LASER EXPOSURE
2-46
A229 SM
2.4.4 DUAL BEAM WRITING
This LD unit has two laser diodes; LD1 [A] and LD2 [B] for writing the image. This
means that each face of the polygon mirror writes two main scan lines, and twelve
main scans are produced when the polygon mirror rotates once. The reasons for
this mechanism are as follows.
1) To reduce the polygon motor rotation speed
2) To reduce the noise generated by the polygon motor
3) To reduce the frequency of the image data clock
Two laser beams are transferred to the polygon mirror [C] through collimating lens
[D] and prism [E]. The two laser beams arrive on the drum surface about 2 mm
away from each other in the main scan direction and about 0.06 mm (at 400 dpi) in
the sub scan direction (see the next page).
The reason for the two-mm difference in the main scan direction is so that the
machine can detect a laser synchronization signal for each beam.
A229D524.WMF
[A]
[B]
[C]
[D]
[E]
[D]
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