Canon LBP-2000 Service Manual page 79

CHAPTER 2
1. Latent static image formation block
This block consists of 2 steps, and is used to form a latent static image on the photosensitive
drum.
At the end of the last step of this block, the area of the surface of the photosensitive drum not
exposed by the laser beam (dark area) will retain negative charges, while the area on the surface of
the photosensitive drum exposed by the laser beam (light area) will be free of negative charges.
The drum image formed by negative charges is not visible to the human eye, and is therefore
called a 'latent static image.'
-100
-500
Step 1: primary charging
Primary charging roller
To prepare for the formation of a latent image, the surface of the photosensitive drum is charged
to a uniform, negative potential.
The Printer uses a method of primary charging in which charges are applied directly to the
surface of the photosensitive drum.
The primary charging roller is made of conducting rubber. To ensure that the surface potential
occurring on the photosensitive drum is uniform, an AC bias is applied to the primary charging
roller in addition to an DC bias. The DC bias is controlled so that it varies in keeping with the
developing DC bias.
2 - 40
0
Light area
Primary
Laser beam
charging
exposure (step 2)
(step 1)
Figure 2-4-5
Photosensitive drum
Figure 2-4-6
Time (t)
Dark
area
Primary
Transfer
charging
(step 4)
(step 1)
AC bias
DC bias