Image Write Control - Konica Minolta 7020 Service Manual

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Image Write Control

CCD
ADB
DCPS
The CCD sensor outputs analog image data. The ADB (A/
D conversion board) converts this data to digital form. The
CB (overall control board) processes this data within
memory, generating a laser recording signal. This signal is
transmitted, by means of a CB control signal, to the LDB
(LD drive board), and is output as an optical signal by the
LDB's laser emitting element. The write start position for
the laser recording signal is detected by the index sensor
on the index sensor board.
1. Operation
a. Image processing
3
The CB carries out the following processing.
(1) AOC (automatic offset correction)
Reading is taken with SW2 (sub power switch) ON
and L1 (exposure lamp) OFF, and the analog offset
voltage for CCD sencer output is automatically
adjusted such that this level become the lower limit
for the A/D converter (In the case of the other than
7035).
In the case of the 7035, IC on ADB automatically
adjusts analog off set voltage of CCD sensor output.
(2) AGC (automatic gain correction)
When SW2 comes ON, the level from the white
reference board is read by turning ON the L1
(exposure lamp), and the analog amplification for the
CCD sensor output is automatically adjusted such
that this level becomes the upper limit for the A/D
converter.
5VDC
SGND
/S/H
/ENB
/VIDEO
SGND
/ALM
NC
DACLK
DI
LD
LDPR+5VDC
5VDC
5VDC
SGND
SGND
12VDC 5VDC
SGND SGND
SGND /IND
12VDC SGND
INDPR+5VDC
CB
(3) Shading correction
Execution timing
White correction / Black correct
• At SW2 (sub power switch) ON
(4) Brightness/density conversion
(5) AE processing
(6) Text/dot pattern judgment
(7) Filtering
LDB
(8) Magnification change processing
(9) Error diffusion processing
(10) Data compression processing
(11) Write density correction
INDEX
b. Write
CB transmits image data one pixel by one pixel to the
LDB. The LDB emits the laser onto the drum in
certain time for each pixel determined by the image
data received from the CB.
(1) MPC (Maximum Power Control)
The CB informs LDB of the maximum laser output
value. The LDB keeps and uses this value in APC
(automatic power control) to maintain the laser
intensity.
<MPC Timing>
(1) After SW2 is set at ON when L detection
adjustment has been completed or the drum
counter has been reset.
(2) When SW is turn ON first thing in the morning.
(3) Every 20th copy during a continuous copy
operation.
(2) APC (Automatic Power Control)
After the CB has set the MPC, it outputs an APC start
command to the LDB in accordance with the following
timing.
<APC Timing>
At detection of M5 (polygon motor) PLL lock.
Thereafter, LDB automatically monitors the laser
drive current for each line, and controls the laser such
that the light intensity is always at MPC.
(3) Write timing
The index board's /IND signal determines the start
time for laser writing of each scan in the drum shaft
direction.
2-D-3
WRITE UNIT