e-STUDIO203S/203SD 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 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 neutralized with negative charges
on the OPC layer.
Charge by the Scorotron charger
Function
The Scorotron charger functions to maintain uniform surface poten-
tial on the drum at all times, It control the surface potential regard-
less of the charge characteristics of the photoconductor.
Basic function
A screen grid is placed between the saw tooth and the photocon-
ductor. 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 unit, the surface potential increases. This increases the cur-
rent 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.
Process controlling
Function
The print pattern signal is converted into an invisible image by the
semiconductor laser using negative to positive (reversible) develop-
ing 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 poten-
tial 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 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.
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 photoconduc-
tor 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
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 developing 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. Therefore, carrier will not make a deposit on the drum
surface.
Semiconductor laser
0
START
STOP
Print potential
Toner attract
potential
2)
3)
1)
Low
4)
High
Drum potential
Developing bias
Time
