Canon LBP-1260 Service Manual page 56

2. Developing stage
Development places particles of toner onto
the areas of the drum that have been
cleared of charge by the laser beam. This
makes a visible image. This printer uses
the toner projection development method
with a single-component toner.
Step S Development
The charges on the light areas on
Note:
the photosensitive drum are shown
as positive in this figure. Actually
they are negative, but they are
more positive than the developing
cylinder and explanation is
simplified by regarding them as
As shown in Ftgure 2-23. the developing
unit consists of a developing cyhnder and
rubber blade. The developing cylinder
rotates around a tlxed internal magnet.
The single-component toner consists of
magnetite and a resin binder, and is held
to the cylinder by magnetic attraction. The
toner is an insulator, and acquires a
negative charge by friction due to the
rotation of the cylinder.
The areas on the drum that were
exposed to the laser beam have a higher
potential (are less negative) than the
negatively charged toner particles on the
developing cylinder. When these areas
approach the cylinder, the potential
difference projects the toner particles onto
them. This is called toner projectton, and
the latent image on the drum becomes
visible.
Developing cylinder
surface potential
0 _._... ..__. . . .._
- -
. . . .
T i m e t -
An AC bias is applied to the developing
cylinder to help project the toner particles
to the drum surface and improve the
contrast of the printed image. The center
voltage of the AC bias (1600 Vp-p) varies
with the DC bias voltage.
The IMAGE DENSITY ADJUSTMENT
signal [sent from the DC controller to the
high-voltage power supply via the serial
line) changes the DC bias, and thus the
potential difference between the cylinder
and drum. This changes the density of the
print.
This printer has a stirring mechanism to
supply toner in the cartridge smoothly to
the cylinder.
Drum surlace
potential
(exposed area)
. . . J
. . -..
potential
(unexposed area)
2-19