Development Stage; Ac Bias; Uniform Toner Application - Canon LBP-CX Series Service Manual

The laser beam scans the drum surface. This
causes charges in areas where the laser strikes to be
neutralized.
2) Development stage
Development converts the electrostatic latent
image on the drum surface into a visible image
composed of toner particles. This printer uses the
Toner Projection Development method with a single-
component developer.
Step 4 Development
Cylinder
l
Magnet
--~
DC bias
Figure 2-18 Development
Developing
cylinder
AC
bias
(1600Vp-p)
]
DC
bias
(Variable)
Note: The potential of the exposed areas of the
drum surface is illustrated as positive, though
it is actually slightly negative (as shown in Fig.
2-14). This means that the drum surface
potential is higher compared with the cylinder
potential applied by the DC bias.
As shown in Figure 2-18, the developing assemb-
ly consists of a developing cylinder comprising a fixed
magnet and cylinder rotating around it, plus a blade
of magnetic material. The single-component deve-
loper, "toner", is made of pigment, magnetite and a
resin binder. The toner is an insulating material, and
is charged to a negative potential by friction with the
rotating cylinder.
Magnet Magnet
Figure 2-19 Uniform toner application
A concentrated magnetic field develops between
the blade and the magnet and attracts toner particles
to the edge of the blade where they are held almost
immobile, like a curtain. This "curtain" skims the
toner particles on the cylinder into a thin, uniform
layer.
The laser beam exposed areas on the drum
approach the toner layer on the developing cylinder
with, compared to the developing cylinder, a higher
potential. Toner particles jump and adhere to the
drum surface because of the potential difference
between the cylinder and the drum surface (which is
higher). This process is called "toner projection
development". It converts the electrostatic latent
image into a visible toner image.
Developing cylinder
surface
potential
f
+V Drum surface
potential
t- ----+----.--~1----t--
r
(exposed area)
~o I
--------------
-
...
~ _ _ _ ___ _ _ _ DC bias
level
~
-V
Time
t
Figure 2-20 AC bias
\ _ Drum surface
potential
(Unexposed area)
The AC bias is applied to the developing cylinder
to ensure that toner is projected· smoothly, thus
ensuring sharp contrast in the printed image. The AC
bias is also applied to the blade to prevent irregular
movement of toner between the blade and cylinder.
The central voltage of the AC bias (1600Vp-p)
varies with the DC bias voltage. A print density
adjustment dial is provided on the left panel of the
printer for changing the DC bias (and, as a result,
the potential difference between the developing
cylinder surface and the drum surface).
2-10
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©
BY CANON INC. CANON LBP-CX SERIES HEV.2 JULY 1985 PRINTED IN JAPAN (IMPRIME AU JAPDIO