Canon imageCLASS MF8450c, Service Manual

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Chapter 7
7-9
7.2.3 D-half Control
0019-5021
imageCLASS MF9170c / imageCLASS MF9150c / imageCLASS MF8450c
This control corrects the gradation data based on the halftone density in order to obtain ideal image gradation.
The DC controller executes this control following the command sent from the main controller.
Explanation of operation
1) When receiving a command of executing density measurement from the main controller, the DC controller forms a pattern image for image gradation correction
for each color on the ETB.
The pattern image for image gradation correction is formed with the specified density for each color (low at the left side and high at the right side), using the
optimum developing bias determined by the environment related corrective control.
2) The DC controller sends a color displacement/density LED drive signal and flashes the light emitter (LED) of the color displacement/density sensor.
The color displacement/density sensor is a reflection type sensor located on the upper side of the ETB. It consists of the light emitter (LED) and light receiver
(PD).
3) The light emitted from the light emitter is reflected at the pattern image for image gradation correction and received at the light receiver of the color displacement/
density sensor.
The intensity of the reflected light varies depending on the toner density.
4) The color displacement/density sensor converts the received light into a voltage, and sends it to the DC controller as a density detection signal (analog value).
5) The DC controller converts the received density detection signal into density data, and sends it to the main controller.
6) The main controller performs gradation correction based on the received density data in order to obtain an ideal halftone image.
F-7-14
Error Codes:
E020 Warning: color displacement/density sensor abnormality
When light could not be received by the light receiver, the machine sets an initial value for the image density correction value and displays the error code
on the control panel.
ETB
Color displacement/density sensor (left)
Color displacement/density LED
drive signal
Color displacement/density
sensor (right)
Color displacement/density signal
Pattern image for image gradation correction
DC controller PCB
Main controller PCB
Light emitter (LED)
Light receiver (PD)