Canon iR2318 series, Service Manual, Page: 159 / 308

Chapter 6
6-7
6.6 Developing Unit
6.6.1 Outline
0020-4100
Major components of the developing assembly are as follows:
F-6-9
[1] Developing Assembly
[2] Stirring plate
[3] Antenna rod
[4] Developing blade
[5] Developing cylinder
6.6.2 Developing Bias Control
0020-4102
A DC bias and an AC bias are applied to the developing cylinder.
The ASIC on the DC controller PCB outputs the developing AC bias drive signal (/DVACFOT), developing AC bias ON/OFF signal (/DVACON), developing DC
bias drive signal (/DVDCFOT), and developing DC bias output level signal (/DVDCPWM) to apply the voltage generated by superimposing the developing AC
bias over the developing DC bias to the developing cylinder.
To prevent fogging of the drum, a DC bias higher than usual applied except during image formation and when the developing AC bias is applied for warm-up
rotation.
The developing DC bias is detected by the developing DC bias detection circuit, and is fed back to the DC generation circuit via the comparison circuit, thus con-
trolling the DC bias voltage. The developing DC bias voltage changes with the primary DC bias voltage according to the image density information sent from the
image processor PCB.
The remaining toner level is detected during warm-up rotation and when the developing AC bias is applied for printing. The remaining toner level detection signal
(TNRCHKT) sampled from the antenna (for remaining toner level check) in the developing assembly is compared with the reference signal (TNRCHKD) received
from the developing bias detection circuit.
F-6-10
[1]
[2]
[3]
[4]
[5]
JP7/JP8
JP1/JP2
TNRCHKT
TNRCHKD
/DVACFOT
/DVDCPWM
/DVDCFOT
To developing
cylinder
From remaining
toner level sensor
Developing bias circuit
ASIC
CPU
Developing DC bias
voltage detection circuit
Developing AC bias
current detection circuit
Remaining toner level
detection circuit
DC generation circuit
AC generation circuit
Comparison
circuit
/DVACON
Superimposition
High-voltage power supply PCB DC controller
PCB