Sharp AL-1551 (serv.man4) Service Manual ▷ View online
AL-1551 COPY PROCESS 6-2
2. Outline of print process
This printer is a non-impact printer that uses a semiconductor laser and
electrostatic print process. This printer uses an OPC (Organic Photo
Conductor) for its photoconductive material.
Conductor) for its photoconductive material.
First, voltage from the main corona unit charges the drum surface and a
latent image is formed on the drum surface using a laser beam. This
latent image forms a visible image on the drum surface when toner is
latent image forms a visible image on the drum surface when toner is
applied. The toner image is then transferred onto the print paper by the
transfer corona and fused on the print paper in the fusing section with a
combination of heat and pressure.
combination of heat and pressure.
Step-1: Charge
Step-2: Exposure
Step-2: Exposure
*
Latent image is formed on the drum.
Step-3: Developing
Latent image formed on the drum is then changed into visible
image with toner.
Step-4: Transfer
The visible image (toner image) on the drum is transferred onto
the print paper.
Step-5: Cleaning
Residual toner on the drum surface is removed and collected by
the cleaning blade.
Step-6: Optical discharge
Residual charge on the drum surface is removed, by
semiconductor laser beam.
3. Actual print process
Step-1: DC charge
A uniform negative charge is applied over the OPC drum surface by the
main charging unit. Stable potential is maintained by means of the
Scorotron charger.
Scorotron charger.
Positive charges are generated in the aluminum layer.
Step-2: Exposure (laser beam, lens)
A Laser beam is generated from the semiconductor laser and controlled
by the print pattern signal. The laser writes onto the OPC drum surface
by the print pattern signal. The laser writes onto the OPC drum surface
through the polygon mirrors and lens. The resistance of the OPC layer
decreases for an area exposed by the laser beam (corresponding to the
print pattern signal). The beam neutralizes the negative charge. An
print pattern signal). The beam neutralizes the negative charge. An
electrostatic latent image is formed on the drum surface.
About
DC5.5KV
( 580V/ 400V)
OPC layer
Pigment
layer
layer
Aluminum
drum
drum
OPC layer
Pigment
layer
layer
Aluminum
layer
layer
Drum surface charge
sfter the exposure
sfter the exposure
Non-image area
Image area
Semiconductor laser
Exposure
(semiconductor laser)
(semiconductor laser)
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AL-1551 COPY PROCESS 6-3
Step-3: Developing (DC bias)
A bias potential is applied to the MG roller in the two component
magnetic brush developing method, and the toner is charged negative
magnetic brush developing method, and the toner is charged negative
through friction with the carrier.
Non-image area of the drum surface charged with negative potential
repel the toner, whereas the laser exposed portions where no negative
repel the toner, whereas the laser exposed portions where no negative
charges exist, attract the toner. As a result, a visible image appears on
the drum surface.
Toner is attracted over the shadowed area because of the developing
bias.
Step-4: Transfer
The visible image on the drum surface is transferred onto the print paper
by applying a positive charge from the transfer corona to the backside of
by applying a positive charge from the transfer corona to the backside of
the print paper.
Step-5: Separation
Since the print paper is charged positively by the transfer corona, it is
discharged by the separation corona. The separation corona is
connected to ground.
connected to ground.
Step-6: Cleaning
Toner remaining on the drum is removed and collected by the cleaning
blade. It is transported to the waste toner collecting section in the
blade. It is transported to the waste toner collecting section in the
cleaning unit by the waste toner transport roller.
S
N
N
:Carrier (Magnetized particle)
:Toner (Charge negative by friction)
(N) (S) Permanent magnet
:Toner (Charge negative by friction)
(N) (S) Permanent magnet
(provided in three locations)
MG roller
DC
400V 8V
About DC 5.2kV
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AL-1551 COPY PROCESS 6-4
Step-7: Optical discharge (Semiconductor laser)
Before the drum rotation is stopped, the semiconductor laser is radiated
onto the drum to reduce the electrical resistance in the OPC layer and
onto the drum to reduce the electrical resistance in the OPC layer and
elimate residual charge, providing a uniform state to the drum surface for
the next page to be printed.
When the electrical resistance is reduced, positive charges on the
When the electrical resistance is reduced, positive charges on the
aluminum layer are moved and neutralized with negative charges on the
OPC layer.
Charge by the Scorotron charger
Function
The Scorotron charger functions to maintain uniform surface potential on
the drum at all times, It control the surface potential regardless of the
the drum at all times, It control the surface potential regardless of the
charge characteristics of the photoconductor.
Basic function
A screen grid is placed between the saw tooth and the photoconductor. A
stable voltage is added to the screen grid to maintain the corona current
on the photoconductor.
As the photoconductor is charged by the saw tooth from the main corona
As the photoconductor is charged by the saw tooth from the main corona
unit, the surface potential increases. This increases the current flowing
through the screen grid. When the photoconductor potential nears the
grid potential, the current turns to flow to the grid so that the
grid potential, the current turns to flow to the grid so that the
photoconductor potential can be maintained at a stable level.
Process controlling
Function
The print pattern signal is converted into an invisible image by the
semiconductor laser using negative to positive (reversible) developing
semiconductor laser using negative to positive (reversible) developing
method. Therefore, if the developing bias is added before the drum is
charged, toner is attracted onto the drum. If the developing bias is not
added when the drum is charged, the carrier is attracted to the drum
added when the drum is charged, the carrier is attracted to the drum
because of the strong electrostatic force of the drum.
To avoid this, the process is controlled by adjusting the drum potential
and the grid potential of the Scorotron charger.
and the grid potential of the Scorotron charger.
Basic function
Voltage added to the screen grid can be selected, high and low. To make
it easily understood, the figure below shows voltage transition at the
it easily understood, the figure below shows voltage transition at the
developer unit.
Start
1) Because the grid potential is at a low level, the drum potential is at
about -400V. (Carrier may not be attracted though the carrier is
pulled towards the drum by the electrostatic force of -400V.
pulled towards the drum by the electrostatic force of -400V.
2) Developing bias (-400V) is applied when the photoconductor
potential is switched from LOW to HIGH.
3) Once developing bias (-400V) is applied and the photo conductor
potential rises to HIGH, toner will not be attracted to the drum.
Stop
The reverse sequence takes place.
Retaining developing bias at an abnormal occurrence
Retaining developing bias at an abnormal occurrence
Function
The developing bias will be lost if the power supply was removed during
print process. In this event, the drum potential slightly abates and the
print process. In this event, the drum potential slightly abates and the
carrier makes deposits on the drum because of strong static power. To
prevent this, the machine incorporates a function to retain the developing
bias for a certain period and decrease the voltage gradually against
bias for a certain period and decrease the voltage gradually against
possible power loss.
Basic function
Normally, the developing bias voltage is retained for a certain time before
the drum comes to a complete stop if the machine should stop before
completing the normal print cycle. The developing bias can be added
before resuming the operation after an abnormal interruption. Therfore,
before resuming the operation after an abnormal interruption. Therfore,
carrier will not make a deposit on the drum surface.
Semiconductor laser
0
START
STOP
Print potentioal
Toner attract
potential
2)
3)
1)
Low
4)
High
Drum potential
Developing bias
Time
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AL-1551 OPERATIONAL DESCRIPTIONS 7-1
[7] OPERATIONAL DESCRIPTIONS
1. Outline of operation
The outline of operation is described referring to the basic configuration.
(Basic configuration)
(Outline of copy operation)
Setting conditions
1) Set copy conditions such as the copy quantity and the copy density with the operation section, and press the COPY button. The information on copy
conditions is sent to the MCU.
Image scanning
2) When the COPY button is pressed, the scanner section starts scanning of images.
The light from the copy lamp is reflected by the document and passed through the lens to the CCD.
Photo signal/Electric signal conversion
3) The image is converted into electrical signals by the CCD circuit and passed to the MCU.
Image process
Image process
4) The document image signal sent from the CCD circuit is processed under the revised conditions and sent to the LSU (laser unit) as print data.
Electric signal/Photo signal (laser beam) conversion
5) The LSU emits laser beams according to the print data.
(Electrical signals are converted into photo signals.)
6) The laser beams are radiated through the polygon mirror and various lenses to the OPC drum.
Printing
7) Electrostatic latent images are formed on the OPC drum according to the laser beams, and the latent images are developed to be visible
images(toner images).
8) Meanwhile the paper is fed to the image transfer section in synchronization with the image lead edge.
9) After the transfer of toner images onto the paper, the toner images are fused to the paper by the fusing section. The copied paper is discharged
onto the exit tray.
Operation
section
Scanner section
CCD
MCU (Main control/image process section)
PCL control
PCL I / F
PC
Laser beam
Paper exit
Fusing section
Paper transport section
Manual paper
feed section
Cassette paper
feed section
Printer section
LSU (Laser unit)
Laser diode, Polygon mirror lens
Laser diode, Polygon mirror lens
Process section
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