SUCTION-BELT DOCUMENT HANDLER

摘要

A document handler (20) for presenting documents to the platen (23) of a copier (10) for copying with a document transport system (32) having document-transport belts (35) movable under a substantially-planar background surface (33a) overlying the platen, and a suction system (33) for applying a partial suction to a document sheet being transported by the movable belts over the platen; with a clamping and unclamping system for moving the background surface against the platen to flatten the belts and a document thereon against the platen for copying. During unclamping, the surface lifts slightly away from the platen, while the document is retained on the belts by suction, by first lifting one edge of the surface 33a up away from the platen substantially before the opposite side, and then subsequently lifting the opposite side, to generate a controlled air flow across the face of the document to retain it on the belts, and moving the belts when the surface is lifted away from the platen. During clamping the one side of the surface 33a moves towards the platen, beginning slightly before the opposite side, to generate a controlled expulsion of air. The disclosed system has two pairs of commonly rotatably driven cams (60, 60a, 62, 62a) with different cam rise times connected to lift the one side of the clamping surface with a motion different from that of the opposite side. The cams can first lift the one side about 2.5 mm, while the opposite side remains in contact with the platen, then lift the opposite side about 0.8 mm, and then the clamping surface can be leveled by lifting the opposite side to about 1.75 mm while the one side is dropped to about 1.75 mm.