GB1360224A - Bias control of electrographic development electrode - Google Patents

Abstract

1360224 Developing apparatus EASTMAN KODAK CO 22 July 1971 [23 July 1970(2)] 34472/71 Heading G2H Electro-photographic developing apparatus comprises a developing electrode earthed through a resistance of 10<SP>6</SP> -10<SP>11</SP> # so that the potential induced on the electrode is proportional to the potential of the part of the electrostatic latent image being developed, the electrode being connected to a circuit which samples the image potential, stores the sample and prevents the electrode potential from falling below a value related to the sample value. As shown, the electrode is constituted by a magnetic brush developing roller 8 connectable to resistors 40, 42, 41 of 10<SP>8</SP>, 10<SP>6</SP> and 10<SP>7</SP> ohms respectively. As an image bearing sheet 16 is fed over the brush, the potential induced in the brush is divided at 46B and stored by a capacitor 48. When the leading edge of sheet 16 trips a switch 30, a relay 46 disconnects the capacitor from the divider 40, 42, connects it to an amplifier circuit 50, 64, 72 and switches in resistor 41. If the potential of the brush falls e.g. when the trailing edge 34 is passing over it, a diode 74 conducts and amplifier 72 applies a bias potential. If the image comprises positive charge, contacts 52A, B, C, D are changed over. Development may alternatively be by liquid, aerosol, powder cloud, cascade or metal-coated fur brush.