20 June 2005 DRUM CHARGE
6-57
Detailed
Descriptions
6.8.2 CHARGE ROLLER VOLTAGE CORRECTION
Correction for Environmental Conditions
The voltage transferred from roller to drum could vary with the temperature and
humidity around the drum charge roller. The lower the temperature or humidity, the
higher the applied voltage required.
The ID sensor measures the effects of ambient conditions, and any small change
in drum potential caused by changes in temperature/humidity is reflected in the
amount of toner transferred to the drum.
This measurement is done immediately after the ID sensor pattern for toner density
control. After creating ID sensor pattern [A], another pattern [B] is made. To do this,
the LD switches off, the charge roller voltage drops, and the drum potential is
reduced to -600V. At the same time, development bias returns 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
pattern [B], and Vsdp, the output voltage, is compared with Vsg which was read
from the bare drum at the same time.
ID Sensor Pattern
t
Drum Potential
Development Bias
ID Sensor Output
-850 V
-600 V
-550 V
-480 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
-1500 V
Sub Scan Direction
B195D506.WMF
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