1.4 DRUM POTENTIAL CONTROL
The characteristics of the drum vary with the temperature around the drum,
and they change as the drum gets older. To take account of these and other
related factors, this machine has the following three drum potential control
routines.
• V
R
pattern correction
• V
L
pattern correction
• T/H correction
1.4.1 V
R
Pattern Correction
As the drum ages, the drum residual voltage gradually increases due to
electrical fatigue (see the upper left chart). In other words, as the drum gets
older, light does not discharge it as much (see the upper right chart). This
may cause dirty background on copies. V
R
pattern detection every 1,000
copies using the ID sensor avoids this problem.
Every time V
R
pattern detection is done, a strip across the drum is charged
using zero development bias and the standard charge on the drum charge
roller that is used for copying (with all corrections included). At the same
time, all the blocks of the erase lamp turn on to illuminate this charged area
of the drum.
Copy volume
Drum
residual
voltage
(V)
Light intensity
Drum
potential
(V)
Old Drum
New Drum
V
R
Pattern
0V Bias
ID Sensor
V
RP
A156/A160/A162 2-18 STM
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