Canon Color iR C3480 Service Manual page 190

Chapter 5
2. Particulars of Control
(1) At the End of a Job (dust detection)
The contact image sensor (CIS) checks the light reflected by the platen roller of the ADF at a point of reading to find out the presence/absence of dust. If the
presence of dust is detected, the contact image sensor moves to the next candidate point (2 times max.; A -> B -> C; B -> C -> A; or C -> A -> B).
The point identified will be used as the point of reading for the next job.
- For the control at the end of a job, the sensor will never move to point D.
- For the control at the end of a job, a message prompting cleaning of the glass surface will be indicated if an original is placed in the ADF while the presence
of dust has been detected at all points (A, B, C). The Start key is disabled until the message is cleared.
(2) At the Start of a Job (dust avoidance)
The same detection mechanism as used at the end of a job is executed; if the presence of dust is detected at all points (A, B, C), the sensor is moved to point D
for reading operation.
If the control is at the end of a job that takes place at point D, it will be after moving the sensor to point D.
(3) Between Sheets
The contact image sensor (CIS) is not moved for detection of dust.
The machine undertakes reading at a point determined by control executed at the end of a job or at the start of a job; if the presence of dust is identified, the
machine executes image correction.
Location
A reading reference location
B point about 0.5 mm toward roller inside from reference position
C point about 1.0 mm toward roller inside from reference position
D point about 4.0 mm toward roller outside from reference position (no dust detection)
5-16
D
At end of job
At start of job
B C
A
Pattern 1
Pattern 2
Pattern 3
F-5-27
T-5-7
Image correction Gain correction against
reference position
yes no
yes no
yes no
no yes