AL-1611/AL-1622
OPERATIONAL DESCRIPTIONS
6 – 5
(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
eliminate 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 aluminum layer are moved and neu-
tralized with negative charges on the OPC layer.
a. Charge by the Scorotron charger
<1> Function
The Scorotron charger functions to maintain the surface potential of the
drum even at all times which. It is used to control the surface potential
regardless of the charge characteristics of the photoconductor.
<2> 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 cur-
rent on the photoconductor. 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 photoconductor potential can be maintained
at a stable level.
b. Process controlling
<1> Function
The print pattern signal is converted into an invisible image by the semi-
conductor 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
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.
<2> 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 developer unit.
<3> 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.)
2) Developing bias (-400V) is applied when the photoconductor poten-
tial 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.
<4> Stop
The reverse sequence takes place.
c. Retaining developing bias at an abnormal occurrence
<1> 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
carrier makes deposits on the drum because of strong static power. To
prevent this, the machine incorporates a function to retain the develop-
ing bias for a certain period and decrease the voltage gradually against
possible power loss.
<2> 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.
Therefore, carrier will not make a deposit on the drum surface.
4. LASER UNIT
The image data sent from the MCU (image process circuit) is sent to the
LSU (laser unit), where it is converted into laser beams.
A. Basic structure
The LSU unit is the writing section of the digital optical system.The
semiconductor laser is used as the light source, and images are formed
on the OPC drum by the polygon mirror and fq lens, etc.
The laser beams are passed through the collimator lens, the cylindrical
lens, the polygon mirror, the fq lens, and the mirror to form images on
the OPC drum in the main scanning direction. The laser emitting PWB
is provided with the APC (auto power control) in order to eliminate fluc-
tuations in the laser power. The BD PWB works for measurement of the
laser writing start point.
Semiconductor laser
0
START
STOP
Print potentioal
Toner attract
potential
2)
3)
1)
Low
4)
High
Drum potential
Developing bias
Time
1
Semiconductor laser
Generates laser beams
2
Collimator lens
Converges laser beams in parallel
3
Polygon mirror,
polygon motor
Reflects laser beams at a constant rpm
4
BD (Mirror, lens, PWB) Detects start timing of laser scanning
5
f
θ
lens
Converges laser beams at a spot on
the drum.
Makes the laser scanning speeds at
both ends of the drum same as each
other. (Refer to the figure below.)
6
Laser emitting PWB
Emits laser beams according to the
image data.
6
5
2
1
3
4
