Sharp AL-840 (serv.man3) Service Manual ▷ View online
b. Major parts functions and operations
1
Developing
roller
roller
5
Toner seal
9
Discharge
brush
brush
2
Doctor
6
Transfer
charger roller
charger roller
10
Main charger
brush
brush
3
Toner stirring
plate
plate
7
Separation
electrode
electrode
11
Toner seal
4
Toner supply
roller
roller
8
Phot conductor
drum
drum
12
Discharge
(Earth) sheet
(Earth) sheet
<1> Photoconductor drum unit
The photoconductor surface is charged and latent electrostatic im-
ages are formed, then visible images are formed with toner.
ages are formed, then visible images are formed with toner.
1) Photoconductor drum
Latent electrostatic images are formed and visible images are formed
with toner.
with toner.
An OPC (Organic Photo Conductor) drum is used. The OPC drum
surface is negatively charged by the main charger brush.
surface is negatively charged by the main charger brush.
When laser beams are radiated on the OPC drum, the electric resis-
tance at the radiated area is reduced to generate an electric charge
inside the OPC drum. As a result, the charges on the OPC drum are
removed. This process is used to form latent electrostatic images.
tance at the radiated area is reduced to generate an electric charge
inside the OPC drum. As a result, the charges on the OPC drum are
removed. This process is used to form latent electrostatic images.
2) Main charger brush
The main charger brush charges the OPC drum surface. It is com-
posed of brush textures and of a roller shape.
posed of brush textures and of a roller shape.
A high voltage of AC 600V (P-P) is applied to DC-850V to charge the
brush.
brush.
The main charger brush is in contact with the OPC drum. By supply-
ing electric charges to the OPC drum, the OPC drum is charged to
about –850V.
ing electric charges to the OPC drum, the OPC drum is charged to
about –850V.
3) Toner seal
The OPC drum has two toner seals. The toner seals are used to
prevent residual toner on the OPC drum from leaking outside.
prevent residual toner on the OPC drum from leaking outside.
<2> Developing unit
Visible images are formed with toner over the latent electrostatic
images formed on the OPC drum surface. Toner is filled in the
developing unit.
images formed on the OPC drum surface. Toner is filled in the
developing unit.
1) Developing roller
The developing roller is made of urethane and it has considerably
high electrical resistance. It is flexible and pressed onto the OPC
drum. Toner is attached to the latent electrostatic images on the OPC
drum to make visible images. A voltage of DC-310V/+200V is applied
to the developing roller. A voltage of –310V is applied when develop-
ing. A voltage of +220V is applied when cleaning.
high electrical resistance. It is flexible and pressed onto the OPC
drum. Toner is attached to the latent electrostatic images on the OPC
drum to make visible images. A voltage of DC-310V/+200V is applied
to the developing roller. A voltage of –310V is applied when develop-
ing. A voltage of +220V is applied when cleaning.
2) Doctor
The doctor is pressed onto the developing roller. It adjust the toner
quantity on the developing roller surface.
quantity on the developing roller surface.
The doctor is made of a conductive material.
3) Toner supply roller
The toner supply roller transports toner to the developing roller.
4) Toner stirring plate
The toner stirring plate stirs toner in the developing unit to transport
toner to the developing roller smoothly.
toner to the developing roller smoothly.
5) Toner seal
The toner seal prevents toner from leaking outside the developing
unit.
unit.
6) Discharge (Earth) sheet
The discharge sheet maintains the developing roller surface potential
at a constant level.
at a constant level.
<3> Transfer charger roller
The transfer charger roller is made of urethane and its electrical
resistance is considerably high. It is flexible and pressed onto the
OPC drum.
resistance is considerably high. It is flexible and pressed onto the
OPC drum.
A high voltage of AC600V (P-P) is applied to DC +3500V.
Paper transported from the paper feed section is charged positively
and negatively charged toner on the OPC drum are transferred onto
the paper.
and negatively charged toner on the OPC drum are transferred onto
the paper.
During cleaning, a voltage of –850V is applied.
<4> Separation electrode
The separation electrode is connected to the drum earth. This dis-
charges paper charged positively in the transfer section to reduce
potential difference with the OPC drum, reducing electrostatic attrac-
tion power between paper and the OPC drum, facilitating paper
separation.
charges paper charged positively in the transfer section to reduce
potential difference with the OPC drum, reducing electrostatic attrac-
tion power between paper and the OPC drum, facilitating paper
separation.
<5> High voltage unit
The high voltage is made by the invertor system, and is supplied to
the main charger unit, the transfer unit, and the developing roller.
the main charger unit, the transfer unit, and the developing roller.
3)
4)
12)
2)
5)
6)
7)
8)
9)
10)
11)
1)
OPC layer
CTL
(Charge Transfer Layer)
(Charge Transfer Layer)
CGL
(Charge Generation Layer)
(Charge Generation Layer)
Aluminum layer
1 – 20
c. Actual image forming process
Step 1 (Cleaning, charging): Residual toner on the OPC drum is
stirred and negative charges are dis-
tributed evenly on the OPC drum.
(The OPC drum is evenly charged.)
tributed evenly on the OPC drum.
(The OPC drum is evenly charged.)
The main charger brush is of roller shape and is rotating.
The main charger brush stirrs residual toner and paper dust on the
OPC drum.
OPC drum.
At the same time, a high voltage of AC 600V (P-P) is applied to DC
–850V and applied to the main charger brush to make electric dis-
charge between the roller and the OPC drum to form positive and
negative charges. The negative charges are attracted to the OPC
drum which is positively charged. And negative charges are evenly
distributed on the OPC drum. (The OPC drum surface is evenly
charged.)
–850V and applied to the main charger brush to make electric dis-
charge between the roller and the OPC drum to form positive and
negative charges. The negative charges are attracted to the OPC
drum which is positively charged. And negative charges are evenly
distributed on the OPC drum. (The OPC drum surface is evenly
charged.)
Residual toner and paper dust stirred by the main charger brush are
distributed evenly on the OPC drum.
distributed evenly on the OPC drum.
Step 2 (Exposure); Laser beam scanning light corresponding to the
print data is radiated onto the OPC drum.
Positive and negative charges are generated in the CGL of the OPC
drum which are radiated with laser beams. The positive charges in
the CGL are moved to the OPC drum surface, and the negative
charges are moved to the aluminum layer.
drum which are radiated with laser beams. The positive charges in
the CGL are moved to the OPC drum surface, and the negative
charges are moved to the aluminum layer.
Therefore, positive and negative charges are neutralized in the OPC
drum exposed with laser beams and the aluminum layer, reducing the
OPC drum surface potential. On the other hand, there is no change in
the area which is not exposed with laser beams. So the OPC drum
surface is kept negatively charged to maintain a high potential. As a
result, latent electrostatic images are formed on the OPC drum.
drum exposed with laser beams and the aluminum layer, reducing the
OPC drum surface potential. On the other hand, there is no change in
the area which is not exposed with laser beams. So the OPC drum
surface is kept negatively charged to maintain a high potential. As a
result, latent electrostatic images are formed on the OPC drum.
AC600V
(P-P)
(P-P)
CTL
CGL
DC-850V
Main charger brush
Residual toner
Aluminum layer
(Drum base)
(Drum base)
OPC drum
CTL
CGL
CTL
CGL
Laser beam
Non-exposure area
Exposure area
Aluminum layer
(Drum base)
(Drum base)
Aluminum layer
(Drum base)
1 – 21
Step 3 (Development): Toner is attached to the latent electrostatic
images formed on the OPC drum.
Toner enters between the developing roller and the doctor, and a thin
layer of toner (a certain fixed amount) is formed on the developing
roller by a pressure applied to the doctor.
layer of toner (a certain fixed amount) is formed on the developing
roller by a pressure applied to the doctor.
Toner is negatively charged by friction when passing between the
developing roller and the doctor.
developing roller and the doctor.
When the OPC drum surface area where there is no charges be-
cause of exposure of laser beams is brought into contact with the
developing roller, toner is moved from the developing roller to the
OPC drum surface. The principle of the process is as follows:
cause of exposure of laser beams is brought into contact with the
developing roller, toner is moved from the developing roller to the
OPC drum surface. The principle of the process is as follows:
A bias voltage of –310V is applied to the developing roller. Toner
which is charged by potential difference between the bias voltage and
the OPC drum surface potential is attracted to the OPC drum surface
(positively charged).
which is charged by potential difference between the bias voltage and
the OPC drum surface potential is attracted to the OPC drum surface
(positively charged).
At that time, the potential of the OPC drum surface where there is no
charge by exposure of laser beams is higher than the developing
roller potential. On the other hand, there are negative charges in the
OPC drum surface area which is not exposed to laser beams. When
that area is brought into contact with the developing roller, if toner is
attached to the OPC drum,. toner is moved to the developing roller
which is in a high potential than the OPC drum.
charge by exposure of laser beams is higher than the developing
roller potential. On the other hand, there are negative charges in the
OPC drum surface area which is not exposed to laser beams. When
that area is brought into contact with the developing roller, if toner is
attached to the OPC drum,. toner is moved to the developing roller
which is in a high potential than the OPC drum.
As a result, unnecessary toner and paper dust on the OPC drum are
collected in the developing unit.
collected in the developing unit.
In this operation, toner is moved from the OPC drum to the develop-
ing roller.
ing roller.
In cleaning operation mode, DC +200V is applied to the developing
roller and cleaning capacity is further increased.
roller and cleaning capacity is further increased.
Step 4 (Transfer): Visible images of toner on the OPC drum are
transferred to the paper.
A high voltage of AC60V (P-P) is applied to DC+350V and applied to
the transfer roller, generating electric discharge between the roller
and the OPC drum, generating positive and negative charges.
the transfer roller, generating electric discharge between the roller
and the OPC drum, generating positive and negative charges.
CGL
CTL
100V
DC
+200V
+200V
DC
-310V
-310V
Developing roller
Doctor
:Toner (Negative charge)
Toner supply roller
OPC drum
Exposure area
(Exposed by
laser beams.)
Non-exposure area
(Not exposed by
laser beams.)
Aluminum layer
(Drum base)
Earth sheet
DC+3500V
DC –850V
AC600V(P-P)
CGL
CTL
OPC drum
Aluminum surface
(Drum base)
(Drum base)
Paper
Transfer roller
1 – 22
The positive charges are attracted to the OPC drum which is nega-
tively charged, and put on the paper transported between the transfer
roller and the OPC drum. The paper, therefore, is charged positively.
tively charged, and put on the paper transported between the transfer
roller and the OPC drum. The paper, therefore, is charged positively.
The negative charged toner on the OPC drum is attracted to the
paper which is positively charged and visible images of toner are
transferred onto the paper.
paper which is positively charged and visible images of toner are
transferred onto the paper.
In the cleaning mode, a voltage of –850 V is applied. If there is toner
on the transfer roller, the toner is attracted to the OPC drum.
on the transfer roller, the toner is attracted to the OPC drum.
Step 5 (Paper separation): Paper is separated from the OPC drum.
An electric force is acting between the paper which is positively
charged in the transfer process and the OPC drum which is negative-
ly charged. Positive charges on the paper are moved to the aluminum
layer through the separation electrode to reduce the potential dif-
ference between the OPC drum and the paper.
charged in the transfer process and the OPC drum which is negative-
ly charged. Positive charges on the paper are moved to the aluminum
layer through the separation electrode to reduce the potential dif-
ference between the OPC drum and the paper.
By this operation, the paper can be easily separated from the OPC
drum.
drum.
Step 6 (Discharging): The drum surface is discharged by the dis-
charge brush to facilitate cleaning. (Residual
toner can be easily collected by the main
charger roller.)
toner can be easily collected by the main
charger roller.)
Step 7 (Cleaning): Residual toner on the OPC drum is removed.
The main charger brush is of roller shape and is rotating.
The main charger brush stirs residual toner and paper dust on the
OPC drum. The residual toner and paper dust are evenly distributed
and put on the OPC drum again to be sent to the developing roller.
OPC drum. The residual toner and paper dust are evenly distributed
and put on the OPC drum again to be sent to the developing roller.
CGL
CTL
Aluminum layer
(Drum base)
Paper
Separation
electrode
Transfer roller
AC600V
(P-P)
(P-P)
CTL
CGL
DC-850V
DC+500V
Main charger brush
Residual toner
Discharge brush
OPC drum
Aluminum layer
(Drum base)
(Drum base)
1 – 23
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