Canon iR3570 Series, Service Manual

Page: 204 / 722

Chapter 5
5-14
F-5-26
5.3.6.2 CCD Drive
0006-5931
iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
The machine's CCD sensor is a 1-line linear image sensor consisting of 7488 photocells. After completion of photoelectric conversion in the light-receiving block,
the signals are output to the AP circuit in the reader controller circuit board in parallel for each channel (total eight channels) of the CCD array.
F-5-27
5.3.6.3 Gain Correction and Offset Correction of the CCD Output
0006-5932
iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
The analog video signal generated by the CCD is corrected so that it will have a specific level (gain correction); moreover, the output voltage occurring in the ab-
sence of incident light is also corrected so that it will have a specific level (offset correction).
5.3.6.4 A/D Conversion of the CCD Output
0006-5933
iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
The analog video signal is further converted into a digital signal that is suited to the voltage level of individual pixels by the A/D converter.
5.3.6.5 Shading Correction (outline)
0006-5936
iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
The output of the CCD is not necessarily even for the following factors even when the density of the original is uniform:
1) Variation in the Sensitivity Among Pixels of the CCD
2) Variation in the Intensity of the Rod Lens Array
The machine executes shading correction to even out the output of the CCD. Shading correction may be shading adjustment executed at power-on or shading cor-
rection executed for each job.
5.3.6.6 Shading Adjustment
0006-5937
iR2270 / iR2870 / iR3570 / iR4570 / / iR2270N / / iR2870N / / iR3570N / / iR4570N / iR2230 / / / iR3530 /
In this adjustment, the machine measures the density of the standard while plate, and stores the results in memory as density data. It then performs computations
on the shading data, and uses the result as the target value for shading correction.
CCD(1 line)
Analog
image
signal
Analog image
processing
-gain correction
-offset correction
A/D
conversion
CCD
drive control
CCD
control signal
Gain
correction
data
Digital
image signal
CCD/AP circuit
10
Digital
image signal
8
Reader controller PCB
Contact image sensor CIS)
Target value
J502
EEP-ROM
SRAM
CPU
Shading
correction
CCD7 CCD5 CCD1 CCD2 CCD8 CCD6
H L L H H L H L H H L
output
Light-receiving block