Sharp FO IS125N - B/W Laser - All-in-One Service Manual page 77

7.5. Functions and operations of major parts
Optical unit(LSU)
2
Toner
3
1 Developing roller
2 Doctor
3 Toner supply roller
4 Transfer roller
7.5.1 OPC drum unit
The OPC drum is charged and latent electrostatic images are formed
on it and developed into visible toner images.
a. OPC drum
Latent electrostatic images are formed and developed into toner
images on the OPC drum.
Organic Photo Conductor is used. The OPC surface is charged nega-
tively by the main charger brush.
When the OPC is exposed to laser beam, the electric resistance of the
exposed section falls and electric charge is generated in the OPC. As
a result, electric charge on the OPC surface is removed. This principle
is used to form latent electrostatic images.
OPC layer
b. Main charger brush
The main charger brush charges the OPC drum surface. It is com-
posed of brush fiber, and is in the shape of a roller. A high voltage of
AC 760V (P-P) and DC-950V are applied to charge the brush.
The main charger brush is in contact with the OPC drum. BY applying
electric charge to the OPC drum, the OPC drum is charged to about
DC-900V.
Paper
1 6 4
Fig. 10
5 Separation sheet
6 OPC drum
7 Main charger brush
CTL (Charge transfer layer)
CGL (Charge generation layer)
Aluminum layer
Fig. 11
7.5.2 Developing unit
Latent electrostatic images formed by laser beam on the OPC drum
are developed to visible images by the developing unit. Toner is filled
in the developing unit.
a. Developing roller
The developing roller is made of silicon and has a high electric resis-
tance. It is flexible and is in close contact with the OPC drum. Toner on
the developing roller is attached to latent electrostatic images on the
7
OPC drum to form visible images on the OPC drum.
A voltage of DC-220V is applied the developing roller.
5
b. Doctor
The doctor is in close contact with the developing roller. It adjusts toner
quantity on the developer roller surface.
The doctor is made of conductive material.
c. Toner supply roller
Toner is supplied to the developing roller by the sponge roller which is
connected to the developing roller.
7.5.3 Transfer charger roller
The transfer charger roller is made of urethane and has a high electric
resistance. It is flexible and is in close contact with the OPC drum.
A high voltage of AC 760V (P-P) and DC +3600V are applied to
charge.
It positively charges paper transported from the paper feed section,
which transfers negatively charged toner on the OPC drum onto the
paper.
7.5.4 Separation sheet
This sheet is connected to the drum ground. It discharges paper which
was positively charged in the transfer section to reduce the potential
difference with the OPC drum to reduce static electricity between the
paper and the OPC drum, thus facilitating separation of paper.
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FO-IS125N