Ricoh FT5233 Service Manual page 37

PROCESS CONTROL
1.3.2 V Pattern Detection
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The V pattern is made on the drum before the original latent image, as in
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the case of the ID sensor pattern.
During V pattern detection, the drum surface is charged with a fixed grid
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bias voltage: – 500V + V
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
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
voltage (0V). If there is residual voltage on the drum, this area of the drum
will attract some toner, making a V
reflectivity of the V
The CPU notes the ratio, Vrp/Vrg. This V
row during the copy cycle (among 5 copies) and the CPU takes their average.
During the 5 V pattern check cycles, if color copies are made, or if a toner
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density check is done, the CPU skips the V
the next copy cycles.
If an ID sensor abnormal condition occurs, the CPU does not perform the V
pattern detection because toner density may not be proper.
V Pattern
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correction (see 1.6 Drum Rotation Time Control).
G
correction + V
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pattern and this sensor output voltage is called Vrp.
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Image
0V Bias
Non-image
Fixed Bias
Vrg
V Sensor
Vrp
Data correction (See 1.5 Drum
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pattern. The V sensor checks the
pattern check is done 5 times in a
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pattern check and will do it in
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2-8
12 February 1992
pattern bias
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