Document Density Measurement (Ae; Pc420/430/Fc220) - Canon PC400 Service Manual

CHPTER 4 IMAGE FORMATION SYSTEM
F. Document Density Measurement (AE; PC420/430/FC220)
1. Outline
The copier is equipped with an automatic density control (AE) mechanism that
controls 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
exposure.
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>
4-14
COPYRIGHT © 1998 CANON INC.
Power switch ON
Sequence STBY
Copyboard
Main motor
1
(M1)
Copyboard position
2
sensor (Q902)
AE
3
measurement
Developing
4
DC bias
Figure 4-101F
CANON PC400/420/430,FC200/220 REV.0 JAN.1998 PRINTED IN JAPAN (IMPRIME AU JAPON)
Copy Start key ON
INTR COPY
CBFW
CBRV STOP