Canon 1000 Service Manual page 152

3. OPERATION AND TIMING
b. Measuring the Color Toner Density
The Y, M, and C developing assemblies each are equipped with a color toner density sensor inside them
(Figure 3-535), and each sensor is used to measure the density of toner retained on its respective cylinder.
Toner supply clutch
Bk
The mechanism of measurement is as follows:
The CLC1000's developer is a two-component developer consisting of carrier and toner. When exposed
to infrared light, the color toner will reflect infrared light while the carrier will absorb it. In other words, when the
amount of toner decreases because of consumption over time, the reflection of infrared light will decrease
because of the changing toner/carrier ratio of the developer.
Using an infrared diode, the toner/carrier ratio
is computed from the intensity of the infrared light
reflected by the developer on the developing
cylinder.
To make up for the deterioration occurring in
the infrared diode and changes in temperature, the
direct light is also measured at the same time.
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COPYRIGHT © 2001 CANON INC.
Toner supply signal
CL
Direct intensity/reflected intensity signal
Color toner density sensor
C
Transfer belt
Figure 3-535
CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
DC controller PCB
Developing
cylinder
M
Reflected intensity signal
Detection of
reflected light
Cylinder
Figure 3-536
Y
Mirror
Direct intensity signal
LED
Detection of direct light