Primary Corona; Preconditioning Exposure; Scanning Exposure; Surface Exposure - Canon LBP-CX Series Service Manual

1) Electrostatic latent image formation stage intro-
duction
This stage has three steps which together produce
a pattern of electrical charges on the drum. At the
end of the stage, negative charges remain in unexposed
areas corresponding to dark areas, and are absent
from areas corresponding to light areas where the
laser beam exposed the drum.
Since this image of negative charges on the drum
is invisible to human eyes, it is called an "electrostatic
latent image".
+100
Time (t)
0 1--~-t~~-Hr--~-1-~~~~~~~~~
Precon-
I
I
I
I
I
/~------
/ Exposed area
,' Unexposed area
dition- Primary Scanning exposure
ing corona
expo-
sure
(Step1) (Step2) (Step3)
Figure 2-14 Surface potentials
Step 1 Preconditioning exposure
Figure 2-15 Preconditioning exposure
Ptior to the primary corona step, the drum
is
preconditioned by exposure to the preconditioning
exposure lamp. This neutralizes any leftover charges
on the drum, preparing the drum for uniform primary
corona exposure.
Reference:
The drum surface potential before the precondi-
tioning exposure lamps turn on is lOOV (because
of the positive corona charge from the transfer
corona assembly). Drum surface potential does not
change even after the preconditioning exposure
lamps turn on because the photoconductive layer
functions as a rectifier. When receiving light from
the preconditioning exposure lamps, the conductive
layer of the drum becomes conductive for negative
charges on the drum and intercepts positive
charges on the drum. That is, positive charges on
the drum neither join with the negative charges
from the aluminum base of the drum nor disap-
pear, but remain as is.
Step 2 Primary corona
Figure 2-16 Primary corona exposure
The primary corona applies a uniform layer of
negative charges over the drum surface. The grid
ensures that the charge is distributed uniformly over
the drum.
Step 3 Scanning exposure
Laser beam
I
l ! !
. . . : : : . . . . . . . . . : · :
~\~r ~1;;-~(.·:
Unexposed area Exposed area
Figure 2-17 Laser beam exposure
COPYRIGHT
©
BY CANON INC. CANON LBP-CX SERIES REY.2 JULY 1985 PRINTED Ill JAPAN (IMPRIME AU JAPOllJ
2-9