Dual Beam Writing - Gestetner B147 Service Manual

6.6.4 DUAL BEAM WRITING

Dual Beam Mechanism
The LD unit for black has two laser diodes. Each face of the polygon mirror writes
two main scan lines. This only happens for black and white printing.
Laser Beam Pitch Change Mechanism
[A]
[B]
[C]
There is a spring [A] at the front end of the black LD unit [E], and there is a
positioning motor [D] at the right end. The spring pushes the unit clockwise, while
the motor pushes it counterclockwise. These two components drive the unit to one
of the following three positions:
• 600-dpi position
• 1,200-dpi position [ ]
• Home position
Before it is driven to the 600-dpi position or the 1,200-dpi position, the black LD unit
is set to its home position. When driven from one position to another, the unit goes
as follows:
• 600-dpi position → Home position →
• 1,200-dpi position → Home position →
The home position is detected by the home position sensor [B]. When the unit is in
its home position, the actuator [C] is out of the sensor. The 600-dpi and 1,200-dpi
positions are determined by the distance from the home position. The distance is
calculated from the operation time of the LD positioning motor.
SM
1
2
3
[D]
B146D525.WMF
[ ]
[ ]
6-41
LASER EXPOSURE
[E]
1,200-dpi position
600-dpi position
B147/B149/B190
B146D524.WMF