COPYRIGHT © 1999 CANON INC. CANON imageRUNNER 400/330 REV.0 JAN. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
5-3
CHAPTER 5 LASER EXPOSURE SYSTEM
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.
Figure 5-200
BD detection PCB
BD mirror
Laser
Collimating lens
Polygon mirror (8-facet)
Photosensitive drum
Laser scanner unit
Image area
Image area shifted to the rear
Copy paper
Copy paper shifted to the rear
(front)
(rear)
Horizontal registration sensor
Laser ON
Laser OFF
Laser ON
Laser OFF
Image area
Horizontal registration
sensor detecting copy
paper shifted to the rear