Xerox DocuColor 12/DCCS50, Service Manual

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10-112 DocuColor 12/DCCS50
Charging
Reissue
Principles of Operation
Charging
The surface of the rotating Photoreceptor Drum receives negative charge VH from the Charge
Corotron in preparation to the image exposure from the Laser. The level of this negative charge
on the Drum is measured by the Electrostatic Voltmeter (
ESV ) and is shown in Table 1 . Note
that the charge voltage varies with the temperature and humidity as measured by the
machine’s Environmental Sensor (ENV). The charge voltage will also decrease after the first
50,000 cycles of the Photoreceptor Drum at a ratio of -1 V per 10,000 cycles.
The laser beam from the ROS writes an image onto the negatively charged Photoreceptor
Drum. When the laser writes the image data to the Photoreceptor Drum, the voltage on the
part of the Drum containing the image is discharged from VH to VL, also shown in Table 2.
(The background or non-image areas remain at VH.) This “black writing” technique creates the
latent image that the negatively charged developer will be attracted to, developing this image
area.
Note that the level of Vh varies with ambient temperature and humidity. Temperature and
humidity are measured by a dedicated sensor which is connected to the IOT Drive and Control
PWBAs. The IOT CPU PWBA uses these parameters as one input in adjusting the output volt-
age and current of the Charge Corotron Grid/Preclean Corotron High Voltage Power Supply
(CC/PCC-HVPS) (PSHV-L2).
Charge Corotron
The Charge Corotron is replaced every time the customer replaces the Photoreceptor Drum (a
CRU). The Charge Corotron can also be replaced by the service engineer (an Engineer
Replaceable Unit, ERU) This unit consists of a single 30 micron diameter wire and a metal
screen grid positioned between the Corotron Wire and the Drum.
The Charge Corotron provides a constant current for charging the surface of the Photoreceptor
Drum with a uniform negative potential. This bias voltage on the Corotron Grid determines the
potential to which the drum is charged. As shown in
Figure 2 , this bias voltage and current is
supplied by the CC/PCC-HVPS (PSHV-L2). The power supply output voltage can vary
between -300 VDC and -1000 VDC. The output current is a constant 700 microamperes. The
IOT Drive provides the +24 VDC power source to the power supply. It also controls and moni-
tors the output voltage.
Figure 2 shows the location of the CC/PCC-HVPS (PSHV-L2)
The Corotron Grid is coated with a neutralizing agent (catalyst) so that it cannot give off any
substance that would be detrimental to the life of the Photoreceptor.
Figure 1 Charging Circuit
Table 1 Photoreceptor Drum Voltages
Zone Temperature Humidity VH VL VBias
A 28 ° C 85% 623 300 510
B 22 ° C 55% 700
(for 0-50K cycles,
then decreases by -1
V/10K cycles) 300 560
C 10 ° C 20% 710 300 656
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