Canon LBP-1210 Service Manual page 98

CHAPTER 2
The transfer charging bias circuit generates positive or negative DC voltage applies either of
them to the transfer charging roller.
These circuits are controlled by the CPU (IC201) on the engine controller.
The following section discusses each of the circuits.
b. Operation
1) Primary charging bias generation
The primary charging bias (PR1) is generated based on the two signals, the PRIMARY CHARG-
ING AC BIAS DRIVE (PRACC) signal and the PRIMARY CHARGING DC BIAS DRIVE (PRDCC) sig-
nal output form the CPU.
The PRACC signal is a clock signal for AC bias generation, while the PRDCC signal is for DC
bias generation. Based on these signals, the primary charging AC and DC bias is generated.
The primary charging AC bias or the combined voltage of the primary charging AC and DC bias
is applied to the primary charging roller.
The primary DC bias changes along with the developing DC bias, according to the image den-
sity information output from the interface controller.
2) Developing bias generation
The developing bias (DEV) is generated based on the DEVELOPING AC BIAS DRIVE (DVACC) sig-
nal output from the CPU.
The DVACC signal is a clock signal for AC bias generation. Based on this signal, the devel-
oping AC bias is generated. The developing DC bias is generated on the instruction from the
developing AC bias generation circuit. The developing DC bias or the combined voltage of the
developing AC and DC bias is applied to the developing cylinder.
The developing DC bias changes along with the primary charging DC bias according to the
image density information sent from the interface controller.
3) Transfer charging bias generation
The transfer bias (TRS) is generated based on the two signals, the TRANSFER POSITIVE BIAS
DRIVE (TRPWM) signal and the TRANSFER NEGATIVE BIAS DRIVE (TRNFOT) signal.
The TRPWM signal is a clock signal for positive bias generation, whereas the TRNFOT signal
is for negative bias generation. Based on these signals, the transfer positive and negative bias-
es are generated. Either the transfer positive or negative bias is applied to the transfer charg-
ing roller.
The CPU performs rated current control by switching the value of the TRPWM signal accord-
ing to the TRANSFER CURRENT FEEDBACK (TRFAD) signal sent from the transfer charging bias
circuit.
According to the print sequence, cleaning bias, between-page bias, or print bias is applied to
the transfer charging roller.
• Cleaning bias
This bias cleans the transfer charging roller by moving the toner adhering to the roller onto the
photosensitive drum during the warming-up or the last rotation sequence. To clean the roller,
the transfer negative bias is applied to the transfer charging roller.
• Between-sheet bias
During between-sheet in continuous printing, this bias prevents residual toner on the photo-
sensitive drum from adhering to the transfer charging roller. Infinitesimal transfer positive bias
is applied to the transfer charging roller.
• Print bias
Toner on the photosensitive drum surface is transferred onto print paper by this bias during the
print sequence. The transfer positive bias is applied to the transfer charging roller.
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