Sharp AR-5132 Service Manual page 19

3
The developing bias voltage is obtained from comparison with the
standard patch density.
255
R
Standard
patch
density
3
0
-290
Developing bias voltage (V)
In the AR-5132, the absolute value of the density sensor output
value is not directly used for the control calculation, but the ratio of
the drum surface sensor output value (BSn) and the toner patch
image sensor output value (PTn) is used for the control calcula-
tion.
Since the ratio of PTn/BSn) is not affected by the change in the
absolute value of the light quantity of the reflection type sensor
due to dirt or deterioration, stable control is performed.
4
In the developing bias/MC grid voltage correction, the value of vV
of the developing bias voltage calculated with the standard patch
density and the process control is fed back to the bias voltage and
the MC grid voltage in each mode.
When the developing bias voltage is corrected, the corresponding
MC grid bias is calculated and controlled.
5
When a value reaching the reference level is not obtained in a
series of control procedures, the patch forming conditions are
shifted toward the reference level side and repeat the series of
control procedures. The repetition is allowed for max. five times.
LD power correction
The LD power correction is performed depending on the result of the
developing bias voltage calculation. When the correction width üV of
the developing bias voltage becomes greater, the MC grid voltage is
corrected accordingly. If the LD power is the same at that time, the
apparent sensitivity of the OPC drum is changed. To correct this, the
LD power is made greater when the developing bias voltage is in-
creased; on the contrary the LD power is made smaller when the
developing bias voltage is decreased. The width of decrease or in-
crease is determined according to the built-in table. This correction
stabilizes half tone prints.
Process control timing
In the AR-5132, the process control is performed at the following
timing.
a. When the power switch is turned on. (during warming up)
b. When the accumulated copy time reaches 30 min, the process
control will be made in the next copying.
c. When the standby time reaches 1 hour, the process control will be
made in the next copying.
d. When simulation 46 is executed.
1
R1=PT1/BS1 x 255
2
R2=PT2/BS2 x 255
R3=PT3/BS3 x 255
V
-240 -190
GB PAT
Drum marking
In the AR-5132, toner patch images are formed at the same position
on the OPC drum to improve accuracy of the process control.
That is, a marking is provided on the drum, and the marking point is
sensed and toner patch images are formed at a certain position.
If the marking is not sensed, the copy density is extremely reduced.
F
2 – 6
R