Sharp AM-900 Service Manual page 60

AM-900U
8.6. Image forming operation
STEP 1 (Cleaning, Charging): Residual toner the OPC drum is
The main charger is a rotating brush roller.
The main charger removes residual toner from the OPC drum by its
rotating sweeping action and causes it to stick to the brush.
At the same time, a high voltage of -950V is applied to the main
charger roller to generate a discharge of electricity between the roller
and the OPC drum, generating positive and negative charges. The
negative charges are attracted to the OPC drum, and evenly distrib-
uted on the OPC drum. (The OPC drum surface is evenly charged.)
Residual
toner
AC760V
(P-P)
Aluminum layer (drum base)
CTL
CGL
DC-950V
Fig. 12
stirred and negative charges are
scattered evenly on the OPC drum.
(The OPC drum surface is evenly
charged.)
Main
charger
brush
OPC drum
STEP 2 (Exposure): Laser beam scanning light corresponding to
the print data is radiated on the OPC drum.
Positive and negative charges are generated in the OPC drum CGL
exposed with the laser beam.
Positive charges generated in the CGL are attracted toward the OPC
drum surface (negative charges), and negative charges toward the
aluminum layer (positive charges).
Therefore, the positive and negative charges neutralize each other in
the laser-exposed area of the OPC drum surface and the aluminum
layer, decreasing the potential of the OPC drum surface.
The area which is not exposed to laser beam has no change, and the
OPC drum surface remains negatively charged to keep a high poten-
tial. As a result, latent electrostatic images are formed on the OPC
drum.
Laser beam
Exposed area
CTL
CGL
Aluminum layer
(Drum base)
CTL
CGL
Aluminum layer
(Drum base)
3 – 13
Non-exposed area
Fig. 13