U.S. patent number RE36,841 [Application Number 08/755,656] was granted by the patent office on 2000-08-29 for multi-beam laser printer with beam spacing detection during blanking time.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Akira Arimoto, Takeshi Mochizuki, Susumu Saito.
United States Patent |
RE36,841 |
Arimoto , et al. |
August 29, 2000 |
Multi-beam laser printer with beam spacing detection during
blanking time
Abstract
In a laser printer wherein a photoconductive drum is scanned by
utilizing a plurality of laser beams, there are detected spacings
between the plural laser beams, such detection being confined to a
blanking time. On the basis of the detected results, the spacings
between the plural laser beams are controlled; and this state is
maintained for a printing time. With this arrangement, it is
possible to accurately detect the spacings between the plural laser
beams thereby to obtain the practicable laser printer employing the
plural laser beams.
Inventors: |
Arimoto; Akira
(Musashimurayama, JP), Saito; Susumu (Hachioji,
JP), Mochizuki; Takeshi (Mito, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
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Family
ID: |
27305174 |
Appl.
No.: |
08/755,656 |
Filed: |
November 25, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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480935 |
Feb 16, 1990 |
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Reissue of: |
854947 |
Apr 23, 1986 |
04725855 |
Feb 16, 1988 |
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Foreign Application Priority Data
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Apr 25, 1985 [JP] |
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60-86446 |
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Current U.S.
Class: |
347/250; 347/257;
358/296 |
Current CPC
Class: |
G06K
15/1261 (20130101); H04N 1/113 (20130101); H04N
2201/04755 (20130101) |
Current International
Class: |
G06K
15/12 (20060101); H04N 1/113 (20060101); B41J
002/435 () |
Field of
Search: |
;347/250,257
;346/107.1,107.4 ;358/296,480,481 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Le; N.
Assistant Examiner: Anderson; L.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP
Parent Case Text
.Iadd.This application is a continuation application of Ser. No.
07/480,935, filed Feb. 16, 1990, now abandoned, which is a reissue
application of U.S. application Ser. No. 06/854,947, filed on Apr.
23, 1986, now U.S. Pat. No. 4,725,855, issued Feb. 16, 1988.
.Iaddend.
Claims
What is claimed is:
1. A laser printer comprising: a source for generating a plurality
of laser beams;
an optical device deflecting said plural laser beams for
scanning;
a printing photoconductive drum scanned simultaneously and
parallelly by specific irradiation of said .[.polarized.].
.Iadd.plural .Iaddend.laser beams;
a detector for optically detecting deviation in spacings between
said plural laser beams by making use of part of said plural laser
beams; and
actuators for adjusting spots irradiated with said plural laser
beams in response to an output signal of said detector, wherein
there is provided a controller which performs a controlling
operation so that the detection of positional deviation relative to
the spacings between said laser beams is carried out only for a
blanking time associated with said laser printer.
2. A laser printer as set forth in claim 1, wherein operational
timing of a controlling means for detecting said blanking time is
effected with the aid of an output signal of a photodetector for
detecting a scanning start point provided in the vicinity of a
print starting position on the scanning line for said laser beam on
said printing photo conductive drum.
3. A laser printer as set forth in claim 1, wherein said source for
generating said plural laser beams is constituted by a plurality of
semiconductor lasers.
4. A laser printer as set forth in claim 1, wherein said controller
controls said source for generating a plurality of laser beams so
that said laser beams are in the ON condition without intensity
variation thereof during said blanking time so as to enable
accurate detection of positional deviation relative to the spacings
between said laser beams. .Iadd.
5. A laser printer as set forth in claim 3, wherein there is
provided a prism for synthesizing said plural laser beams from said
source in the same direction at such spacings that said plural
laser beams slightly deviate from each other. .Iaddend..Iadd.6. A
laser printer as set forth in claim 5, wherein said detector
receives beams which are partially taken out of said prism.
.Iaddend..Iadd.7. A laser printer as set forth in claim 1, wherein
there is provided a scanning lens between said optical device for
deflecting said plural laser beams and said printing
photoconductive drum. .Iaddend..Iadd.8. A laser printer as set
forth in claim 7, wherein said scanning lens is an F.theta. lens.
.Iaddend..Iadd.9. A laser printer as set forth in claim 1, wherein
said optical device is a rotating polygonal mirror.
.Iaddend..Iadd.10. A laser printer comprising:
a plurality of semiconductor lasers generating a plurality of laser
beams;
a prism synthesizing said plural laser beams in the same direction
and with slightly deviated positions from each other;
a deflector deflecting said plural beams for scanning;
a photoconductive element scanned parallely on the surface thereof
by said plural laser beams;
a detector detecting deviation between said plural laser beams on
said surface by part of said plural laser beams; and
actuators adjusting the positions of said plural laser beams from
each other on said surface in accordance with said detected
deviation within a
blanking time of said laser printer. .Iaddend..Iadd.11. A laser
printer as set forth in claim 10, wherein there are provided a
photodetector which detects each printing start timing for scanning
lines on said surface of said photoconductive element and a
controller which is connected to said actuators and said
photodetector, said controller controlling operations of said
actuators in accordance with an output signal of said photodetector
so that the positions of said plural laser beams on said surface
are adjusted in accordance with said detected deviation within a
blanking time of said laser printer and are kept for a printing
time of said laser printer. .Iaddend..Iadd.12. A laser printer as
set forth in claim 11, wherein said controller is connected to said
plural semiconductor lasers and controls said plural semiconductor
lasers so that said laser beams are in the ON condition within said
blanking time in order to detect the deviation between said laser
beams.
.Iaddend..Iadd. A laser printer as set forth in claim 11, wherein
said detector receives beams which are partially taken out of said
prism. .Iaddend..Iadd.14. A laser printer as set forth in claim 11,
wherein there is provided a scanning lens between said deflector
and said photoconductive device. .Iaddend..Iadd.15. A laser printer
as set forth in claim 14, wherein said scanning lens is an F.theta.
lens. .Iaddend..Iadd.16. A laser printer as set forth in claim 11,
wherein said deflector is a rotating polygonal mirror.
.Iaddend..Iadd.17. A laser printer as set forth in claim 11,
wherein said detector has a plurality of segments combined with
each other so as to receive respective images of said plural laser
beams and detects the deviation between said plural laser beams on
the basis of a relation between the segments. .Iaddend..Iadd.18. A
laser printer comprising:
a source for generating a plurality of laser beams;
a deflector deflecting said plural laser beams for scanning;
a photoconductive device scanned parallely on the surface thereof
by said plural laser beams;
a detector detecting deviation between said plural laser beams on
said surface by part of said plural laser beams;
actuators connected to said detector and adjusting the positions of
said plural laser beams on said surface in accordance with said
detected deviation within a blanking time of said laser
printer;
a photodetector detecting a predetermined position corresponding to
each start position of an effective part of said surface for
printing; and
a controller connected to said actuators and said photoconductor,
said controller controlling the operations of said actuators in
accordance with an output signal of said photodetector so that the
positions of said plural laser beams on said surface are kept for a
printing time of said
laser printer. .Iaddend..Iadd.19. A laser printer as set forth in
claim 18, wherein said photodetector is provided to receive said
laser beams deflected by said deflector. .Iaddend..Iadd.20. A laser
printer as set forth in claim 18, wherein said source for
generating said plural laser beams is constituted by a plurality of
semiconductor lasers. .Iaddend..Iadd.21. A laser printer as set
forth in claim 18, wherein said controller is connected to said
source for generating a plurality of laser beams and controls said
source for generating a plurality of laser beams so that said laser
beams are in the ON condition within said blanking time so as to
detect the deviation between said laser beams.
.Iaddend..Iadd. A laser printer as set forth in claim 20, wherein
there is provided a prism between said semiconductor lasers and
said deflector, said prism synthesizing said plural laser beams
from said plural semiconductor lasers in the same direction at
spacings such that said plural laser beams slightly deviate from
each other. .Iaddend..Iadd.23. A laser printer as set forth in
claim 22, wherein said detector receives beams which are partially
taken out of said prism. .Iaddend..Iadd.24. A laser printer as set
forth in claim 18, wherein there is provided a scanning lens
between said deflector and said photoconductive device.
.Iaddend..Iadd.25. A laser printer as set forth in claim 18,
wherein said deflector is a rotating polygonal mirror.
.Iaddend..Iadd.26. A laser printer as set forth in claim 18,
wherein said detector has a plurality of segments combined with
each other so as to receive respective images of said plural laser
beams and detects the deviation between said plural laser beams on
the basis of a relation between the segments. .Iaddend..Iadd.27. A
laser printer comprising:
a source for generating a plurality of laser beams;
a deflector deflecting said plural laser beams for scanning;
a photoconductive device scanned parallely on the surface thereof
by said plural laser beams;
a detector having a plurality of segments combined with each other
so as to receive respective images of said plural laser beams and
detecting deviation between said plural laser beams and said
surface, on the basis of a relation between the segments;
means for maintaining the deviation between said plural laser beams
by a negative feedback control operation using said detected
deviation so that the positions of said plural laser beams on said
surface are held in a predetermined relation;
a photodetector provided in the vicinity of said photoconductive
device for detecting a position corresponding to each start
position of said surface for printing; and
a controller connected to said maintaining means, said source and
said photodetector, said controller controlling the operation of
said maintaining means so that said negative feedback control
operation is kept during a printing time of said laser printer and
controlling said source so that said laser beams are in the ON
condition within a period other than said printing time so as to
detect the deviation between said laser beams, in accordance with
an output signal of said photodetector.
.Iaddend..Iadd.28. A laser printer as set forth in claim 27,
wherein said maintaining means includes actuators which are driven
in accordance with outputs of said segments. .Iaddend..Iadd.29. A
laser printer as set forth in claim 27, wherein said source for
generating said plural laser beams includes a plurality of
semiconductor lasers. .Iaddend..Iadd.30. A laser printer as set
forth in claim 27, wherein said photoconductor is disposed so as to
receive said laser beams deflected by said deflector.
.Iaddend..Iadd.31. A laser printer as set forth in claim 29,
wherein said controller controls said semiconductor lasers so that
said laser beams are in the ON condition within said period.
.Iaddend..Iadd.32. A laser printer as set forth in claim 29,
wherein there is provided a prism between said semiconductor lasers
and said deflector, said prism synthesizes said plural laser beams
from said plural semiconductor lasers in the same direction and
with positions slightly deviated from each other.
.Iaddend..Iadd.33. A laser printer as set forth in claim 32,
wherein said detector receives beams which are partially taken out
of said prism. .Iaddend..Iadd.34. A laser printer as set forth in
claim 27, wherein there is provided a scanning lens between said
deflector and said
photoconductive device. .Iaddend..Iadd.35. A laser printer as set
forth in claim 27, wherein said deflector is a rotating polygonal
mirror. .Iaddend..Iadd.36. A laser printer comprising:
two semiconductor lasers;
a prism synthesizing two laser beams generated from said two
semiconductor lasers in the same direction and with positions
slightly deviated from each other;
a deflector deflecting said two laser beams for scanning;
a photoconductive device scanned parallely on the surface thereof
by said two laser beams;
a detector which has a plurality of segments combined with each
other so as to receive respective images of said two laser beams by
part of said two laser beams, and which detects a deviation between
said two laser beams on said surface on the basis of a relation
between the segments;
actuators adjusting the positions of said two laser beams on said
surface in accordance with said detected deviation;
a photoconductor provided in the vicinity of said photoconductive
device to receive said laser beams deflected by said deflector and
detecting a position corresponding to each start position of said
surface for printing; and
a controller connected to said actuators, said semiconductor lasers
and said photodetector, said controller controlling the operations
of said actuators so that the positions of said two laser beams on
said surface are kept for a printing time of said laser printer and
controlling said semiconductor lasers so that said two laser beams
are in the ON condition within a blanking time of said laser
printer so as to detect the deviation between said two laser beams,
in accordance with an output signal of said
photodetector. .Iaddend..Iadd.37. A laser printer as set forth in
claim 36, wherein said detector receives beams which are partially
taken out of said prism. .Iaddend..Iadd.38. A laser printer as set
forth in claim 36, wherein there is provided a scanning lens
between said deflector and said photoconductive device.
.Iaddend..Iadd.39. A laser printer as set forth in claim 36,
wherein said deflector is a rotating polygonal mirror. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a laser printer which is capable
of printing high grade characters and images by scanning laser
beams.
A conventional laser printer whose printing velocity is medium or
low usually utilizes a single diode laser beam. On the other hand,
a printer in which the printing is effected at an extra-high speed
is at present arranged such that the single gas laser beam is
intactly employed, or this single gas laser beam is divided into
plural gas laser beams by means of an acoustic optical deflector;
and both the frequency band region of a modulator and the rate at
which a rotating polygonal mirror rotates are reduced by scanning
the plural gas laser beams simultaneously.
In either case, however, so far as the gas laser is employed as
mentioned above, it is impossible to steer clear of the large
consumption of electricity and miniaturize the apparatus. Under
such circumstances, there is recently focussed an introduction of a
semiconductor laser which is capable of executing direct modulation
for itself. However, this kind of semiconductor laser involves
defects wherein the wavelength thereof is 1.5.about.2-fold as long
as that of the gas laser, which requires a large-sized
configuration of the rotating polygonal mirror, and it has been
quite difficult to constitute a laser printer by using a single
laser beam on account of deteriorated photoconductivity which
responds to a long wavelength of the foregoing semiconductor
laser.
Such being the case, there is a growing expectation in a method
where parallel scanning is effected by making use of a plurality of
semiconductor laser beams. Some means for actualizing this end have
been disclosed in the specifications of U.S. patent application No.
680497, West German patent application No. P3445751.8, U.S. patent
application No. 804940 and West German patent pplication No.
P3543472.4 with which some of the inventors of the present
invention are associated. However, provided that the printing is
performed during the detection of the spacings between plural
semiconductor laser beams, it is inconveniently unfeasible to
accurately detect it.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention which
obviates the above-described problems to provide a laser printer
which is capable of precisely detecting spacings between a
plurality of laser beams thereby to control the desired spacings.
To accomplish this end, the present invention is characterized such
that there is prescribed a timing at which to detect the spacings
between the aforementioned plural laser beams.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing a constitution of a laser printer of one
embodiment according to the present invention, the laser printer
utilizing a plurality of laser beams to control the spacings
therebetween;
FIG. 2 is a view showing the timing at which locations of the laser
beams relative to this invention are detected; and
FIG. 3 is a view showing a constitution of a photodetector for
detecting the spacings between the plural laser beams relative to
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown a laser printer which
employs two semiconductor lasers of one embodiment according to the
present invention.
Laser beams respectively emitted from two lasers 11, 12 pass
through a synthesizing prism 5 where the laser beams are
synthesized in the same direction at such a spacing that the two
laser beams slightly deviate from each other. In the wake of this,
the beams are directed toward a rotating polygonal mirror 6 and
then turns to an F.theta. lens 7 serving as a scanning lens. On a
photoconductive drum 8, the two laser beams are adjusted to a
predetermined spacing, and at the same time, it is required to
render this spacing immutable. As shown in FIG. 1, for this purpose
is proposed an apparatus in which the spacing between the two laser
beams is read with the aid of a divided detector 13 by making use
of the light which is partially leaked out of the prism 5 designed
for synthesizing the beam; and the above-described spacing is
controlled by virtue of the resultant signal.
The laser printer employing the semiconductor, however, creates the
following drawback. It is feasible for the laser itself to modulate
at a printing time, so that the modulated light enters the divided
detector 13. As a result, intensity of the laser beams varies and
hence it is difficult to detect the position thereof. Consequently,
as for the present invention, the arrangement is such that the
detection is carried out within a blanking time for which the
printing is not effected; the spacings between the laser beams are
controlled on the basis of the thus detected results; and this
state is maintained in a printing time. If the rotating polygonal
mirror is commonly used, an angle at which the light is
theoretically able to scan in the case of an n-faced mirror can be
given by:
Inasmuch as the light which is incident upon the rotating polygonal
mirror usually has a specified magnitude, it is common that the
actual angle at which the photo-scanning is performed on the
polygonal mirror comes to 60-70% of the above-described theoretical
value.
Accordingly, a period of 60-70% is, as described above, employed
for printing, whereas a period of 30-40% is defined as non-scanning
time. Generally speaking, this non-scanning time is considered to
be rather disadvantageous, since effective utilization of the laser
beams is unfeasible during this time. The present invention,
however, is characterized in detecting the position by setting the
two laser beams in a state of "ON" for this blanking time. FIG.
2(a) shows the timing relative to modulation of semiconductor
lasers (marked with 11, 12 in FIG. 1) of an embodiment according to
the present invention. Namely, in case that the positional control
is conducted with respect to the two laser beams which are
respectively emitted from the semiconductor lasers 11, 12 by the
use of a signal (hereinafter referred to as a spacing error signal)
which is detected for the blanking time, it is, as mentioned
before, not easy to obtain the spacing error signal for the
printing time. Hence the so-called sample holding mode is adopted,
wherein the aforecited positional control is performed by using the
spacing error signal obtained for the blanking time only, and such
a state is arranged to be kept for the printing time. A blanking
time 9 can be detected as follows. It can be observed through FIG.
1 that the photodetector 3 is disposed outside a print starting
position on the scanning line for the laser beam, this
photodetector 3 being designed for setting the start timing at
which the laser beam is scanned. To be specific, the time just when
the scanning laser beam passes through the photodetector 3 is
defined as the scanning start timing. The timing positions are
indicated by the reference numeral 120 in FIGS. 2(a), 2(b). It is
to be noted that FIG. 2(b) shows the timing of an output signal
emitted from the photodetector 3. A width T of a scanning period 10
for which the scanning is effected with respect to a predetermined
width measured from the point 120 is expressed such as:
where L is the printing width of a rotating polygonal mirror, n is
the number of revolution thereof, and f is the focal length of the
F.theta. lens 7 employed therein. After traversing the width T, the
blanking time 9 is present. For this period, the laser beam
continue to light up on direct current. Namely, the blanking time 9
is a time till the laser beam in the next scanning plan comes to
the photodetector 3 again. The divided type photodetector 13
detects the spacing error for the blanking time. A configuration of
such a photodetector is, as described at full length in
the specifications of U.S. patent application Ser. No. 680,497 or
West German patent application No. P3445751.8, typified by that of
the photodetector 13 shown in FIG. 3. The photodetector 13 is
constituted by two pairs of divided detectors 141, 142 and 143, 144
and is arranged to read the positions of the respective laser beams
by a differential motion.
In FIG. 3, suppose that the laser beams on the detectors 151, 152
are so located as to be impartially applied to the divided
detectors 141, 142 and 143, 144, the foregoing differential output
is zero. However, if the beams are located so that they are
asymmetrically applied thereto, there appears a differential signal
which displays the differential output corresponding to the
positions of the laser beams. Consequently, there are provided
controllers 61, 62 consisting of, for example, a gain adjusting
unit or the like which has a function to effect a negative feedback
with a view to controlling actuators 21, 22. With this arrangement,
the differential signal remains to be zero, this signal being
obtained by means of differential devices 41, 42 (for instance, a
differential amplifier or the like) shown in FIG. 1.
Coupling lenses 1, 2 are moved by dint of the motion of the
actuators 21, 22 in such a way that the surfaces of the lenses are
so directed to be perpendicular to the optical axes, whereby two
spots irradiated with the laser beams are adjusted in order that no
positional deviation is produced.
With the aid of the signals (See FIG. 2(b)) created when the
scanning laser beams shown in FIG. 1 passes through the detector 3,
the controller 60 shown in the same Figure performs controlling
operations with respect to "ON" and "OFF" of the laser beam, the
sample holding processing, detection of the spacing error signal
and the timing of various kinds of operations as in the case of the
actuators 21, 22 by which the above-described differential signal
comes to zero.
As can be clarified from the description thus far made, the present
invention yields the following effects.
An output-load of the laser for use is reduced by executing the
positional control of the aforementioned laser beams. Moreover, it
is feasible to actualize an extra-speed laser printer which is
capable of effectively decreasing a light modulation frequency of
the laser.
* * * * *