Panasonic FP-7742 / FP-7750 (serv.man2) Service Manual ▷ View online
3-28
b) Setting the scanning speed of optics system
The copy ratio in the paper feed direction is changed by changing the
scanning speed of the optics system full-speed unit.
• For reduction, the optical image guided by the mirror and lens is reduced
on the drum in the direction of drum shaft.
• For the direction of paper feed, in the case of reduction as shown in the
following figure, the original image A+B+C is reduced on the drum as the
image a+b+c. Therefore, the scanning speed is faster so that the exposure
of original image A+B+C is transferred during the movement of distance
for the drum image a+b+c. Consequently, The more the original is reduced,
the more the optics system scanning speed increases, and for
enlargement, the scanning speed slows.
Ratio
Optics scan speed
Calculation
129(141)%
264(241) mm/sec.
340/1.29
100%
340 mm/sec.
340/1.00
65(71)%
523(479) mm/sec.
340/0.65
340 mm/sec FP-7750 Process speed
A
B
C
Lens
Paper
Lens
drum
c) Setting exposure
• Using the original slit exposure method, the exposure on the drum is
changed during zoom, but, it is corrected by adjusting the quantity of light.
• In enlargement, the light reduces the illuminance on the drum surface, and
the area is extended. In reduction, the illuminace on the drum surface
increases and the area reduces with the constant exposure on the drum
surface.
a
b
c
(Reduction)
Lens
(Enlargement)
Original
Slit
glass
glass
Lens
Drum
Drum
Sub Assemblies
3-29
d) Lighting blacking prevention lamp (black belt at both ends)
• In reduction, both ends of drum surface are not lit by the exposure lamp,
and these areas forms black, which is increase in toner consumption.
The both ends of blacking prevention lamp (LED) are selectively lit to
prevent blacking.
• The blacking prevention lamp lights when the optics system scans with
normal rotation and the exposure lamp turns on, and the lighting area varys
depending on the copy ratio. In the return of optics system, the blacking
prevention lamp always turns ON.
a
a
b
b
c
c
d
d
184
202
232
238
202
232
238
Platen cover
Original
Exposure lamp
Drum
Lens
Ratio
Length of LED array OFF
0.61
184 mm
0.65
202 mm
0.77
232 mm
0.79
238 mm
Ratio
Length of LED array OFF
0.61
184 mm
0.71
214 mm
0.82
249 mm
0.87
263 mm
(For North America)
(Except North America)
3-30
4)
Optics system initialization
• The positioning of the optics system is determined by turning on/off the optics
home position sensor (which is mounted at left side of copier frame), with
the position detecting plate which is installed on the full-speed unit.
• When turning ON power, the full-speed unit moves toward the optics home
position sensor and stops where the position detecting plate shuts off the
optics home position sensor. (Copy start position)
When the optics home position sensor has detected the position detecting
plate, after the full-speed unit moves to the opposite direction of the optics
home position sensor, it returns to the direction of optics home position
sensor again, and stops and wait where the position detecting plate shuts off
the optics home position sensor.
Full-speed unit
Sensor
Half-speed unit
Lens
4/5 mirror
Drum
Full-speed unit position
detecting plate
detecting plate
Sub Assemblies
3-31
5)
Optics system operation when print key is pressed
a) Pre-scanning
• Pressing the print key lights the exposure lamp and starts the main motor.
• For automatic exposure mode, After a specified time, the optics motor
rotates, and the optics unit (full-speed unit and half-speed unit) start to
scan. With the movement of approx. 15cm, the optics reverse.
• During this return operation, AE sensor reads the background density of the
original to be copied and the value is set in the CPU. Comparing this with
the standard density mark, the exposure voltage and the development bias
voltage suitable to the original to be copied are set.
• When the optics home position sensor detects the optics unit, the optics
unit stops and copying starts in accordance with the set process conditions.
b) Copying
• The optics home position sensor turns on by the movement of the optics
unit (passing through the light). At a predetermined time, the timing roller
clutch turns on to feed the paper into the machine.
• After the optics unit scans the paper , the optics motor rotates in reverse at
full speed, the exposure lamp turns off and the optics unit returns to the
optics home postion.
• A stepping motor is used for the optics motor. The driving power is controlled
by a pulse provided by the CPU control P.C.B.
Auto original density control operation (Pre-scan)
40mm
AE sensor (Auto
original density
sensor)
original density
sensor)
Sensor
mark
mark
Platen
glass
glass
Lens
Original
No. 2
mirror
mirror
No. 3
mirror
mirror
AE sensor
Original
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