Laser Control; Auto Power Control (Apc); Laser Scanner Motor Control; Overview - Canon LBP3250 Series Service Manual

Table of Contents

2.3.3 Laser Control

2.3.3.1 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 equiv-

alent 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.

2.3.4 Laser Scanner Motor Control

2.3.4.1 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

CPU

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.

ASIC

+24VA

Frequency

comparator

Reference

clock

Oscillator

Motor driver PCB

/BDI

ACC

DEC