Canon PC300 Service Manual page 22

' COPYING PROCESS «
5. Latent Static Image
Formation
The latent static image formation block
consists of two steps: primary charging and
image exposure. At the end of the block,
negative charges are left on the surface of
the photosensitive drum corresponding to
the black areas of the document, while neg-
ative charges are removed from the surface
corresponding to the white areas.
Since the images created by electric
charges are not visible to the human eye,
they are.called latent static images.
Time (t) —->
Light area
=
ss -500
Cc
2
3|
g 71000) Primary
charging Image exposure
(step 1) (step 2)
Figure 2-4
Step 1 Primary Charging
= DC bias
Figure 2-5
2-2 COPYRIGHT © 1904 CANONINC.
The surface of the photosensitive drum
is charged to a uniform negative potential to
prepare for the formation of latent static
images.
The copier uses its primary charging
roller to charge the photosensitive drum
directly.
The primary charging roller is construct-
ed of conductive rubber to which a DC bias
as well as an AC bias is applied.
The AC bias serves to maintain the sur-
face potential of the photosensitive drum
uniform, eliminating the necessity for pre-
exposure.
The DC bias applied at the same time as
the AC bias helps produce primary potential.
Note:
Compared to conventional corona charg-
ing, direct charging requires less applica-
tion voltage and hardly generates ozone.
CANON PC300/320/325, FC210/290 REV.0 JULY 1994 PRINTED IN JAPAN (IMPRIME AU JAPON)