Canon iR C2880 Series Service Manual page 189

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)
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
Chapter 5
Gain correction against
reference position
yes no
yes no
yes no
no yes
5-15