Canon PC300 Service Manual page 54

D
=, Document Density
Measurement (AE;
PC320/325/F C230)
{. Cutline
The copier is equipped with an automat-
ic density control (AE) mechanism that con-
trols the DC component of the developing
bias. The copier's AE mechanism does not
execute an AE scan, but instead measures
the document density during image expo-
sure.
2. Operations
Document measurement is started while
the copyboard is moving forward; i.e., when
the leading edge of the document begins to
be exposed (copyboard position sensor
Q902 goes OFF).
At the time, the photodiode (PD602)
checks the reflected light.
The output of the photodiode (PD602) is
amplified, and sent to the microprocessor as
AE signals.
<AE Measurement Timing Chart>
Power switch ON Copy Start key ON
V7 7
[Sequence —[ [ste¥| _ I N T R _ _ [ ~ COPY
Pcosmean | feaelet care
i eae a ae
4 Developing
DC bias
Figure 3-21
COPYRIGHT © 1994 CANON INC.
PERATIONS AND TIMING
The microprocessor takes measure-
ments of the AE signals four times every 1.3
mm, and generates the developing DC bias
control command (DCBPWM) to suit the
average document density. See Figure 3-22
for the points at which the document density
is measured in relation to the copyboard
glass.
6mm
30 mm (approx.) §
33.5 mm (approx.
sss: Points of measurement
Figure 3-22
3. Adjusting the AE Mechanism (VR602,
R603)
You must adjust the AE mechanism if
you have replaced the scanning lamp unit,
control panel PCB, or intensity/AE sensor;
see p. 3-50.
Note:
Adjust the AE mechanism only after
adjusting the intensity of the scanning
lamp.
CANON PC300920/925, FC210/230 REV.0 JULY 1994. PRINTED IN JAPAN (IMPRIME AU JAPON) 3-27