Canon imageRUNNER 2520 Series, Service Manual, Page: 43 / 402

• 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 in the positions A, B and C without concern of presence/absence of
dust.
1) Dust detection is performed once at position A.
2) CIS moves to the position B and dust detection is performed once.
3) CIS moves to the position C and dust detection is performed once.
4-a) CIS moves to the position where there is no dust, with priority for the detecting position; A>B>C.
4-b) If dust is detected at all points A, B, and C, move back to position A and the original is scanned at position A.
A
B C
• 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.
Point Description
A Read reference position
B About 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
■ Image Processing
● Overview
Major specifications and functions of the image processing system are as follows:
• CMOS (image sensor)
Number of lines: 1
Number of pixels: Total 7488 (incl. 7176 effective pixels)
Pixel size: 32 x 46.9 um
• Shading correction
Shading correction: Made for each job.
Shading adjustment: Made in the Service mode.
Reader relay PCB
CMOS
sensor
Analog image processor
Digital image processor
Shading
processing
Analog
image
processing
A/D
conversion
Contact image
sensor (CIS)
Controller
Functions of the image processing system are summarized below.
• Reader relay PCB:CMOS sensor drive, analog image processing, A/D, conversion, and shading correction
2. Technical Explanation
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