Laser Scanner Motor Control; Outline; Scanner Motor Speed Control; Detection Of A Fault In The Scanner Motor - Canon LBP2900 series Service Manual

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Note 1:

The term "initial APC" refers to APC executed during initial rotation and in which the laser intensity is controlled by means of APC.

Note 2:

The term "interval APC" refers to APC executed during printing and in which the laser intensity is adjusted for a single line before the start of the line.

2.3.4 Laser Scanner Motor Control

2.3.4.1 Outline

The machine controls the laser scanner to make sure that the scanner motor rotates at a specific speed at all times.

The scanner motor is a 3-phase DC brushless motor possessing a Hall element, and it is constructed as part of the drive circuit.

The following is a diagram showing the circuit used to control the scanner motor:

Engine controller PCB

IC902

CPU

+24V

Frequency

comparator

Standard

clock

X902

Oscillator

F-2-4

2.3.4.2 Scanner Motor Speed Control

The machine controls the scanner motor so that the motor rotates at a specific speed; specifically,

1. When the scanner motor is starting up, the CPU sends the /ACC signal to the scanner driver IC to force the scanner motor to increase its speed, thereby

causing the scanner motor to rotate.

2. The CPU forces the laser to go on at specific intervals, and compares th /BDI signal against the reference clock pulses to find out the revolution of the

scanner motor.

3. If the revolution of the scanner motor exceeds a specific value, the CPU generates the /DECK signal to decelerate the scanner motor; thereafter, the CPU

controls the /ACC or /DECK signal until the revolution of the scanner motor reaches a specific value, thereby controlling the rotation of the scanner motor.

2.3.4.3 Detection of a Fault in the Scanner Motor

The CPU of the engine controller monitors the frequency comparator to find out whether the scanner motor is rotating at a specific speed. The CPU will

assume any of the following conditions to be a fault or error in the scanner motor and stop the engine, while at the same time communicating the fact

to the video controller.

1. Scanner Fault

If the /BDI signal cannot be detected 1.5 sec after the end of forced acceleration of the scanner motor, the period of detection will be extended by 120 sec.

If the cycle of the /BDI signal is not of a specific value during the period, the machine will assume the fact to indicate a fault in the scanner.

2. BD Fault

If the /BDI signal cannot be detected within 100 msec after the end of the forced acceleration of the scanner motor, or the cycle of the /BDI signal is not a

specific value continuously for 2 sec or more after the scanner motor has reached a specific speed, the machine will assume the condition to indicate a BD

fault.

3. BD Error

When the /BDI signal is not detected at a specific cycle while the /BDI signal is being generated for the interface controller, the machine will assume the

condition to indicate an BD error.

If the door is identified as being open within 200 msec after the detection of a BD error, the CPU will not communicate the presence of a BD error to the

interface controller.

/BDI

J904-9

J801-9

J905-1

J002-4

J905-2

/ACC

J002-3

J905-3

/DEC

J002-2