Ricoh A230, Service Manual, Page: 94 / 1134

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DRUM CHARGE
2-31
A230/A231/A232 SM
2.5.2 CHARGE ROLLER VOLTAGE CORRECTION
Correction for Environmental Conditions
In the drum charge roller system, the voltage transferred from roller to drum varies
with the temperature and humidity around the drum charge roller. The lower the
temperature or humidity is, the higher the applied voltage.
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 drops so that drum potential is reduced to -600V. At the same time,
development bias goes back to -550V. The drum potential is now slightly higher
than the development bias, so only 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).
ID Sensor Pattern
t
Drum Potential
Development Bias
ID Sensor Output
-950 V
-600 V
-550 V
-380 V
-150 V
V sg (4.00 V)
V sdp (3.50 V)
V sp (0.31 V)
Charge Voltage
Laser Diode
3
cm
3 cm 3 cm
On
Off
-1650 V (NAD40)
-1630 V (NAD30)
Sub Scan Direction
A231D506.WMF
[A] [B]
Rev. 03/99
⇒