Duplexing in automatic document feeder utilizing a path shorter than the length of the document to be duplexed

The present invention relates to the feeding of individual document sheets to be scanned in a document scanner and, more particularly to the document delivery system which receives the scanned documents and, if desired, routes the individual sheets back to the scanning region for duplex scanning, i.e., scanning of both sides of the document sheet. As used herein, the term "document scanning device" is intended to be broadly defined to include, but not necessarily be limited to, stand alone document copiers, facsimile machines, document scanning machines and combinations of such units. The footprint of a document scanning unit such as a copier, facsimile machine or document scanner or combinations thereof is reduced by causing overlap of the leading and trailing edges of long document sheets to be scanned in the document delivery roller system downstream of the scanning station. Differential slippage of the overlapping ends between a drive roller and a pinch roller is provided in a first embodiment. A second embodiment uses a moveable pinch roller in the document delivery system to selectively open and close a gap to permit slippage of the leading and trailing edges of the document. A third embodiment uses three document delivery rollers defining two spaced nips in which the leading and trailing edges of a long document are simultaneously present and a crenellated roller surface to guide the leading edge of the document to the desired nip in the delivery system.