Generating The Bd Signal - Canon GP215 Service Manual

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.
Laser scanner unit
Laser
BD mirror
Front
Laser ON
Laser OFF
Laser ON
Laser OFF
COPYRIGHT © 1996 CANON INC.
Image area
Image area when
shifted to the rear
Image area
Figure 3-402
CANON GP215/200 REV.0 JULY 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)
3. OPERATIONS AND TIMING
Polygon mirror (6-facet)
Imaging lens
BD detection PCB
Photosensitive drum
Rear
Copy paper
Copy paper shifted
to the rear
Horizontal registration
sensor
Horizontal registation
sensor detecting
copy paper shifted to the rear
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