Controlling The Laser; Outline; Laser Emission Control - Canon MF8100 Series Service Manual

8) When the four-sided mirror rotates at a constant speed, the laser beam striking the photosensitive drum scans on the drum at a constant speed.
9) When the photosensitive drum rotates and the laser beam scans on the photosensitive drum, at each specified speed, a latent image is formed on the drum.
Twin beam method
Two laser diodes (LD1, LD2) are built into the laser unit. In one scanning operation, the laser unit emits light from the LD1 and LD2 and writes two lines simulta-
neously. This enables a two-fold printing at the same print speed.

2.2.2 Controlling the Laser

2.2.2.1 Outline

This control is utilized to turn on/off the two laser diodes (LD1, LD2) based on the LASER CONTROL signal sent from the DCNT Board.
The circuit diagram of the laser control is illustrated below.
The DCNT Board sends the VIDEO (VDO1, /VDO1, VDO2, /VDO2) signals for image formation and the LASER CONTROL (CNT0, CNT1, CNT2) signals for
changing the operation mode of the laser, to the logic circuit in the laser driver IC. The laser driver performs the laser control responsive to a combination of the
CNT0, CNT1, CNT2 signals.
Operation mode
Standby mode
Print mode
LD1 force on mode
LD2 force on mode
LD force off mode
The following four controls are performed with the LASER CONTROL signals:

1) Laser emission control

First scan
Second scan
Third scan
Fourth scan
Feed direction
DCNT Board
IC101
+5V
CPU
J102 J11
-13
-2 -12
VDO1
-4 /VDO1 -10
VDO2
-8
-10 /VDO2
IC102
-11 PDOUT
ASIC
-5 CNT0
-6 CNT1
-7
CNT2
-3/9/12
-2/5/11
J116-2 /BDI J31-2
CNT0
L
H
L
H
H
Image areas
F-2-8
Laser driver circuit
LD1 PD
-1
VCC
LD1
switching
circuit
-6
-4
Comparator
Standard voltage
-3
C16
Sample
hold circuit
-9
-8
Logic circuit
-7
GND
BD circuit
F-2-9
T-2-4
CNT1 CNT2 Details
L L Laser control off status
H H Laser emission is executable according to the
VIDEO signals.
H L Turns on the LD1 forcefully
L L Turns on LD2 forcefully
H L Turns off the LD1 and LD2 forcefully
LD1 scan line
LD2 scan line
LD2
LD2
switching
circuit
Comparator
C18
Sample
hold circuit
Laser driver IC
Chapter 2
0008-1541
2-5