Ricoh FT8680, Service Manual

Page: 28 / 389

The above figure shows the relationship between the drum potential and the
original density (exposing light intensity). To get constant copy quality, this
relationship must be maintained.
Since this relationship tends to change to the one represented by the dotted
line by various factors, compensations are required as follows:
A decrease in dark voltage (Vd) is compensated for by increasing the charge
corona output. A increase in light voltage (V
L
) is compensated for by
increasing the exposure lamp voltage. Since the residual voltage (Vr)
increase cannot be compensated for by increasing the lamp voltage, it is
compensated by increasing the development bias voltage and changing the
Vd and V
L
standard value.
1.2.2 Image Density Control
To maintain constant copy image density, the ID sensor detects the toner
amount of the ID sensor pattern. From this, it is understood that drum
potential is stabilized with the above compensations. According to the
detection results, the toner density in the development unit is controlled so
that the toner amount on the sensor pattern is constant.
The following sections explain the details of these compensations.
V
0
Vd
V
L
Vr
Drum
Potential
Light Original Density Dark
A171D519.wmf
PROCESS CONTROL 31 July 1995
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