Ricoh K-C3.5L Service Training page 51

Charge Roller Voltage Correction
Slide 51
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
ID Sensor Pattern
Charge Voltage
On
Laser Diode
Off
Drum Potential
Development Bias
ID Sensor Output
Details are in the notes section below.
51
Sub-scan direction
Model K-C3.5L