Canon NP6012F Service Manual page 75

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H. Controlling the Transfer
Roller Bias
1. Outline
The copier uses a direct transfer method
with a roller. For this reason, it controls the
bias differently from the conventional copiers
that employ corona charging.
The transfer roller bias may be either of
the following three types; see the descrip-
tions for the function and output timing of
each:
a. Transfer, Bias
This bias corresponds to the transfer
bias of a conventional copier, and is a nega-
tive voltage.
b. Cleaning Bias
The copier uses a direct charging
method, and could allow adhesion of toner
to the transfer roller moving from the photo-
sensitive drum because of a jam.
To remove such toner, the copier applies
a positive voltage at a specific timing to
return the toner from the transfer roller to the
photosensitive drum.
l
during initial rotation after the Copy
Start key is pressed.
l
while the scanner is moving in reverse.
l
during last rotation.
c. Reference Bias (ATVC)
Changes in the environment or deterio-
ration of the transfer roller can change the
resistance of the transfer roller, ultimately
affecting the transfer efficiency.
To suppress the changes in the copy
images caused by changes in the transfer
efficiency, the copier corrects the level of
transfer bias application.
The transfer ATVC bias is a bias applied
each time the Copy Start key is pressed to
determine the correction value.
r
Power switch ON
rCopy
Start key ON
Figure 3-320
COPYRIGHT 0 1995 CANONINC. CANON~NP60121NP6012F/NP6212 REV.1 SEPT.1995 PRlNTEOINJAPAN(IMPRIM~AUJAPON)
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