Toshiba e-STUDIO 550, Service Manual

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e-STUDIO550/650/810 COPY PROCESS 3 - 2 JUNE 2002 © TOSHIBA TEC
3. 2. Details of Copy Process
(1) Photoconductive drum
The photoconductive drum has two layers, an outer
and an inner layer. The outer layer is a photoconductive
layer made of an organic photoconductive carrier
(OPC). The inner layer is an aluminum conductive
base in a cylindrical form.
The photoconductive carrier has the characteristic
that its electrical resistance changes depending on
the strength of the light exposed.
Example:
· Strong light
촞
Resistance is decreased (works as a conductor.)
· Weak light
촞
Resistance is increased (works as an insulator.)
[Formation of electrostatic latent image]
In the processes of charging, scanning, printing and
discharging described below, negative potential on
the areas of the drum corresponding to black areas
of the original is eliminated, while the areas of the
drum corresponding to white areas remains the
negative charge.
As this image on the drum formed by the negative
potential is invisible, it is called an “electrostatic la-
tent image.”
(2) Charging
Charging is a process of uniformly applying a charge
uniformly to the photoconductive drum surface.
The charger wire produces a negative corona dis-
charge, which is controlled by the grid so that the
drum surface is uniformly charged with negative po-
tential.
The surface potential on the drum is determined by
the grid potential and controlled to a certain value
by the grid control circuit.
Structure of the photoconductive drum (OPC)
Photoconductive layer
0
– 500
– 1000
Time (t)
Surface potential (V)
Black area of original
White area of original
Electric potential on the photoconductive drum
Rotation of drum
Main charger
Grid control circuit
Discharge
transformer
Dis-
charging
process
Charging
process
Aluminum conductive base