Sharp AR-5132 Service Manual page 18

(4) OPC drum sensitivity reduction correction
In the AR-5132, deterioration of copy quality is prevented by correc-
tion with the charging grid voltage against the potential reduction of
the OPC drum due to repeated use.
The drum wear increases the grid voltage to maintain the drum sur-
face potential at a constant level, and the apparent sensitivity of the
OPC drum is decreased. To correct this, the laser beam strength is
increased when the coefficient of the drum rotating time for correction
of the charging grid voltage reaches a certain level.
Cleaner
section
OPC drum
(5) Process control function
[Outline]
The density of the reference toner image formed on the OPC drum
surface is used as the standard patch density, and the developing
bias and the charging grid voltage are controlled to provide the same
density as the standard patch density for stabilizing the copy images.
That is, the process conditions are set, and the high voltage output is
changed and corrected so that the toner density is stabilized under
the conditions.
R
Main control PWB
CPU density
judgement
I/O MC grid
developing bias
output selection
Developing
section
F
Process density
sensor PWB
Density detection
level setting (VR2)
High voltage PWB
Each mode MC
grid developing
bias output
(density correction)
(Light quantity
correction)
2 – 5
(New)
CTL
CGL
CLV
Grid voltage
correction value
0 1 2
Coefficient for rotation time
Process control
1
Toner patch images are formed on the OPC drum surface under
the three kinds of conditions (MC grid bias voltage) and the
developing bias. (The voltage is an actually measured value.)
In the process control, toner patch images are formed at the laser
output of the reference grid voltage (–410V) and the developing
bias (–240V) ±50V and duty of 100%.
2
The three kinds of toner patch images and the drum surface are
measured with the process density sensor to obtain the relation-
ship between them.
Potential (V)
Toner
Surface Surface
image
Light
potential
1
BV 2
BS1
3
PT1
3
PV
2
1
(After use)
CTL
CGL
3 4 5 33 34
Toner Toner
Surface Surface
image image
Drum
surface
potential
Developing
bias
BS2 BS3
PT2
PT3
Wear
35