Sharp SF-2014 Service Manual page 37

2. Optical unit correction (Dirt correction)
Diagram of correction system in the optical section
Referance refrection plate
Copy
lamp
AC power supply unit
(Copy lamp control circuit)
The purpose of this correction is to maintain the copy density even
though the optical unit is contaminated and to reduce troublesome
cleaning of the optical unit.
When the lamp, the mirror, and the reflector are dirtied with dusts and
toner, the light quantity radiated to the photoconductor drum is re-
duced, increasing the copy density and producing unnecessary back-
ground copy.
The above trouble is removed by changing the copy lamp voltage to
adjust the copy density. It, however, requires serviceman's operation.
In this model, the AE sensor senses dirt on the copy lamp, the mirror,
and the reflector, and the copy lamp light quantity is changed accord-
ing to the dirt level to reduce the change in the copy density due to
the optical unit dirt.
When the optical parts are dirtied, the reflection rate is reduced to
reduce the quantity of light which is passed to the optical dirt sensor.
In this manner the dirt level is sensed.
[Initial setting]
After making a copy by Simulation 46, the scanner unit stops at the
position of the standard reflection plate on the back of the document
stopper to light the copy lamp at a certain level, and the AE sensor
output level at that time is recorded as the reference value. (The
reference value can be checked with Simulation 44-2.)
[Correction timing]
The correction is performed after the copy cycle after turning on the
power, or after the specified time of rotation of the photoconductor
drum.
[Correction operation]
The same operation as the initializing is performed to change the
copy lamp voltage until the AE sensor output level reaches the same
level as the reference value, performing the correction.
The copy lamp voltage is revised to a new value at every correction,
and the new value will be used in the next correction.
(The correction voltage value can be checked with Simulation 44-3.)
[Correction timing]
•
When the power is turned on.
•
Once for every 77.5 min. of drum rotation.
Mirror AE SENSOR
AMP
Driver
5 – 13
Referance refrection plate
Table glass
MAIN CONTROL PWB
CPU
Timer
A/D
Arithmetic unit
converter
Copy lamp control
clock generator
START
The scanner starts
initializing.
The scanner unit stops
at the standard reflection
plate position.
NO
Copy lamp ON
Correction mode ?
(67.7V/135V)
YES
Sensor output =
Reference level
Copy lamp ON
(DSENS) ?
(67.7V/135V)
YES
Optical dirt sensor
reference level No correction is made.
(DSENS) memory
Copy lamp voltage
correction
END
AE sensor
(Next to the lens)
EE-PROM
Copy lamp
referance control
level
Copy lamp voltage
0.3V (0.6V) up
Copy lamp ON
Sensor output =
NO
Reference level
(DSENS) ?
YES
Sensor output
NO
< Reference level
(DSENS) ?
Copy lamp voltage
0.3V (0.6V) down
Copy lamp ON
Sensor output =
NO
Reference level
(DSENS) ?
YES
Copy lamp correction
voltage calculation
YES