Ricoh Aficio Color 4006, Service Manual

Page: 55 / 487

PROCESS CONTROL 24 February, 1999
2-6
Step 3: Sensor Pattern Potential Detection
Process
The potential sensor detects the potential on each grade of the 16-grade sensor
pattern latent image, for each colour, and the output is stored in memory.
Feedback Type Potential Sensor
This copier uses a feedback potential sensor. A description of the principles of
feedback potential sensors follows.
The detector [A] detects the strength of electric fields emitted from the drum
surface, which depend on the surface potential of the drum. The feedback circuit
applies voltage to the probe [B] until the electric field strength is offset at the
detector. The level of this voltage determines the magnitude of the surface
potential on the drum surface and is presented as output.
The major features of this measurement method are:
•
Even if the distance [d] between the drum (1) and the potential sensor (2)
fluctuates, the measurement of the drum surface potential is still accurate.
•
The potential sensor does not have to be calibrated before the process control
self check, so the calibration step required for previous models can be skipped.
•
Residual potential affected the calibration for the older type of sensor, so before
process control self checks, the machine had to wait 10 minutes in standby
mode for the residual voltage to disappear. For this new sensor, calibration is
not needed, so the influence of residual potential on the drum can be ignored.
V
Feedback circuit
d c
d
A259A003.WMF
[A]
[B]