Copying apparatus with automatic bottom feeder

Abstract

A bottom feeder for copy paper feeding has means for imparting a curvature to the sheets, the curvature being in the direction the sheets will be withdrawn. The curvature provides transverse rigidity to permit lifting weight of stack off the bottom sheet. This facilitates withdrawing the sheets one at a time from the bottom of the stack. A curved paper tray imparts a curvature to the paper. A pair of holding clamps are provided, one on either side of the stack of paper, which are partially withdrawn from the sides of the paper stack so that paper may be added to the stack. When sheets are to be fed, the clamps which comprise a pair of plates having a friction material on the paper facing side thereof are moved in to engage the sides of the stack of paper. An arrangement is provided to thereafter lower the paper tray slightly from the bottom of the stack, or lift the clamps and the curved paper stack. In either event, the pressure of the stack weight is now removed from the bottom sheet. A vacuum type feed belt which passes under the stack of paper can now pick off one sheet at a time without the sheets being restrained by friction against the paper tray or created between the tray and the stack of paper. The friction material on the holding plates in a preferred embodiment comprises bristles angled upward away from the paper tray to retain the stack lifted from the paper tray while allowing relatively easy withdrawal of each sheet. A stack-height sensor, preferably a switch on the face of one of the plates, senses the condition where, as the height of the stack diminishes, the pressure of the holding clamp plates may be slightly reduced to avoid binding of the paper. Timing means, which in the disclosed embodiment comprise cams riding on a common shaft, are provided to coordinate the movement of the clamps toward and away from the sides of the stack with the movement of the paper tray away from the bottom of the stack of paper.