Laser Control; Auto Power Control (Apc); Laser Scanner Motor Control; Overview - Canon MF4500 Series Service Manual

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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 LD1 forced ON mode (CNT0, CNT1, CNT2), the laser
driver emits LD1 forcibly.
2) The emission level of LD1 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) with the comparator.
3) The laser driver controls the laser current to achieve the voltage of LD1 target level.
4) When the laser control signal enters LD forced OFF mode, the LD1 is forcibly turned off.
The laser driver saves the adjusted laser intensity of the capacitor (C16).
5) When the adjustment of LD1 laser intensity is completed, the laser control signal enters
LD2 forced ON mode; the laser driver emits LD2 forcibly.
The laser driver adjusts the LD2 laser intensity as in the case of LD1 and saves the
adjusted laser intensity to the capacitor (C18).
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.
2 Technical Overview > Laser Exposure System > Laser Scanner Motor Control > Overview

Laser Scanner Motor Control

■ Overview

This is the control to rotate the scanner motor 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.
Engine controller
Motor driver PCB
/BDI
CPU ASIC
+24VA
ACC
Frequency
comparator
DEC
Reference
clock
Oscillator
X300
The engine controller creates standard clock based on oscillation frequency of the oscillator
(X300); 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 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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Laser scanner unit
BD PCB
Scanner motor
+24VA
Scanner driver IC
Drive
Integration
circuit
circuit
M
F-2-16
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