Single pass duplexing by sequential transfer

Claim 1

Apparatus for producing a duplex copy including means to sequentially formulate a first and a second image of charged toner grounded on a moving grounded photoconductive surface, a biased transfer roll bearing a charge opposite to that of said toner arranged to move in timed relation with said photoconductive surface through a region of electrical communication with said photoconductive surface wherein a first toner image is electrostatically transferred from the photoconductive surface to the roll surface and recirculated thereon through said region in synchronization with said second image on the photoconductive surface, gripping means operatively associated with said transfer roll to, and in electrical contact with, secure a sheet of final support materIal to said transfer roll with a first side of said sheet overlying said first image prior to recirculating said first image through the region of electrical communication wherein said second image is electrostatically transferred to the second side of said sheet, corona generating means positioned in a region of low voltage contrast to apply corona to the second side of said sheet to transfer electrostatically said first image from said roll surface to said first side of said sheet, switching means synchronized with said transfer roll to remove the bias from said transfer roll and to energize said corona generating means after said second image is transferred to said sheet to transfer said first image from said transfer roll to said sheet and means to strip said sheet from said transfer roll including said means for securing the sheet to said transfer roll, whereby said second and first images are sequentially transferred to said sheet.