Charge Roller Voltage Correction - Ricoh B245-62 Service Training

Charge Roller Voltage Correction

Temperature and humidity
affect the efficiency of voltage
transfer from the drum charge
roller to the drum.
Lower humidity causes a
higher drum charge voltage.
As a result, less toner is
transferred.
To determine whether to
change the drum charge roller
voltage, the machine
compares Vsdp with Vsg.
Vsdp/Vsg > 0.95 = Make the
drum charge voltage less
negative (smaller) by 50 V
Vsdp/Vsg < 0.90 = Make the
drum charge voltage more
negative (larger) by 50 V
Slide 56
•Vsdp = Check for environmental correction (charge applied with bias at –600 V).
•Vsg = Check reflectivity of bare drum (charge not applied and bias at –650 V).
•Vsdp and Vsg are checked immediately after checking reflectivity of the ID sensor pattern (Vsp).
- More Details -
With a drum charge roller system, the voltage transferred from roller to drum varies with the temperature
and humidity around the drum charge roller. The higher the temperature or humidity is the higher the
applied voltage required.
To compensate, the machine uses the ID sensor to measure the effects of current environmental
conditions. For this measurement, the process control parameters are balanced so that any small change
in drum potential caused by environmental effects is reflected in a change in the amount of toner
transferred to the drum.
This measurement is made immediately after the ID sensor pattern for toner density control. Immediately
after making ID sensor pattern [A], the charge roller voltage stays the same, but the development bias
goes up to –600 V; as a result the drum potential is reduced to –650 V. The laser diode is not switched on,
and the drum potential is now slightly higher than the development bias, so a very small amount of toner
transfers to the drum. The ID sensor measures the density of this pattern [B], and the output voltage is
known as Vsdp. This voltage is compared with Vsg (read from the bare drum at the same time).
If the humidity drops, the drum potential goes up (to a higher negative voltage) even if the charge roller
voltage supply stays the same (efficiency of voltage transfer is higher with lower humidity). As a result, less
toner is transferred to ID sensor pattern [B]. If the sensor output reaches a certain point, the drum charge
voltage will be reduced.
To determine whether to change the drum charge roller voltage, the machine compares Vsdp with Vsg.
§
Vsdp/Vsg > 0.95 = Make the drum charge voltage less negative (smaller) by 50 V
§
Vsdp/Vsg < 0.90 = Make the drum charge voltage more negative (larger) by 50 V
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B245-62 / PD-C4