Canon CP660, Service Manual

Page: 121 / 407

COPYRIGHT © 1999 CANON INC. CANON 660/2100 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
D. Detecting the Density
Figure 4-501
The density of the density detection pattern drawn on the intermediate transfer drum
is checked by the density sensor. The density sensor is mounted on the density detec-
tion PCB; the light of a LED is directed to the density pattern on the intermediate trans-
fer drum, and the reflected light is received by the photodiode 1.
The DC controller PCB generates the LED activation signal (LEDCNT) at such times
as needed. The light from the LED is checked by the photodiode 2 directly, and the result
is sent to the density detection circuit as the intensity feedback signal (DENREF), and is
used to control the intensity of the LED to a specific level.
The light from the LED is also directed to the density detection pattern on the inter-
mediate transfer drum, and the reflected light is directed to the photodiode 1.
The density detection PCB forwards the density signals to the DC controller PCB as
the toner density detection signal (DNS). The DC controller PCB, in turn, converts the
density detection signal (analog value) into density levels (digital value) for storage in
memory.
Figure 4-502
CHAPTER 4 IMAGE FORMATION SYSTEM
4-23
Intermediate transfer drum
Photodiode 2
Density detection pattern
Density sensor
Photodiode 1
LED
DC controller
PCB
Density detection PCB
Density sensor
Photodiode
1
DNS
Intermediate
transfer
drum
LEDCNT
DENREF
LED
Photodiode
2
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