The amount of toner supplied to the V
SP
pattern must remain constant. To
ensure this, the machine applies a correction to the development bias for
V
SP
patterns when combined readings from the TD and ID sensors indicate
that the carrier is aging. This correction is called "ID Correction".
- Toner Supply -
There are three toner supply modes.
Detect toner supply:
Toner supply varies with paper size, the latest TD
sensor reading, and the latest V
SP
and V
SG
readings by the ID sensor. For
example, toner supply will be increased if the toner weight ratio in the
developer is decreasing, or if the most recent V
SP
pattern was detected as
being relatively light.
Fixed supply mode:
The toner supply remains constant, but can be
adjusted with an SP mode.
TD supply mode:
Toner supply varies with TD sensor output. For example,
if the toner weight ratio has decreased since TD sensor supply mode was
selected, toner supply is increased.
1.1.3.3 Drum Potential Control
This is how the machine compensates for aging of the drum and the
exposure lamp, and for the temperature around the drum charge roller.
- V
R
Pattern Detection and V
R
Correction -
As the drum gets older, the drum’s residual voltage gradually increases due
to electrical fatigue. Light from the exposure lamp will not dissipate the
increased residual voltage effectively and dirty background will result.
Every 1,000 copies, part of the drum is developed with the V
R
pattern
development bias. If there is residual voltage on the drum, this area of the
drum will attract some toner, making a V
R
pattern. The ID sensor response
to this pattern is compared with the response of the ID sensor to a bare area
of the drum. The higher the residual voltage on the drum is, the darker the
V
R
pattern is. If the pattern is too dark, the drum will not be discharged
sufficiently. As a result, the machine will increase the negative development
bias to prevent dirty background. If it does, image density will drop. To
prevent this, the machine will also increase the negative drum charge roller
voltage.
(The V
RP
/V
RG
range to which the above mentioned bias and charge
corrections are applied may be shifted to cancel the effect of ID correction.)
V
R
correction data must be reset by SP mode (forced V
R
detection) if the
drum is changed or if the ID sensor is cleaned or replaced.
Rev. 6/95
A156/A160/A162 2-6 STM
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