Details Of Copying Process - Toshiba DP1600 Service Manual

3.2 Details of Copying Process

(1) Photosensitive Drum
The photosensitive drum has two layers, an
outer and an inner layer. The outer layer is a
photoconductive layer that uses an organic pho-
toconductive carrier (OPC), and the inner layer
is an aluminum, conductive cylindrical drum.
The resistance held by the drum material
changes (increases, decreases) according to
the strength of the light incident to the photo-
conductive carrier.
(Example)
• When incident light is strong, the resistance
decreases (photosensitive drum becomes a
carrier).
• When incident light is weak, the resistance
increases (photosensitive drum becomes an
insulator).
[Formation of Electrostatic Latent Image]
The minus potential on the drum surface corre-
sponding to black areas of the original are re-
moved by the charging, scanning, printing and
discharging processes (described later), and the
minus potential remains on areas correspond-
ing to white areas of the original.
The image on the drum resulting from this mi-
nus potential is called a "latent image" as it can-
not be seen directly by the human eye.
(2) Charging
"Charging" is the process of uniformly applying
a charge to the surface of the photosensitive
drum.
The minus corona discharge of the charger wire
is controlled by the grid to charge the drum sur-
face to a uniform minus potential.
The drum surface potential is determined by the
potential of the grid, and the grid is determined
by the grid control circuit inside the transformer.
1600/2000/2500 COPYING PROCESS
Fig. 3-2-1 Structure of the photosensitive drum
0
– 500
– 1000 Dis- Charg-
charge ing
process process
Electric potential of the photosensitive drum
Main charger
Transformer
3 - 2
Photoconductive layer
Base
Time (t)
Black area of original
White area of original
Fig. 3-2-2
Rotation of drum
Grid control circuit
Fig. 3-2-3
December 2000 © TOSHIBA TEC
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