U.S. patent application number 09/257934 was filed with the patent office on 2001-11-29 for laser driving method and apparatus and image-forming apparatus.
Invention is credited to KATAOKA, TATSUHITO, KAWAKAMI, TAKAYUKI, KOGA, KATSUHIDE, NAKAYAMA, KAZUMI, NAKAYAMA, TOMOBUMI, SATO, ISAMU, YOKOYAMA, YUKIO.
Application Number | 20010046242 09/257934 |
Document ID | / |
Family ID | 12833940 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046242 |
Kind Code |
A1 |
KAWAKAMI, TAKAYUKI ; et
al. |
November 29, 2001 |
LASER DRIVING METHOD AND APPARATUS AND IMAGE-FORMING APPARATUS
Abstract
A laser driving method is adapted for driving a plurality of
laser emitting devices. A first current to be supplied to each of
the plurality of laser emitting devices is always generated. A
plurality of second currents controlled according to a control
signal supplied from the outside are generated when necessary. The
plurality of second currents are supplied to the respective laser
emitting devices under supply of the respective first currents,
thereby making the laser emitting devices emit respective laser
beams. The plurality of laser emitting devices are caused to emit
the laser beams in time division at predetermined timing to detect
each of emitted light amounts by one laser monitor. Adjustment is
made to at least one of the first current and the second current
supplied to each of the laser emitting devices according to a
plurality of detected light amounts detected. Supply of the current
to the laser emitting devices not driven is stopped when the
plurality of laser emitting devices are adjusted in light amount in
time division.
Inventors: |
KAWAKAMI, TAKAYUKI;
(SHIZUOKA-KEN, JP) ; NAKAYAMA, TOMOBUMI; (TOKYO,
JP) ; NAKAYAMA, KAZUMI; (TOKYO, JP) ; SATO,
ISAMU; (SHIZUOKA-KEN, JP) ; KATAOKA, TATSUHITO;
(SHIZUOKA-KEN, JP) ; KOGA, KATSUHIDE;
(SHIZUOKA-KEN, JP) ; YOKOYAMA, YUKIO;
(SHIZUOKA-KEN, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
101123801
|
Family ID: |
12833940 |
Appl. No.: |
09/257934 |
Filed: |
February 26, 1999 |
Current U.S.
Class: |
372/38.02 |
Current CPC
Class: |
H01S 5/0683 20130101;
H01S 5/4025 20130101 |
Class at
Publication: |
372/38.02 |
International
Class: |
H01S 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 1998 |
JP |
10-049537 |
Claims
What is claimed is:
1. A laser driving method for driving a plurality of laser emitting
means, the laser driving method comprising the following steps: a
step of always generating a first current to be supplied to each of
the plurality of laser emitting means; a step of generating a
plurality of second currents controlled according to a control
signal supplied from the outside, when necessary; a step of
supplying said plurality of second currents to the respective laser
emitting means under supply of the respective first currents,
thereby making the laser emitting means emit respective laser
beams; a step of making said plurality of laser emitting means emit
the laser beams in time division at predetermined timing, and
detecting each of emitted light amounts by one laser monitor means;
a step of adjusting at least one of the first current and the
second current supplied to each of said plurality of laser emitting
means according to a plurality of detected light amounts detected;
and a step of stopping supply of the current to the laser emitting
means not driven when said plurality of laser emitting means are
adjusted in light amount in time division.
2. A laser driving apparatus comprising: signal input means through
which a control signal is supplied from the outside; a plurality of
second current supply means for generating a second current
controlled according to the control signal supplied from the
outside through said signal input means, when necessary; a
plurality of first current supply means for always generating a
first current; a plurality of laser emitting means for individually
emitting a laser beam according to the second current and the first
current supplied respectively from either of said plurality of
second current supply means and from either of said plurality of
first current supply means; driving means for making said plurality
of second current supply means generate the predetermined second
current at predetermined timing to make said plurality of laser
emitting means emit respective laser beams in time division; one
laser monitor means for monitoring each of the laser beams which
said driving means makes said plurality of laser emitting means
emit in time division, to detect emitted light amounts of the
respective laser beams; current adjusting means for individually
adjusting an output current from at least either said first current
supply means or said second current supply means according to a
plurality of detection results of said laser monitor means; and
current control means for stopping supply of the current to the
laser emitting means not driven when said driving means drives said
plurality of laser emitting means in time division.
3. The laser driving apparatus according to claim 2, wherein said
current control means comprises: at least one third current supply
means for generating a current for canceling out a current near a
laser emission threshold, generated by said first current supply
means and said second current supply means; and a plurality of
switching means for connecting said third current supply means to
said plurality of laser emitting means each so as to be freely
switched on and off.
4. The laser driving apparatus according to claim 3, wherein said
first current supply means are comprised of slow starter power
supplies.
5. An image-forming apparatus comprising: signal input means
through which a control signal is supplied from the outside; a
plurality of second current supply means for generating a second
current controlled according to the control signal supplied from
the outside through said signal input means, when necessary; a
plurality of first current supply means for always generating a
first current; a plurality of laser emitting means for individually
emitting a laser beam according to the second current and the first
current supplied respectively from either of said plurality of
second current supply means and from either of said plurality of
first current supply means; driving means for making said plurality
of second current supply means generate the predetermined second
current at predetermined timing to make said plurality of laser
emitting means emit respective laser beams in time division; one
laser monitor means for monitoring each of the laser beams which
said driving means makes said plurality of laser emitting means
emit in time division, to detect emitted light amounts of the
respective laser beams; current adjusting means for individually
adjusting an output current from at least either said first current
supply means or said second current supply means according to a
plurality of detection results of said laser monitor means; current
control means for stopping supply of the current to the laser
emitting means not driven when said driving means drives said
plurality of laser emitting means in time division; data supply
means for supplying image data as the control signal to said signal
input means; beam deflecting means for deflecting the plural laser
beams emitted from the plurality of laser emitting means to effect
scanning in a main scanning direction according to the control
signal supplied from said data supply means; latent image carrying
means arranged to be exposed to and scanned with the plural laser
beams under the deflection scanning carried out by said beam
deflecting means; sub-scanning means for moving said latent image
carrying means relative to said beam deflecting means in a
sub-scanning direction; latent image developing means for
developing a latent image formed on said latent image carrying
means with toner; toner transferring means for transferring the
toner on said latent image carrying means, developed by said latent
image developing means, onto a recording medium; and toner fixing
means for fixing the toner transferred onto the recording medium by
said toner transferring means.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a laser driving method and
apparatus for making a laser emitting device emit a laser beam
controlled according to a control signal and to an image-forming
apparatus of an electrophotographic method making use of the laser
driving apparatus for emitting the laser beam by the laser driving
method.
[0003] 2. Related Background Art
[0004] The conventional image-forming apparatus of the
electrophotographic method such as laser printers or the like are
provided with the laser driving apparatus and this laser driving
apparatus emits the laser beam according to image data. The laser
driving apparatus of this type is provided, for example, with a
semiconductor laser as laser emitting means and a pulse current is
supplied to this semiconductor laser, whereupon the semiconductor
laser emits the laser beam in a light amount according to the
current.
[0005] At this time, the laser beam emitted from the semiconductor
laser is controlled according to the image data and this laser beam
is deflected by a rotating polygon mirror or the like to scan in
the main scanning direction. At the same time as it, a
photosensitive drum as latent image carrying means is rotated to
move a peripheral surface thereof at an exposure position in the
sub-scanning direction and the peripheral surface of the
photosensitive drum moving in the sub-scanning direction is charged
by a charging charger.
[0006] The peripheral surface of the photosensitive drum rotating
in the sub-scanning direction as being charged is exposed to and
scanned with the laser beam thus deflected to scan, so as to form
an electrostatic latent image thereon and this electrostatic latent
image is developed with toner by a developing device as latent
image developing means. The toner on the peripheral surface of the
photosensitive drum, thus developed, is transferred onto a
recording medium by a transfer charger as toner transferring means
and the toner transferred onto the recording medium is fixed by a
fixing device as toner fixing means.
[0007] Some of the image-forming apparatus described above are
arranged to always supply a current near a laser emission threshold
to the semiconductor laser and supply a pulse current or a bias
current controlled according to the image data when necessary.
Since a photodiode to function as laser monitor means is usually
integrated in the semiconductor laser, it is also normal practice
to monitor the amount of emitted light from the semiconductor laser
by this photodiode and maintain the laser light amount constant by
adjusting the bias current or the pulse current.
[0008] A conventional example of the image-forming apparatus as
described above will be explained referring to FIG. 1 to FIG. 3.
FIG. 1 is a schematic block diagram to show the main part of the
image-forming apparatus, FIG. 2 is a schematic plan view to show
part of an optical system of the image-forming apparatus, and FIG.
3 is a time chart to show the relation among various signals.
[0009] First, the image-forming apparatus 1 of this conventional
example has a laser device 2, as illustrated in FIG. 1, and this
laser device 2 is constructed in an integral form comprised of a
semiconductor laser 3 as laser emitting means and a photodiode 4 as
laser monitor means. The semiconductor laser 3 emits the laser beam
in response to supply of current, and the photodiode 4 monitors the
laser beam emitted from the semiconductor laser 3 and outputs a
current signal according to the light amount of the laser beam.
[0010] Connected to the laser device 2 are a power supply 5 of the
main body and a laser driver 6, and this laser driver 6
incorporates a pulse current source 7 being pulse supply means, a
bias current source 8 being bias supply means, and an APC
(Automatic Power Control) circuit 9 being current adjusting
means.
[0011] The two current sources 7, 8 are connected in parallel to
one semiconductor laser 3, the pulse current source 7 being
connected directly to the semiconductor laser 3 while the bias
current source 8 being connected via a high-speed analog switch 10,
such as a CMOS (Complementary Metal Oxide Semiconductor) or the
like, to the semiconductor laser 3.
[0012] The pulse current source 7 generates a pulse current and
supply it to the semiconductor laser 3, whereas the bias current
source 8 supplies a bias current controlled by on/off of the analog
switch 10 according to a control signal supplied from the outside,
to the semiconductor laser 3 when necessary.
[0013] The APC circuit 9 is connected to the photodiode 4 and to
the pulse current source 7 and adjusts the pulse current of the
pulse current source 7 according to the result of detection by the
photodiode 4. More specifically, the APC circuit 9 is comprised of
a current-voltage converter 11, a sample hold circuit 12, a
constant voltage supply 13, a comparator 14, etc., and converts a
current sinal outputted from the photodiode 4 to a voltage signal
by the current-voltage converter 11.
[0014] The sample hold circuit 12 samples and holds the voltage
signal from the current-voltage converter 11 at predetermined
timing and the comparator 14 compares the hold voltage of the
sample hold circuit 12 with a reference voltage of the constant
voltage supply 13 to increase or decrease the pulse current
generated from the pulse current source 7.
[0015] An image processing circuit 15 being signal input means is
connected to the analog switch 10, which is connected to the bias
current source 8, and a system controller 16 is connected to this
image processing circuit 15. The image processing circuit 15
switches the analog switch 10 on and off, using image data supplied
as a control signal from the outside, and the system controller 16
systematically controls the circuits including the image processing
circuit 15 etc.
[0016] A reflective surface of a polygon mirror 21 being beam
deflecting means is located through a collimator lens 20 on the
optical axis of the semiconductor laser 3 of the laser device 2, as
illustrated in FIG. 2, and the peripheral surface of a
photosensitive drum 23 being the latent image carrying means is
located, for example, through a correction optical system 22 of an
f.theta. lens or the like on the reflected light path of this
polygon mirror 21.
[0017] The polygon mirror 21 is rotatably supported by a scanner
motor (not illustrated) and deflects the laser beam emitted from
the semiconductor laser 3 to effect scanning in the main scanning
direction. The photosensitive drum 23 is rotatably supported by a
drum driving mechanism (not illustrated) being sub-scanning means
and the peripheral surface thereof exposed to and scanned with the
laser beam is relatively moved in the sub-scanning direction.
[0018] A BD (Beam Detect) sensor 24 being beam detecting means is
placed at a forward position in the main scanning direction with
respect to the photosensitive drum 23 in the scanning range of the
polygon mirror 21 and this BD sensor 24 detects the laser beam
under deflection scanning by the polygon mirror 21 immediately
before irradiation of the photosensitive drum 23 therewith.
[0019] The BD sensor 24 is also connected, for example, through an
amplifier (not illustrated) or the like to the system controller 16
and this system controller 16 controls the operation of the image
processing circuit 15, the APC circuit 9, etc. according to the
timing of detection of the laser beam by the BD sensor 24 and the
like.
[0020] In that case, as illustrated in (b) in FIG. 3, during the
time period "T.sub.1 to T.sub.2" of initial setting, the analog
switch 10 is kept continuously on by the data signal being a
control signal of the image processing circuit 15, to make the bias
current source 8 and the pulse current source 7 supply the
respective currents to the semiconductor laser 3, thereby making
the semiconductor laser 3 continuously emit the laser beam.
[0021] At this time, because the voltage according to the emitted
light amount of the laser beam continuously emitted from the
semiconductor laser 3 is sampled by the sample hold circuit 12 in
the APC circuit 9 as illustrated in (c) in FIG. 3, the pulse
current IT of the pulse current source 7 is initially set according
to the voltage sampled by this sample hold circuit 12 as
illustrated in (a) in FIG. 3.
[0022] After completion of the initial setting as described above,
the deflection scanning with the laser beam is started with
rotational driving of the polygon mirror 21 and the pulse current
source 7 is finely adjusted every main scanning line by the APC
circuit 9 during the time period "T.sub.3 to T.sub.4" immediately
before the laser beam under the deflection scanning is detected by
the BD sensor 24.
[0023] During the time period "T.sub.5 to T.sub.6" immediately
after it, the laser beam under the deflection scanning is detected
by the BD sensor 24 and after a lapse of a predetermined time from
this beam detection, the laser beam starts exposure and scanning of
the image area of the photosensitive drum 23. In this case, the
image processing circuit 15 controls on/off of the analog switch 10
according to the image data to make the bias current source 8 and
the pulse current source 7 supply the bias current and the pulse
current to the semiconductor laser 3 so as to make the
semiconductor laser 3 emit the laser beam controlled according to
the image data.
[0024] Although omitted from the illustration and description
because of the generally known structure, various devices,
including a charging charger as carrier charging means, a
developing device as latent image developing means, a transfer
charger as toner transferring means, and so on, in addition to the
laser scanning mechanism described above, are opposed to the
peripheral surface of the photosensitive drum 23 and a conveyance
passage of a print sheet being a recording medium is also created
in a gap between the transfer charger and the photosensitive drum
23.
[0025] The image-forming apparatus 1 of the above-stated structure
can form an image by the electrophotographic method.
[0026] Since the image processing circuit 15 controls on/off of the
analog switch 10 of the bias current source 8 according to the
image data while the pulse current source 7 supplies the pulse
current to the semiconductor laser 3, this causes the semiconductor
laser 3 to emit the laser beam controlled according to the image
data.
[0027] The laser beam thus emitted according to the image data from
the semiconductor laser 3 is deflected by the rotating polygon
mirror 21 to scan in the main scanning direction and irradiate the
peripheral surface of the photosensitive drum 23 rotating in the
sub-scanning direction, whereby an electrostatic latent image is
formed thereon in the form of a lot of main scanning lines.
[0028] At this time, the laser beam under the deflection scanning
is detected by the BD sensor 24 immediately before the irradiation
of the photosensitive drum 23. Emission of the laser beam according
to the image data is started at a predetermined time after the
detection of the beam by the BD sensor 24, whereby start positions
of the many main scanning lines continuous in the sub-scanning
direction can be aligned.
[0029] Since the laser beam needs to be detected by the BD sensor
24 prior to the image scanning as described above, the
semiconductor laser 3 is driven by the system controller 16 and the
image processing circuit 15 at the timing when the laser beam under
the deflection scanning irradiates the BD sensor 24.
[0030] The semiconductor laser 3 is also driven for the APC
operation immediately before the BD sensor 24 detects the laser
beam. The emitted light amount of the laser beam is detected by the
photodiode 4 and the pulse current from the pulse current source 7
is adjusted by the APC circuit 9 of the laser driver 6.
[0031] Since in the above-stated image-forming apparatus 1 the
pulse current is adjusted so as to keep constant the emitted light
amount of the laser beam emitted from the semiconductor laser 3,
the image can be formed with good quality. Further, because the
bias current controlled according to the image data is supplied
while the pulse current is supplied to the semiconductor laser 3,
the image can be formed at high speed with the semiconductor laser
3 being driven in good response. The image-forming apparatus
described above is arranged to adjust the pulse current, but it can
also be contemplated, conversely, that the bias current is adjusted
to keep the emitted light amount of the laser beam constant.
[0032] The image-forming apparatus 1 described above is arranged to
enhance the response of the semiconductor laser 3 so as to perform
the image formation at high speed by supplying the bias current
controlled according to the image data to the semiconductor laser 3
under supply of the pulse current, and it is now under research to
simultaneously form plural main scanning lines using a plurality of
semiconductor lasers in the laser device in order to further
increase the speed of image formation of the image-forming
apparatus.
[0033] In general, even if the laser device is comprised of a
plurality of semiconductor lasers as described above, it is
preferable to use only one photodiode in terms of productivity and
scale reduction. For detecting amounts of emitted light from the
respective semiconductor lasers in order to adjust the pulse
current or the bias current, one photodiode is arranged to detect
each of the emitted light amounts while the semiconductor lasers
are driven in order.
[0034] However, where the current near the laser emission threshold
is always supplied to the plural semiconductor lasers by use of the
pulse current and the bias current in order to enhance the response
as described above, this current near the threshold sometimes
causes a semiconductor laser in a non-driven state to emit a small
amount of light, which does not allow accurate detection of the
emitted light amount of the semiconductor laser in a driven state.
This results in failing to properly adjust the bias currents of the
plural semiconductor lasers, thereby degrading the quality of the
image formed by the image-forming apparatus.
SUMMARY OF THE INVENTION
[0035] The present invention has been accomplished in view of the
above-stated issue and an object of the present invention is to
provide a laser driving method and apparatus capable of accurately
detecting and correcting emitted light amounts of plural laser
emitting means under supply of the pulse current and bias current
by one laser monitor means, and also to provide an image-forming
apparatus capable of forming an image with high quality.
[0036] A laser driving method of the present invention is a laser
driving method comprising steps of always generating a first
current to be supplied to each of plural laser emitting means,
generating plural second currents controlled according to a control
signal supplied from the outside, when necessary, supplying these
plural second currents to the respective laser emitting means under
supply of the respective first currents to make the plural laser
emitting means emit respective laser beams, making these plural
laser emitting means emit the laser beams in time division at
predetermined timing and making one laser monitor means detect each
of emitted light amounts, and adjusting at least one of the first
current and the second current supplied to each of the plural laser
emitting means according to these light amounts detected,
[0037] wherein supply of the current to the laser emitting means
not driven is stopped when the plural laser emitting means are
adjusted in light amount in time division.
[0038] Therefore, the current is not supplied to the laser emitting
means not driven when the plural laser emitting means are adjusted
in light amount in time division and one laser monitor means
detects the laser light amounts, so that when only one of the
plural laser emitting means is driven for the measurement of light
amount, the laser emitting means not driven are prevented from
emitting a small amount of light.
[0039] A laser driving apparatus of the present invention
comprises: signal input means through which a control signal is
supplied from the outside; a plurality of second current supply
means for generating a second current controlled according to the
control signal supplied from the outside through said signal input
means, when necessary; a plurality of first current supply means
for always generating a first current; a plurality of laser
emitting means for individually emitting a laser beam according to
the second current and the first current supplied respectively from
either of said plurality of second current supply means and from
either of said plurality of first current supply means; driving
means for making said plurality of second current supply means
generate the predetermined second current at predetermined timing
to make said plurality of laser emitting means emit respective
laser beams in time division; one laser monitor means for
monitoring each of the laser beams which said driving means makes
said plurality of laser emitting means emit in time division, to
detect emitted light amounts of the respective laser beams; current
adjusting means for individually adjusting an output current from
at least either said first current supply means or said second
current supply means according to a plurality of detection results
of said laser monitor means; and current control means for stopping
supply of the current to the laser emitting means not driven when
said driving means drives said plurality of laser emitting means in
time division.
[0040] When the control signal is supplied from the outside into
the signal input means, the plurality of second current supply
means generate the second currents controlled according to this
control signal, when necessary. At this time the plurality of first
current supply means always generate the first currents and thus
the plural laser emitting means emit the respective laser beams
according to the second current and the first current supplied to
each means from the plurality of second current supply means and
from the plurality of first current supply means. When the driving
means makes the plurality of second current supply means generate
the predetermined second currents at predetermined timing to make
the plural laser emitting means emit the laser beams in time
division, each of the laser beams emitted in time division from the
plural laser emitting means is monitored by one laser monitor means
to detect each emitted light amount, and each of the output
currents from the first current supply means and second current
supply means is adjusted by the current adjusting means according
to the plural detection results. Since the supply of current to the
laser emitting means not driven is stopped by the current control
means when the plural laser emitting means are driven in time
division and their laser light amounts are detected by one laser
monitor means as described above, the laser emitting means not
driven, however, are prevented from emitting a small amount of
light when only one of the plural laser emitting means is driven
for the measurement of light amount.
[0041] The present invention also provides the above-stated laser
driving apparatus wherein said current control means comprises: at
least one third current supply means for generating a current for
canceling out a current near a laser emission threshold, generated
by said first current supply means and said second current supply
means; and a plurality of switching means for connecting said third
current supply means to said plurality of laser emitting means each
so as to be freely switched on and off.
[0042] Accordingly, the third current supply means for generating
the current for canceling out the current near the laser emission
threshold, generated by the first current supply means and the
second current supply means, is connected to the plural laser
emitting means by the plural switching means each so as to be
freely turned on and off, whereby the supply of current to the
laser emitting means not driven is stopped by the current control
means. Namely, the supply of the current near the laser emission
threshold to the laser emitting means is turned on and off at high
speed without turning on and off the connection of the laser
emitting means to the first current supply means and the second
current supply means.
[0043] The present invention also provides the above-stated laser
driving apparatus wherein the first current supply means are
comprised of slow starter power supplies. Therefore, the first
current supply means do not generate too high inrush currents as
pulse currents, whereby the laser emitting means can be protected
well. Since the connection is not turned on and off between the
laser emitting means and the first current supply means in order to
turn on and off the supply of the current near the laser emission
threshold to the laser emitting means at high speed, the first
current supply means can supply the pulse current without a delay
even if they are comprised of the slow starter power supplies.
[0044] An image-forming apparatus of the present invention
comprises the laser driving apparatus described above, data supply
means for supplying image data as the control signal to said signal
input means; beam deflecting means for deflecting the plural laser
beams emitted from said laser driving apparatus to effect scanning
in a main scanning direction according to the control signal
supplied from said data supply means; latent image carrying means
arranged to be exposed to and scanned with the plural laser beams
under deflection scanning carried out by said beam deflecting
means; sub-scanning means for moving said latent image carrying
means relative to said beam deflecting means in a sub-scanning
direction; latent image developing means for developing a latent
image formed on said latent image carrying means with toner; toner
transferring means for transferring the toner on said latent image
carrying means, developed by said latent image developing means,
onto a recording medium; and toner fixing means for fixing the
toner transferred onto the recording medium by said toner
transferring means.
[0045] In the image-forming apparatus of the present invention,
therefore, the data supply means supplies the image data as a
control signal to the signal input means of the laser driving
apparatus of the present invention, so that the laser emitting
means of the laser driving apparatus emit the respective laser
beams controlled according to the image data. These plural laser
beams are deflected by the beam deflecting means to scan in the
main scanning direction, the latent image carrying means is exposed
to and scanned with the laser beams thus deflected to scan, and the
latent image carrying means thus exposed and scanned is moved
relative to the beam deflecting means in the sub-scanning direction
by the sub-scanning means. The latent image thus formed on the
latent image carrying means is developed with the toner by the
latent image developing means and the toner thus developed on the
latent image carrying means is transferred onto the recording
medium by the toner transferring means. The toner transferred onto
the recording medium is fixed by the toner fixing means, so that
the image corresponding to the image data is formed as a toner
image on the recording medium by the electrophotographic method. In
the image-forming apparatus of the present invention utilizing the
laser driving apparatus of the present invention, the image is
formed while the laser beams are controlled according to the image
data. Since a plurality of main scanning lines are exposed
simultaneously with the plural laser beams, the image of a dot
matrix is formed at high speed. The image is formed with high
quality, because the emitted light amounts of the plural laser
beams are adjusted each properly.
[0046] The various means stated in the present invention can be any
means that can implement their functions; for example, they permit
dedicated hardware, a computer provided with the appropriate
functions in the form of programs, functions implemented inside a
computer by appropriate programs, a combination of these, and so
on.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a schematic block diagram to show the main part of
the image-forming apparatus of the conventional example;
[0048] FIG. 2 is a schematic plan view to show part of the optical
system of the image-forming apparatus of the conventional
example;
[0049] FIG. 3 is a time chart to show the relation among various
signals;
[0050] FIG. 4 is a block diagram to show a laser driving apparatus
in an embodiment of the present invention;
[0051] FIG. 5 is a schematic, vertically sectional, side view to
show a laser printer as an embodiment of the image-forming
apparatus of the present invention;
[0052] FIG. 6 is a time chart to show the relation among various
signals; and
[0053] FIG. 7 is a characteristic diagram to show the relationship
between current and light amount of the semiconductor laser being
laser emitting means.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0054] An embodiment of the present invention will be described
referring to FIG. 4 to FIG. 7. In the present embodiment the same
portions as in the conventional example described above will be
referred to as the same names and the detailed description thereof
will be omitted.
[0055] FIG. 4 is a block diagram to show a laser driving apparatus
of the present embodiment and FIG. 5 is a schematic, vertically
sectional, side view to show a laser printer which is an
image-forming apparatus of the present embodiment. FIG. 6 is a time
chart to show the relation among various signals and FIG. 7 is a
characteristic diagram to show the relationship between current and
light amount of the semiconductor laser which is laser emitting
means.
[0056] First, the laser driving apparatus 30 of the present
embodiment is constructed as part of printer section 32 which is
the image-forming device of digital copier 31, and it is provided
with a laser device 33 as illustrated in FIG. 4. This laser device
33 is constructed in integral structure comprised of two
semiconductor lasers 34, 35, which are plural laser emitting means,
and one photodiode 36, which is laser monitor means. They are
connected to the laser driver 37.
[0057] This laser driver 37 is composed of two bias current sources
40, 41 which are plural bias supply means, two pulse current
sources 38, 39 which are plural pulse supply means, two current
sources 42, 43 which are plural current supply means, and two APC
circuits 44, 45 which are two current adjusting means.
[0058] The three types of current sources 38 to 43 two each per
type as described above are connected to the two semiconductor
lasers 34, 35, one each in each type. More specifically, the pulse
current source 38 or 39 is connected directly to the semiconductor
laser 34 or 35, respectively, and the bias current source 40 or 41
is connected via a high-speed analog switch 46 or 47, respectively,
such as a CMOS or the like, to the semiconductor laser 34 or 35,
respectively.
[0059] Two analog switches 48, 49 being plural switching means are
connected to the respective current sources 42, 43 and each of
these analog switches 48, 49 is connected to a middle point of
connection between the pulse current source 38, 39 and the
semiconductor laser 34, 35, thus forming a current control circuit
50 as current control means.
[0060] Each of the two current sources 42, 43 generates a current
to cancel out the current near the laser emission threshold
supplied to the semiconductor laser 34, 35 by use of the pulse
current source 38, 39 and the bias current source 40, 41 and each
of the two analog switches 48, 49 connects the current source 42,
43 to the semiconductor laser 34, 35 so as to be freely switched on
and off. The pulse current sources 38, 39 are slow starter power
supplies not permitting easy high-speed switching whereas the other
current sources 40 to 43 are ordinary power supplies permitting
easy high-speed switching.
[0061] The two APC circuits 44, 45 share a current-voltage
converter 51 and each of them has a sample hold circuit 52, 53, a
constant voltage supply 54, 55, a comparator 56, 57, etc. They are
connected both to one photodiode 36 and respectively to the two
pulse current sources 38, 39.
[0062] The image processing circuit 61 corresponding to signal
input means and continuous driving means is connected to the analog
switches 46, 47, which are connected to the respective bias current
sources 40, 41, and the system controller 62 is connected to this
image processing circuit 61. The image processing circuit 61, which
will be detailed hereinafter, is arranged to switch the analog
switches 46, 47 on and off according to the image data supplied
from the outside as the control signal and also switch the analog
switches 48, 49 on and off at such predetermined timing as not to
carry out image exposure.
[0063] The laser driving apparatus 30 of the structure as described
above is used in the printer section 32 of the digital copier 31 as
described previously. This digital copier 31 has a scanner section
71 as an image reader, and the printer section 32, these sections
being formed integrally, as illustrated in FIG. 5.
[0064] The scanner section 71 has contact glass 72 placed
horizontally and RDF (Recycle Document Feeder) 73 is disposed on
the upper surface of this contact glass 72. There are first, second
scanning units 74, 75, a zooming optical system 76, a line sensor
77, etc. disposed below the contact glass 72.
[0065] The first scanning unit 74 has fluorescent tubes 78 of a
straight tube type and a reflection mirror 79 inclined at
45.degree. and is opposed to the contact glass 72 thereunder as
being supported so as to be movable in the sub-scanning direction
(from left to right and vice versa in the figure). The second
scanning unit 75 has a pair of reflection mirrors 80, 81 opposed
each in an inclined state at 45.degree. and is supported so as to
be movable at a speed equal to half of that of the first scanning
unit 74.
[0066] The zooming optical system 76 is supported so as to be
freely displaced along the optical axis and is arranged to focus
light from a read original (not illustrated) placed on the contact
glass 72, after reflected by the above-stated reflection mirrors 79
to 81, at a variable magnification at the position of line sensor
77. This line sensor 77 is composed of many CCDs (Charge Coupled
Devices) arrayed in the main scanning direction (or in the
direction passing through the figure) and reads to scan the image
data in the form of main scanning lines from the read original.
[0067] The scanner section 71 of the structure as described above
generates image data of a dot matrix comprised of many main
scanning lines from the read original. The line sensor 77 of this
canner section 71 is connected via various correction circuits (not
illustrated) and the like to the image processing circuit 61 of the
laser driving apparatus 30 in the printer section 32.
[0068] The two semiconductor lasers 34, 35 of the laser driving
apparatus 30 are arranged up and down, i.e., along the sub-scanning
direction in a print image, and are opposed to the reflective
surface of the polygon mirror 181 corresponding to beam deflecting
means supported so as to be rotatable in the horizontal direction,
i.e., in the main scanning direction by scanner motor 180,
similarly to the case of the aforementioned conventional example
illustrated in FIG. 2.
[0069] On the reflected light path of this polygon mirror 81 there
is the peripheral surface of the photosensitive drum 84 as latent
image carrying means located via a correction optical system 82 of
an f.theta. lens or the like and a reflection mirror 83, and this
photosensitive drum 84 is rotatably supported so that the
peripheral surface is relatively moved in the sub-scanning
direction by the drum driving mechanism (not illustrated) being
sub-scanning means.
[0070] The BD sensor 85 being beam detecting means is located at a
forward position in the main scanning direction with respect to the
photosensitive drum 84 in the scanning range of the polygon mirror
81 and this BD sensor 85 is connected, for example, via an
amplifier (not illustrated) to the system controller 62.
[0071] Around the peripheral surface of the photosensitive drum 84,
there are also provided, in addition to the reflection mirror 83
described above, a toner cleaner 86, a charging charger 87 as
carrier charging means, developing devices 88, 89 as latent image
developing means, a transfer charger 90 as toner transferring
means, a peeling charger 91 as medium peeling means, etc. and a
conveyance passage of a print sheet P as a recording medium is also
formed in the gap between these chargers 90, 91 and the
photosensitive drum 84.
[0072] This sheet conveyance passage is constructed of many feed
rollers 92, guide plates 93, etc. and is in communication with
sheet cassettes 94, 95 and with a sheet discharge tray 96. In this
sheet conveyance passage there are also a fixing device 97 as toner
fixing means and a sheet inverting mechanism 98 as medium inverting
means, and another sheet conveyance passage is also created for
circulating the print sheet P from this sheet inverting mechanism
98 to the position of the photosensitive drum 84.
[0073] As in the case of the aforementioned conventional example,
the laser driving apparatus 30 of the present embodiment is
arranged so that the system controller 62 controls the operation of
the image processing circuit 61, the APC circuits 44, 45, etc. at
predetermined timing, as illustrated in FIG. 6. Since the laser
driving apparatus 30 of the present embodiment has the two
semiconductor lasers 34, 35 and one photodiode 64, the image
processing circuit 61 drives the two semiconductor lasers 34, 35 in
time division during execution of the APC operation, however.
[0074] When the two semiconductor lasers 34, 35 are driven in time
division for the APC operation to adjust the light amounts of the
two semiconductor lasers 34, 35 in this way, the image processing
circuit 61 successively switches the two analog switches 48, 49 of
the current control circuit 50 on and off to connect the current
source 42, 43 to the semiconductor laser 34, 35 in order, so as to
supply the current for canceling out the current near the laser
emission threshold from these current sources 42, 43 to the
semiconductor lasers 34, 35, thereby terminating emission
completely.
[0075] In the above-described structure, the digital copier 31 of
the present embodiment can read to scan the image data of the dot
matrix in the form of many main scanning lines from the read
original by the scanner section 71 and print this image data out on
the print sheet P in the electrophotographic method by the printer
section 32.
[0076] In that case, in the laser driving apparatus 30 of the
present embodiment, the bias currents supplied from the laser
driver 37 to the two semiconductor lasers 34, 35 of the laser
device 33 are controlled by the image processing circuit 61
according to the image data supplied from the scanner section
71.
[0077] Namely, the image processing circuit 61 controls on/off of
the analog switches 46, 47 of the bias current sources 40, 41
according to the image data while the pulse currents are always
supplied from the pulse current sources 38, 39 to the respective
semiconductor lasers 34, 35. This turns the bias currents on and
off under application of the pulse currents, so that the
semiconductor lasers 34, 35 emit the laser beams in predetermined
light amounts controlled according to the image data.
[0078] The two laser beams respectively emitted according to the
image data by the two semiconductor lasers 34, 35 are
simultaneously deflected to scan in the main scanning direction by
the rotating polygon mirror 81, thereby irradiating the peripheral
surface of the photosensitive drum 84 rotating in the sub-scanning
direction. At this time, since the photosensitive drum 84 is
charged in the peripheral surface by corona discharge of the
charging charger 87, an electrostatic latent image is formed here
in the form of many main scanning lines by exposure scanning of the
laser beams.
[0079] The electrostatic latent image formed on the peripheral
surface of the photosensitive drum 84 in this way is developed with
toner supplied from one of the two developing devices 88, 89 and
this developed toner is transferred onto the print sheet P conveyed
from the sheet supply cassette 94 or the like by a potential
generated by the transfer charger 90. Since the print sheet P to
which the toner was transferred in this way is heated and pressed
to be fixed by the fixing device 97, this completes the formation
of image by the printer section 32 of the digital copier 31.
[0080] Since the digital copier 31 of the present embodiment
controls the laser beams according to the image data, it can form
the print image of the dot matrix. At this time, the two
semiconductor lasers 34, 35 from two main scanning lines each time,
and the print image comprised of many main scanning lines can be
formed at high speed.
[0081] Since the two laser beams deflected to scan are detected
simultaneously by the BD sensor 85 immediately before the
irradiation of the photosensitive drum 84, the start positions of
the many main scanning lines succeeding in the sub-scanning
direction are aligned by carrying out the emission of the laser
beams according to the image data at a predetermining time after
this beam detection of the BD sensor 85.
[0082] Since the laser beams need to be detected by the BD sensor
85 prior to the image scanning in this way, the two semiconductor
lasers 34, 35 are driven by the system controller 62 and the image
processing circuit 61 at the timing when the laser beams under the
deflection scanning irradiate the BD sensor 85.
[0083] The two semiconductor lasers 34, 35 are driven in time
division for the APC operation immediately before the laser beams
are detected by the BD sensor 85. The emitted light amounts are
detected in time division by one photodiode 36 and the pulse
currents of the pulse current sources 38, 39 are adjusted
individually by the two APC circuits 44, 45 of the laser driver
37.
[0084] In the laser driving apparatus 30 of the present embodiment,
however, when the two semiconductor lasers 34, 35 are driven in
time division for the APC operation as described above, the image
processing circuit 61 switches the analog switches 46, 47 of the
bias current sources 40, 41 on and off by the DATA signal and, at
the same time as it, also switches the analog switches 48, 49 of
the current sources 42, 43 on and off.
[0085] FIG. 6 is a time chart to show the relation among the
various signals and FIG. 7 is a characteristic diagram to show the
relationship between current and light amount of the semiconductor
laser as laser emitting means.
[0086] As illustrated in FIG. 6, the APC operation of the
semiconductor laser 34 is carried out first.
[0087] The pulse current I.sub.TB is supplied from the pulse
current supply 38 to the semiconductor laser 34 to effect such
adjustment by the APC circuit 45 in the time period "T.sub.11 to
T.sub.12" as to make the pulse current I.sub.TB of the pulse
current source 38 equal to the initial value I.sub.tA shown in FIG.
7. At this time the two analog switches 46, 48 are off, so that the
bias current (current I.sub.a1) and the predetermined current
(current I.sub.a2) are not applied to the semiconductor laser 34.
At this time the pulse current I.sub.TA of the pulse current source
39 is not applied to the other semiconductor laser 35. At this time
the two analog switches 47, 49 are on, but the bias current is
canceled out by the predetermined current. Therefore, no current is
supplied to the other semiconductor laser 35, so as to effect no
emission.
[0088] The APC operation of the semiconductor laser 35 is carried
out next. The pulse current I.sub.TA is supplied from the pulse
current source 39 to the semiconductor laser 35 to effect such
adjustment by the APC circuit 44 in the time period "T.sub.13 to
T.sub.14" as to make the pulse current I.sub.TA of the pulse
current source 39 equal to the initial value I.sub.tA shown in FIG.
7. At this time the two analog switches 47, 49 are off, so that the
bias current (current I.sub.a1) and the predetermined current
(current I.sub.a2) are not applied to the semiconductor laser 35.
At this time the pulse current I.sub.TB Of the pulse current supply
38 is applied to the other semiconductor 34, but the two analog
switches 46, 48 are on at this time, so that the aforementioned
pulse current I.sub.TB is canceled out by the bias current and the
predetermined current. Therefore, the current is not supplied to
the other semiconductor laser 34, so as to effect no emission.
[0089] The APC operation of the semiconductor lasers as described
above is also carried out similarly in the time period "T.sub.15 to
T.sub.16" and in the time period "T.sub.17 to T.sub.18."
[0090] After completion of the APC operation, the pulse current and
bias current are applied to the semiconductor lasers, so that the
semiconductor lasers are made to stand by in a state of a current
I.sub.bA as a result of subtraction of the bias current (current
I.sub.a1) from the pulse current (current I.sub.tA). This current
I.sub.bA is a value near the laser emission threshold current
I.sub.th.
[0091] In the laser driving apparatus 30 of the present embodiment,
therefore, when the two semiconductor lasers 34, 35 are driven one
by one in time division for the APC operation, the other laser not
driven is prevented from emitting a small amount of light because
of the current near the laser emission threshold. Therefore, the
emitted light amounts of the two semiconductor lasers 34, 35 can be
detected accurately by one photodiode 36 and the pulse currents of
the two pulse current sources 38, 39 can be adjusted each properly
by the APC circuits 44, 45.
[0092] Since the laser driving apparatus 30 of the present
embodiment can properly adjust each of the laser light amounts of
the two semiconductor lasers 34, 35 as described above, the digital
copier 31 of the present embodiment utilizing it can form the image
with good quality and at high speed.
[0093] Particularly, since the laser driving apparatus 30 of the
present embodiment uses the pulse current sources 38, 39 of the
slow starter power supplies, the semiconductor lasers 34, 35 can be
protected well. Although the pulse current supplies 38, 39
comprised of the slow starter power supplies in this way cannot be
switched on and off at high speed, the supply of bias currents to
the semiconductor lasers 34, 35 can be turned properly on and off,
because the bias current sources 40, 41 are connected to the
semiconductor lasers 34, 35 by the analog switches 46, 47.
[0094] It is noted that the present invention is by no means
intended to be limited to the above embodiment, but the present
invention embraces a variety of modifications within the scope not
departing from the spirit of the invention. For example, the above
embodiment exemplified the adjustment of only the pulse current for
the APC operation, but it is also possible to adjust the bias
current or to adjust the both currents. In addition, the above
embodiment exemplified the two semiconductor lasers 34, 35 as
plural laser emitting means, but the plural laser emitting means
can also be three or more semiconductor lasers.
[0095] The present invention presents the effects described below
because of the structure as described above.
[0096] The laser driving method of the present invention is
arranged so that when the plural laser emitting means are
continuously driven in time division during the adjustment of light
amount, the supply of current is stopped to the laser emitting
means not driven,
[0097] whereby when only one of the plural laser emitting means is
driven for the measurement of light amount, the laser emitting
means not driven are prevented from emitting a small amount of
light because of the current near the laser emission threshold;
therefore, the emitted light amounts of the plural laser emitting
means can be detected accurately by one laser monitor means and the
emitted light amounts can be corrected properly by properly
adjusting the bias current and pulse current of each of the plural
laser emitting means.
[0098] The laser driving apparatus of the present invention
comprises signal input means through which a control signal is
supplied from the outside, a plurality of second current supply
means for generating a second current controlled according to the
control signal supplied from the outside through the signal input
means, when necessary, a plurality of first current supply means
for always generating a first current, a plurality of laser
emitting means for individually emitting a laser beam according to
the second current and the first current supplied respectively from
either of the plurality of second current supply means and from
either of the plurality of first current supply means, driving
means for making the plurality of second current supply means
generate the predetermined second current at predetermined timing
to make the plurality of laser emitting means emit respective laser
beams in time division, one laser monitor means for monitoring each
of the laser beams which the driving means makes the plurality of
laser emitting means emit in time division, to detect an emitted
light amount of each beam, current adjusting means for individually
adjusting an output current from at least either the first current
supply means or the second current supply means according to plural
detection results of the laser monitor means, and current control
means for stopping supply of the current to the laser emitting
means not driven when the plurality of laser emitting means are
driven in time division by the driving means,
[0099] whereby the laser emitting means not driven are prevented
from emitting a small amount of light when only one of the plural
laser emitting means is driven for the measurement of light amount;
therefore, the emitted light amounts of the plural laser emitting
means can be detected accurately by one laser monitor means and the
emitted light amounts of the plural laser emitting means can be
corrected properly by properly adjusting the output currents from
the plural first current supply means and second current supply
means.
[0100] The present invention also provides the above-stated laser
driving apparatus wherein the current control means comprises at
least one third current supply means for generating a current to
cancel out a current near the laser emission threshold, generated
by the first current supply means and the second current supply
means, and a plurality of switching means for connecting the third
current supply means to the plurality of laser emitting means each
so as to be freely switched on and off,
[0101] whereby the supply of current to the laser emitting means
can be turned on and off at high speed without turning the
connection between the laser emitting means and the first current
supply means on and off.
[0102] The present invention also provides the above-described
laser driving apparatus wherein the first current supply means are
comprised of slow starter power supplies,
[0103] whereby the laser emitting means can be protected well.
[0104] The image-forming apparatus of the present invention
comprises the above-described laser driving apparatus, data supply
means for supplying image data as a control signal to the signal
input means of the laser driving apparatus, beam deflecting means
for deflecting a plurality of laser beams emitted from the laser
driving apparatus to effect scanning in the main scanning direction
according to the control signal supplied from the data supply
means, latent image carrying means arranged to be exposed to and
scanned with the plurality of laser beams under the deflection
scanning carried out by the beam deflecting means, sub-scanning
means for moving the latent image carrying means relative to the
beam deflecting means in the sub-scanning direction, latent image
developing means for developing a latent image formed on the latent
image carrying means with toner, toner transferring means for
transferring the toner on the latent image carrying means,
developed by the latent image developing means, onto a recording
medium, and toner fixing means for fixing the toner transferred
onto the recording medium by the toner transferring means,
[0105] whereby the emitted light amounts of the plural laser beams
can be adjusted each properly, so that the image can be formed with
high quality.
* * * * *