Electrostatographic apparatus comprising developing bias means

Details Electrostatographic apparatus comprising developing bias means Electrostatographic apparatus comprising developing bias means

1979-03-06

1981-05-12

Braun, Fred L.

Photocopying

Projection printing and copying cameras

Combined with or convertible to a contact printer

118668, 324457, 355 3DD, G03G 1500

Patent

active

042668700

ABSTRACT:
An electrode (17) is provided adjacent to a photoconductive drum (12) to sense the background area potential at a leading edge of an electrostatic image on the drum (12). An electrically conductive shield (26) surrounds all surfaces of the electrode (17) except a surface which faces the drum (12). A voltage follower (18) has an input connected to the electrode (17) and an output connected to the shield (26). This makes the capacitance between the electrode (17) and the drum (12) much greater than the capacitance between the electrode (17) and ground. The surface of the electrode (17) facing the drum (12) is formed with a pattern of projections and depressions to increase the surface area thereof and thereby the capacitance between the electrode (17) and the drum (12). The output of the voltage follower (18) is connected through a sample and hold circuit (53), (54), (56), (57), (62) to a developing bias voltage generator (58), (69), (71) which applies a bias voltage to a developing unit (23) in accordance with the output of the voltage follower (18) and thereby the potential of the electrostatic image on the drum (12).

REFERENCES:
patent: 3611982 (1971-10-01), Coriale et al.
patent: 3852668 (1974-12-01), Hardenbrook et al.
patent: 3921087 (1975-11-01), Vosteen
patent: 4063154 (1977-12-01), Andrus et al.
patent: 4063155 (1977-12-01), Buchheit
patent: 4079266 (1978-03-01), Vipond
patent: 4141643 (1979-02-01), Eda et al.

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