Canon iR2020 Series Service Manual page 153

[Description of Control]
- At job end (Dust detection)
The contact image sensor (CIS) checks the light reflected by the ADF platen roller surface at the read position for presence/absence of dust. After completion of a
job, dust detection is performed maximum six times in 3 point of A, B and C. First, dust detection is performed once at position A. If no dust is detected at position
A, dust detection is performed twice there. If no dust is detected, the original is scanned at position A. If dust is detected at position A, move to position B and dust
detection is performed twice at position B. If no dust is detected at position B, the original is scanned at position B. If dust is also detected at position B, move to
position C and dust detection is performed once at position C. If dust is also detected at position C, a relevant message is displayed on the operation panel. In this
case, move back to position A and the original is scanned at position A.
- At job start (Dust bypass)
Presence/absence of dust is detected at all points A, B, and C in this order at job end. The original is read at the point where least dust is detected.
- Immediately before scanning (one sheet at a time)
The contact image sensor (CIS) does not move to detect dust.
The original is read at the position determined at job end or start. If presence of dust is detected there, the read image is corrected.
Main power
Start key
switch
ON
ON
WMUPR STBY
Dust detection control
B
A
Point Description
A Read reference position
B out 0.5 mm from the reference position to the inside of the
roller
C About 1.0 mm from the reference position to the inside of
the roller
1st 2nd
SCAN SCAN
Dust detection control
Dust detection control
F-4-26
C
F-4-27
T-4-8
Chapter 4
4-13