Pitney Bowes Inc.

Harold M Stahl

Lawrence E Clifford

Robert C Ariotti

In an electrostatic xerographic copying process and apparatus in which a photoconductive insulating master is sensitized by application of a uniform electrostatic charge to the photoresponsive surface thereof, the charge is removed in non-image areas by exposure to a light image corresponding to the non-image areas of an illuminated original to leave charged latent image areas capable of development with coloring material. The sensitized photoreceptive surface is pre-exposed to an electroluminescent element of sufficient intensity to completely or partially remove the charge from all areas or some areas of the surface prior to the exposure to the light image. Complete removal of the charge is advantageous in spaced transverse portions of a continuous master which are not to be exposed to the illuminated original sheet, thereby desensitizing such areas. Partial removal of the charge is advantageous in the case of masters having slow photoresponse, which can be overcome by reducing the surface potential thereof.

Electrostatic copying process

A powder density control means is provided for use in a photocopier machine of the type in which a photoconductor is charged in accordance with an image to be recorded thereon and is developed by contact with a toner powder attracted thereto from a mixture of carrier particles and toner powder carried by a developer assembly including a replenishment means for periodically adding toner powder. A high value resistance and a bias supply are serially coupled to a magnetic brush of the developer assembly. The voltage across the magnetic brush provides an indication of how heavily the latent image on the photoconductor is being toned. The change in magnitude of the voltage on the brush is sensed and when a predetermined amount of voltage change is detected, an additional amount of toner powder is supplied by the replenisher to the developer unit for such change.

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Ridgefield, CT, United States of America

Harold M Stahl