B. Generating the BD Signal
A laser ON signal (horizontal sync signal) is needed when directing a laser beam to the photosensitive
drum, and the laser beam detection signal (BD) is used to generate such a start signal.
The GP215/GP200 is designed to detect the edge of copy paper which has been re-picked up for two-
sided/overlay copying to measure the discrepancy, if any, toward the rear/front.
Using the result of this measurement, the laser ON timing is varied in relation to the BD signal to ensure
that the image will be at a specific position on every copy. For details on how the end of copy paper is
detected, see p. 3-114.
3–53
COPYRIGHT © 1996 CANON INC. CANON GP215/200 REV.0 JULY 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)
3. OPERATIONS AND TIMING
Figure 3-402
Laser scanner unit
Laser
BD mirror
Polygon mirror (6-facet)
Imaging lens
BD detection PCB
Photosensitive drum
Front
Rear
Image area
Image area
Image area when
shifted to the rear
Laser ON
Laser OFF
Laser ON
Laser OFF
Copy paper
Copy paper shifted
to the rear
Horizontal registration
sensor
Horizontal registation
sensor detecting
copy paper shifted to the rear
