Canon FAXPHONE L100, Service Manual, Page: 35 / 186

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Technical Overview > Laser Exposure System > Laser Scanner Motor Control > Overview
Technical Overview > Laser Exposure System > Laser Scanner Motor Control > Overview
Laser Control
■ Auto Power Control (APC)
This is the control to emit a constant level of laser diode.
There are two types of APC; initial APC (note 1), and line space APC (note 2). The laser
driver executes the same procedure for both controls. The following is the details of the
control procedure.
1) When the laser control signal enters APC mode (CNT0=H, CNT1=L), the laser driver emits
LD in APC mode.
2) The emission level of LD is detected with photo diode (PD), converted from current output
to voltage, and compared with the standard voltage (voltage equivalent to the target laser
level).
3) The laser driver controls the laser current to achieve the voltage of LD target level.
4) When the laser control signal enters LD forced OFF mode, the LD is forcibly turned off. The
laser driver saves the adjusted laser intensity to the capacitor (C1).
NOTE:
1. Initial APC
APC that is executed during initial rotation. APC adjusts laser intensity and detects
faults in the laser.
2. Line space APC
APC that is executed during printing. Laser intensity for one line is adjusted before
writing one line.
Laser Scanner Motor Control
■ Overview
This is the control to rotate the Scanner Motor (M2) at a constant speed to emit the laser
beam on the correct position on the photosensitive drum.
The following is the control circuit of the Scanner Motor (M2).
Engine controller
Motor driver PCB
BD PCB
Oscillator
Reference
clock
Frequency
comparator
Laser scanner unit
Integration
circuit
M
Scanner motor
driver IC
Scanner motor
ACC
DEC
/BDI
Drive
circuit
CPU ASIC
X501
+24VA
+24VA
The engine controller creates standard clock based on oscillation frequency of the oscillator
(X501); the cycles of the standard clock is compared with that of BD input signal (/BDI) with a
frequency comparator and the rotations of the Scanner Motor (M2) is monitored.
The engine controller sends the scanner motor acceleration signal (ACC) and scanner motor
deceleration signal (DEC) to the scanner motor driver according to the detected rotation
speed to control the rotation speed.
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