Sheet stacking apparatus

Abstract

A dual exit tray xerographic machine, having a hot roll fuser, supplies its output copy sheets to a large-capacity exit pocket whereat the sheets are stacked in a vertically extending pile, on a servo-movable elevator platform. The platform height is servo controlled so as to maintain the stack's top sheet at a fixed position relative to a fixed-position, generally horizontally extending, sheet discharge path. Sheet stacking is enhanced by a pair of movable bars. A hold-down bar, in its quiescent position, presses the stack's trailing edge portion down to insure reliable insertion of the next sheet. A pusher bar is maintained in an elevated quiescent position during such insertion. After the sheet has been inserted, the pusher bar lowers onto the stack, at a position between the hold-down bar and the stack's leading edge. The pusher bar thus holds the just-inserted sheet down. The hold-down bar synchronously moves in a generally elliptical path, to first clear the trailing edge of the just-inserted sheet. The hold-down bar then moves in an upward path until it again overlies the stack's trailing edge. The hold-down bar now descends onto the stack, as the pusher bar returns to its quiescent position.