Coherent light generators – Particular component circuitry – For driving or controlling laser
Reexamination Certificate
1999-02-26
2002-05-28
Font, Frank G. (Department: 2877)
Coherent light generators
Particular component circuitry
For driving or controlling laser
C372S029015, C250S205000
Reexamination Certificate
active
06396858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Related Background Art
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.
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.
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.
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.
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.
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.
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.
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
.
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.
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
.
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
.
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.
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&thgr; lens or the like on the reflected light path of this polygon mirror
21
.
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.
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.
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.
In that case, as illustrated in (b) in
FIG. 3
, during the time period “T
1
to T
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.
At this time, because the voltage according to the emitted light amount of the laser beam continuously emitted fro
Kataoka Tatsuhito
Kawakami Takayuki
Koga Katsuhide
Nakayama Kazumi
Nakayama Tomobumi
Font Frank G.
Nakayama Kazumi
Rodriguez Amando
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