Development Bias Mechanism - Ricoh A028 Service Training Manual

1 July 1994

2.9.4 Development bias mechanism

The bias voltage is applied to the three rollers from the
development power pack to prevent a dirty background
and to adjust the image density (-210V to -525V).
The output of the development power pack is applied to
the rollers via a bearing. The 1st and 2nd rollers are on
a common line, but the 3rd roller is independent. This
allows a different voltage to be applied to the 3rd
development roller.
For example, at the 4th level of the image density keys,
a bias value of -210V is applied to the 1st and 2nd
rollers, and a larger voltage of -330V is applied to the
3rd roller to enhance contrast and prevent a dirty
background. The bias voltage changes, depending on
the selected image density level, detected image density
in AID mode, or process control condition.
2.9.5 Toner density control and supply mechanism
Part of the developer is fed from the 3rd roller through
the inside of the toner density sensor. If the toner
density changes, the quantity of toner which passes
through the sensor changes, and the self-inductance of
the coil wound around the toner density sensor also
changes, thereby permitting detection of the toner
density. If the toner density in the developer drops
below the reference value, the toner supply motor is
turned ON and the supply roller turns. At the same time,
the agitator motor is turned ON. The toner on the
surface of the supply roller is scraped off by the sponge
blade and put in the development tank.
The reference value of the toner density sensor is
determined by detection of the ID sensor pattern level.
For details, refer to Toner density control section.
When the toner supply motor is turned ON together with
the agitator, the large agitator mounted in the toner
cartridge begins to rotate to prevent the toner from
blocking and moves the toner beside the toner near-end
sensor.
The toner is also transported on to the toner supply roller
by the large agitator. To prevent the toner from sticking
to the toner supply roller, it is agitated by the small
agitator.
The toner supply motor and agitator motor each
incorporates an overload detection circuit on the DC
drive board to stop the motor if a motor overload is
detected.
3rd development roller
Development
power pack
Bias harness
Toner supply roller
Photoconductor
2-67
Development
2nd development roller
Developer
Toner density
sensor bobbin
Coil
Toner supply motor
Seal mylar
Agitator motor
Sponge blade
Small agitator
Main agitator
1st development
roller