Xerox WorkCentre M20 Service Manual page 172

Paper Feeding
When the paper is fed into the set and passes through the actuator of the feed sensor unit,
transistor inside the photo interrupter will turn on, 'nFEED' signal will turn low and inform CPU
that the paper is currently fed into the system. CPU detects this signal and sprays video data
after certain time (related to paper adjustment). If the paper does not hit the feed sensor within
certain time, CPU detects this and informs as "Paper Jam0" (red LED on the OP panel will turn
on)
Paper Exit Sensing
The system detects the paper going out of the set with the exit sensor assembled to the actua-
tor attached to the frame. If CPU does not turn back high a while after the paper hits the exit
sensor, CPU detects this and inform as "Paper Jam2" (red LEDs on the OP panel will turn on).
LSU Circuit
Polygon Motor Unit (actuated by +24V)
The polygon motor inside LSU rotates by the 'PMOTOR' signal. When it reaches the motor
constant velocity section through the initial transient (transient response) section, it sends the
'nLREADY' signal to the CPU.
The 'clock' pin is the pin that receives clock of the required frequency when LSU uses external
CLK as the motor rotational frequency. Currently the external clock circuit is located in the
HVPS and 1686Hz = 6.9083MHz (crystal frequency)212(74HC4060N IC), is used as the rota-
tional frequency of the polygon motor.
Laser Unit (actuated by +5V)
After laser is turned on by 'nLD_ON' signal, it is reflected by 6 mirrors (polygon mirror) attached
to the polygon motor and performs scan in horizontal way.When the laser beam hits the corner
of the polygon mirror, it generates 'nHSYNC' signal (pulse) and the CPU forms the left margin
of the image using this signal (horizontal synchronous signal).
Fan/Solenoid Actuation Circuit
The fan actuation circuit its power using NPN TR. When it receives 'FAN' signal from the CPU.
The TR will turn on to make the voltage supplied to the fan to 24V in order to actuate the fan.
The solenoid is actuated in the same way. When it receives control signal from the CPU, the
solenoid for paper feeding is actuated by switching circuit.
D29(1N4003) diode is applied to the both ends of the output terminal
Q22(KSC1008-Y) from noise pulse induced while the solenoid is de-energized.
PTL Actuation Circuit
PTL actuation circuit switches its power using NPN TR.
Motor Actuation Circuit
Motor actuation circuit is determined while selecting the initial driver IC (provided by the ven-
dor). This system uses TEA3718(U57, U58), A2918(U59)'s motor driver IC. However, the
sensing resistance (R273, R274, R292, R293) and reference resistance (R284, R289, R294,
R295) can vary depending on the motor actuation current value.
General Procedures and Information
GP 16
It receives motor enable signal (2 phase) from CPU and generates bipolar pulse (constant-
current) and sends its output to stepping motor input.
High Voltage Power Supply
Summary
It is the high voltage power supply that has DC+24V/DC+5V (used for the image forming
device in OA digital picture developing method) as the rated inputs. It supplies electrifying volt-
age (MHV), supply voltage (SUPPLY), developing voltage (DEV), blade voltage (BLADE) and
transferring voltage (THV). Each high voltage supply shows the voltage required in each digital
picture process.
Digital Picture Process
Digital picture developing method is widely used by copy machine, laser beam printer and fax
paper. The process is comprised of electrification, exposure, develop, transfer and fixing. Refer
to Figure 1.
to protect
First, in the electrification process, retain constant charge at approximately -900V for the elec-
tric potential on the OPC surface by electrifying OPC drum at approximately -1.4KV through
the electrification roller. The electrified surface of OPC is exposed responding to the video data
by the LSU that received print command due to rotation. The unexposed non-video section will
retain the original electric potential of -900V, but the electric potential of the image area
exposed by LSU will be approximately -180V that it will form the electrostatic latent image. The
surface of the photo-conductive drum where the electrostatic latent image is formed reaches
the developer as the drum rotates. Then the electrostatic latent image formed on the OPC
drum is developed by the toner supplied to the developing roller by supplying roller and it is
transformed into visible image. It is the process to change the afterimage on the OPC drum
surface formed by LSU into visible image by the toner particles.
March 2004
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Figure 1 Process
Work Centre M20 Family