Sheet feeding apparatus and automatic document feeder

Abstract

An automatic document feeder having a pick-up roller for feeding a document out of a tray, a conveyer belt for conveying and stopping the document on a platen and ejecting the document from the platen, and a register roller for stopping the document fed by the pick-up roller once and feeding the document onto the platen. A driving mechanism for driving the belt and the register roller is connected with the belt and the register roller with no clutches in-between. The driving mechanism is driven by pulses, and the document conveying amount is controlled by detecting the number of pulses. In the automatic document feeder, if two successive documents are of a size smaller than a half of the platen, the two documents are set on the platen side by side, and a next document is fed out of the tray. If a latter document of two successive documents is of a size larger than a half of the platen, feeding of a next document is inhibited. Further, if two successive documents are of a size smaller than the platen, the documents are fed successively and intermittently to a pre-step position where the leading edge of a document is positioned at an intermediate reference point which is located substantially in the center of the platen and then to a scanning position where the leading edge of a document is positioned at a scanning reference point which is located in a downstream portion of the platen, and a next document is fed to an entrance of the platen.