Canon NP6012 Service Manual page 84

SLA ae OP EA ATIONS AND TIMING Gl
2. Turning On and Off the Transfer
Roller Bias
The microprocessor on the DC controller
PCB sends the transfer bias on signal to the
microprocessor on the composite power
supply PCB. In response, the microproces-
sor on the composite power supply gener-
ates the transfer bias on signal to drive the
transformer (T401), thereby supplying the
transfer charging roller with transfer bias.
3. Controlling the Transfer Bias to a
Specific Voltage
The transfer bias is controlled to a spe-
cific voltage by the microprocessor on the
composite power supply PCB. The micropro-
cessor on the composite power supply PCB
monitors the voltage of the transfer bias at
all times. The microprocessor on the com-
posite power supply PCB sends the transfer
bias control signal through the pulse/DC
conversion circuit according to the detected
voltage to the voltage control circuit to main-
tain the transfer bias to a specific voltage.
4. Correcting the Voltage Level of the
Transfer Bias
The copier corrects the voltage level of
the transfer bias in any of the following two
ways:
* before starting copying (ATVC)
* after starting copying
a. Before Starting Copying (ATVC)
To correct changes in the transfer effi-
ciency caused by changes in the environ-
ment or deterioration of the transfer roller,
the copier automatically corrects the applica-
tion voltage level of the transfer bias.
During initial rotation after the Copy Start
key is pressed, the copier feeds a specific
current to the transfer rofler. The current
detection circuit on the composite power
supply PCB sends measurements of the cur-
rent to the microprocessor in the form of the
current detection signal. The microprocessor
determines the voltage to be applied to the
transter roller based on such data.
This control is executed once during ini-
tial rotation after a press on the Copy Start
key.
COPYRIGHT © 1995 CANON INC.
CANON NP6O12/NPGO12F /NP6212 REV.1 SEPT. 1995 PRINTED IN JAPAN (IMPRINE AU JAPON)
b. After Starting Copying
The copier automatically corrects the
application voltage during copying operation
to compensate for the changes in the trans-
fer efficiency caused by different types of
copy paper.
The current detection circuit detects the
current flowing through the transfer charging
roller and sends the data to the microproces-
sor on the composite power supply PCB.
Using the data, the microprocessor deter-
mines the voltage to be applied to the trans-
fer charging roller and controls the DC bias
voltage by generating the transfer DC bias
control signal so that the voltage will be opti-
mum.
5. Switching the Polarity of the DC Bias
(cleaning)
The microprocessor on the DC controller
PCB sends the transfer bias switching timing
signal to the microprocessor on the compos-
ite power supply PCB.
The microprocessor on the composite
power supply PCB, on the other hand, turns
off the transfer DC bias on signal and, at the
same time, sends the transfer positive DC
bias on signal to the positive bias control cir-
cuit. The voltage from the positive bias con-
trol circuit is sent to the transfer charging
roller through the transformer/rectifier circuit.
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