In conventional xerography, a xerographic suface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support latent electrostatic images. In the process, the xerographic surface is electrostatically charged and the charged surface is then exposed to a light pattern of the image being reproduced to thereby discharge the surface in the areas where the light strikes the surface. The undischarged areas of the surface thus form an electrostatic charge pattern in conformity with the configuration of the original pattern.
The latent electrostatic image may then be developed by contacting it with a finely divided electrostatically attractable material, ordinarily a pigmented resinous powder, referred to herein as "toner." The toner particles are attracted to the electrostatic image from the carrier to produce a visible toner image on the xerographic surface.
After the image is developed, a transfer member, ordinarily copy paper, is caused to move in synchronized contact with the photoconductive surface. During this time an electrical potential opposite from the polarity on the toner is applied to the side of the paper remote from the photoconductive surface to electrostatically attract the toner image from the xerographic surface to the copy paper. The copy paper, which is an insulator, retains the charge while inducing a reverse charge on the non-discharged ares of the xerographic surface. This charge orientation creates an electrostatic bond between the paper and the xerographic surface. Removal of the copy sheet which is electrostatically bonded to the surface, without disturbing the toner image loosely adhering thereto, has long been a problem in the xerographic art.
In order to separate the copy sheet from the xerographic surface, the charge on the copy sheet may be neutralized or reduced with a corona discharge device while the sheet is on the xerographic surface. Assuming the copy sheet is partially neutralized thereby, a vacuum stripping device may be employed for pulling the leading edge of the copy sheet from the xerographic surface for subsequent movement of the copy sheet away from the xerographic surface by a suitable paper transport.
Stripping of the copy sheet from the xerographic surface may be further complicated by an inherent curl in the copy sheet which causes it to conform to the curved surface of the photoreceptor such that the beam strength of the paper cannot be relied upon to aid in the stripping process. It has been found that this inherent curl is variable from sheet to sheet within a stack of sheets from the paper supply tray.
It is therefore an object of the present invention to subject each sheet supplied from the paper supply tray to conditions similar to the conditions existing downstream from the transfer area whereat the copy paper with the transferred image thereon is stripped from the photoreceptor and to remove sheets from the paper path which will in all probability create problems at the stripping area.