Generating The Bd Signal - Canon GP405 Service Manual

II. GENERATING THE BD SIGNAL
The laser beam must be led to the photosensitive drum at a specific time, requiring a laser
emission start (horizontal sync) signal, and the BD (beam detect) signal is used to generate such a
signal.
The machine checks the edge of copy paper being fed after re-pick up (for a double-sided copy)
to find out the degree of displacement to the rear/front. It uses the result of measurement to vary the
laser emission timing (determined in reference to the BD signal) so as to ensure that a specific
image is always in a specific position of copy paper.
BD detection PCB
BD mirror
Laser ON
Laser OFF
Laser ON
Laser OFF
COPYRIGHT © 1999 CANON INC. CANON 405/335 REV.0 JAN. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
Laser scanner unit
(front)
Image area
Image area shifted to the rear
Image area
CHAPTER 5 LASER EXPOSURE SYSTEM
Polygon mirror (8-facet)
Collimating lens
Figure 5-200
Laser
Photosensitive drum
(rear)
Copy paper
Copy paper shifted to the rear
Horizontal registration sensor
Horizontal registration
sensor detecting copy
paper shifted to the rear
5-3