CHAPTER 4 IMAGE FORMATION SYSTEM

2. Turning On and Off the Transfer Roller Bias

The TFWON signal is generated under the control of the microprocessor (Q512) on the composite power supply PCB. The signal causes the secondary side of the transfer transformer (T402) to turn on, thereby applying a DC bias to the transfer roller.

Table 4-102 shows combinations of signals that are used when determining the transfer roller bias.

 

TREVON*

TFWON*

TFWPWM

 

 

 

 

Transfer bias output

OFF

ON

ON

 

 

 

 

Cleaning bias output

ON

OFF

OFF

 

 

 

 

Reference bias output (A TVC)

OFF

ON

OFF

 

 

 

 

Table 4-102

3. Controlling the Transfer Bias to a Constant Voltage

While the transfer DC bias is being generated, the microprocessor (Q512) on the composite power supply PCB reads the TFWS signal (analog signal) from the constant voltage control circuit and changes the duty ratio so that the application voltage is maintained at a constant level, thereby controlling the TFWPWM signal.

4. Controlling the Transfer Bias Voltage Level Correction (ATVC control)

To correct the changes in the transfer efficiency caused by changes in the environment or deterioration of the transfer roller, the application voltage level of the transfer bias is corrected automatically.

A constant current (–10 µA) is let to flow during initial rotation after a press on the Copy Start key. The microprocessor (Q512) on the composite power supply PCB takes in the transfer roller application voltage at the time from the constant voltage control circuit, and sends the data to the microprocessor (Q512) on the DC controller; the DC controller, in turn, determines the level of the voltage to be applied to the transfer roller based on the data.

This control is executed only once during initial rotation immediately after a press on the Copy Start button; for this reason, the application voltage will never vary during continuous copying operation.

5. Current Limiter Circuit (transfer bias)

Should an overcurrent flow to the secondary side of the transformer (T402) while a transfer bias is being generated because of changes in the environment, the current limiter circuit exerts control so as to prevent any occurrence of a current which is 50 µA or more.

6. Current Limiter Circuit (cleaning bias)

Should an overcurrent flow to the secondary side of the transformer (T402) while a transfer bias is being generated, the current limiter circuit exerts control to prevent any occurrence of a current which is 10 µA or more.

COPYRIGHT © 1997 CANON INC.

CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)

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Canon FY8-13EX-000 Turning On and Off the Transfer Roller Bias, Controlling the Transfer Bias to a Constant Voltage