Canon    LBP3310, Service Manual

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Chapter 2
2-5
2.3.2 Controlling the Laser Activation Timing
2.3.2.1 Laser emission control
0018-3095
LBP3370 / LBP3310
The laser emission control controls the laser diodes (LD1, LD2) to turn ON/OFF at constant light intensity according to the VIDEO signals (VDO1, /VDO1, VDO2,
/VDO2) from the video controller.
When the LASER CONTROL signals (CNT0, CNT1, CNT2) are put into print mode, the laser driver turns the laser diodes ON/OFF according to the VIDEO sig-
nals.
2.3.2.2 Horizontal synchronous control
0018-3096
LBP3370 / LBP3310
The horizontal synchronous control is to horizontally align the starting position of writing the image.
The following is the sequence of this control.
1) The DC controller puts the LASER CONTROL signal into LD1APCON mode or LD2APCON mode during the unblanking interval (see Note). Accordingly,
the laser driver allows the laser diode (LD1, LD2) to emit light with APC.
2) Each laser beam is sent to the BD PCB in the scanning optical path of the laser beam.
3) The BD PCB detects these laser beams, generates BD INPUT signal (/BDI), and sends it to the DC controller.
4) The DC controller generates the HORIZONTAL SYNCHRONOUS signal (/BDO) based on the /BDI signal and sends the /BPO signal to the video controller.
5) The video controller outputs the VIDEO signals (VDO1, /VDO1, VDO2, /VDO2) to the DC controller to horizontally align the starting position of writing the
image, when it inputs the /BDO signal
Unblanking interval
The interval when a laser diode emits light in the non-image area.
2.3.3 Laser Control
2.3.3.1 Automatic power control (APC)
0018-3097
LBP3370 / LBP3310
The automatic power control is to maintain the light intensity emitted from the laser diode to be constant.
There are two APCs, one is the initial APC (Note 1) and the other is the between-lines APC (Note 2). Both are controlled by the laser driver in the same way. The
following is the sequence of this control.
1) When the LASER CONTROL signals (CNT0, CNT1, CNT2) put into the LD1APC mode, the laser driver allows the LD1 to emit light.
2) The light intensity of the LD1 is detected by the photo diode (PD) and it is converted from current to voltage. Then it is compared with the reference voltage
(voltage equivalent to the target laser light intensity).
3) The laser driver controls the laser current until it reaches the voltage level of the LD1's targeted light intensity.
4) The LD1 is turned OFF forcefully when the LASER CONTROL signal puts into the force LD OFF mode. The laser driver stores the adjusted light intensity in
C802.
5) After the light intensity adjustment of LD1 is completed, the LASER CONTROL signal puts into the LD2APCON mode and the laser driver allows the LD2 to
emit light with APC. The laser light intensity of LD2 is adjusted and stored in C803 as same as LD1.
1) Initial APC
Performed during the INTER period. It adjusts the laser light intensity by APC.
2) Between-lines APC
Performed during the printing period. It adjusts the laser light intensity for one line before the line starts to be written.
2.3.3.2 Image masking control
0018-3098
LBP3370 / LBP3310
The image masking control is to prevent a laser beam emission in the non-image area except during the unblanking interval.
The engine controller puts the LASER CONTROL signal into the Force LD OFF mode and turns the laser diodes (LD1, LD2) OFF forcefully, while the laser scans
a non-image area except during the unblanking interval. This is called the image-masked status, and the laser diodes (LD1, LD2) do not emit light during this period
even if the VIDEO signals (VDO1, /VDO1, VDO2, /VDO2) are sent. The timing to start the image masking control depends on the paper size information sent
from the video controller.
If the paper size measured by the top of page sensor (PS912) is smaller than the paper size information, the engine controller masks the image forcefully to prevent
the transfer charging roller to be soiled.