Canon LASER SHOT LBP-1210, Service Manual

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Step 3: Developing
Figure 2-5-8
Note: Charges in the exposed areas of the photosensitive drum are shown as positive in the
figure, even though they are actually negative. It means that the photosensitive drum
potential is higher as compared with that of the cylinder.
As shown in Figure 2-5-8, the developing unit consists of the developing cylinder and rubber
blade. The developing cylinder consists of the fixed magnet and cylinder which rotates around
the magnet.
The single-component toner consists of magnetic substances and a resin binder, and is held
to the cylinder by magnetic attraction. The toner is an insulator, and acquires a negative charge
from friction of the rotating 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 (higher on the drum) projects the toner par-
ticles to them.
This is called toner projection, making the latent image on the drum visible.
Figure 2-5-9
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
CHAPTER 2
2 - 39
+V
-V
Voltage (V)
Developing cylinder
surface potential
Drum surface potential
(
Exposed area
)
Time (t)
DC bias
Drum surface potential
(
Unexposed area
)
Stirrer
Blade
Developing cylinder
Photosensitive
drum
AC bias
DC bias
Cylinder
Magnet