Canon LBP-1000 Service Manual page 63

As shown in Figure 2-4-8, 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 magnetite and a resin binder, and is held to the cylin-
der by magnetic attraction. The toner is an insulator, and acquires a negative charge from fric-
tion 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.
+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.
(1600Vp-p) varies with the DC bias voltage. The change in the DC bias changes the potential
difference between the cylinder and drum so the density of the print can be adjusted. The
adjustment is made through a command from the video controller.
This printer has a stirring mechanism in the cartridge to ensure that toner is applied smooth-
ly to the cylinder.
3. Transfer block
In this block, the toner image is transferred from the drum surface to the paper.
Step 4: Transfer
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)
The center voltage of the AC bias
Paper
CHAPTER 2
2 - 29