Measuring The Dark Area Potential Attenuation; Controlling The Environment Contrast Potential - Canon CLC 1120 Service Manual

3. Measuring the Dark Area Potential Attenuation

The operation referred to as "dark area potential attenuation measurement" consists in
measuring the rate of attenuation to prevent fogging and carrier adhesion. (The potential created on
the photosensitive drum by primary charging tends to decrease if left alone in a dark area.)
In practice, the degree of decrease of the potential created by primary charging is detected at the
point of development, and the result is used as feedback when controlling the developing bias.
The grid bias (Vg) of the primary charging assembly is set to +500 and +700 V, and the dark
area potential (VD3, VD4) occurring when the laser is off and the light area potential (VL3, VL4)
occurring when the laser is on are measured by the potential sensor.
The measurements taken during the first rotation (VD3, VD4, VL3, VL4) and the
measurements taken during the second rotation (VD5, VD6, VVL5, VL6) are compared, and the
differences (= VD3 - VD5, = VL3 - VL5, = VD4 - VD6, = VL4 - VL6) are used to determine the
rate of attenuation.
Dark area potential attenuation measurement is executed during initial multiple rotation at time
of power-on and every two hours thereafter.

4. Controlling the Environment Contrast Potential

The operation referred to as "environment contrast potential control" consists in measuring the
environment (temperature/humidity) around the developing assembly to determine the target
contrast potential.
Changes in the environment around the developing assembly change the characteristics of
developing agents and, consequently, affect the image density. To make up for such changes, the
environment (temperature/humidity) around the developing assembly is measured by the
environment sensor to determine the target contrast potential.
Figure 6-203 shows the relationship between changes in the environment and the target
contrast potential.
Target contrast
potential
COPYRIGHT © 1999 CANON INC.
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CANON CLC1120/1130/1150 REV.0 MAR. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 6 IMAGE FORMATION SYSTEM
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