U.S. patent application number 10/862474 was filed with the patent office on 2004-11-11 for optical scanning device.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Shiraishi, Takashi, Yamaguchi, Masao.
Application Number | 20040223048 10/862474 |
Document ID | / |
Family ID | 17547812 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040223048 |
Kind Code |
A1 |
Shiraishi, Takashi ; et
al. |
November 11, 2004 |
Optical scanning device
Abstract
An optical scanning device of the present invention includes a
light source, forwardly deflecting optical set including a first
lens for providing light beams from the light source with a
predetermined characteristic, and a second lens for converging the
light beams from the first lens in a first direction, a polygonal
mirror unit for deflecting the light beams from the forwardly
deflecting optical set into a second direction substantially
perpendicular to the first direction, and a third lens for forming
the light beams deflected by the polygonal mirror unit as an image
onto a predetermined image surface at substantially equal speed.
The second lens includes a resin lens and a glass cylinder
lens.
Inventors: |
Shiraishi, Takashi;
(Kawasaki-shi, JP) ; Yamaguchi, Masao;
(Funabashi-shi, JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
TOSHIBA TEC KABUSHIKI KAISHA
|
Family ID: |
17547812 |
Appl. No.: |
10/862474 |
Filed: |
June 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10862474 |
Jun 8, 2004 |
|
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09665177 |
Sep 19, 2000 |
|
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6778202 |
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Current U.S.
Class: |
347/244 |
Current CPC
Class: |
G02B 26/123 20130101;
B41J 2/473 20130101 |
Class at
Publication: |
347/244 |
International
Class: |
B41J 015/14; B41J
027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 1999 |
JP |
11-274878 |
Claims
1. An optical scanning device comprising: a light source; a
forwardly deflecting optical set including a first lens for
providing light beams from said light source with a predetermined
characteristic, and a second lens for converging said light beams
from said first lens in a first direction; a polygonal mirror unit
for deflecting the light beams from said forwardly deflecting
optical set into a second direction substantially perpendicular to
said first direction; and a third lens for forming the light beams
deflected by said polygonal mirror unit as an image onto a
predetermined image surface at a substantially equal speed, wherein
said second lens includes a resin lens and a glass cylinder lens
made of glass having a positive power in said first direction and
wherein the resin lens of said second lens having a surface whose
radius of curvature in said first direction is varied along said
second direction.
2. An optical scanning device comprising: a light source; a
forwardly deflecting optical set including a first lens for
providing light beams from said light source with a predetermined
characteristic, and a second lens for converging said light beams
from said first lens in a first direction; a polygonal mirror unit
for deflecting the light beams from said forwardly deflecting
optical set into a second direction substantially perpendicular to
said first direction; and a third lens for forming the light beams
deflected by said polygonal mirror unit as an image onto a
predetermined image surface at a substantially equal speed, wherein
said second lens includes a resin lens and a glass cylinder lens
made of glass having a positive power in said first direction and
wherein the resin lens of said second lens having a surface whose
radius of curvature in said second direction is varied along said
second direction.
3. An image forming apparatus comprising: an optical scanning
device which includes: a light source; a forwardly deflecting
optical set including a first lens for providing light beams from
said light source with a predetermined characteristic; a second
lens for converging said light beams from said first lens in a
first direction; a polygonal mirror unit for deflecting the light
beams from said forwardly deflecting optical set into a second
direction substantially perpendicular to said first direction; and
a third lens for forming the light beams deflected by said
polygonal mirror unit as an image onto a predetermined image
surface at a substantially equal speed, wherein said second lens
includes a resin lens and a glass cylinder lens made of glass
having a positive power in the first direction and wherein the
resin lens of said second lens has a surface whose radius of
curvature in the second direction is varied along the second
direction; a photoreceptor drum which receives said light beam from
said optical scanning device; and a transferring apparatus which
transfers a toner image on said photoreceptor drum to a medium.
4. An image forming apparatus comprising: an optical scanning
device which includes: a light source; forwarding deflecting
optical set including a first lens for providing light beams from
said light source with a predetermined characteristic, and a second
lens from converging said light beams from said first lens in a
first direction; a polygonal mirror unit for deflecting the light
beams from said forwardly deflecting optical set into a second
direction substantially perpendicular to said first direction; a
third lens for forming the light beams deflected by said polygonal
mirror unit as an image onto a predetermined image surface at
substantially equal speed; wherein said second lens includes a
resin lens including a surface having a negative power in said
first direction, and a glass lens including one convex surface
having a positive power in said first direction, said resin lens of
said second lens includes a projection which abuts in a direction
of said convex surface of said glass lens, and wherein the
projection of said resin lens and said glass cylinder lens contact
with each other; a photosensitive member for receiving a light beam
output from said optical scanning device; and a developing device
for providing a developing material to the photosensitive member.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 09/665,177, filed Sep. 19, 2000, the entire
contents of which are incorporated herein by reference.
[0002] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 11-274878,
filed Sep. 28, 1999, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to a multi-beam optical
scanning device capable of being utilized for a multi-drum type
color printer, a multi-drum type color copier, a high-seed laser
printer, a digital copier and the like for scanning a plurality of
beams.
[0004] In an image forming apparatus such as the multi-drum type
color printer or the multi-drum type color copier, for example, a
plurality of image forming units corresponding to separated color
components, and an optical scanning device (laser light exposure
apparatus) for supplying, to the image forming units, image data,
i.e., a plurality of laser beams corresponding to the color
components are used.
[0005] Two types of this kind of image forming apparatuses are
known, i.e., a type in which a plurality of optical scanning
devices corresponding to the image forming units are disposed, and
a type in which a multi-beam optical scanning device capable of
supplying a plurality of laser beams is disposed.
[0006] The optical scanning device includes a plurality of
semiconductor laser elements (laser diodes) as light sources, a
first lens group (forwardly deflecting optical system) for reducing
a sectional beam diameter of each of a plurality of laser beams
ejected from each of the laser diodes, a polygonal mirror unit for
continuously reflecting the plurality of laser beams stopped down
by the first lens group in a direction perpendicular to a direction
into which a photosensitive member is transferred, and a second
lens group (post deflecting optical system) for forming an image of
the laser beams deflected by the polygonal mirror unit onto a
predetermined position of the photosensitive member. In many cases,
a direction in which the laser beams are deflected by the polygonal
mirror unit is indicated as a sub-scanning direction perpendicular
to the direction into which the photosensitive member is
transferred, i.e., a main-scanning direction.
[0007] The plurality of laser beams which has passed through the
first lens group are continuously reflected (deflected) by a
reflecting surface of a polygonal mirror which is rotated at a
predetermined rotation number, and are deflected to the
main-scanning direction. Each deflected laser beam is formed as an
image on a predetermined position of the photosensitive member.
[0008] The second lens group provides the laser beam scanned by the
polygonal mirror with substantially the same sectional beam
diameter on the photosensitive member, and provides the laser beam
with different focusing degree whenever the beam is reflected by
the polygonal mirror.
[0009] If a plastic lens having a surface-inclination correcting
function is used in the post deflecting optical system (second lens
group) of the above-described optical scanning device, it is
necessary to avoid influence of temperature and moisture. To avoid
this, Jpn. Pat. Appln. KOKAI Publication No. 9-189872 and the like
proposed a hybrid cylinder lens having a resin cylinder lens which
has a negative power in the sub-scanning direction but does not
have a power in the main-scanning direction, and a glass cylinder
lens having a positive power in the sub-scanning direction.
[0010] When the hybrid cylinder lens including the plastic lens
having the surface-inclination correcting function is used in the
post deflecting optical system as described above, since the a
radius of curvature is constant in the sub-scanning direction, it
is difficult to set spherical aberration and coma aberration to
predetermined values to cancel the spherical aberration and the
coma aberration generated in the post deflecting optical system.
This deteriorates RMS-OPD on an image surface, and there is a
problem that a flare in the sub-scanning direction and the like are
increased.
[0011] Further, the conventional optical scanning device only has
the same function as a flat plate in the main-scanning direction,
and the aberration and the like can not be provided positively.
Therefore, it is difficult to correct the spherical aberration
generated in the post deflecting optical system. This deteriorates
RMS-OPD on an image surface, and there is a problem that a flare in
the main-scanning direction and the like are increased.
[0012] Further, in the case of the hybrid lens, since it is
necessary that a concave surface of the plastic lens and a convex
surface of the glass cylinder lens having the positive power in the
sub-scanning direction must have the same curvatures, it is
difficult to optimize both the coma aberration and the spherical
aberration.
[0013] If surfaces having curvatures of the glass lens and the
plastic lens are connected to each other, automatic aligning
mechanism functions, and there is a merit that parallelism of the
buses can be maintained, but on the other hand, if the shape of the
plastic lens loses and non-contact surface is created between the
plastic lens and the glass lens, the contacting surface has the
curvature of glass and the non-contact surface has the curvature of
plastic and as a result, the lens has two focal points. Therefore,
there is a problem that a flare is generated in the image surface
and the beam diameter is increased.
BRIEF SUMMARY OF THE INVENTION
[0014] It is an object of the present invention to provide an
optical scanning device capable of preventing a flare from being
generated and a beam diameter from increasing by using a post
deflecting optical system including a plastic lens.
[0015] The present invention provides an optical scanning device
comprising: a light source; forwardly deflecting optical set
including a first lens for providing light beams from the light
source with a predetermined characteristic, and a second lens for
converging the light beams from the first lens in a first
direction; a polygonal mirror unit for deflecting the light beams
from the forwardly deflecting optical set into a second direction
substantially perpendicular to the first direction; a third lens
for forming the light beams deflected by the polygonal mirror unit
as an image onto a predetermined image surface at substantially
equal speed; wherein the second lens includes a resin lens and a
glass cylinder lens made of glass having a positive power in the
first direction and wherein the resin lens of the second lens
having a surface whose radius of curvature in the first direction
is varied along the first direction.
[0016] Further, the present invention provides an optical scanning
device comprising: a light source; forwardly deflecting optical set
including a first lens for providing light beams from the light
source with a predetermined characteristic, and a second lens for
converging the light beams from the first lens in a first
direction; a polygonal mirror unit for deflecting the light beams
from the forwardly deflecting optical set into a second direction
substantially perpendicular to the first direction; a third lens
for forming the light beams deflected by the polygonal mirror unit
as an image onto a predetermined image surface at substantially
equal speed; wherein the third lens having a positive power in the
second direction, and the second lens having a power in the second
direction.
[0017] Furthermore, the present invention provides an optical
scanning device comprising: a light source; forwardly deflecting
optical set including a first lens for providing light beams from
the light source with a predetermined characteristic, and a second
lens for converging the light beams from the first lens in a first
direction; a polygonal mirror unit for deflecting the light beams
from the forwardly deflecting optical set into a second direction
substantially perpendicular to the first direction; a third lens
for forming the light beams deflected by the polygonal mirror unit
as an image onto a predetermined image surface at substantially
equal speed; wherein the second lens includes a resin lens
including a surface having a negative power in the first direction,
and a glass lens including one convex surface having a positive
power in the first direction, the resin lens of the second includes
a projection which abuts in a direction of the convex surface of
the glass lens, and wherein the projection of the resin lens and
the glass cylinder lens contact with each other.
[0018] Still further, the present invention provides an optical
scanning device comprising: a light source; forwardly deflecting
optical set including a first lens for providing light beams from
the light source with a predetermined characteristic, and a second
lens for converging the light beams from the first lens in a first
direction; a polygonal mirror unit for deflecting the light beams
from the forwardly deflecting optical set into a second direction
substantially perpendicular to the first direction; a third lens
for forming the light beams deflected by the polygonal mirror unit
as an image onto a predetermined image surface at substantially
equal speed; wherein the second lens includes a resin lens
including a surface having a negative power in the first direction,
and a glass lens including one convex surface having a positive
power in the first direction, a deformable sheet having a
substantially constant thickness is provided between the resin lens
and the glass cylinder lens, and each of the resin lens and the
glass cylinder lens has a space portion when both the lenses come
into contact with each other.
[0019] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0020] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0021] FIG. 1 is a schematic sectional view of an image forming
apparatus in which a multi-beam optical scanning device of
embodiments of the present invention is utilized;
[0022] FIG. 2 is a schematic plane view showing a layout of optical
members of the optical scanning device incorporated in the image
forming apparatus shown in FIG. 1;
[0023] FIG. 3 is a schematic sectional view for explaining a state
of the optical scanning device shown in FIG. 2 in which a
reflection point of a deflector and a central portion of the post
deflecting optical system in the sub-scanning direction are
cut;
[0024] FIG. 4 is a sectional view showing a state in which one beam
of a forwardly deflecting optical system of the optical scanning
device shown in FIG. 2 passes;
[0025] FIG. 5 is a schematic view showing one example of one of
hybrid lens structure through which laser beams of the forwardly
deflecting optical system of the optical scanning device shown in
FIG. 2 pass;
[0026] FIG. 6 is a schematic view for explaining one of hybrid
lenses through which laser beams of the forwardly deflecting
optical system of the optical scanning device shown in FIG. 2 pass,
respectively;
[0027] FIG. 7 is a schematic view for explaining one of hybrid
lenses through which laser beams of the forwardly deflecting
optical system of the optical scanning device shown in FIG. 2 pass,
respectively;
[0028] FIG. 8 is a graph showing RMS-OPD in a known optical
scanning device;
[0029] FIG. 9 is a graph showing OPD (p-v) in the known optical
scanning device;
[0030] FIG. 10 is a graph showing a beam diameter in a
main-scanning direction of the known optical scanning device;
[0031] FIG. 11 is a graph showing the beam diameter in a
sub-scanning direction of the known optical scanning device;
[0032] FIG. 12 is a graph showing a flare amount in the
main-scanning direction of the known optical scanning device;
[0033] FIG. 13 is a graph showing the flare amount in the
sub-scanning direction of the known optical scanning device;
[0034] FIG. 14 is a graph showing RMS-OPD in an optical scanning
device of a third embodiment;
[0035] FIG. 15 is a graph showing OPD (p-v) in the optical scanning
device of the third embodiment;
[0036] FIG. 16 is a graph showing a beam diameter in a
main-scanning direction of the optical scanning device of the third
embodiment;
[0037] FIG. 17 is a graph showing the beam diameter in a
sub-scanning direction of the optical scanning device of the third
embodiment;
[0038] FIG. 18 is a graph showing a flare amount in the
main-scanning direction of the optical scanning device of the third
embodiment;
[0039] FIG. 19 is a graph showing the flare amount in the
sub-scanning direction of the optical scanning device of the third
embodiment;
[0040] FIG. 20 is a graph showing RMS-OPD in an optical scanning
device of a fourth embodiment;
[0041] FIG. 21 is a graph showing OPD (p-v) in the optical scanning
device of the fourth embodiment;
[0042] FIG. 22 is a graph showing a beam diameter in a
main-scanning direction of the optical scanning device of the
fourth embodiment;
[0043] FIG. 23 is a graph showing the beam diameter in a
sub-scanning direction of the optical scanning device of the fourth
embodiment;
[0044] FIG. 24 is a graph showing a flare amount in the
main-scanning direction of the optical scanning device of the
fourth embodiment;
[0045] FIG. 25 is a graph showing the flare amount in the
sub-scanning direction of the optical scanning device of the fourth
embodiment;
[0046] FIG. 26 is a graph showing RMS-OPD in an optical scanning
device of a fifth embodiment;
[0047] FIG. 27 is a graph showing OPD (p-v) in the optical scanning
device of the fifth embodiment;
[0048] FIG. 28 is a graph showing a beam diameter in a
main-scanning direction of the optical scanning device of the fifth
embodiment;
[0049] FIG. 29 is a graph showing the beam diameter in a
sub-scanning direction of the optical scanning device of the fifth
embodiment;
[0050] FIG. 30 is a graph showing a flare amount in the
main-scanning direction of the optical scanning device of the fifth
embodiment; and
[0051] FIG. 31 is a graph showing the flare amount in the
sub-scanning direction of the optical scanning device of the fifth
embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0052] An embodiment of an optical scanning device and an image
forming apparatus utilizing the optical scanning device of the
present invention will be explained in detail with reference to the
drawings below.
[0053] FIG. 1 shows a color image forming apparatus in which a
multi-beam optical scanning device which is a first embodiment of
the present invention is utilized. In this kind of color image
forming apparatus, various four sets of apparatuses are utilized
for forming images for each of four kinds of image data separated
into Y, i.e., yellow; M, i.e., magenta; C, i.e., cyan; and B, i.e.,
black, and color components respectively corresponding to Y, M, C
and B. Therefore, Y, M, C and B are added to each of reference
symbols to identify apparatuses corresponding to the image data of
color components.
[0054] As shown in FIG. 1, the image forming apparatus 100 has
first to fourth image forming sections 50Y, 50M, 50C and 50B for
forming images separately for separated color components, Y, M, C,
and B.
[0055] The image forming sections 50Y, 50M, 50C and 50B are
arranged in series in this order below an optical scanning device 1
at locations corresponding to positions where laser beams L (Y, M,
C and B) corresponding to respective color component images are
ejected through third loopback mirrors 37Y, 37M, 37C and first
loopback mirror 33B of the multi-beam optical scanning device 1
which will be described later using FIG. 8.
[0056] A transfer belt 52 for transferring a transfer material on
which an image formed by each of the image forming section 50 (Y,
M, C and B) is to be transferred is disposed below each of the
image forming sections 50 (Y, M, C and B).
[0057] The transfer belt 52 is wound around a belt driving roller
56 and a tension roller 54 which are rotated in a direction of
arrow, and the transfer belt 52 is rotated at a predetermined speed
by a motor (not shown) in a direction to which the belt driving
roller 56 is rotated.
[0058] Each of the image forming sections 50 (Y, M, C and B) is
formed into a cylindrical drum shape such that the image forming
section 50 can rotate in the direction of arrow. The image forming
sections 50 (Y, M, C and B) respectively includes photoreceptor
drums 58Y, 58M, 58C and 58B on which electrostatic latent image
corresponding to the image is to be formed.
[0059] Around each of the photoreceptor drums 58 (Y, M, C and B),
the following members are disposed in the named order along a
rotational direction of the photoreceptor drums 58, charging
apparatuses 60 (Y, M, C and B) for supplying predetermined
potential to surfaces of the photoreceptor drums 58 (Y, M, C and
B), developing apparatuses 62 for supplying toner having colors
corresponding to the electrostatic latent image corresponding to
the image formed on the surfaces of the photoreceptor drums 58 (Y,
M, C and B), thereby developing the images, transferring
apparatuses 64 (Y, M, C and B) facing the photoreceptor drums 58
(Y, M, C and B) in a state where the transfer belts 52 are
interposed between the photoreceptor drums 58 (Y, M, C and B) and
the transferring apparatuses 64 (Y, M, C and B) for transferring
toner images of the photoreceptor drums 58 (Y, M, C and B) to
transferred material, i.e., paper P sheet, cleaners 66 (Y, M, C and
B) for removing residue toner remaining on the photoreceptor drums
58 (Y, M, C and B) after the toner images were transferred through
the transferring apparatuses 64 (Y, M, C and B), and negative
charging apparatuses 68 (Y, M, C and B) for removing residue
potential remaining on the photoreceptor drums 58 (Y, M, C and B)
after the toner images were transferred through the transferring
apparatuses 64 (Y, M, C and B).
[0060] Light beams for writing latent images onto the photoreceptor
drums 58 (Y, M, C and B) respectively becomes two beams in the
sub-scanning direction on the photoreceptor drums 58 guided by the
mirrors 37 (Y, M, C and B) of the optical scanning device 1.
[0061] The laser beams L (Y, M, C and B) including combined two
light beams are applied between the charging apparatuses 60 (Y, M,
C and B) and the developing apparatuses 62 (Y, M, C and B)
respectively.
[0062] A paper cassette 70 for accommodating the paper sheets P on
which images formed by the image forming section 50 (Y, M, C and B)
are to be transferred is disposed below the transfer belt 52.
[0063] A substantially semicircular feed roller 72 for taking out
the paper sheets P one sheet-by-one sheet from the top of the paper
sheets P accommodated in the paper cassette 70 is disposed at one
end side of the paper cassette 70 closer to the tension roller
54.
[0064] A registration roller 74 is disposed between the feed roller
72 and the tension roller 54 for aligning a tip end of the one
paper sheet P taken out from the paper cassette 70 with a tip end
of the toner image formed on the photoreceptor drum 58B of the
image forming section 50B (black).
[0065] An absorption roller 76 is disposed between the registration
roller 74 and the first image forming section 50Y in the vicinity
of the tension roller 54 on an outer periphery of the tension
roller 54 such as to sandwich the transfer belt 52 between the
tension roller 54 and the absorption roller 76. The absorption
roller 76 supplies a predetermined electrostatic absorbing force.
An axis of the absorption roller 76 and an axis of the tension
roller 54 are set parallel to each other.
[0066] Registration sensors 78 and 80 are disposed on one end of
the transfer belt 52 in the vicinity of the belt driving roller 56
on the outer periphery of the belt driving roller 56 such as to
sandwich the transfer belt 52 between the registration sensors 78
and 80 and the belt driving roller 56. The registration sensors 78
and 80 detect positions of images formed on the paper sheets P
transferred by the transfer belt 52 or a transfer belt. The
registration sensors 78 and 80 are disposed at a predetermined
distance in an axial direction of the belt driving roller 56 (since
FIG. 1 is a sectional front view, only the rear sensor 80 is
shown).
[0067] A transfer belt cleaner 82 for removing toner or paper
residues of paper sheets P attached on the transfer belt 52 is
disposed on the transfer belt 52 at location corresponding to the
belt driving roller 56.
[0068] A fixing apparatus 84 for fixing, to the paper sheets P, the
toner image transferred onto the paper sheets P is disposed in a
direction to which the paper sheets P transferred through the
transfer belt 52 moves away from the tension roller 56 and further
transferred.
[0069] FIG. 2 shows the multi-beam optical scanning device utilized
in the color image-forming apparatus shown in FIG. 1.
[0070] As shown in FIG. 2, the multi-beam optical scanning device 1
includes a single deflector (polygonal mirror unit) 5 as deflecting
means for deflecting laser beams ejected from a laser element as a
light source toward predetermined positions of an image surface
disposed at a predetermined position, i.e., the photoreceptor drums
58 (Y, M, C and B) of the first to fourth image forming sections 50
(Y, M, C and B) shown in FIG. 1. A direction in which the laser
beams are deflected by the polygonal mirror unit 5 is called as a
main-scanning direction hereinafter.
[0071] The polygonal mirror unit 5 includes a polygon mirror body
5a in which octahedral plane reflection mirrors (surface) are
disposed equilaterally, and a motor 5b for rotating the polygon
mirror body 5a at a predetermined speed in the main-scanning
direction.
[0072] The polygon mirror body 5a is made of aluminum for example.
Each of the reflection surfaces of the polygon mirror body 5a is
formed by cutting the reflection surfaces along the sub-scanning
direction perpendicular to the surface including the rotation
direction of the polygon mirror body 5a, i.e., the main-scanning
direction and then by evaporating a surface protecting layer such
as S.sub.iO.sub.2 onto the cut surfaces.
[0073] Disposed between the polygonal mirror unit 5 and the image
surface is a post deflecting optical system 30 having first and
second image-forming lenses 30a and 30b for providing the laser
beams deflected into a predetermined direction by the reflecting
surface of the polygonal mirror unit 5 with a predetermined optical
characteristic. Further, a single sub-scanning direction beam
position/main-scanning direction timing detecting sensor 23 for
detecting that the individual beams of the laser beams L (Y, M, C
and B) ejected from the second image-forming lens 30b of the post
deflecting optical system 30 reach a predetermined position in
front of a region where the image is written is also disposed
between the polygonal mirror unit 5 and the image surface. A prism
26 is also disposed between the polygonal mirror unit 5 and the
image surface. The prism 26 is located between the post deflecting
optical system 30 and the sub-scanning direction beam
position/main-scanning direction timing detecting sensor 23. A
batch of laser beam L (Y, M, C and B) including two+two+two+two,
i.e., eight laser beams which had passed through the two lenses 30a
and 30b of the post deflecting optical system 30 is reflected into
the sub-scanning direction if the laser beams are guided by the
individual photoreceptor drums 58 when the polygon mirror body 5a
of the polygonal mirror unit 5 swings through a predetermined
angle, and is reflected into a direction other than the
sub-scanning direction if the beam guided by another photoreceptor
drums 58 so that the prism 26 which is an optical element varies an
ejection angle by wavelength for canceling the variation of
position by a lens by influence of the variation of the wavelength
so that positions of the beams in the main-scanning direction on a
loopback mirror 25 for sub-scanning direction beam
position/main-scanning direction timing detecting sensor for
guiding the beam to the single sub-scanning direction beam
position/main-scanning direction timing detecting sensor 23 and on
the sub-scanning direction beam position/main-scanning direction
timing detecting sensor 23 do not become different among the beams
with respect to the swinging angle of the polygon mirror body
5a.
[0074] The first and second image-forming lenses 30a and 30b have
positive power in the sub-scanning direction so that the image
surface and the reflection point on the polygon mirror have
conjugate relation to prevent the position in the sub-scanning
direction in the image surface from being varied due to an
influence of the surface-inclination (inclination between angle of
each of the reflecting surfaces and an axis passing through a
center axis) of each of the reflecting surfaces of the polygon
mirror body 5a.
[0075] Tables 1 and 2 show optical numeric data of the post
deflecting optical system.
1TABLE 1 Post deflecting Absolute coordinates: optical system
eccentricity in y-direction-4.333 Curvature Lens CUY CUZ Thickness
surface No. Material 0.019021 -0.0147546 -35.435 1 Air (Incidence
plane of lens 30A) 0.02040817 0.01793626 -6.524 2 PMMA (Ejection
plane of lens 30A) 0.0029042340 -0.00634328 -106.530 3 Air
(Incidence plane of lens 30b) 0.002112237 0.01552636 -6.0077405 4
PMMA (Ejection plane of lens 30A) Plane Plane -9.0000 Air Plane
Plane -2.000 BK7 Plane Plane -164.000 Air
[0076]
2TABLE 2 Lens surface No. 1 (incidence plane of lens 30a)
coefficient n/m 0 1 2 3 4 5 0 0.000E+00 -5.075E-02 0.000E+00
3.402E-05 -5.413E-06 -8.876E-09 1 0.000E+00 -5.988E-06 1.407E-07
1.467E-07 1.155E-08 -6.891E-10 2 -8.696E-05 -3.944E-06 -4.335E-07
5.183E-08 -1.916E-09 4.486E-11 3 1.008E-05 7.221E-08 2.189E-08
-1.459E-09 1.338E-10 -8.773E-12 4 -2.309E-07 -1.553E-10 -5.827E-10
4.448E-11 -9.423E-13 0.000E+00 n/m 6 7 8 9 10 0 -3.297E-10
3.380E-11 -6.406E-13 -1.116E-14 7.120E-16 1 6.566E-12 -5.297E-13
1.169E-14 5.802E-16 -1.260E-17 2 3.950E-12 -2.012E-13 -4.174E-17
-3.424E-16 1.399E-17 3 -1.468E-13 1.466E-14 -1.448E-16 2.661E-17
-9.120E-19 4 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 Lens
surface No. 2 (ejection plane of lens 30a) coefficient n/m 0 1 2 3
4 5 0 0.000E+00 -6.687E-02 0.000E+00 2.044E-05 -4.684E-06 7.391E-09
1 0.000E+00 -1.127E-06 -2.689E-06 1.774E-07 -1.558E-09 -2.888E-10 2
2.387E-05 -4.140E-06 -3.284E-07 3.799E-08 2.264E-12 6.067E-12 3
-8.930E-05 1.961E-07 1.661E-08 -2.529E-09 8.180E-11 2.810E-12 4
2.522E-07 -3.095E-09 -5.120E-10 4.207E-11 -9.508E-13 0.000E+00 n/m
6 7 8 9 10 0 -9.888E-10 1.234E-11 -2.037E-13 -9.521E-17 2.607E-16 1
2.046E-11 -7.927E-13 5.657E-15 -3.536E-16 1.618E-17 2 -2.478E-12
-6.435E-14 3.196E-15 1.237E-16 -3.821E-18 3 -2.949E-14 -6.090E-15
6.149E-17 4.649E-18 -6.623E-20 4 0.000E+00 0.000E+00 0.000E+00
0.000E+00 0.000E+00 Lens surface No. 3 (incidence plane of lens
30b) coefficient n/m 0 1 2 3 4 5 0 0.000E+00 1.660E-02 0.000E+00
-3.927E-06 -2.133E-07 3.818E-10 1 0.000E+00 -2.644E-05 5.823E-07
-1.140E-10 8.057E-11 1.705E-13 2 -8.028E-06 -5.092E-08 1.020E-11
1.569E-11 -6.288E-15 -2.339E-16 3 -3.363E-09 1.290E-10 3.133E-12
5.319E-14 -8.741E-17 -2.001E-18 4 2.025E-10 1.118E-12 -8.987E-15
-1.688E-16 -9.048E-18 0.000E+00 n/m 6 7 8 9 10 0 1.505E-11
2.572E-14 -8.037E-16 1.475E-18 -1.904E-20 1 -1.613E-14 7.102E-17
-8.131E-19 3.084E-21 1.349E-23 2 1.893E-17 -6.265E-19 1.203E-21
3.247E-23 -1.577E-25 3 1.135E-19 -3.473E-22 6.745E-24 -4.288E-27
-5.142E-29 4 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 Lens
surface No. 4 (ejection plane of lens 30b) coefficient n/m 0 1 2 3
4 5 0 0.000E+00 1.022E-02 0.000E+00 -4.091E-06 -4.387E-08 4.082E-10
1 0.000E+00 -1.972E-05 3.253E-07 -1.081E-09 2.945E-11 2.841E-13 2
-8.691E-06 -5.126E-08 2.922E-10 1.530E-11 -1.618E-15 -1.539E-15 3
-8.160E-09 4.185E-11 1.989E-12 4.893E-14 2.992E-16 2.713E-18 4
1.658E-10 1.372E-12 -3.279E-15 -1.813E-16 -7.667E-18 0.000E+00 n/m
6 7 8 9 10 0 1.591E-12 9.148E-16 2.739E-16 4.265E-18 -7.011E-20 1
-9.708E-16 1.800E-17 -1.643E-18 1.058E-20 -3.151E-23 2 -3.743E-18
-6.221E-20 2.589E-21 -1.455E-23 -9.009E-26 3 7.095E-20 -6.659E-22
-5.008E-24 -4.140E-26 1.614E-27 4 0.000E+00 0.000E+00 0.000E+00
0.000E+00 0.000E+00
[0077] The lens shape of the post deflecting optical system shown
in Tables 1 and 2 is expressed by the following equation (1):
X=(cuyxy.sup.2+cuzxz.sup.2)/(1+sqrt(1-cuy.sup.2xy.sup.2-cuz.sup.2xz.sup.2)-
)+a.sub.mnxy.sup.mz.sup.(2n) (1).
[0078] If an imaging lens set 30 that has two image-forming lenses
30a and 30b are included in the post deflecting optical system 21
under a condition that intervals between the plurality of beams are
maintained constantly in all the scanning regions, wave aberration
can not be corrected with a conventional toric lens or symmetry
rotation aspheric surface having symmetry axis of rotation, and the
image surface beam diameter can not be stopped down to 100 .mu.m or
smaller. This fact was found by simulation and therefore, the lens
of the post deflecting optical system shown in Tables 1 and 2 has
the above-described shape.
[0079] Since lens surfaces (incident surface of 30a, incident
surface of 30b, leaving surface of 30a and leaving surface of 30b)
of each of the two image-forming lenses (the imaging lens set 30)
are formed into the shape having no symmetry axis of rotation, it
is possible to stop down the image surface beam diameter to about
50 .mu.m while constantly maintaining the intervals between the
plurality of beams in all the scanning regions.
[0080] If specifications of various elements of the post deflecting
optical system 21 are formed in accordance with the data shown in
Tables 1 and 2, it is possible to suppress the beam positional
deviation on the image surface down to 4 .mu.m even if the
reflecting surface of the polygonal mirror unit 5 is inclined
through one minute.
[0081] That is, this optical scanning device has a function to
correct an undesirable characteristic (surface inclination) which
is given when each of the reflecting surfaces of the polygon mirror
body 5a of the polygonal mirror unit 5 is inclined with respect to
the rotation axis, and the correcting magnification is {fraction
(1/48)} times.
[0082] When the optical scanning device does not have the
surface-inclination correcting function, if the surface inclination
is continued for more than two seconds, jitter component is
adversely sensed on the image and thus, the polygon mirror body 5a
becomes extremely expensive.
[0083] Next, the forwardly deflecting optical system 7 between the
laser element as a light source and the polygonal mirror unit 5
will be explained in detail.
[0084] The optical scanning device 1 includes two, i.e., first and
second laser elements for radiating light beams guided by the
photoreceptors 58 (Y, M, C and B), and first to fourth light
sources 3 (Y, M, C and B) generating laser beams corresponding to
image data separated into three primary colors of light.
[0085] The first to fourth light sources 3 (Y, M, C and B)
respectively include a first yellow laser 3Ya and a second yellow
laser 3Yb for radiating laser beams corresponding to Y, i.e.,
yellow image; a first magenta laser 3Ma and a second magenta laser
3Mb for radiating laser beams corresponding to M, i.e., magenta
image; a first cyan laser 3Ca and a second cyan laser 3Cb for
radiating laser beams corresponding to C, i.e., cyan image; and a
first black laser 3Ba and a second black laser 3Bb for radiating
laser beams corresponding to B, i.e., black image. The laser beams
from the light sources 3 (Y, M, C and B) are gathered together to
such a degree that the laser beams can be handled together with
laser beams from the mating laser element as one beam.
[0086] Four sets of forwardly deflecting optical system 7 (Y, M, C
and B) are respectively disposed between the laser elements 3Ya,
3Ma, 3Ca, 3Ba and the polygonal mirror unit 5 for forming sectional
beam spot shapes of the laser beams LYa, LMa, LCa and LBa from the
laser elements 3Ya, 3Ma, 3Ca and 3Ba into predetermined shapes.
[0087] Here, the forwardly deflecting optical system 7Y will be
explained as a representative of laser beam LYa ejected from the
first yellow laser 3Ya to the polygonal mirror unit 5, as shown in
FIG. 4.
[0088] An emanative laser beam LYa ejected from the first yellow
laser 3Ya is converged to a predetermined value by a finite focal
lens 9Ya and then, the sectional beam shape is shaped into a
predetermined form by an aperture 10Ya.
[0089] The laser beam LYa which had passed the aperture 10Ya is
further converged to a predetermined value only in the sub-scanning
direction by a hybrid lens 11Y and guided to the polygonal mirror
unit 5.
[0090] A half mirror 12Y is inserted in between the finite focal
lens 9Ya and the hybrid lens 11Y at a predetermined angle with
respective to an optical axis between the infinite focal lens 9Ya
and the hybrid lens 11Y.
[0091] On a surface opposite from a surface which the laser beam
Lya enters from the first yellow laser 3Ya on the half mirror 12Y,
a laser beam LYb from the second yellow laser 3Yb disposed such
that a predetermined beam distance can be provided in the
sub-scanning direction with respect to the laser beam LYa from the
first yellow laser 3Ya enters at a predetermined beam distance in
the sub-scanning direction with respect to the laser beam LYa from
the first yellow laser 3Ya. A finite focal lens 9Yb and an aperture
10Yb are disposed between the second yellow laser 3Yb and the half
mirror 12Y for converging the laser beam LYb from the second yellow
laser 3Yb to a predetermined value.
[0092] The laser beams LYa and LYb combined into substantially one
laser beam having a predetermined beam distance in the sub-scanning
direction by the half mirror 12Y pass through laser combining
mirrors 13M, 13C and 13B, and guided to the polygonal mirror unit
5. M, C and B also have the same structure.
[0093] As the finite focal lenses 9 (Y, M, C and B) a and 9 (Y, M,
C and B) b, an aspherical glass lens or a single lens comprising an
aspherical glass lens and UV cure plastic aspheric lens laminated
on the aspherical glass lens can be utilized.
[0094] As shown in FIG. 4, the hybrid lens 11Y is formed with a
PMMA lens 17Y and a glass cylinder lens 19Y. The hybrid lens 11Y
has a structure in which the lens 17Y and the cylinder lens 19Y has
an air layer between the leaving surface of the lens 17Y and the
cylinder lens 19Y, and a portion of the lens through which light
does not pass is provided with a portion in which both the lenses
are in contact with each other, shown in FIG. 5.
[0095] The post deflecting optical system 21 including the imaging
lens set has the positive power in the sub-scanning direction, and
if a temperature rises, index of refraction is reduced and the lens
is expanded and, thus the power (symbol is +(plus)) is reduced.
[0096] In order to maintain the beam gathering position constantly
on the image surface, it is necessary to bring a subject away from
the lens of the post deflecting optical system when a temperature
rises.
[0097] In order to provide the forwardly deflecting optical system
7 with such a function, if the lens is made of material similar to
plastic material used in the post deflecting optical system 21, and
a lens having negative power in the sub-scanning direction is used,
the lens power (symbol is-(minus)) is reduced in index of
refraction if a temperature rises and the lens is expanded and
thus, the absolute value of the power is reduced.
[0098] For this reason, the power is increased, and the
above-described condition (subject is moved away from the lens of
the post deflecting optical system) can be satisfied.
[0099] Further, the plastic lens 17Y is disposed on the side of a
surface having a curvature of the glass lens 19Y, a member which
comes into contact with a portion having the curvature of the glass
lens 19Y to maintain the distance constantly is provided. With this
structure, an automatic centering function by a cylindrical portion
of the glass lens and the plastic lens having the member spreading
in tangent direction can be achieved.
[0100] That is, parallelism of the plane of symmetry and the bus
can be maintained.
[0101] However, if the air layer is inserted as shown in FIG. 5, a
region which is in contact with the glass lens and has the glass
shape and a region having the original plastic lens shape are
generated in a region through which the light of plastic passes as
shown in FIG. 5. If there is a slight deviation in shape of both
the surfaces, the focus position is deviated between the region
having the glass shape and the region of the plastic lens, which
makes it difficult to obtain optical beam shape at one location.
The first embodiment has a structure for solving the above problem,
as shown in FIG. 6.
[0102] As shown in FIG. 6, the plastic lens 17 is made of material
such as PMMA (polymethyl methacrylate). The glass cylinder lens 19
is made of material such as SF6.
[0103] When the plastic lens 17 of the hybrid cylinder lens 11 has
a surface of negative power in the sub-scanning direction, and the
plastic lens 17 and the glass cylinder lens 19 are assembled, a
space portion is formed while sandwiching one convex surface of the
glass cylinder lens 19, and the plastic lens 17 has at least two of
the projection portions 17a abutting in the convex surface.
[0104] With this structure, in order to provide the automatic
centering function for correcting the inclination of the two lenses
in the region through which beams do not pass, the convex portion
of the glass lens and a plastic surface having a portion of a
surface in the tangent direction are connected to each other.
Further, the glass and the plastic lens are set such that they do
not come into contact with each other in a position where the beam
passes.
[0105] With this structure, the automatic centering function is
utilized, parallelism of the plane of symmetry and the bus is
maintained, and even if the shapes of the plastic lenses are
deviated, the curvature is prevented from being varied abruptly,
and the flare in the image surface and the increase of the beam
diameter can be prevented.
[0106] FIG. 7 is for explaining another embodiment of the optical
scanning device of the present invention. The hybrid cylinder lens
11 includes a one side convex glass cylinder having curvature of
substantially the same absolute value as that of the resin lens
having negative power surface and having positive power in the
sub-scanning direction. The resin lens and the glass cylinder lens
have a space portion sandwiching the one side convex surface, and
have a substantially constant thickness therebetween, and a
deformable sheet is inserted.
[0107] In the example shown in FIG. 7, a Mylar sheet which is a
plastic sheet 18 having 0.05 mm thickness is sandwiched.
[0108] In this case, it is preferable that the connected surfaces
of the glass lens and the plastic lens have the same curvature, but
slight difference can be accepted. With this structure, the same
effect as that of the first embodiment shown in FIG. 5 can be
obtained. Tables 4A and 4B are for explaining a third embodiment,
and show parameters explaining the lens shape.
3TABLE 3A Cylinder lens coefficient Curvature in Curvature in
main-scanning sub-scanning Thickness direction direction Material
1.5 0 -0.002426985 PMMA 0 0 0.048259651 Air 5 0 0.048259651 SF6 0
0
[0109]
4TABLE 3B Free-form surface of PMMA lens (plastic lens) n/m 1 2 3 4
5 1 0 0 0 0 0 2 0 0 0 0 0 3 0 0 0 0 0
[0110]
5TABLE 4A Aspheric coefficient in sub-scanning direction Curvature
in Curvature in man-scanning sub-scanning Thickness direction
direction Material Note 1.5 0 -0.003973344 PMMA Free-form 0.05 0
0.048259651 Air surface 5 0 0.048259651 SF6 0 0
[0111]
6TABLE 4B Free-form surface of PMMA lens (plastic lens) n/m 0 1 2 3
4 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 1 5.56E-04
0.00E+00 0.00E+00 0.00E+00 0.00E+00 2 1.07E-06 0.00E+00 0.00E+00
0.00E+00 0.00E+00 3 -2.71E-07 0.00E+00 0.00E+00 0.00E+00 0.00E+00 4
1.18E-08 0.00E+00 0.00E+00 0.00E+00 0.00E+00
[0112] In Tables 4, the incident surface shape of the plastic lens
17Y is the same as the equation (1) showing the shape of the post
deflecting optical system. For comparison, numerical data of the
conventional example is shown in Tables 3 and FIGS. 8 to 13. FIGS.
14 to 19 show the RMS-OPD of the lens having a shape shown in
Tables 4, OPD (p-v), beam diameter in the main-scanning direction,
beam diameter in the sub-scanning direction, flare amount in the
main-scanning direction, and flare amount in the sub-scanning
direction. In each of the drawings, a curve a (solid line) shows
performance when ambient temperature is 20.degree. C., a curve b
(dotted line) shows performance when ambient temperature is
50.degree. C., and a curve c (chain line) shows performance when
ambient temperature is -10.degree. C. Lateral axes show position in
the main-scanning direction in the image surface.
[0113] In the case of the conventional hybrid lens, since the
radius of curvature is constant along the sub-scanning direction,
in order to cancel the spherical aberration and the coma aberration
as the entire hybrid lens by the spherical aberration and the coma
aberration generated in the post deflecting optical system 21, it
is difficult to set the aberrations to predetermined values.
[0114] This deteriorates the RMS-OPD in the image surface, and the
flare in the sub-scanning direction is increased.
[0115] To solve this problem, the plastic cylinder lens of the
conventional hybrid lens is replaced by a resin lens having surface
whose radius of curvature of the sub-scanning direction is varied
in the sub-scanning direction.
[0116] That is, it is possible to optimize the radius of curvature
in the sub-scanning direction depending upon locations by providing
the coefficient portion of n=2 with a component other than "0" in
the "a.sub.mn.times.y.sup.mz.sup.(2n)" of the equation (1) in Table
4.
[0117] In each of the drawings, a curve a (solid line) shows
performance when ambient temperature is 20.degree. C., a curve b
(dotted line) shows performance when ambient temperature is
50.degree. C., and a curve c (chain line) shows performance when
ambient temperature is -10.degree. C. Lateral axes show position in
the main-scanning direction in the image surface.
[0118] From the comparison (RMS-OPD) between FIG. 8 and FIG. 4,
improvement can be found in the vicinity of the central portion of
the RMS-OPD as compared with the conventional technique.
[0119] From the comparison (flare amount in the sub-scanning
direction) between FIG. 12 and FIG. 18, it can be confirmed that
the flare amount in the sub-scanning direction is reduced in the
vicinity of the central portion.
[0120] Table 5 shows data for explaining another embodiment
(corresponding to claims 2 and 3) of the lens shape, and shows that
if the lens is formed in accordance with the data shown in Table 5,
it is possible, as shown in FIGS. 20 to 25, to improve the RMS-OPD
(FIG. 20), the OPD (p-v) (FIG. 21), the beam diameter in the
main-scanning direction (FIG. 22), the beam diameter in the
sub-scanning direction (FIG. 23), the flare amount in the
main-scanning direction (FIG. 24) and the flare amount in the
sub-scanning direction (FIG. 25), as compared with the examples
shown in FIGS. 8 to 13. In each of the drawings, a curve a (solid
line) shows performance when ambient temperature is 20.degree. C.,
a curve b (dotted line) shows performance when ambient temperature
is 50.degree. C., and a curve c (chain line) shows performance when
ambient temperature is -10.degree. C. Lateral axes show position in
the main-scanning direction in the image surface. In this
embodiment, it is confirmed that the variations in the RMS-OPD, OPD
(p-v), the beam diameter in the main-scanning direction and the
flare amount in the main-scanning direction due to an ambient
temperature are reduced.
7TABLE 5A Aspheric coefficient in main-/sub-scanning direction
Curvature in Curvature in main-scanning sub-scanning Thickness
direction direction Material Note 1.5 -3.72E-04 -0.003910705 PMMA
Free-form 0.05 0.00E+00 0.048259651 Air surface 5 0.00E+00
0.048259651 SF6 0.00E+00 0
[0121]
8TABLE 5B Free-form surface of PMMA lens (plastic lens) n/m 0 1 2 3
4 0 0.00E+00 -3.75E-04 -2.27E-04 -2.21E-07 -5.15E-07 1 3.27E-04
-8.27E-07 1.08E-06 5.04E-08 -7.74E-08 2 5.89E-07 1.26E-07 -1.72E-07
4.56E-09 2.06E-08 3 -2.32E-07 7.45E-10 9.33E-09 -2.95E-09 -8.78E-10
4 1.07E-08 -3.40E-10 3.04E-10 1.81E-10 -4.48E-11
[0122] Table 6 shows data for explaining another embodiment of the
lens shape, and shows that if the lens is formed in accordance with
the data shown in Table 6, it is possible, as shown in FIGS. 26 to
31, to improve the RMS-OPD (FIG. 26), the OPD (p-v) (FIG. 27), the
beam diameter in the main-scanning direction (FIG. 28), the beam
diameter in the sub-scanning direction (FIG. 29), the flare amount
in the main-scanning direction (FIG. 30) and the flare amount in
the sub-scanning direction (FIG. 31), as compared with the examples
shown in FIGS. 8 to 13. In each of the drawings, a curve a (solid
line) shows performance when ambient temperature is 20.degree. C.,
a curve b (dotted line) shows performance when ambient temperature
is 50.degree. C., and a curve c (chain line) shows performance when
ambient temperature is -10.degree. C. Lateral axes show position in
the main-scanning direction in the image surface.
9TABLE 6A Aspheric coefficient in main-/sub-scanning direction with
a curvature of glass lens is not equal Curvature in Curvature in
main-scanning sub-scanning Thickness direction direction Material
Note 1.5 -3.72E-04 -0.003911252 PMMA Free-form 0.05 0.00E+00
0.048260174 Air surface 5 0.00E+00 0.048259547 SF6 0.00E+00 0
[0123]
10TABLE 6B Free-form surface of PMMA lens (plastic lens) n/m 0 1 2
3 4 0 0.00E+00 -4.34E-04 -2.27E-04 -2.15E-07 -5.17E-07 1 3.27E-04
-8.09E-07 1.09E-06 4.774E-08 -7.77E-08 2 6.31E-07 1.28E-07
-1.73E-07 4.61E-09 2.05E-08 3 -2.34E-07 5.86E-10 9.23E-09 -2.94E-09
-8.73E-10 4 1.07E-08 -3.61E-10 3.00E-10 1.82E-10 -4.32E-11
[0124] As described above, according to the optical scanning device
of the embodiment of the present invention, in the hybrid cylinder
lens comprising the plastic lens and the glass lens capable of
correcting the surface-inclination, it is possible to bring the
radius of curvature of the plastic lens surface close to a
predetermined value by varying the radius of curvature by the
height in the sub-scanning direction to cancel the spherical
aberration and the coma aberration as the entire hybrid lens by the
spherical aberration and the coma aberration generated in the post
deflecting optical system, and it is possible to improved the
RMS-OPD in the image surface and to reduce the flare in the
sub-scanning direction.
[0125] That is, the conventional plastic cylinder lens of the
hybrid lens is replaced by the resin lens having a surface having
power in the main-scanning direction. In the embodiment, the
curvature of one surface in the main-scanning direction in Table 5
is "-", this provides the lens with negative power in the
main-scanning direction, thereby canceling the variation of the
image-forming position which is caused by temperature variation
with respect to the positive power of the post deflecting optical
system in the main-scanning direction.
[0126] Further, it is possible to reduce the necessity for
controlling the lens-holding position for initially gathering or
bringing the light from the laser element into parallelism with
each other with respect to characteristic thereof against the
temperature and moisture variation of the post deflecting optical
system, and it is possible to optimize the lens only in terms of
the performance the cost. Furthermore, it is possible to provide a
power to cancel the deviation in focus position which is caused due
to the temperature and moisture variation in the main-scanning
direction generated in the post deflecting optical system, and to
suppress the deviation of the focus due to the temperature and
moisture variation as total.
[0127] Further, since the conventional plastic cylinder lens of the
hybrid lens is replaced by the resin lens having a surface whose
radius of curvature in the main-scanning direction can be varied
along the main-scanning direction, it is possible to positively
provide aberration in a direction into which the spherical
aberration generated in the post deflecting optical system is
canceled, and to improve the RMS-OPD in the image surface and
reduce the flare and beam diameter in the main-scanning direction.
In the embodiment, this corresponds to the term
"a.sub.mn.times.y.sup.mz.sup.(2n)" of the equation (1), and it is
possible to optimize the radius of curvature in the sub-scanning
direction depending upon locations by providing the coefficient
portion of n=2 with a component other than "0".
[0128] In the embodiment, if both the m and n are other than "0",
the coefficient is also other than "0". Therefore, the
main-scanning curvature and sub-scanning curvature are optimized
with respect to the sub-scanning direction, and the main-scanning
curvature and sub-scanning curvature are optimized with respect to
the main-scanning direction.
[0129] That is, if FIG. 8 and FIG. 20 are compared with each other,
it is found that the entire RMS-OPD is improved as compared with
the conventional example. It is found from FIGS. 13 and 25 that the
amount of flare in the sub-scanning direction is reduced in the
vicinity of the center. In addition, if FIGS. 10, 22 and FIGS. 12,
24 are compared with each other, it is found that the beam diameter
in the main-scanning direction and the temperature dependence of
the flare amount are also reduced. This is because that the
variation of the image-forming point caused by the temperature
variation in the main-scanning direction among the temperature
dependency of fO lens, infinite lens and holding member is
suppressed by providing the plastic lens 17Y with the power in the
main-scanning direction.
[0130] Further, the conventional plastic cylinder lens of the
hybrid lens is replaced by the resin lens having a holding surface
portion which is contact with the convex surface side of the glass
lens provided in the region through which the light does not pass,
and having, at the convex surface of the glass lens in the region
through which the light passes, the surface of a curvature
different from that of the convex surface of the glass. Therefore,
in the embodiment, the fact that a curvature of two surfaces and a
curvature of three surface of the curvature in the sub-scanning
direction of the Table 6 are different indicates this.
[0131] With this structure, since the curvature of the glass
cylinder lens and the curvature of the plastic lens can be set
independently, it is possible to further optimize the coma
aberration, the spherical aberration and the characteristics of the
post deflecting optical system in the direction to which they are
canceled.
[0132] This fact can be found from the fact that the entire RMS-OPD
could be improved as compared with the conventional example from
the comparison between FIG. 8 and FIG. 26, and the fact that the
flare amount in the sub-scanning direction could be reduced in the
vicinity of the center from the comparison between FIG. 13 and FIG.
31. In addition, if FIGS. 10, 23 and FIGS. 12, 30 are compared, it
is found that the beam diameter in the main-scanning direction and
the temperature dependence of the flare amount are also
reduced.
[0133] Further, the conventional plastic cylinder lens of the
hybrid lens is replaced by the lens having a holding surface having
negative power in the sub-scanning direction, the plastic lens and
the glass cylinder lens have space portions while sandwiching the
one-side convex surface, the second resin lens has the projection
abutting in the one-surface convex direction, or the resin lens and
the glass cylinder lens have the space portion while sandwiching
the one-surface convex and the deformable sheet having a
substantially constant thickness is inserted in therebetween. In
order to provide the automatic centering function for correcting
the inclination of the two lenses in the region through which the
beams do not pass, the glass lens and the plastic surface are
connected with each other at the convex portion of the glass lens
and the surface having the curvature, and the glass and the plastic
lens do not come into contact with each other at the position where
the beams pass. With this structure, even if the shape of the
plastic lens is slightly varied, it is possible to prevent the
curvature from being varied abruptly, and to prevent the flare and
the beam diameter from increasing in the image surface.
[0134] As explained above, according to the optical scanning device
of the present invention, in a single color or color laser beam
printer, a digital copier and the like, it is possible to provide
an inexpensive and highly reliably beam scanner capable of reducing
the temperature dependency and providing fine image while reducing
the beams on the image surface in which a portion or all of a post
deflecting lens is made of plastic.
[0135] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
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