Electrophotographic reversal developing apparatus with control of developing electrode bias potential

Claim 1

An electrophotographic apparatus for producing and developing an electrostatic latent image on an electrophotosensitive material, comprising charging means for applying an electrostatic saturation charging voltage of predetermined polarity to an electrophotosensitive material to produce an electrostatically charged and electrophotosensitive material; means for exposing said electrostatically charged electrophotosensitive material to an image to be reproduced to form a corresponding electrostatic latent image thereon; and developing means for developing said electrostatic latent image to a reversal electrophotographic image, said developing means comprising: supply means for supplying a one-component magnetic toner; bias means for applying a bias voltage of the same polarity as said electrostatic saturation charging voltage to said one-component magnetic toner, said bias voltage and said electrostatically charged electrophotosensitive material having a predetermined differential; magnetic brush means for applying said one-component magnetic toner to said electrophotosensitive material having said electrostatic latent image thereon; means for determining the environmental conditions in which said electrophotosensitive material is placed and supplying a signal representing the so determined environmental conditions; and control means, responsive to said signal, for changing the voltage differential between said bias voltage and said electrostatically charged electrophotosensitive material by setting said bias voltage to a value appropriate for preventing appearance of fog in a reversal electrophotographic image and assuring good contrast therein.