Canon ImageCLASS MF4690 Service Manual - page 63

Chapter 5

5-3

5.4 Controlling the Laser Scanner Motor

5.4.1 Overview

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This is the control to rotate the scanner motor at constant speed.

The scanner motor is the 3-phase DC brush-less motor with hall element included, and is combined with the drive circuit.

The following chart shows the control circuit for the scanner motor.

F-5-3

5.4.2 Scanner Motor Speed Control

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This is the control to rotate the scanner motor at constant speed.

The following is the procedure of this control.

1) At activating the scanner motor, CPU outputs /ACC signal to the scanner driver IC to accelerate the scanner motor forcedly. The scanner motor will start rotating.

2) CPU periodically turns on the laser, and compares /BDI signal and the cycle of the reference clock to detect the rotation of the scanner motor.

3) When the rotation of the scanner motor exceeds the specified value, CPU outputs /DEC signal to decelerate the scanner motor. CPU controls /ACC or /DEC

signal to control the rotation of the scanner motor until it becomes its specified value.

5.4.3 Detection of Fault of the Scanner Motor

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CPU of the DCNT board monitors the frequency comparator to judge if the scanner motor rotates at the specified rotation frequency.

When the following statuses occur, CPU judges that there is a fault or error and stops the engine. At the same time, it notices the details of the error to the SCNT

board.

1) Scanner fault

If /BDI signal cannot be detected 1.5 sec after completing forced acceleration of the scanner motor, extend the detection time by 120sec. If the specified cycle of /

BDI signal cannot be detected, it should be judged as scanner fault.

2) BD fault

If /BDI signal cannot be detected in 100msec after forced acceleration of the scanner motor or the specified cycle of /BDI signal cannot be detected for 2 sec or

more after the scanner motor reached its specified rotation, it should be judged as BD fault.

3) BD error

If /BDI signal cannot be detected at the specified cycle while CPU outputs /BD signal to the SCNT board, it should be judged as BD error.

If door open is detected in 200msec after BD error was detected, CPU does not transmit BD error to the SCNT board.

DCNT board 

M

J931-9

X902

IC902

CPU

J932-4

J932-3

J932-2

J932-1

J902-1

J904-1

J904-2

J904-3

J904-4

/ACC

/DEC

/BDI

BD sensor

Divider

Reference 

clock

Frequency 

comparator

Laser / scanner block

Integration 

circuit

Scanner driver IC

Scanner motor

Drive 

circuit

+24V

+24V