Details Of Copying Process - Toshiba 8070 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
semi-conductive layer. It uses an organic pho-
toconductive carrier (OPC) material. The inner
layer is Aluminum and is a conductive mate-
rial.
The resistance of the drum's semi-conductive
outer layer changes depending on the strength
of the incident light.
• When the incident light is strong, its resist-
ance decreases and the photosensitive drum
becomes a conductor.
• When the incident light is weak, the resist-
ance increases and the photosensitive drum
becomes an insulator.
Formation of "Latent Image" is performed in the
following manner. The minus (negative) poten-
tial on the drum surface, corresponding to the
black areas of the original document, are re-
moved (neutralized) by light from the scanner/
optics system while the minus charge remains
on the surface of the drum corresponding to
the white areas of the original document. The
resultant image (which the human eye cannot
see) is called "Latent Image."
(2) Charging
Charging is the process of uniformly applying
a charge to the surface of the photosensitive
drum.
The minus (negative) electrostatic charge pro-
duced by the charge corona assembly is ap-
plied to the charge corona "grid." Its purpose is
to produce a uniform minus (negative) electro-
static charge across the photosensitive drum
surface. The Grid Control Circuit that is part of
the Discharge Transformer ultimately deter-
mines the voltage potential on the drum sur-
face. (See illustration)
8070/6570/5570/4580 COPYING PROCESS 8070/6570/5570/4580 COPYING PROCESS
Structure of the photosensitive drum
0
– 500
Discharge
Charging
process
process
– 1000
Electric potential of the photosensitive drum
Main charger
Discharge
transformer
3 - 2A 3 - 2
Photoconductive layer
Base
Time (t)
Black area of original
White area of original
Rotation of drum
Grid control circuit
Mar. 2000 © TOSHIBA TEC Mar. 2000 © TOSHIBA TEC