Canon iR2318 series, Руководство по обслуживанию, Страница: 158 / 308

Chapter 6
6-6
6.5 Drum Unit
6.5.1 Outline of the Drum Unit
6.5.1.1 Outline
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Major components of the drum unit are as follows:
F-6-7
[1] Photosensitive drum
[2] Cleaning blade
[3] Primary charging roller
6.5.2 Charging Mechanism
6.5.2.1 Primary Charging Bias Control
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With the primary charging bias method, the drum is charged directly by the charging roller. In addition to a DC bias, an AC bias is applied to the primary charging
roller to stabilize charging. When the drum is charged, both AC and DC biases are applied. When the drum is discharged, only the AC bias is applied.
The ASIC on the DC controller PCB outputs the primary bias drive signal (/PRACFOT), primary AC bias ON/OFF signal (/PRACON), primary DC bias drive
signal (/PRDCFOT), and primary DC bias output level signal (/PRDCPWM) to apply the voltage generated by superimposing the primary AC bias over the primary
DC bias to the primary charging roller.
The primary AC bias is detected by the primary AC bias current detection circuit, and is fed back to the AC generator circuit via the comparison circuit.
The primary DC bias is detected by the primary DC bias current detection circuit, and is fed back to the DC generator circuit via the comparison circuit. Thus, this
machine controls the primary DC bias voltage. The primary DC bias voltage changes with the developing DC bias voltage according to the image density informa-
tion sent from the image processor PCB.
F-6-8
[3]
[1]
[2]
JP3/JP4
/PRACON
/PRACFOT
/PRDCPWM
/PRDCFOT
To primary
charging roller
Primary bias circuit
ASIC
CPU
Primary DC bias voltage
detection circuit
DC generation circuit
AC generation circuit
Compariso
circuit
Primary AC bias current
detection circuit
Comparison
circuit
Superimposition
High-voltage power supply PCB DC controller PCB
J214
J100
/PRACMONI