Canon LBP-1120 Service Manual page 46

2. Developing Stage
Toner is applied to the electrostatic latent image on photosensitive drum surface to form a visible image. This printer
performs the toner projection development with a single-component toner.
Step 3: Development
Note:
Charges in the exposed areas of the photosensitive drum are shown as positive in this figure, even
though they are actually negative. It means that the photosensitive drum potential is higher as
compared with that of cylinder.
As shown in Figure 2-4-8, the developing unit consists of a developing cylinder and rubber blade. The developing
cylinder consists of a fixed magnet and a cylinder which rotates around the magnet.
The single-component toner mainly consists of magnetite and resin binder and is held to the cylinder by magnetic
attraction. The toner functions as an insulator, and acquires a negative charge by friction due to 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 toner layer of the cylinder
(with negative charges), the potential difference (higher on the drum) projects the toner particles to them.
This is called toner projection development, which develops the latent image on the drum into a visible image.
Stirrer
Blade
Photosensitive
drum
Developing cylinder
Figure 2-4-8
Developing cylinder
surface potential
+V
0
-V
Time (t)
Figure 2-4-9
AC bias
DC bias
Drum surface
potential
(Lightarea)
DC bias
Drum surface
potential
(Darkarea)
CHAPTER 2
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