Detecting Dirt On The Window - Canon CLC 1120 Service Manual

CHAPTER 6 IMAGE FORMATION SYSTEM
When measuring the concentration of black toner during copying operation, it is necessary to
prerent adhesion of toner on the photosensitive drum to the transfer sheet. To prevent such a
problem, the CPU PCB controls the timing at which the laser is turned on so that the black toner
image will come face-to-face with the metal transfer sheet.

4. Detecting Dirt on the Window

The LED is turned on when the power switch is turned on or while control rotation (CNTR)
takes place during copying operation to measure Bk-SGNL without toner on the photosensitive
drum.
The level of Bk-SGNL is low if the sensor window is soiled. The ratio between the level of Bk-
SGNL and a predetermined value is stored in memory and used to correct the output of the sensor
while controlling the concentration of the toner inside the black developing assembly.
If the level of Bk-SGNL is ±30% or more of a predetermined level, the copier will indicate
'E020'.
6-38
COPYRIGHT © 1999 CANON INC.
Photosensitive
drum
Transfer
drum
Figure 6-406
Photosensitive drum
Photodiode
Figure 6-407
CANON CLC1120/1130/1150 REV.0 MAR. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
Laser exposure
Black toner
Developing cylinder
Black toner concentration
sensor
Transfer sheet fixing plate
Dirt on sensor
LED