2.11.2 Methods of process control
OPC potential detection
How OPC potential is detected
The potential of the black and white portions is
measured by the OPC potential sensor by forming an
electrostatic latent image of the potential pattern
attached to the back of the original scale beside the
exposure glass.
During a copying run, the potential pattern, which has
uniform and standard black and white areas (pattern ID :
white: 0.2, black: 1.6), is reflected and exposed onto the
OPC surface. This forms latent images of the black and
white patterns on the OPC. The latent image potential of
each pattern is measured by the potential sensor. The
latent image is erased by the eraser without developing.
The black portion potential is called VD and the white
portion is called VL. Although the latent images of the
black and white patterns are formed together, their
potentials are measured separately. For 10 continuous
copies, the black (VD) or white potential (VL) is
alternately measured.
The residual potential, called VR, is the potential after
removal of charge by the quenching lamp of the OPC
unit. At power on of the machine and after every 500 or
more copies, VR is also measured.
For details of the timing of the VD, VL, and VR
measurements, refer to the process control flow chart.
Potential sensor
There are two potential sensors built in one unit. A
sensor is used for the VD measurement only. B sensor
is used for the VL, VR, VPCC, and AID reference
voltage measurements, and is located at the center of
the OPC.
NOTE
Potential is induced to the electrode in the sensor
by the lines of electric force from the electric charge
on the surface of the photoconductor. The feedback
signal from the potential sensor is transmitted to the
potential control board, where the potential is
measured.
White pattern
Black pattern
Lens
B sensor
OPC potential sensor
A sensor
OPC belt
Exposure glass
(Rear)
OPC potential sensor
A: For measuring black potential
B: For measuring white potential
(Front)
B sensor
A sensor
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