Ricoh A085, Manual

Page: 263 / 617

1.3.2 V
R
Pattern Detection
The V
R
pattern is made on the drum before the original latent image, as in
the case of the ID sensor pattern.
During V
R
pattern detection, the drum surface is charged with a fixed grid
bias voltage: – 500V + V
G
correction (see 1.6 Drum Rotation Time Control).
At the same time all the blocks of the erase lamp unit turn on to illuminate this
charged area of the drum.
The exposed area of the drum is developed with a fixed bias voltage for
non-image area: – 160V + V
R
corr V
R
Data correction (See 1.5 Drum
Temperature Control) + Black Bias correction (SP mode #37). The V sensor
checks the reflectivity of the bare area of the drum and this sensor output
voltage is called Vrg. (The meaning of Vrg is the same as that of Vsg
detected by the ID sensor.)
Just next to this bare drum area, the drum is developed with V
R
pattern bias
voltage (0V). If there is residual voltage on the drum, this area of the drum
will attract some toner, making a V
R
pattern. The V sensor checks the
reflectivity of the V
R
pattern and this sensor output voltage is called Vrp.
The CPU notes the ratio, Vrp/Vrg. This V
R
pattern check is done 5 times in a
row during the copy cycle (among 5 copies) and the CPU takes their average.
During the 5 V
R
pattern check cycles, if color copies are made, or if a toner
density check is done, the CPU skips the V
R
pattern check and will do it in
the next copy cycles.
If an ID sensor abnormal condition occurs, the CPU does not perform the V
R
pattern detection because toner density may not be proper.
V Sensor
Vrg
Vrp
V
R
Pattern
0V Bias
Non-image
Fixed Bias
Image
PROCESS CONTROL 12 February 1992
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