Canon LBP1760P Service Manual page 72

CHAPTER 2
As shown in Figure 2-4-8, the developing unit consists of a fixed magnet, a developing cylinder
and a rubber blade. The developing cylinder rotates around the fixed imagnet.
The single-component toner consists of magnetite and a resin binder, and is held to the cylin-
der by magnetic attraction. The toner functions as an insulator, and is charged negative by the
friction with the rotating cylinder.
The areas on the drum that were exposed to the laser beam have a higher potential 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, which makes the latent image on the drum visible.
+V
0
Voltage (V)
-V
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 changes in the DC bias change the potential differ-
ence between the cylinder and drum so that the density of the print can be adjusted. The adjust-
ment is made through a command from an external device.
This printer has a stirring mechanism in the cartridge to ensure that the toner is applied
smoothly to the cylinder.
3. Transfer block
In this block, the toner image is transferred from the drum surface to the paper.
Step 4: Transfer
2 - 34
Developing cylinder surface potential
Time t
Figure 2-4-9
Photo-
sensitive
drum
Transfer charging roller
Figure 2-4-10
Drum surface potential (exposed area)
DC bias
Drum surface potential (unexposed area)
Paper