection device
having the above-mentioned configuration, the transmitted light
causes diffraction light thanks to the above-mentioned diffraction
lattice pattern (in the vertical direction of FIG. 4A). When the
voltage value of the voltage in the low frequency is changed, the
lattice pitch in the diffraction lattice pattern changes, and the
diffraction angle changes (see paragraph [0057] of the
above-mentioned Japanese laid-open patent application No.
8-313941).
Accordingly, as to .+-.1st light of the above-mentioned diffraction
for example, the beam can be deflected in a predetermined direction
(the vertical direction of FIG. 4A, in this example) by
appropriately adjusting the deflection angle of the 1st light.
Moreover, when the voltage applied between the transparent
electrodes 6A and 6B in the above-mentioned liquid crystal
deflection device shown in FIG. 4A is made into a high frequency
voltage, the diffraction lattice pattern in the direction which
intersects perpendicularly to the orientation direction of the
liquid crystal 1 occurs, and the diffracted light in the direction
which intersects perpendicularly to FIG. 4A can be obtained. In
this case, the diffraction angle can be controlled by controlling
the envelope voltage of the high frequency voltage applied to the
liquid crystal (see paragraph [0060] of the above-mentioned
Japanese laid-open patent application No. 8-313941).
In the above, description has been made on the liquid crystal
deflection device in the type which deflects an incident beam by an
electric signal briefly.
According to the embodiment of the present invention, a liquid
crystal deflection device having such a well-known configuration
(not only in the above-mentioned type of being driven by an
electric signal but also in a type of being driven by a magnetic
signal which is also known) is utilized for correcting scanning
characteristics occurring due to beam deflection onto a scanning
surface by means of an optical scanning device, and also, for
correcting the above-mentioned scan line bending which includes
modes of scan line inclination and scan line positional
deviation.
The liquid crystal deflection device array (an array of the
above-mentioned liquid crystal deflection devices) may be provided
either on the light source side of the optical deflection scanning
device or in the scanning surface side of the optical deflection
scanning device. The former plan can miniaturize the liquid crystal
deflection device as compared with the latter plane, and, thus, is
advantageous in terms of reduction in costs. However, in order to
correct the scan line bendinging satisfactorily, ii is necessary to
drive the liquid crystal deflection device array at a sufficiently
high deflection rate with respect to the scanning frequency in the
optical deflection scanning device. Generally, the liquid crystal
deflection device inherently has the property such that the
response speed becomes lower as the required beam deflection angle
is increased (decreasing in proportion to the approximately 2nd
power of the deflection angle). Accordingly, high-speed correction
operation is difficult to be achieved. The case where providing the
liquid crystal deflection device on the light source side of the
optical deflection scanning device has this issue.
In contrast thereto, in case the liquid crystal deflection device
array is provided on the scanning surface side of the optical
deflection scanning device, the required rate of changing the
correction amount in the beam deflection angle provided by the
liquid crystal deflection device array should not be increased so
much. In other words, a certain value in the beam deflection angle
once set may be maintained for a relatively long interval. For
example, in case a required amount by which the beam deflection
angle is to be changed is within five minutes, the response rate of
less than approximately 0.1 seconds can be achieved, and, thus, a
sufficient response rate can be provided. Accordingly, it is
preferable that the liquid crystal deflection device array be
provided on a deflected beam as in the configuration shown in FIG.
1.
According to the first embodiment of the present invention
described above, since the scan line bending of the optical spot
performing the optical scanning for every photoconductor is
detected, even when a change occurs in the scan line bending
resulting from a change in the characteristics of the f.theta. lens
due to aging, environmental change or so arises, proper scan line
bending correction can be achieved at any time.
The scan line bending state may be detected before the color image
formation process is performed each time, or may be detected at
predetermined intervals, i.e., once a day, every three days, or the
like, or, may be performed on an input operation by a users. In
case the color image formation process is repeated successively,
change in the scan line bending state resulting from temperature
rise inside the machine occurring due to the continuation image
formation process can be coped with by carrying out the detection
of the scan line bending state once, or several time per every
image formation process.
With reference to FIGS. 5A through 5D, description of the liquid
crystal deflection device array 21Y according to the first
embodiment of the present invention will now be made for a case of
correction in the scan line bending on the photoconductor 20Y shown
in FIG. 1. In FIG. 5A, the liquid crystal deflection device array
21Y is controlled by the controller 23. This liquid crystal
deflection device array 21Y includes a plurality of liquid crystal
deflection devices L1 through L10 arranged along the main scanning
direction. Each device Li (i=1 through 10) of the liquid crystal
deflection device array 21Y has a function of deflecting an
incident beam along the subscanning direction (vertical direction
in FIG. 5A). The plurality of devices of the liquid crystal
deflection device array 21Y are continuously arranged without gaps
therebetween. As described above, each liquid crystal deflection
device of the liquid crystal deflection device array 21Y may be
controlled either by an electric signal or by a magnetic signal,
and thereby, deflects the incident beam at an arbitrary deflection
angle. In this embodiment, the respective devices of the liquid
crystal deflection device array 21Y have the same size, and are
arranged at equal pitches therebetween.
Each liquid crystal deflection device of the liquid crystal
deflection device array 21Y includes a driver circuit Di (i=1
through 10) for a relevant liquid crystal deflection device Li of
the liquid crystal deflection device array 21Y, and each driver
circuit Di is controlled by the controller 23. Each liquid crystal
deflection device Li is the same as the liquid crystal deflection
device shown in FIGS. 2A and 2B described above, for example, and
is driven by an electric signal. In this case, the orientation
films 2A, 2B which sandwich the liquid crystal and the transparent
electrode 6 are common for the plurality of liquid crystal
deflection devices L1 through L10 while the electrodes 7A, 7B and
the transparent resistance film 4 which connects therebetween are
provided for each liquid crystal deflection device Li of the
plurality of liquid crystal deflection devices L1 through L10.
Then, each liquid crystal deflection device Li of the liquid
crystal deflection device array 21Y is individually driven by the
relevant driver circuit Di via the electrodes 7A and 7B.
Optical sensors P1 through P10 are provided for the respective ones
of the above-mentioned liquid crystal deflection devices L1 through
L10 of the liquid crystal deflection device array corresponding, on
the scan line bending detection device 22Y as shown in FIG. 5B. The
respective light-receiving surfaces of these sensors P1 through P10
are arranged in the main scanning direction. These light-receiving
surfaces correspond to the respective liquid crystal deflection
devices L1 through L10 of the liquid crystal deflection device
array 21Y. Then, when an optical spot is detected at the center of
the light-receiving surface of each optical sensor Pi, the
deflection beam which forms this optical spot can be regarded as
passing through the center of the corresponding liquid crystal
deflection device Li. In addition, a range RY shown in FIG. 5B
corresponds to an effective drawing range (responsible scanning
range) on the photoconductor 20Y.
Each optical sensor Pi of scan line bending detection device 22Y
detects the position of the subscanning direction (the vertical
direction in FIG. 5B) of the optical spot of the incident beam.
The optical sensors Pi are fixed on a fixing plate 22S made of a
material having a thermal expansion coefficient not more than
1.0.times.10.sup.-5/.degree. C. such as a glass (thermal expansion
coefficient of 0.5.times.10.sup.-5/.degree. C.), a ceramic material
(alumina of thermal expansion coefficient of
0.7.times.10.sup.-5/.degree. C., silicon-carbide of thermal
expansion coefficient of 0.4.times.10.sup.-5/.degree. C.), or the
like. Thereby, detection accuracy can be prevented from being
degraded due to an absolute shift or relative shifts of the
light-receiving surfaces of the optical sensors Pi, caused by
temperature change or the like, substantially.
Moreover, in order to avoid an influence of electric noise
generated between the optical sensors Pi, a
non-electric-conductivity material as mentioned above is suitable
for the material of the fixing plate 22S. For example, if the
fixing plate 22S were made by an aluminum alloy having the thermal
expansion coefficient of 2.4.times.10.sup.5/.degree. C., the scan
line bending detection accuracy might be degraded due to
temperature change.
The scan line bending detection and scan line bending correction
are performed by the following procedures in the configuration
described above:
In FIG. 1, the optical deflection scanning device 15 is rotated
before an actual color image forming process, and then, one
light-emission source of the light source device 11Y is made to
emit a light. At this time, the light emission of the
light-emission source is performed intermittently, and the optical
spot of beam LY reflected by the liquid crystal deflection device
21Y for every light-emission is made incident onto each of the
optical sensors P1 through P10 of the scan line bending detection
device 22Y, one by one.
The scan line bending detection device 22Y outputs a signal
indicating the position of the optical spot along the subscanning
direction on each of the optical sensor Pi detects, to the
controller 23. FIG. 5C shows the thus-detected positions of the
optical spots along the subscanning direction by black dots. The
broken line in the same figure denotes the ideal scan line which is
linear along the main scanning direction
The controller 23 approximates the thus-detected shape of the scan
line by a polynomial by means of the well-known least-square
method, or the like, based on thus-detected ten positions of the
optical spots along the subscanning direction. This polynomial
expresses a detected scan line bending state shown in FIG. 5C by a
solid curve.
The controller 23 calculates the direction and the amount
(deflection angle) by which each liquid crystal deflection device
Li of the liquid crystal deflection device array 21Y should provide
a beam deflection for the scan line bending correction along the
subscanning direction, one by one. A range Si (i=1 through 10) in
FIG. 5C denotes a scanning range where each liquid crystal
deflection device Li of the liquid crystal deflection device array
21Y should deflect an incident beam, and a vertical arrow in each
range Si denotes the direction of the required beam deflection to
be provided for the purpose of correction.
The controller 23 determines a signal by which the above-mentioned
direction and the amount of beam deflection should be provided by
each liquid crystal deflection device Li of the liquid crystal
deflection device array 21Y, and applies it to the relevant driver
circuit Di. In this embodiment, the direction of beam deflection is
controlled by controlling the direction of voltage applied to the
terminal A and B (see FIG. 2A) of each liquid crystal deflection
device, while the amount of beam deflection is controlled by
controlling the duty ratio of the pulse signal of the voltage
applied to the same terminals A and B, as mentioned above.
Thus, before starting of actual color image formation process, the
direction and the amount of beam deflection provided by each liquid
crystal deflection device Li of the liquid crystal deflection
device array 21Y along the subscanning direction is adjusted. In
FIG. 1, the same manner is applied also for each of the other
photoconductors for the respective color components.
The direction and amount of beam deflection provided by each liquid
crystal deflection device Li of the liquid crystal deflection
device array 21Y which is thus set once is maintained until an
alteration is needed. Thus, each liquid crystal deflection device
Li of the liquid crystal deflection device array 21Y provides the
same direction and amount of deflection to an incident beam each
time the optical scanning is performed.
It is noted that, in case the detected deviation of the position of
actual optical spot from the ideal one is so small that no
correction is needed for each optical sensor Pi, the relevant
liquid crystal deflection device Li of the liquid crystal
deflection device array 21Y should provide no deflection on an
incident beam, and, thus, the relevant driver circuit Di is made to
output the driving signal of 0.
After that, when performing an optical scan (multi-beam scan) on
each photoconductor in this state, the optical scan can be achieved
in a condition in which the scan line bending is well corrected. In
fact, the optical scan to each photoconductor is of a multi-beam
manner. However, since the scan line bending state is substantially
same between the optical spots formed by the optical scans of the
same photoconductor simultaneously as mentioned above, the scan
line bending is well corrected on each optical spot for a
respective color component.
FIG. 5D shows the state of the thus-corrected scan line. In the
figure, Yi (i=1 through 10) denotes a portion of scan line which
each liquid crystal deflection device Li of the liquid crystal
deflection device array 21Y corrects on the photoconductor 20Y.
Although the scan line shown in the figure by a solid curve seems
not very flat, this is merely because the scan line bending state
is shown in FIG. 5C in a manner of exaggerated for the purpose of
clear illustration. An actual case of scan line bending is at most
on the order of 0.1 through 0.2 mm. Accordingly, even assuming that
each liquid crystal deflection device Li of the liquid crystal
deflection device array 21Y takes charge of the portion Yi of scan
line is 30 mm, for example, a substantially flat scan line can be
achieved.
When the number of the liquid crystal deflection device Li form the
entire liquid crystal deflection device array 21Y is increased,
scan line bending can be corrected more precisely or finely
accordingly. Especially, by sufficiently reducing the width in the
main scanning direction of each liquid crystal deflection device Li
of the liquid crystal deflection device array 21Y, for example, on
the order of 2 through 5 mm, the differences between respective
adjacent liquid crystal deflection devices can be substantially
regarded as a smooth one, and, thus, the scan line can be corrected
into substantially continuous straight line more strictly.
By the above-described scan line bending correction operation, each
of various modes of scan line bending such as inclination of scan
line, positional deviation of scan line and so forth can be well
corrected.
Moreover, it is also possible to intentionally provide difference
in the pitch and density of the particular liquid crystal
deflection device forming the entire liquid crystal deflection
device array 21Y according to a given characteristics of scanning
image-formation optical system (f.theta. lens, or the like).
Specifically, especially in a portion in which the scanning
position deviation is likely to occur due to temperature change or
the like, the main scanning direction size of each liquid crystal
deflection device Li of the liquid crystal deflection device array
may be made smaller, and simultaneously the number of liquid
crystal deflection device Li disposed there may be increased there.
Thereby, without increasing the whole number of liquid crystal
deflection device Li of the liquid crystal deflection device array
much, and, thus, without increasing the whole number of optical
sensors much, minimum necessary scan line bending correction can be
well achieved.
With the color image formation device of FIG. 1, since, as
described above, the scan line bending occurring due to optical
scanning is well corrected for each photoconductor, the phenomenon
of the above-mentioned color deviation in the subscanning direction
resulting from disagreement of scan lines among the respective
photoconductors can be reduced effectively. Thereby, satisfactory
full-color images not substantially having color deviation in the
subscanning direction can be obtained.
In the above-described embodiment of the present invention, the
liquid crystal deflection device array has the series of liquid
crystal subscanning-directional deflection devices, and a part of
image-formation beam having passed through the scanning
image-formation optical system (f.theta. lens) is detected by the
scan line bendinging detection device. In particular, a part of
image-formation beam having passed-through the scanning
image-formation optical system is extracted and is directed toward
a detection surface which is equivalent to the scanning surface
(photoconductor) by means of the liquid crystal deflection device
array being inclined with respect to the subscanning direction, and
the grass substrate of the liquid crystal deflection device array
reflecting a part of the incident beam and directing it to the
detection surface.
However, other than this method, as an alternative way, a special
beam extracting device may be provided with a prism having a
hemi-transparent film having the reflective factor on the order of
1 through 2%, for example, which may be disposed on the light path
of the image-formation beam.
Furthermore, as a further alternative way, even in case of using
the liquid crystal deflection device array itself as a beam
extracting device in the case of the above-mentioned embodiment, as
shown in FIG. 6A the sizes of the spacers 3A and 3B sealing the
liquid crystal may be differed from each other. Consequently, it is
possible to give an angle between the glass substrate 5a (forming
the transparent electrode, transparent resistance film and
orientation film) and the glass substrate 5b (forming the
transparent electrode and orientation film). Thereby, even in case
the liquid crystal deflection device itself is not inclined,
appropriate inclination of the glass substrate 5a by which a part
of image-formation beams is extracted and directed toward the
detection surface can be obtained.
The scan line bending is corrected in the embodiment described
above using the series of liquid crystal subscanning-directional
deflection devices. Thus, the problem of optical scanning
concerning the subscanning direction is solved. However, there also
is a problem of optical scanning concerning the main scanning
direction, i.e., a problem on the uniform velocity. If distortions
in the main scanning direction among the respective color component
images differ mutually due to the insufficient performance of
uniform velocity, a problem of a color deviation may occur in the
main scanning direction.
Such an insufficiency in the uniform velocity performance can be
detected by detecting a position of optical spot along the main
scanning direction with each area sensor Pi (i=1 through n) shown
in FIG. 5B, for example (As to specific may, a description will be
made later). Thus, the area sensors Pi may be used both as the
above-mentioned scan line bending detecting device and a uniform
velocity performance detecting device. Then, by using the
respective liquid crystal deflection devices Li (i=1 through n) of
liquid crystal deflection device array 21Y shown in FIG. 5A in this
case each having its deflection direction set in the main scanning
direction, the relevant correction can be performed. Specifically,
similar to the above-mentioned case of correcting the scan line
bending, the incident beam is deflected, in this case, in the main
scanning direction appropriately, so that the insufficiency in the
uniform velocity performance can be corrected.
By providing both the series of liquid crystal
subscanning-directional deflection devices and the series of liquid
crystal main-scanning-directional deflection devices
simultaneously, both the scan line bending and uniform velocity
performance insufficiency can be corrected. In this case, as shown
in FIG. 6B, it is preferable to provide an integrally combined
structure of both the series of liquid crystal
subscanning-directional deflection devices 21A and the series of
liquid crystal main-scanning-directional deflection devices 21B,
each being arranged in the main scanning direction which is
perpendicular to the figure. These respective series of devices 21A
and 21B are arranged along the beam transmission direction
(horizontal direction in the figure)
FIG. 7 shows an image formation device in a second embodiment of
the present invention. This device is also a color image formation
device in a tandem type as the above-mentioned first embodiment
shown in FIG. 1. In the configuration shown in FIG. 7, two polygon
mirrors 51 and 52 are provided. These polygon minors 51 and 52 have
the same configuration and are provided on a common rotation shaft
so that they are rotated integrally. They act as optical deflection
scanning devices. Although not shown, four light source devices are
also provided. Beams coming from two thereof are incident on the
polygon mirror 51 while two beams coming from the other two light
source devices are incident on the polygon mirror 52. Arrangement
of the respective light source devices and the optical arrangement
on the optical path from each light source device to the polygon
mirror 51/52 are the same as those in the configuration shown in
FIG. 1.
Deflected beams LSY and LSK deflected by the polygon mirror 52 are
beams for drawing a yellow component image and a black component
image, respectively. After passing through lenses LNY1 and LNY2
which form an f.theta. lens as a scanning image-formation optical
system, the deflected beam LSY is reflected by optical-path bending
mirrors MY1, MY2, and MY3, in sequence, then, is directed to a
photosensitive surface (acting as the scanning surface) of a
photoconductor 50Y having an optical conductivity, and performs an
optical scanning operation onto the above-mentioned photosensitive
surface. The photoconductor 50Y has a cylinder shape, and uniform
electrification is carried out thereon by means of an
electrification device CY, is rotated in a direction of the arrow
shown, the optical scanning is carried out thereon with an optical
spot of the above-mentioned deflected beam LSY, and thus, a yellow
component image is written thereon. Thereby, a yellow latent image
is formed thereon.
After passing through lenses LNK1 and LNK2 which form an f.theta.
lens as a scanning image-formation optical system, the deflected
beam LSK is reflected by optical-path bending mirrors MK1, MK2, and
MK3, in sequence, then, is directed to a photosensitive surface
(acting as the scanning surface) of a photoconductor 50K having an
optical conductivity, and performs an optical scanning operation
onto the above-mentioned photosensitive surface. The photoconductor
50K has a cylinder shape, and uniform electrification is carried
out thereon by means of an electrification device CK, is rotated in
a direction of the arrow shown, the optical scanning is carried out
thereon with an optical spot of the above-mentioned deflected beam
LSK, and a black component image is written thereon. Thereby, a
black latent image is formed thereon.
Deflected beams LSM and LSC deflected by the polygon mirror 51 are
beams for drawing a magenta component image and a cyan component
image, respectively. After passing through lenses LNM1 and LNM2
which form an f.theta. lens as a scanning image-formation optical
system, the deflected beam LSM is reflected by optical-path bending
mirrors MM1, MM2, and MM3, in sequence, then, is directed to a
photosensitive surface (acting as the scanning surface) of a
photoconductor 50M having an optical conductivity, and performs an
optical scanning operation onto the above-mentioned photosensitive
surface. The photoconductor 50M has a cylinder shape, and uniform
electrification is carried out thereon by means of an
electrification device CM, is rotated in a direction of the arrow
shown, the optical scanning is carried out thereon with an optical
spot of the above-mentioned deflected beam LSM, and the magenta
component image is written thereon. Thereby, the magenta latent
image is formed thereon.
After passing through lenses LNC1 and LNC2 which form an f.theta.
lens as a scanning image-formation optical system, the deflected
beam LSC is reflected by optical-path bending mirrors MC1, MC2, and
MC3, in sequence, then, is directed to a photosensitive surface
(acting as the scanning surface) of a photoconductor 50C having an
optical conductivity, and performs an optical scanning operation
onto the above-mentioned photosensitive surface. The photoconductor
50C has a cylinder shape, and uniform electrification is carried
out thereon by means of an electrification device CC, is rotated in
a direction of the arrow shown, the optical scanning is carried out
thereon with an optical spot of the above-mentioned deflected beam
LSC, and the cyan component image is written thereon. Thereby, the
cyan latent image is formed thereon.
Either the single beam scanning method or the multi-beam scanning
method (as in FIG. 14A, for example) may be applied to the optical
scan of each photoconductor. Moreover, as the electrification
device for each photoconductor, not only the device of a corona
electric discharge type but also a device of a contact type, such
as an electrification roller or an electrification brush may be
applied.
The respective latent images of yellow, magenta, cyan and black
formed on the photoconductors 50Y, 50M, 50C, and 50K are developed
by toners (yellow toner, magenta toner, cyan toner, black toner) of
respective development devices 53Y, 53M, 53C, and 53K,
respectively, and thus are visualized. Thus, the black toner image
is formed on the photoconductor 50K, the yellow toner image is
formed on the photoconductor 50Y, the magenta toner image is formed
on the photoconductor 50M, and the cyan toner image is formed on
the photoconductor 50C, respectively. Each of these color-component
toner images is transferred onto a transfer paper S which is a
sheet-like recording medium, as follows.
That is, an endless-type conveyance belt 54 is hung on pulleys 55
and 56, and the photoconductors 50Y, 50M, 50C, and 50K are touched
at the lower part therefor as shown in FIG. 7. These
photoconductors 50Y through 50K are faced with transfer devices
57Y, 57M, 57C, and 57K (may be of a contact type, such as transfer
rollers, although ones of a corona electric discharge type are
shown) in the inner surface of the conveyance belt 54 through the
belt sheet.
The transfer paper S is provided from a cassette 58, is fed via
rollers 59 onto the conveyance belt 54, and in response to
electrification with an electrification device 60, an electrostatic
adsorption effect occurs thereby, and it is held by a perimeter
part of the conveyance belt 54. The conveyance belt 54 rotates
counterclockwise, and conveys the transfer paper S along the
circumferential surface of the belt. While the transfer paper S is
thus conveyed, first, the transfer device 57Y transfers the yellow
toner image onto the transfer paper S from the photoconductor 50Y,
then similarly, the transfer devices 57M, 57C and 57K transfer the
other color-component toner images from the respective
photoconductors 50M and 50C and 50K to the same transfer paper in
sequence in a piling-up manner. The transfer of each
color-component toner image is performed in such a manner that
mutual position registration or alignment is performed
appropriately. Thus, a full-color image is formed on the transfer
paper S.
The transfer paper S which has the full-color image formed thereon
undergoes charge removal by a charge removal device 61, and
separates from the conveyance belt 54 by its own hardness, and,
then, the full-color image is fixed on this paper with a fixing
device 62. Then, the paper is ejected onto a tray 64 which is a top
plate of the image formation device, with an ejecting roller
63.
Each photoconductor after the toner image is transferred therefrom
then undergoes cleaning of remaining toner, paper dust, and so
forth by a corresponding cleaner 65Y, 65M, 65C, or 65K. Moreover,
the conveyance belt 54 undergoes electricity removal by an
electricity removal device 66, and is cleaned with a cleaner
67.
The above is an outline of the image formation process. The way of
toner image transfer to the transfer paper of each color toner
image in the embodiment shown in FIG. 7 may also be applied to the
first embodiment shown in FIG. 1. Similarly, the way of transfer of
each color-component toner image to the intermediate transfer belt,
after that, into a transfer paper in the embodiment of FIG. 1 may
be applied to the embodiment shown in FIG. 7.
In the second embodiment shown in FIG. 7, the scanning
image-formation optical system of f.theta. lens is provided for
each of the four deflected beams coming from the two polygon
mirrors 51 and 52. Thus, total 4 sets of f.theta. lenses are
provided, each including two lenses. These 4 sets of f.theta.
lenses are optically equivalent mutually, and the optical path
length toward the relevant photoconductor from each light source
device is also set up equally. Moreover, each f.theta. lens is held
respectively at a plate PTY, PTM, PTC, or PTK, and is fixed to an
optical housing 75. Each plate touches the relevant lenses by the
whole or partial surfaces thereof.
The lenses LNY1, LNM1, and LNC1 are made of a same resin material,
and, also, the lenses LNY2, LNM2, and LNC2 are made of a same resin
material. As these materials, a polycarbonate, or a synthetic resin
which includes a polycarbonate as a main ingredient thereof
superior in low water absorptivity, high transparency, and
fabrication easiness is suitable. By applying such a resin
material, formation of a non-spherical surface can be easily
achieved, with low costs, and, thus, cost reduction of the entire
full-color image formation device can be achieved.
On the other hand, the lenses LNK1 and LNK2 are used in this
embodiment an optical system used as a `scanning position standard
or reference`. Accordingly, they are made of a material with a
small thermal expansion coefficient (for example, a glass (thermal
expansion coefficient of 0.5.times.10.sup.-.sub.5/.degree. C.)) in
order to avoid deformation thereof due to temperature change. In
fact, if plastic lenses (having a thermal expansion coefficient of
7.0.times.10.sup.-5/.degree. C.) such as polycarbonate ones were
used, since the image-formation position of optical spot would
change remarkably due to temperature change, they could not be used
as a standard or reference.
Further, in the embodiment shown in FIG. 7, on the light path of
the deflected beams LSY, LSM, and LSC, liquid crystal deflection
devices 70Y, 70M, and 70C are disposed as shown, while, on the
light path of deflected beam LSK, a transparent parallel glass
plate 70K is disposed.
Each of the liquid crystal deflection device arrays 70Y, 70M, and
70C may be same as that described above with reference to FIG. 1
(first embodiment), which is a main-scanning-directional deflective
liquid crystal deflection device array and/or a
subscanning-directional-deflective liquid crystal deflection device
array, or an integral combination thereof as shown in FIG. 6B.
Moreover, although not shown in FIG. 7, the reflected light from a
glass substrate of each of the liquid crystal deflection device
arrays 70Y, 70M, and 70C on the incidence side is directed to a
detection surface optically equivalent to the scanning surface
(photoconductor surface to be scanned by image-formation beam), and
a scan line bendinging detection device (not shown) can detect the
scanning characteristics (the above-mentioned uniform velocity
performance and/or the scan line bending) from each deflected beam
LSY, LSM, or LSC. Detection of such scanning characteristics can be
performed in a manner as in the case of the first embodiment shown
in FIG. 1.
On the other hand, a transparent parallel glass plate 70K is
inserted for the purpose of light path adjustment among the
deflected beams LSY, LSM, LSC and LSK. As mentioned above, 4 sets
of f.theta. lenses are optically equivalent mutually, and the light
path length toward the photoconductor from each light source device
is also set up equally. However, since the liquid crystal
deflection device arrays 70Y, 70M, and 70C are inserted into the
light paths of the deflected beam LSY, LSM, and LSC, respectively,
and thus, the light path length of these beam becomes shorter than
actual light path length optically. Therefore, the transparent
parallel glass plate 70Y is inserted in order to equalize the light
path length of deflected beam LSK with the optical light path
length of any other deflected beams.
Therefore, the transparent parallel glass plate 70K has an optical
thickness (i.e., a product of the physical thickness by the
refractive index) set up so that it becomes equivalent to the
optical thickness of any other liquid crystal deflection device
array.
In this second embodiment, the optical system which forms the light
path of deflected beam LSK is made of a glass material with the
small thermal expansion coefficient. Accordingly, it is hardly
affected by ambient temperature and humidity. Thus, the optical
characteristic thereof is unchanged even due to environmental
change, and therefore, the scanning characteristics (scan line
bending and uniform velocity performance) of optical scanning
performed by the deflected beam LSK is regarded as a standard.
Since the f.theta. lens which forms the light path is a product
made of a resin, the scanning characteristics in the optical
scanning performed by each of the deflected beam LSY, LSM, and LSC
changes due to change in ambient temperature and humidity. This
change in the scanning characteristics is detected by means of the
above-mentioned detection device, and based on the detection
result, the same is corrected by means of the liquid crystal
deflection device array. This correction is performed in a manner
such that the scanning characteristics of each of the deflected
beams LSY, LSM, and LSC be coincide with the scanning
characteristics of deflected beam LSK which is regarded as the
standard scanning characteristics, as mentioned above. Actually,
the liquid crystal deflection device arrays 70Y, 70M, and 70C are
appropriately controlled by a controller which is not shown.
According to this way, it is not necessity of providing the liquid
crystal deflection device on each of all the deflected beams, and,
also, an expensive glass lens should be used only for the scanning
image-formation optical system used as the standard while plastic
lenses can be used for the other scanning image-formation optical
systems. As a result, color image formation device can be reduced
in the cost while it is possible to obtain a quality full-color
image with an effectively reduced color deviation.
In addition, in the first embodiment of FIG. 1, although the
optical scanning of each photoconductor is performed by the
multi-beam scanning scheme, it is also possible to apply a single
beam scanning scheme instead. Moreover, in the first and second
embodiments of FIG. 1 and FIG. 7, the number of photoconductors may
be reduced. In case where two of photoconductors are used,
two-color image formation can be performed. In case a single
photoconductor is used, image formation of monochrome type can be
performed.
Moreover, although, in the embodiments of FIG. 1 and FIG. 7, the
liquid crystal deflection device array is arranged between the
light path bending mirrors in the light path of deflected beam, the
position of liquid crystal deflection device may be determined
instead, between the light path bending mirror and the scanning
surface, between the scanning image-formation optical system and
the first light path bending mirror, or between the optical
deflection scanning device and the scanning image-formation optical
system.
In case providing the main-scanning-directional deflective liquid
crystal deflection device array and subscanning-directional
deflective liquid crystal deflection array such as those 21A and
21B shown in FIG. 6B separately, the main-scanning-directional
deflective liquid crystal deflection device array may be provided
near the optical deflection scanning device rather than near the
scanning image-formation optical system, and the
subscanning-directional deflective liquid crystal deflection device
array may be provided near the scanning surface rather than near
the scanning image-formation optical system.
The aspect of the present invention described in the description of
the second embodiment of the present invention will now be
described in more detail.
As the scan line bending detection device, the same described above
with reference to FIGS. 5A through 5D may be applied. However, it
is also possible to apply a scheme which will be described in the
description of a third embodiment of the present invention shown in
FIG. 10A, instead. FIGS. 8A and 8B illustrate one example of a mode
of correcting scan lines according to the above-mentioned aspect of
the present invention.
FIG. 8A shows each scan line (state in which it is visualized and
transferred onto a common medium) detected by the scan line
deviation detection device. `K` denotes a scan line of a beam which
writes a black component image; `C` denotes a scan line of a beam
which writes a cyan color component image; `Y` denotes a scan line
of a beam which writes in a yellow color component image; and `M`
denotes a scan line of a beam which writes a magenta color
component image.
In FIG. 8A, each of the scan lines Y, M, C, and K has a scan line
bending, and also, is shifted relatively in the subscanning
direction. Then, the scan line bending on the scan line K is
regarded as a standard scan line bending, and, the scan line
correcting device array corrects the scan line bending of any other
scan lines M, C, and Y in a manner such that each of the scan lines
Y, M and C be coincide with or approximate the scan line K, as
indicated as the scan lines Y', M', and C' shown in FIG. 8B. In
other words, correction is made such that scan line bending of each
of the scan lines Y, M and C approximate the standard scan line
bending (of the scan line K), and, thus, the mutual positional
shift in the subscanning direction be eliminated. In other words,
the correction includes a correction of each scan line bending
manner to approximate the scan line bending manner of the standard
scan line bending, and each scan line is corrected to approximate
in subscanning-directional position the standard, scan line.
Although it may be difficult to achieve complete coincidence of
each of the scan lines Y', M' and C' with the scan line K even by
the above-mentioned correction operation, approximate coincidence
thereof is possible as shown in FIG. 8B. In fact, as long as the
mutual positional difference falls within 30 .mu.m, it is possible
to provide a full-color image having no conspicuous color deviation
in a practical situation.
FIG. 8B illustrates an example in which the scan line bending of
the scan line K is regarded as a standard scan line bending.
Similarly, it is also possible that the scan line bending on any
other scan line Y, M or C is regarded as a standard scan line
bending, instead. FIG. 9A illustrates an example in which the scan
line bending of the scan line M is regarded as a standard scan line
bending, and the scan line bending of each of the other scan lines
Y, C and K is corrected to approximate the scan line bending of the
scan line M. FIG. 9B illustrates an example in which the scan line
bending of the scan line C is regarded as a standard scan line
bending, and the scan line bending of each of the other scan lines
Y, M and K is corrected to approximate the scan line bending of the
scan line C. FIG. 9C illustrates an example in which the scan line
bending of the scan line Y is regarded as a standard scan line
bending, and the scan line bending of each of the other scan lines
M, C and K is corrected to approximate the scan line bending of the
scan line Y.
In FIGS. 9A through 9C, the scan lines M, C and Y are the same as
those shown in FIG. 8A. As shown, in this example, among the scan
lines Y, M, C and K, the scan line Y has the minimum scan line
bending, or is nearest to a straight line. Accordingly, in this
case, by regarding the scan line bending of the scan line Y as the
standard, and correcting the scan line bending of each of the other
scan lines M, C and K to approximate the scan line bending of the
scan line Y, as shown in FIG. 9C, the scan line bending on each
scan line comes to have the minimum difference from a straight line
as a whole.
FIG. 10A shows a perspective view of an image formation device in a
third embodiment of the present invention. In this configuration,
four sets of light source devices 110 are provided, each including
a semiconductor laser Ls, a coupling lens Le1, and a cylindrical
lens Le2. A beam emitted from each semiconductor laser Ls is
transformed into a beam in a form (of a parallel beam, a slightly
divergent beam or a slightly convergent beam) suitable for a
subsequent optical system by means of the coupling lens Le1, is
converged in the subscanning direction by the cylindrical lens Le2,
and is imaged as a line image long in the main scanning direction
near a deflection reflective surface of a polygon mirror 112 which
is an optical deflection scanning device. The four semiconductor
lasers Ls as the light sources emit beams for writing yellow,
magenta, cyan, and black color component images, respectively.
The four beams are simultaneously deflected by a polygon mirror
112, and then, pass through a lens 114. The beam which writes a
black component image forms an optical spot on a photoconductor 20K
(in particular, a circumferential scanning surface thereof) having
an optical conductivity with a shape of a drum, after being
reflected by a mirror 116K, passing through a lens 117K, passing
through a half mirror 119K. Thus, the optical spot carries out
optical scanning of the photoconductor 20K in the direction of an
arrow shown. Similarly, the beam which writes a yellow color
component image forms an optical spot on a photoconductor 20Y (in
particular, a circumferential scanning surface thereof) having an
optical conductivity with a shape of a drum, after being reflected
by a mirror 116Y, passing through a lens 117Y, being reflected by a
mirror 118Y, passing through a half mirror 119Y. Thus, the optical
spot carries out optical scanning of the photoconductor 20Y in the
direction of the arrow shown.
Similarly, the beam which writes a magenta color component image
forms an optical spot on a photoconductor 20M (in particular, a
circumferential scanning surface thereof) having an optical
conductivity with a shape of a drum, after being reflected by a
mirror 116M, passing through a lens 117M, being reflected by a
mirror 118M, passing through a half mirror 119M. Thus, the optical
spot carries out optical scanning of the photoconductor 20M in the
direction of the arrow shown. Similarly, the beam which writes a
cyan color component image forms an optical spot on a
photoconductor 20C (in particular, a circumferential scanning
surface thereof) having an optical conductivity with a shape of a
drum, after being reflected by a mirror 116C, passing through a
lens 117C, being reflected by a mirror 118C, passing through a half
mirror 119C. Thus, the optical spot carries out optical scanning of
the photoconductor 20C in the direction of an arrow shown. Thus,
electrostatic latent image of each color component is formed onto
the relevant one of the photoconductors through the optical
scanning operations.
These electrostatic latent images are visualized by toners of
respective color components by means of respective development
devices not illustrated, and then, the thus-created toner images
are transferred onto an intermediate transfer belt 121. In the case
of transfer, each color-component toner image is piled up mutually
one by one and thus forms a full-color image. The thus-obtained
full-color image on the intermediate transfer belt 121 is then
transferred onto a sheet-like recording-medium or transfer paper,
and it is fixed onto this medium/paper. The intermediate transfer
belt 121 after the full-color picture has been transferred
therefrom is cleaned with a cleaning device which is not
illustrated.
In addition, a portion of each deflected beam separated or
extracted by means of the half mirror is detected by a respective
one of light-receiving devices P1Y, P2Y, P1M, P2M, P1C, P2C, P1K,
and P2K, at the beginning end and ending end of a respective
scanning range. Based on the detection at the scanning-range
beginning end, a synchronization timing of the writing start by
each beam is determined. Based on the detection time delay between
the beginning end and ending end of the scanning range, the
frequency of driving clock signal for each beam is adjusted, and
thus, writing range defined by each beam is made equal.
In FIG. 10A, the reference numeral 111 denotes a windowpane of a
noise isolation housing (not shown) houses the polygon minor 112.
The windowpane 111 enables each beam coming from the light source
110 passing therethrough toward the polygon mirror 112, and, also,
enables the deflected beam passing therethrough toward the lens 114
therethrough.
In FIG. 10A, the reference numerals 22A, 23A, and 24A denote
detection devices acting as the above-mentioned scan line deviation
detecting devices. The detection devices 22A, 23A, and 24A condense
beams coming from semiconductor lasers Ls1 with condensing lenses
Le3, irradiate therewith predetermined positions of the
intermediate transfer belt 121, and form images of beams reflected
by the intermediate transfer belt 121 onto light-receiving devices
Pd with lenses Le4. Thereby, images formed on the intermediate
transfer belt 121 can be detected at the respective predetermined
positions thereof. When performing the scan line deviation
detection, three predetermined portions on one scan line are
written onto the respective photoconductor by each beam, and they
are visualized by the toner, and are transferred from the
photoconductor onto the intermediate transfer belt 121. At this
time, partial line toner images of the respective color components
are formed in a manner such that they have predetermined intervals
therebetween in the subscanning direction on the intermediate
transfer belt 121.
These partial line images, as shown, are detected by the respective
detection units of the scan line deviation detection device, and
thus, the scan line bending (inclination of each scan line and the
position deviation therebetween) is determined based on the
detection result. Each scan lines Y, M, C, and K shown in FIG. 8A
mentioned above are determined in this way, for example.
As shown in FIG. 10A, a scan line correcting device 115 is arranged
just behind the lens 114. The scan line correcting device 115 has
four portions 15K, 15C, 15M, and 15Y, as shown in FIG. 10B. The
portion 15K is transparent, and each of the portions 15Y, 15M, and
15C includes a liquid crystal deflection device array which is one
previously described with reference to FIG. 5A, for example. Almost
all the elements of a liquid crystal device, such as a grounding
electrode, a liquid crystal layer, a cover glass and so forth are
common for these liquid crystal deflection device arrays 15Y, 15M,
and 15C. That is, in this embodiment, the liquid crystal deflection
device arrays are combined integrally.
These portions 15K, 15C, 15M and 15Y are disposed in the scan line
correcting device 115 such a way that the respective beams of the
color components of K, C, M and Y coming from the respective light
source devices 110 via the polygon mirror 112 be incident on the
respective portions. Therefore, the scan line correcting device 115
transmits the incident beam which writes a black component image,
and corrects scan line bending of the incident beams which write
cyan, magenta and yellow color component images appropriately as
described above with reference to FIGS. 5A through 5D, based on the
detection results on the present scan line bending of the
respective scan lines K, C, M and Y.
The correction of the scan line bending is made in such a manner
that the scan line bending of each scan line other than the scan
line K is made coincide with or made nearer to the standard scan
line bending of the scan line K as described above with reference
to FIGS. 8A through 8C. A controller not shown performs calculation
and setting of the correcting amounts performed by the scan line
correcting device 115.
As shown in FIG. 10A, the liquid crystal deflection device arrays
15Y 15M, and 15C of respective color components can be easily made
integrated as the scan line correcting device 115 is located behind
the common light path (lens 114).
Instead of the configuration shown in FIG. 10A, it is also possible
to embody the above-mentioned aspect of the present invention
through the configuration shown in FIG. 7. Also in this case, the
liquid crystal deflection device arrays 70Y, 70M, and 70C each of
which may be the same as the liquid crystal deflection device array
21Y shown in FIG. 5A correct the scan line bending of the scan
lines for yellow, magenta and cyan color component images in a
manner such that the scan line bending be coincide with or made
nearer to the standard scan line bending of the scan line for a
black component image. Thus, the problem of color deviation can be
effectively solved.
Although not shown in FIG. 7, the scanning position of optical spot
which each of the deflected beams LSY through LSK forms on a
correspondence photoconductor is detected by a device which may be
the same as the scanning position detecting device 22Y shown in
FIG. 5B. For the purpose of directing a part of each deflected beam
toward the above-mentioned detecting device, the liquid crystal
deflection device arrays 70Y, 70M, 70C and transparent glass plate
70K are slightly inclined so that the part of the deflected beam be
reflected toward the detecting device.
In each of the image formation devices in the above-mentioned
embodiments described with reference to FIGS. 1, 7 and 10A, in case
many times of image forming processes are performed continuously or
successively so as to produce a many sheets of color image prints,
the internal temperature rises sharply as shown in FIG. 11 due to
the heat generated by a motor driving the polygon minor, the heat
generated by the fixing device and so forth included in the image
formation device. Such a temperature change may change the optical
characteristics of the optical devices (lenses, mirrors and so
forth) made of resin in the scanning image-formation optical
system, and thus, the above-mentioned color deviation may occur.
For this reason, a color tone of a produced color image may changes
between a case of first printing and a case of printing after
several sheets of printing (for example, `A` sheets shown in FIG.
11).
In order to solve this problem, it is preferable to change the
correction amounts in the above-mentioned scan line correction
devices (scan line bending correcting devices/uniform velocity
performance correction devices) based on the current detection
results obtained from the above-mentioned scan line deviation
detection devices such as the device 22Y shown in FIG. 5B during
the above-mentioned continuous/successive image forming processes.
Specifically, after the detection of the scan line state such as
that shown in FIG. 8A, actual adjustment of the scan line
correction amounts provided by the scan line correction device
based on the detection result (which is referred to as a scan line
correction amount adjustment control process) should be performed
between an end of image formation process on one sheet and a
beginning of image formation process on another sheet. Accordingly,
the above-mentioned correction amount adjustment control process be
performed preferably within a time interval of T.sub.A obtained by
the following formula especially in the cases of the configurations
shown in FIGS. 7 and 10A: T.sub.A<0.8.times.(D/V) where:
D denotes a distance between adjacent sheets of transfer paper on
the intermediate conveyance belt 54/121; and
V denotes a speed of the sheet-shaped transfer paper on the
intermediate conveyance belt.
Thereby, it becomes possible to proceed with the continuous image
forming process substantially without interrupting the process.
The above-mentioned scan line state detection process should be
performed preferably within a time interval Ts obtained by the
following formula: Ts<10.times.(L/V) where:
L denotes a length along the sheet conveyance direction of each
sheet of transfer paper on the intermediate conveyance belt 54/121;
and
V denotes a speed of the sheet-shaped transfer paper on the
intermediate conveyance belt.
Thereby, even when a rapid temperature change occurs, the scan line
bending or the like can be corrected at least every ten sheets of
image forming process. Accordingly, it becomes possible to
effectively reduce color tone change by color deviation.
An optical scanning device in a fourth embodiment of the present
invention will now be described with reference to FIGS. 12A and
12B. In this embodiment, as shown in FIG. 12A, a beam emitted from
a light source device (wherein a light source and a coupling lens
are included) 210 is a parallel beam (which may be slightly
convergent or divergent beam), and is made to pass through an
aperture stop (not shown) for obtaining a diameter of optical spot
suitable for a scanning surface 220. After that, the beam is
incident on a cylindrical lens 212 which acts as a line-image
forming optical system (which has a positive power only in the
subscanning direction). Then, the beam converges only in the
subscanning direction thereby, and forms a line image long in the
main scanning direction near the deflection reflective surface of a
polygon mirror 214 of an optical deflection scanning device.
With a uniform rotation of the polygon mirror 214, the beam
reflected by the deflection reflective surface thereof is thus
deflected in an equal angular velocity, and passes through two
lenses 2161 and 2162 which act as an f.theta. lens 216 as a
scanning image-formation optical system. After that, the beam
passes through a liquid crystal deflection device array 218,
reaches the scanning surface 220, and thus focuses as an optical
spot on the scanning surface 220 by the function of the f.theta.
lens 216, and carries out optical scanning of the scanning surface
220.
The liquid crystal deflection device array 218 is long in the main
scanning direction as shown, and performs position adjustment of
the optical spot formed on the scanning surface 220. Further, the
liquid crystal deflection device array 218 has a plurality of
individually controllable liquid crystal deflection devices
arranged along the main scanning direction, is disposed in the
light path from the polygon mirror 214 toward the scanning surface
220. Thereby, for each liquid crystal deflection device, the amount
of deflection given thereby to the incident beam is controlled in
the main scanning direction and/or subscanning direction.
Consequently, the position of the optical spot on the scanning
surface is adjusted for the main scanning direction and/or the
subscanning direction.
A controller 222 shown includes a microcomputer etc., and controls
the liquid crystal deflection device array 218 so that the amount
of deflection given by each liquid crystal deflection device of the
liquid crystal deflection device array 218 to an incident beam is
controlled. The controller 222 may be also realized as a partial
function of a system controller which controls a whole image
formation device which includes the optical scanning device shown
in FIG. 12A.
FIG. 12B shows an optical arrangement between the deflection
reflective surface of the polygon mirror 214 and the scanning
surface 220 shown in FIG. 12A viewed from the subscanning
direction. Although the liquid crystal deflection device array 218
is disposed between the lens 2162 of the f.theta. lens 216 and the
scanning surface 220 as shown in FIG. 12A, the position of the
liquid crystal deflection device array is not limited thereto. For
example, the liquid crystal deflection device array 218 may be
instead disposed between the deflection reflective surface of the
polygon mirror 214 and the lens 2161 in the f.theta. lens 216 as
the liquid crystal deflection device array 218A shown in FIG. 12B.
Thereby, the required length of the main scanning direction of the
liquid crystal deflection device array may be shortened so that the
costs thereof may be reduced as the liquid crystal deflection
device array is approached toward the optical deviation scanning
device.
However, in this case (218A), on the other hand, there may occur a
problem as follows: The deflected beam incident onto the liquid
crystal deflection device array 218A shown is deflected in the
uniform angular velocity as mentioned above. Where `D` denotes a
distance between the beam deflection starting point on the
deflection reflective surface on the polygon mirror 214 and the
beam incident point on the liquid crystal deflection device array
218A for the same beam; and also, .theta. denotes the deflection
angle of the same beam, the position on the liquid crystal
deflection device array 218A at which the deflected beam (chief
ray) is incident is expressed by Dtan .theta.. Then, the distance
by which the deflected beam moves on the liquid crystal deflection
device array 218A along the main scanning direction with respect to
a minute deflection angle .DELTA..theta. is expressed by
.DELTA.S=D.DELTA..theta./cos.sup.2.theta.. Accordingly, the larger
the deflection angle .theta. becomes, the distance by which the
deflected beams moves on the liquid crystal deflection device array
218A becomes longer.
Therefore, in case the size in the main scanning direction of each
liquid crystal deflection device in the liquid crystal deflection
device array 218A is uniform, and is arranged in the main scanning
direction at a uniform pitch/interval, a range in the main scanning
direction on the scanning surface 220 for which a responsible is
taken (referred to as a responsible range) by each liquid crystal
deflection device becomes longer as the relevant liquid crystal
deflection device is located at a position on which the deflected
beam of the larger deflection angle is incident. Accordingly, the
optical spot adjustment accuracy becomes degraded as the deflection
angle of the deflected beam is larger.
For the purpose of solving this problem, one idea is such that the
main-directional size of each liquid crystal deflection device is
made smaller as the relevant liquid crystal deflection device is
located further from the center of the liquid crystal deflection
device array 218A on which the deflected beam of the deflection
angle of zero is incident, and, also, the arrangement
pitch/interval of the liquid crystal deflection device is made
shorter as the relevant liquid crystal deflection device is located
further from the center of the liquid crystal deflection device
array 218A. However, since the deflected beam is not sufficiently
condensed in the main scanning direction and thus has a
considerably large beam diameter (several millimeters) near the
deflection reflective surface of the polygon mirror, the
main-directional size of the liquid crystal deflection device may
not be made sufficiently smaller.
By such a reason, it is preferable that the liquid crystal
deflection device array be located near the scanning surface 220
rather than near the scanning image-formation optical system. In
fact, in case the liquid crystal deflection device array 218 is
located as shown in FIGS. 12A and 12B, i.e., it is located between
the f.theta. lens 216 and the scanning surface 220, the incident
deflected beam is already sufficiently condensed by the optical
system, and, also, the deflection of the deflected beam is made at
uniform velocity by the function of the f.theta. lens 216.
Therefore, even in case where the liquid crystal device array 218
has a configuration such that each liquid crystal deflection device
have an equal main-directional size, and be arranged at a uniform
pitch/interval, sufficient optical spot positional adjustment is
achievable. Also, the above-mentioned arrangement pitch/interval
should not be made so smaller/finer. Such an effect is increased as
the liquid crystal device array 218 is located nearer to the
scanning surface 220.
Details of the above-mentioned liquid crystal device array 218 may
be the same as that described above with reference to FIG. 5A, and
be provided together with the scan line state detection device
shown in FIG. 5B, in a configuration described above with reference
to FIGS. 5A through 5D. Actually, before performing a substantial
image forming process, the polygon mirror 214 is rotated, and the
light sources 210 is made to emit a beam as a trial basis. This
emission may be made intermittently so that the deflected beam or
detection beam on each color component be incident on the
respective area sensors P1 through P10 shown in FIG. 5B.
In the above-described configuration, the scanning position of
optical spot is detected, the scan line bending which should be
corrected is specified, and the amount of deflection to be given
with the liquid crystal deflection device Li is set according
thereto. According to this way in which the actual scanning
position is detected at any time, even when the scan line bending
mode changes due to a time elapse, or in case the f.theta. lens 216
is made of a resin and thus the scan line bending changes due to an
environmental change, it is possible to perform proper scan line
bending correction at any time based on the detection result.
In case no substantial change occurs in the scan line bending state
even due to aging or environmental change, for example, in case the
f.theta. lens 216 is made not of a resin but of a glass, the scan
line bending state or scan line inclination is measured before the
shipment of the product of image formation device, and the amount
of deflection given by each liquid crystal deflection device Li is
estimated and is stored in a memory of the controller, which amount
is then used at any time of actual performance of image formation
process in the machine.
Also in this embodiment, the liquid crystal deflection device array
218 may be used not only as the subscanning-directional deflective
device but also as the main-scanning-directional deflective device
(in which each liquid crystal deflection device Li has a
performance of deflecting an incident beam in the main scanning
direction) by which the uniform velocity performance such as
f.theta. characteristics may be corrected well.
In this case, the position of the optical spot in the main scanning
direction in the area sensor Pi of the scanning position detection
device is detected. Then, the uniform velocity performance (a
deviation from the ideal uniform scanning state) of the optical
scanning as in the above-mentioned case of control for correcting
the scan line bending by the controller. Correction of the uniform
velocity performance can be performed by selling up the amount of
deflection in the main scanning direction to be provided by the
liquid crystal deflection device Li in order to correct the uniform
velocity performance by adjusting the amount of deflection in the
main scanning direction on the incident deflected beam.
Finer correction of the uniform velocity performance can be
performed as the number of the liquid crystal deflection devices in
the main-scanning-directional liquid crystal deflection device
array is increased and also the correction responsible range of
each liquid crystal deflection device Li is made small. By making
the length in the main scanning direction of each
main-scanning-directional liquid crystal deflection device Li in
the main-scanning-directional liquid crystal deflection device
array small enough (for example, approximately 2-5 millimeters), it
is possible to achieve a state such that deflection amount
difference between each adjacent main-scanning-directional liquid
crystal deflection devices be regarded as a substantially
continuous smooth variation, and, thus, the optical scanning can be
performed substantially at a uniform velocity.
According to this way, the scanning position of optical spot is
detected, the uniform velocity performance which should be
corrected is specified based thereon, and the amount of deflection
to be provided by the liquid crystal deflection device Li is set
accordingly. Thereby, in case the uniform velocity performance
changes due to aging, or the f.theta. lens 216 is made of a resin
so that the uniform velocity performance changes due to
environmental change, it is possible to perform a proper optical
scanning correction at any time.
In case no substantial change occurs in the uniform velocity
performance even due to aging or environmental change, for example,
in case the f.theta. lens 216 is made not of a resin but of a
glass, the uniform velocity performance is measured before shipment
of the product, and the amount of deflection to be given by each
liquid crystal deflection device Li is stored in a memory of the
controller, which amount is then used at any time of actual
performance of image formation process in the machine.
Also in this embodiment, the liquid crystal deflection device array
218 may be used not only as the subscanning-directional deflective
device but also as the main-scanning-directional deflective device
(in which each liquid crystal deflection device Li has a
performance of deflecting an incident beam both in the main
scanning direction and subscanning direction) by which the scan
line bending or scan line inclination as well as the uniform
velocity performance such as f.theta. characteristics may be
corrected well simultaneously. For this purpose, the configuration
of the liquid crystal deflection device array having a
configuration such as that described above with reference to FIG.
6B may be applied. Further, instead of integrally combining the
main-scanning-directional deflection device and
sub-scanning-directional deflection device as shown in FIG. 6B, it
is also possible to configure such that both the deflection devices
are disposed separately.
Various available ways of detection of the scanning position by the
scanning position detection device in the fourth embodiment will
now be described with reference to FIGS. 13A and 13B. In each case,
a configuration is made such that the light-receiving surface of
each area sensor Li of the detection device be regarded optically
equivalent to the scanning surface 220 with respect to the
deflected beam or image-formation beam given.
In FIG. 13A, the direction which intersects perpendicularly with
the figure corresponds to the main scanning direction, and the
vertical direction corresponds to the subscanning direction. The
scanning position detection in the optical scanning device shown in
FIG. 12A may be performed by the configuration as shown in FIG.
13A, and the liquid crystal deflection device array 218 is disposed
in a manner inclined with respect to the subscanning direction on
the optical path of the image-formation beam deflected in the main
scanning direction. In this configuration, the image-formation beam
forms an optical spot on the light-receiving surface of the
scanning position detection device 223 after being partially
reflected by the incidence surface of the liquid crystal deflection
device array 218 in FIG. 13A, and, thus, the scanning position is
detected by the detection device 223.
Also in the configuration shown in FIG. 13B, the direction which
intersects perpendicularly with the figure corresponds to the main
scanning direction, while the vertical direction corresponds to the
subscanning direction. In this configuration, the image-formation
beam passing through the liquid crystal deflection device array is
incident on a half mirror 219 inclined with respect to the
subscanning direction. Then, the beam is reflected thereby, forms a
beam spot on the light-receiving surface of the scanning position
detection device 223. Thus, the scanning position is detected
thereby.
The half mirror or reflective surface member 219 may be made of a
transparent glass, is disposed always at the same position shown,
or may be disposed to one side so that the image-formation beam is
incident thereon only when the beam is deflected to the one side.
Alternatively, the member 219 may be inserted on the course of the
image-formation beam only in a case the scanning position detection
is actually performed.
FIG. 13C illustrates another way of the scanning position
detection. In this case, a photoconductor 225 providing the
scanning surface 220 is utilized. Since the scanning position
corresponds to the optical spot position in a scan line drawn for a
trial basis on the photoconductor 25, visualizing of a
thus-obtained electrostatic latent image is performed, and, from
the thus obtained line-shaped toner image LTI, it is possible to
obtain a scan line for detection in the form of the toner image
LTI. This toner image LTI is then made to be irradiated by a lamp
226, and the thus-generated reflected beam is incident on an image
sensor 228 via an image-formation optical system 227. Thereby, the
scan line bending state can be detected.
In a configuration shown in FIG. 13D illustrating a further other
way of scanning position detection, a toner image transferred onto
an intermediate transfer belt 229 from the photoconductor 225 is
utilized. The linear toner image LTI formed on the photoconductor
25 like in the case of FIG. 13C is transferred onto the
intermediate transfer belt 229 by a transfer device 230, and the
thus-transferred toner image LTI is irradiated by a lamp 226, and
the thus-occurring reflected beam forms an image via an
image-formation optical system 227 onto an image sensor 228.
Thereby, the scanning line bending state is detected. In each of
the cases of FIGS. 13C and 13D, the photoconductor 225 and the
intermediate transfer belt 229 are cleaned by a cleaning device of
the toner image LTI before an actual image formation process is
performed.
For the purpose of detecting the uniform velocity performance, in
order to perform the scanning position detection with respect to
the main scanning direction, a plurality of lines each having a
certain length in the subscanning direction are written for a trial
basis along the main scanning direction in mutually parallel, and
are visualized. These lines should have appropriately equal
intervals. Then, the thus-visualized lines are detected on the
photoconductor or intermediately transfer belt, and, then, from the
thus measured intervals of the detected lines, the uniform velocity
performance can be determined, as in the same manner shown in FIGS.
13C and 13D.
Furthermore, as a further alternative way, even in case of using
the liquid crystal deflection device array itself as a beam
extracting device in the case of the above-mentioned embodiment, as
shown in FIG. 6A the sizes of the spacers 3A and 3B sealing the
liquid crystal are differed from each other. Consequently, it is
possible to give an angle between the glass substrate 5a (forming
the transparent electrode, transparent resistance film and
orientation film) and the glass substrate 5b (forming the
transparent electrode and orientation film). Thereby, even in case
the liquid crystal deflection device itself is not inclined,
appropriate inclination of glass substrate 5a by which a part of
image-formation beams is extracted and directed toward the
detection surface can be obtained as shown.
FIG. 14A shows an optical scanning device in a fifth embodiment of
the present invention. This optical scanning device is of a
multi-beam type in which a plurality of beams are emitted from a
light source device, and optical scanning of a scanning surface is
carried out by a corresponding plurality of optical spots. The
light source device 240 has light sources 2401 and 2402 of
semiconductor lasers, and coupling lenses 2403 and 2404. The beams
emitted from the light sources 2401 and 2402 pass through the
coupling lenses 2403 and 2404, respectively, they are thus
transformed into parallel beams (or slightly convergent or
divergent beams), converge in the subscanning direction with
cylindrical lens 242, and form line images near a deflection
reflective surface of a polygon mirror 244, which line images are
long along the main scanning direction and mutually separated in
the subscanning direction.
As the polygon mirror 244 carries out uniform rotation, each beam
is deflected thereby at a uniform angular velocity, passes through
a liquid crystal deflection device array 248, and passes through an
f.theta. lens 246 which is a combination of lenses 2461 and 2462.
Then, optical spots mutually separated in the subscanning direction
are formed on a photosensitive surface (scanning surface) of a
photoconductor 250 (which carries out a uniform rotation in the
direction of an arrow shown) having a photoconductivity, after the
beams courses are bent by a light-path bending mirror 247. Thus,
optical scanning of the photoconductor 250 is carried out so as to
write two scan lines simultaneously. One side of scanning range of
the deflected beam is intercepted by an optical sensor 249 on the
way toward the effective scanning range, and thereby,
synchronization of optical scanning start of each optical spot is
determined based on the output of the optical sensor 249.
As shown in FIG. 14C, a configuration is made such that the
respective beams FL1 and FL2 from the light sources 2401 and 2402
cross one another viewed from the subscanning direction (direction
which intersects perpendicularly with the figure) at the deflection
reflective surface 2441 of the polygon mirror. Thereby, since the
beam which forms an image at a same position (in the main scanning
direction) on the scanning surface 250 passes through a same
portion of the lenses 2461 and 2462, the same uniform velocity
performance is obtained on each of the beams FL1 and FL2. Moreover,
a configuration is made such that each of the beams FL1 and FL2
passes through the lenses 2461 and 2462 on the same side with
respect to the optical axis in the subscanning direction. Thereby,
the scan line bending state of each scan line on the scanning
surface 250 becomes substantially same as the other one. Therefore,
after the liquid crystal deflection device array 248 is used for
adjusting the amounts of deflection in the main scanning and/or
subscanning directions, the scan line bending, scan line
inclination or the uniform velocity performance of scan line can be
corrected simultaneously on the two beams. Thus, the multi-beam
scanning by the beams FL1 and FL2 can be performed
satisfactorily.
As shown in FIG. 14B, if the beams FL1 and FL2 from the light
sources 2401 and 2402 did not cross in the main scanning direction
on the deflection reflective surface 2441 of the polygon mirror
244, since the beam which would form an image at the same position
on the scanning surface 250 did not pass through the same portion
of the lenses 2461 and 2462, neither the uniform velocity
performance nor the scan line bending could become coincident
between the beams FL1 and FL2. Thereby, neither the uniform
velocity performance nor the scan line bending on the respective
two beams could not be satisfactorily corrected by the single
liquid crystal deflection device sequence device 248.
Since the liquid crystal deflection device array 248 is arranged
between the polygon mirror 244 and the lens 2461, as described
above, the arrangement pitches of the respective liquid crystal
deflection devices therein should not be very smaller even in a
range in which the deflection angle is larger, as the distance from
the deflection reflective surface 2441 of the polygon mirror 244 is
made longer.
FIG. 15 illustrates an image formation device in which any of the
above-mentioned optical scanning devices in the fourth and fifth
embodiments of the present invention may be applied. This image
formation device which is a monochrome-type laser printer, for
example, has a function of transfer of a toner image onto a
sheet-like recording medium, which toner image is obtained through
visualization with a toner from electrostatic latent image. The
electrostatic latent image is formed on a photoconductor as a
result of the above-mentioned optical scanning thereof is performed
by the optical scanning device as shown in FIG. 12A or 14A.
This laser printer 2100 has the photoconductor 2111 having a
photoconductivity formed in a shape of a cylinder. Around the
photoconductor 2111, an electrification roller 2112 as an
electrification device, a development device 2113, a transfer
roller 2114, and a cleaning device 2115 are arranged. The
electrification roller 2112 may be replaced by a corona charger or
an electrification brush. The transfer roller 2114 may be replaced
by a corona-electric-discharge-type one.
The optical scanning device 2117 which performs an optical scanning
by a laser beam LB is provided, and an exposure by optical writing
or scanning is performed at a position between the electrification
roller 2112 and development device 2113. Furthermore, a fixing
device 4116, a cassette 2118, a registration roller pair 2119, a
paper feeding roller 2120, a paper conveyance passage 2121, and a
tray 2123 are provided.
When an image formation process is performed, a uniform rotation of
the photoconductor 2111 is carried out clockwise, and a uniform
electrification of the surface (scanning surface) thereof is
carried out with the electrification roller 2112. After that, the
optical scanning device 2117 writes an electrostatic latent image
onto the photoconductor 2111 with the laser beam LB coming
therefrom. The latent image is formed on the scanning surface in
response to exposure by the optical writing with the laser beam LB.
The thus-formed electrostatic latent image is a so-called negative
latent image where an image part is exposed. Reversal development
of this electrostatic latent image is carried out by the
development device 2113, and thus, a toner image is formed on the
photoconductor 2111.
A transfer paper P fed one by one by the paper feeding roller 2120
from the cassette 2118 is caught by the registration roller pair
2119. The registration roller pair 2119 feeds the paper P onto the
photoconductor 2111 at a transfer position in timing well
controlled according to the rotation of the photoconductor 2111.
The thus-fed transfer paper P is placed on the toner image at the
transfer part, and an action of the transfer roller 114 carries
out, electrostatic transfer of the toner image onto the paper P.
The transfer paper P which thus has the toner image transferred is
fixed by the fixing device 2116, which is then made to pass through
the conveyance passage 2121, driven by the delivery roller pair
2122, and then, is ejected onto the tray 2123. The surface of the
photoconductor 2111 after the toner image is transferred therefrom
is cleaned by the cleaning device 2115, and thus, remaining toner,
paper dust, etc. are removed.
The (latent) image writing by optical scanning is performed by the
optical scanning device 2117 which may have the configuration
described with reference to FIGS. 12A or 14A which includes the
liquid crystal deflection device array, and thereby, adjustment of
the position of the optical spot on the scanning surface
(photoconductor 111) in the main scanning direction and/or the
subscanning direction is performed. Thus, the above-mentioned scan
line bending, inclination of scan line, and the uniform velocity
performance are well controlled or corrected, thereby, satisfactory
latent image writing being achieved. Accordingly, a satisfactory
monochrome image is created thereby, without distortion.
In each of the above-mentioned fourth and fifth embodiments, the
scanning position detection process may be performed periodically,
for example, once a mouth, and, based on the result thereof, the
amount of deflection of each liquid crystal deflection device is
determined. Then, the thus-determined deflection amounts may be
stored in a memory of the system controller of the machine, and, is
actually set in each liquid crystal deflection device at a time a
power supply is made to the machine. Alternatively, it is also
possible that, in advance of each regular image formation process,
the scanning position detection device detects the scanning
position of optical spot, and the amount of deflection in each
liquid crystal deflection device of the liquid crystal deflection
device array is set based on the detection result.
In case the uniform velocity performance degradation, scan line
bending and/or the scan line inclination may occur due to
environmental change, for example, the temperature inside the
machine may rise gradually while many sheets of image formation is
performed continuously. In such a case, it is preferable to perform
scanning position detection and set up or update the amount of
deflection in each liquid crystal deflection device of the liquid
crystal deflection device array accordingly, at appropriate
intervals, for example, once per five times of image formation
process.
In such a case, in the embodiment shown in FIG. 15, it is
preferable that the above-mentioned scanning position detection
with the scanning position detecting device 223 shown in FIG. 13A,
13B, 13C or 13D be performed within an interval between successive
processing of transfer papers P, i.e., after a transfer paper P has
been processed and before a subsequent transfer paper P is
processed.
It is assumed, for example, that: the above-mentioned paper
processing interval: h; the time required for the scanning position
detection: h1; and the time required for updating the setting in
the each liquid crystal deflection device: h2.
In this case, when h.ltoreq.h1+h2, detection of the scanning
position and updating the deflection amount based on the detection
result are performed within a same paper processing interval.
However, when h<h1+h2, and also, h>h1, h>h2, updating the
deflection amount should be performed at a subsequent paper
processing interval after a paper processing internal in which
detection of scanning position is performed.
In case h2>h, it is not possible to perform updating the
deflection amount within a regular paper processing interval. In
such a case, for example, once per ten times of image formation
process, the paper processing interval is slightly elongated so
that h2<h, and therein, the updating of the deflection amount
should be performed.
As one example, a case is assumed where a speed of an image
formation process can be switched among three modes, i.e., a
quality mode, a high-speed mode, and a fastest mode. Further,
h1=0.05 secs. (including the scanning position detection with the
scanning position detecting device 223, and calculating the amount
of deflection to be newly set in each device of the liquid crystal
deflection device array 218); h2=0.05 secs. (including setting the
thus-determined deflection amount in each device of the liquid
crystal deflection device array); and h=0.25 secs (in the quality
mode); 0.055 secs (in the high-speed mode); 0.03 secs (in the
fastest mode).
FIG. 16 shows a flow chart of operation in this case. In a step S1,
an initial setup is performed in which a standard amount of
deflection is set in each device of the liquid crystal deflection
device array. The amounts of deflection set at this time are those
set up at the end of a normal operation state of the machine in the
past.
In a step S2, it is determined whether or not a current image
formation process is of a continuous or successive image formation
process or not. When it is determined that it is a continuation
process, it is determined whether the number of times of process N
is not less than 20 (this means that the total number of sheets of
printed images to be produced is at this time not less than 20), or
not. Even in case image formation is performed continuously, as
long as the number of times of producing sheet of image is less
than 20, the temperature in the machine does not rise much, and
thus, does not need updating the amount of deflection in each
device of the liquid crystal deflection device array. Therefore,
the usual image formation process is performed in this case, and
the value of the deflection amount in each liquid crystal
deflection device of the liquid crystal deflection device array to
be set is the same as in the initial setting in the step S1.
In a step S5, it is determined whether the mode of image formation
process is `quality`. In the quality mode, as the paper processing
interval h is as long as 0.25 seconds, the scanning position
detection and updating of the amount of deflection in each liquid
crystal deflection device are performed within the same paper
processing time interval for every predetermined number of times of
image formation process (producing a sheet of image, for example,
every four sheets) in a step S6.
When it is not the quality mode, then in a step S7, it is determine
whether it is the high-speed mode, and when it is the high-speed
mode, a step S9 is performed. Then, the scanning position detection
operation and operation of determination of the deflection amount
to be set are both performed within a paper processing interval
every predetermined number of times of image formation process.
Then, in a step S10, actual updating the amount of deflection based
on the determination in the step S9 is performed for the amount of
deflection within the subsequent paper processing interval.
When it is not the high-speed mode, this means that it is the
fastest mode in a step S8. In this case, in a step S11, the
scanning position detection and deflection amount setting value
determination is performed within a paper processing interval every
predetermined number of times of image formation process. Then, in
a step S12, the subsequent paper processing interval is elongated
by a predetermined time .DELTA.t (for example, approximately 0.1
secs.). Then, within this elongated interval, the amount of
deflection thus determined is set.
The above-mentioned setting or updating of the amount of deflection
in each device of the liquid crystal deflection device array is
actually performed as long as the amount determined based on the
scanning position detection is such that actual updating be needed.
That is, as long as the scanning position deviation thus detected
is sufficiently small, or transition of change in the scan line
bending amount, scan line inclination amount and/or the uniform
velocity performance degradation amount is sufficiently small, for
example, no correction should be performed by the liquid crystal
deflection device array.
Utilization of the above-mentioned liquid crystal deflection device
array for the purpose of scanning position correction such as scan
line bending correction, scan line inclination correction, uniform
velocity performance correction may cause a plurality of diffracted
beams therefrom, some of which other than a regular scanning beam
may adversely affect a regular optical scanning as ghost light. A
scheme of solving such a problem according to the present invention
will now be described.
FIGS. 17A and 17B illustrate a configuration of a variant
embodiment of the above-mentioned fourth embodiment to which the
above-mentioned scheme of solving the problem occurring due to
generation of diffracted beams as ghost light is applied, i.e., a
ghost removal device 600.
For the purpose of simplification of description, each liquid
crystal deflection device used in the liquid crystal deflection
device array 218 is the subscanning liquid crystal deflection
device, which adjusts the amount of deflection of the incident beam
in the subscanning direction so as to correct scan line bending or
so. In FIG. 17A, the liquid crystal deflection device array 218 has
a plurality of liquid crystal deflection devices each of which has
a function of beam deflection in the subscanning direction such as,
that described above with reference to FIGS. 3A through 3C along
the main scanning direction, and generates diffracted beams.
FIG. 18A shows a 0th light, a .+-.1st light, a .+-.2nd light of
diffraction generated when the image-formation beam (deflected
beam) is incident on the above-mentioned liquid crystal deflection
device array 218. The 0th light is a beam used as a regular optical
scanning beam in this case, and the .+-.1st light and .+-.2nd light
thus act as ghost light with respect to the scanning surface 220.
The above-mentioned ghost light removal device 600 removes the
ghost light. The ghost light removal device 600 has a slit opening
So long in the main scanning direction (direction which intersects
perpendicularly with the figure), and has a light blocking function
except the portion of slit opening So.
By this ghost light removal device 600, the .+-.1st light and
.+-.2nd light acting as ghost light are blocked while only the 0th
light which is the regular optical scanning beam is made to pass
therethrough toward the scanning surface 220 (in the right
direction in the figure) through the slit opening So.
FIG. 18B shows a state in a case where the liquid crystal
deflection device array 218 has another configuration 218B such
that each liquid crystal deflection device thereof applies a
diffraction phenomenon illustrated in FIGS. 4A and 4B and is
disposed along the main scanning direction. In this case, since no
diffraction is performed on and thus no beam deflection is carried
out on the 0th light by the liquid crystal deflection device,
rather the +1st light which has the deflection angle controllable
by the liquid crystal deflection device is used as the regular
optical scanning beam. Accordingly in this case, the other beams,
i.e., the 0th light, -1st light, and .+-.2nd light are blocked by
the ghost light removal device 600, while the +1st light is made to
pass through the slit opening So toward the scanning surface
220.
FIG. 18C illustrates the 0th light as the regular beam and the +1st
light as the ghost light in the case of FIG. 18A. As shown, each of
these beams has a beam width (a 1/e.sup.2 diameter in light
intensity of the beam cross section) `b` in the subscanning
direction (the vertical direction in the figure) in the position
around the slit opening So of the ghost light removal device 600.
Further, the angle formed in the subscanning direction therebetween
is referred to as .theta.; the distance between the liquid crystal
deviation device and the ghost light removal device 600 is referred
to as L, and the length in the subscanning direction of the slit
opening So of the ghost light removal device 600 is referred to as
.DELTA..
Then, the requirements needed for the ghost light removal device
600 to positively block the +1st light are expressed by the
following formula: Ltan .theta.>(b+.DELTA.)/2 Accordingly, the
distance L by which the ghost light removal device 600 to be
distanced from the liquid crystal deflection device is expressed by
the following formula (1): L>(1/2)(b+.DELTA.)/tan .theta. (1)
The same conditions may also be applied to the case of FIG.
18B.
The ghost light removal device 600 shown in FIG. 17A may have a
configuration such that the slit opening So is formed in a long
special separate light blocking plate, or a configuration such that
a dust-proof glass window formed in a housing of an optical
scanning device (see FIG. 7, members 600Y, 600M, 600C and 600K), or
a light-path bending mirror (see FIG. 20, member 247), have a light
blocking film having the slit opening So printed thereon.
FIG. 19 illustrates another configuration 600A of the ghost light
removal device applied to the fourth embodiment shown in FIG. 12A.
In this case, the liquid crystal deflection device array 218A
similar to the deflection device 218 shown in FIG. 17A is inserted
between the polygon mirror 214 and f.theta. lens 216, as shown. The
ghost light removal device 600A is embodied by a light blocking
film having the slit opening So formed on the side of the lens 2162
of the f.theta. lens 216 facing the scanning surface 220. It is
noted that also in this case, the liquid crystal deflection device
array 218A and ghost light removal device 600A satisfy the
above-mentioned formula (1).
FIG. 20 illustrates a case where a scheme of the above-mentioned
ghost light removal device is applied to the above-mentioned fifth
embodiment described with reference to FIG. 14A. As can be seen
from FIG. 20, in this case, the ghost light removal device 600B is
embodied as a light-blocking film having the slit opening So
(reflective surface) long along the main scanning direction
provided on the reflective surface of the light-path bending mirror
247. It is noted that also in this case, the liquid crystal
deflection device array 248 and ghost light removal device 600B
satisfy the above-mentioned formula (1).
Further, also in the third embodiment described above with
reference to FIG. 7, the above-mentioned scheme of ghost light
removal device may be applied. Specifically, in this case, the
ghost light removal devices 600Y, 600M, 600C and 600K are embodied
by respective light-blocking films each having the slot opening So
long along the main scanning direction provided on the respective
ones of dust proof glass window provided on the bottom of an
optical housing 75 which houses the optical scanning device as
shown in FIG. 7. It is noted that also in this case, the liquid
crystal deflection device arrays 70Y through 70K and respective
ghost light removal device 600Y through 600K satisfy the
above-mentioned formula (1) for each pair thereof.
Various additional notes concerning the above-mentioned embodiments
of the present invention will now be described.
In each of the above-mentioned embodiments, the above-mentioned
optical deflection scanning device should not necessarily be the
polygon mirror. In fact, other than this, a rotational single minor
or a rotational double mirror such as a pyramidal mirror, a
mortise-hole-type mirror, a galvano mirror, or the like may be used
instead.
The above-mentioned scanning image-formation optical system may be
of either a lens system such as an f.theta. lens or an
image-formation mirror system such as an f.theta. mirror. A
combination thereof is also possible to be applied.
As to the configuration of the above-mentioned liquid crystal
deflection device array, with respect to the scan line bending
correction, the following scheme may be applied.
That is, each liquid crystal subscanning-directional deflection
device may have a different size. For example, assuming that the
scan line bending is expressed by a function f(H) of the image
height H, many subscanning-directorial deflection devices each
having a small main-scanning-directional length are provided at a
portion in which |df/dH| is large, i.e., the scan line bending is
large, and thus, the scan line bending should be finely corrected.
On the other hand, some subscanning-directorial deflection devices
each having a large main-scanning-directional length are provided
at a portion in which |dl/dH| is small, i.e., the scan line bending
is small. As to a portion in which no scan line bending is
expected, no liquid crystal deflection device is needed.
Similarly, as to the uniform velocity correction, many
main-scanning-directorial deflection devices each having a small
main-scanning-directional length are provided at a portion in which
18 performance change rate is expected to be large, i.e., the
uniform velocity performance degradation is large, and thus, the
uniform velocity performance should be finely corrected. On the
other hand, some main-scanning-directorial deflection devices each
having a large main-scanning-directional length are provided at a
portion in which uniform velocity performance change rate is
expected as small. As to a portion in which no uniform velocity
change occurs, no liquid crystal deflection device is needed.
However, other than the above-mentioned case where the state of
scan line bending or state of the uniform velocity performance is
expected well before the image formation device is actually used,
it may be advantageous that the liquid crystal deflection device
array be a general-purpose product. Accordingly, the
main-scanning-directional size (arrangement pitch) of each liquid
crystal deflection device of the liquid crystal deflection device
array may be determined so that the scanning responsible range
assigned to each deflection device becomes uniform, and also, the
respective liquid crystal deflection devices are disposed
continuously closely.
By applying the liquid crystal deflection device array according to
the present invention, as the scan line bending, scan line
inclination, scan line shift, uniform velocity performance
degradation and so forth can be well corrected, which originally
occur due to working errors or assemble errors in the manufacturing
process of the optical scanning device. Accordingly, by applying
this scheme, it becomes possible to ease the strictness in working
accuracy, assemble accuracy, and so forth. Thereby, working costs,
or assembly costs may be reduced in the optical scanning device.
Specifically, the uniform velocity performance of the scanning
image-formation optical system may not be increased much
originally, and, thus, the other optical performance of the optical
system may be instead increased, i.e., the curvature of field,
wavefront aberration and so forth may be improved.
Further, by disposing the liquid crystal deflection device array
between the scanning image-formation system and the scanning
surface, it becomes possible to reduce the influence with respect
to the wavefront aberration on the image-formation beam by the
scanning image-formation optical system. Further, by inclining the
liquid crystal deflection device array in the subscanning
direction, possible ghost light occurring due to reflection by the
both surfaces of the liquid crystal deflection device array which
may otherwise reach the scanning surface may be avoided.
In case where, in each embodiment, the liquid crystal deflection
device array may be disposed between the light source device and
polygon mirror, correction of scanning characteristics should be
controlled according to the image height at which the optical spot
is incident currently.
As the sensor for detecting the current scanning position in the
scanning position detecting device, a line sensor such as a CCD
sensor having the longitudinal axis coincide with the subscanning
direction or the like may be applied.
As one cause of occurrence of the scan line bending, focal line
bending, shape bending or the like (bending in the subscanning
direction, lens main-line bending, or the like) may be expected in
case each optical device is made of plastic. However, as plastic
optical devise are normally mass-produced by the same manufacturing
process, the focal-line bending and/or shape bending in the same
manner may likely to occur. Accordingly, in case of the
above-mentioned tandem-type full-color image formation device or
the like, the manner of scan line bending is likely to become
similar among the respective color components. Therefore, it is
expected that a control may be performed easier that the scan line
bending of each color component is corrected to be coincide with
the reference scan line bending as mentioned above.
It is advantageous that the scan line bending on the black
component is selected as this reference scan line bending. This is
because, as black has a high contrast in comparison to the other
standard color components, change in beam spot diameter, change in
position of the beam spot, or the like occurring due to vibration,
temperature change or the like may be much likely to adversely
affect an image quality of finally created full-color image. By
selecting the black component as the color component providing the
reference scan line bending, and producing the optical scanning
system for the black component with a material especially superior
in rigidity and/or less thermal expansion, it becomes possible to
provide a high quality full-color image.
Further, it is advantageous that a configuration is made such that
the respective color-component beams be made to pass through a
common optical device of the scanning image-formation optical
system. In fact, thereby, it becomes possible to effectively reduce
a change in position deviation of scan line, scan line bending,
scan line inclination and so forth occurring due to a change in the
optical performance of lens and so forth due to a manufacture
variation or temperature change. This is because, according to the
above-mentioned configuration, as the respective color-component
beams be made to pass through a common optical device of the
scanning image-formation optical system, even in case scan line
bending of each particular beam is large, the manner of the scan
line bending are similar to each other. Accordingly, it becomes
easier to achieve correction such that the scan line bending
manners of the respective color components be coincident with each
other, and, thus, color deviation can be effectively reduced.
Furthermore, by thus utilizing an optical device in common, it
becomes possible to miniaturize the entire optical scanning
device.
Furthermore, in case change of the deflection amount of each liquid
crystal deflection device of the liquid crystal deflection device
array is performed even after a subsequent image formation process
starts, a problem may occur. That is, a scan line may move
unexpectedly, and, thus, an image quality of a finally obtained
full-color image may be remarkably degraded. Accordingly, it is
needed that adjustment or updating of the deflection amount of each
liquid crystal deflection device be performed within an interval
during which no actual image formation process is performed. In
case where the deflection angle in the liquid crystal deflection
device is within 5 minutes, and also, the diameter of beam incident
thereon is not more than 5 mm, the abovementioned requirements
(T.sub.A<0.8.times.(D/V)) may be satisfied.
As to the above-mentioned other requirements
(Ts<10.times.(L/V)), the time Ts (from the beginning of scan
line deviation detection until the end of detection completion)
includes a time required for calculating the amount by which the
scan line bending is to be corrected. Specifically, this
calculation includes calculation of average of detected values for
the purpose of noise removal, performing abnormal value processing,
and so forth so as to improve the detection accuracy.
The above-mentioned slit opening So of the ghost light removal
device may be embodied by: causing a light-blocking film to adhere
to a transparent glass plate or the like; depositing or printing a
light-blocking film to the same; or forming a slit-shaped opening
into a light-blocking-property flat plate. Alternatively, the slit
opening So may be formed of a pair of knife wedges. In this case of
applying a pair of knife wedges, each knife wedge may be located at
a different position along the optical axis. Further, the ghost
light removal device may be provided outside of the optical
scanning device. That is, it may be provided in the photosensitive
body unit, for example.
In the case where the ghost light removal device is integrally
combined with any of the optical system such as a lens or mirror,
or a dust-proof glass window, various ways, such as adhesion,
screwing, or printing, deposition, or the like may be applied as a
method of fixing to parts together.
The above-mentioned photosensitive body or photoconductor used as
the scanning surface in the image formation device according to the
present invention may be replaced by a silver film, for example. In
this case, a latent image formed thereon through optical scanning
may be visualized by a well-known silver halide photographic
process. Such an image formation device may be applied to an
optical plate-making device, an optical drawing device for drawing
a CT-scanned image or the like. Alternatively, as the
photosensitive medium, a coloring medium which cause a color in
response to application of thermal energy of the optical spot may
be used. Further alternatively, a sheet-like zinc-oxide paper may
be used as the photosensitive medium, a selenium photosensitive
body, an organic optical semiconductor may also be applied. Also,
not only a drum shape one but also belt-shaped one is applied as
the photosensitive medium on which the optical scanning is
performed.
As the transfer paper as the recording medium on which the toner
image is transferred from the photosensitive body, an OHP sheet, or
the like may also be used. In case the above-mentioned sheet-shaped
photosensitive medium is used, the toner image is directly fixed
thereon.
Further, the present invention is not limited to the
above-described embodiments, and variations and modifications may
be made without departing from the basic concept of the present
invention.
The present application is based on Japanese priority applications
Nos. 2002-015647, 2002-014255, 2002-036825, 2002-128011 and
2002-350285, filed on Jan. 24, 2002, Jan. 23, 2002, Feb. 14, 2002,
Apr. 30, 2002 and Dec. 2, 2002, respectively, the entire contents
of which are hereby incorporated by reference.
* * * * *