Canon iR C3380 series Service Manual page 225

[1] Photosensitive drum
[2] Developing cylinder
[3] Path image data
[4] Laser output
[5] Developing DC bias
[6] Color D-max control
[7] Black D-max control
UN16: patch image sensor
A. Color D-max Control
1. Start-Up Timing
when a color (Y, M, C) drum unit is replaced with a new unit.
2. Particulars of Control
In the presence of a specific condition, the DC controller forms a patch pattern of the color in question on the ITB. Thereafter, it uses the patch image sensor to
measure the density of the patch, and corrects the output of the laser light of the color in question so that the density will be identical to the target density.
The machine executes this control only for the color of the drum unit that has been replaced.
[1] Patch image data
[2] Laser output
[3] Photosensitive drum
UN16: patch image sensor
MEMO:
In previous machines, density is corrected by varying the developing bias of individual colors. The machine uses the same developing bias for all colors (a design
consideration made to facilitate work at the factory), not being able to vary the developing bias for individual colors. To work around the fact, the machine corrects
the density of individual colors (Y, M, C). It, however, varies the developing bias for Bk as in previous machines.
[1]
[4]
Laser Scanner
unit
[6]
Y
M
Laser Scanner
unit
[3]
ITB
UN16
[2]
[5]
HVT1
[3]
[7]
D-CON
F-7-19
ITB
Y
C
UN16
[2] [1]
D-CON
F-7-20
Chapter 7
7-15