Ricoh FT4215, Руководство по обучению обслуживанию

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2.4 GRID VOLTAGE CORRECTION
To maintain good copy quality over the drum’s life, the grid voltage is
changed by the following:
•
Drum residual voltage correction (Vr correction)
•
Vp correction
2.4.1 Drum Residual Voltage Correction (Vr correction)
During the drum’s life, the drum may fatigue electrically and residual voltage
(Vr) on the drum may gradually increase. When this happens, the corona
charged voltage on the drum is not discharged enough in the quenching and
exposure processes. Even if the development bias is applied in the
development process, the background area of the original on the drum may
attract some toner. This may cause dirty background on copies. The Vr
correction prevents this phenomenon as follows:
A pattern (Vr pattern) is developed on the drum every 1000 copies and its
reflectivity is detected by the ID sensor to measure the residual voltage. This
is called residual voltage detection. If the reflectivity is low, the residual
voltage will be high.) When the Vr pattern is developed, all blocks of the
erase lamp turn on, the grid voltage is –500 volts and the development bias
voltage is 0 volt. (See page 2-8 for standard image density grid voltage.)
The CPU determines what level of Vr correction is necessary depending on
the output (Vr ratio [L]) from the ID sensor.
L =
Vrp
Vsg
x 100(%)
Vrp: ID sensor output for Vr pattern
Vsg: ID sensor output for bare drum
The current Vr ratio is displayed by SP67.
The CPU increases the development bias voltage depending on the Vr ratio
to prevent dirty background on copies. (See page 2-33 for more information.)
The CPU also increases the grid voltage to ensure proper image density
depending on the Vr ratio. (See page 2-8.)
FT4220/4222 2-6 STM