PLURAL BELT DOCUMENT FEEDER

In a document feeder for transporting document sheets over the platen of a copier, with a vacuum belt platen transport system, into registration means for stopping the document sheet at an imaging position on the platen, wherein the vacuum belt platen transport system comprises plural belts moving under a white vacuum plenum backing surface overlying the platen, and includes a vacuum source for applying a partial vacuum to a document sheet being transported by the moving belts, the improvement wherein: the vacuum belt platen transport system belts are transparent or highly translucent thin, low-frictional, non-elastomeric, plastic belts; the transparent or highly translucent belts being unapertured and the vacuum plenum backing surface being unapertured in the imaging position, so that the vacuum belt transport system is effectively invisible through a document sheet to the copier; the belts being spaced apart by defined gaps pneumatically remotely connected with the vacuum source to apply vacuum forces to a document sheet through the gaps sufficient to provide transport of a document sheet with movement of the belts into the registration means, but with low enough the vacuum forces to allow slippage of a document sheet relative to the moving belts at the registration means; wherein the vacuum plenum surface has relatively shallow and smooth-walled elongated channels extending under the belts along the direction of movement of the belts, and vacuum apertures communicating with the channels from the vacuum source from outside of the imaging position; and further comprising transverse vacuum communicating channels for pneumatically communicating a partial vacuum into the gaps under a document sheet between the belts from the channels under the belts without significantly affecting the optical uniformity of the white vacuum plenum backing surface in the gaps. The belts are preferably approximately 0.2 millimeter thick polyester plastic and spaced apart by defined gaps of greater than five millimeters and less than twenty millimeters. Additionally disclosed is a system for automatically reducing the level of the partial vacuum in the vacuum plenum for the transporting of a document sheet of greater than a predetermined size into the registration means, to avoid damage to the document sheet by the registration means, in response to means for prior detection of a document sheet of greater than a predetermined size.