Canon GP200 Service Manual page 118

3. OPERATIONS AND TIMING
a. Transfer Bias
This bias is used for transfer of toner from the photosensitive drum to copy paper and is of a positive
voltage. For output timing, see Figure 3-505.
b. Cleaning Bias
Since the machine uses direct transfer, toner from the photosensitive drum can stick to transfer charg-
ing roller because of a jam. A negative voltage is applied as follows, thereby returning the toner from the
transfer charging roller to the photosensitive drum:
• During initial rotation after a press on the Copy Start key
• Part of the last rotation period
• During roller cleaning initiated in user mode ('adjustment/cleaning'; in this case, the primary charg-
ing roller is cleaned at the same time)
c. Reference Bias
At times, the transfer efficiency varies because of changes in the environment or in the resistance of
the transfer charging roller. To prevent deterioration of images by such variations, the level of the applica-
tion voltage to the transfer charging roller is corrected.
The reference bias is applied each time the Copy Start key is pressed, thereby correcting the voltage
level.
d. Sheet-to-Sheet Distance
In continuous copying, the bias value is decreased so as to prevent adhesion of toner to the transfer
charging roller between sheets of copy paper.
Main power
switch ON
SLEEP
Main motor (M1)
Cleaning bias
Reference bias
Sheet-to-sheet bias
Transfer bias
3–64
COPYRIGHT © 1996 CANON INC.
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Control power Copy Start
switch ON key ON
STBY
INTR
Figure 3-505
CANON GP215/200 REV.0 JULY 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)
SCFW
SCFW
LSTR STBY