Determining The Optimum Grid Bias; Grid Bias Corrective Control - Canon imageRUNNER 7095 Service Manual

Chapter 7

7.4.3 Determining the Optimum Grid Bias

The grid bias is determined so that the drum surface potential will be identical to the target potential. (The
primary charging bias is set to a fixed value.)
Measurements are taken multiple times to
determine the relationship between the drum
surface potential (VD) and the grid bias.
VD3
VD2
VD1
550V 650V 750V
Grid bias
Potential sensor
Primary charging bias
Grid bias
Potential control sequence started

7.4.4 Grid Bias Corrective Control

If the optimum grid bias cannot be determined at the end of drum surface potential measurement, the ma-
chine starts its compensatory control sequence to determine the bias.
Continues to take measurements while varying
the value of the grid bias so that it will be closer
to the target VD.
TargetVD
Potential sensor
Primary charging bias(DC)
Grid bas
7-6
Charging characteristics
curve
193
WMUP
Measurement(VD2) Measurement(VD1orVD3) Measurement (target VD)
650 V
VD1
VD3
VD2
VD-NG
193
WMUP
WMUPR
650 V
550 V
or
750 V
Potential control
sequence started
If the target VD is attained using this
measurement, the control is ended;
otherwise, compensatory control is
WMUPR
Vg
550 V or 750 V
A grid bias (Vg) needed to attain
the target VD is determined.
F-7-7
When the measurement is identical to the target VD,
ends the control. The machine executes measurement a
maximum of 8 times, possibly using an approximate
target VD.
VD-NG VD1 VD2 VD3
Vg
Vg1 Vg2 Vg3 Vg8
Compensatory control
A grid bias (Vg) needed to attain the
sequence started
target VD is determined.
F-7-8
198
STBY
198
STBY
VD8
0010-8041
0010-8042