Sheet stacker

Claim 1

A sheet stacking apparatus for receiving and stacking sheets including: a sheet tray having a planar base plate for stacking sheets thereon and a side wall for abutting sheets thereagainst; guide means disposed adjacent said tray to direct sheets therein at an angle relative to the plane of said base plate, said base plate being movable in a vertical direction to maintain the top of the stacked sheets adjacent said guide means as the stack height increases with the addition of sheets thereto; feed means associated with said guide means to feed sheets through said guide means into said tray; air plenum means having a plurality of air discharge ports therein canted at an angle relative to said base plate for discharge of air against incoming sheets in the direction of movement of the sheets to forward the sheets toward said wall, said air plenum means being disposed above the sheets in the stack for discharge of air in a downward, angled direction; said air plenum means being mounted for limited movement in a vertical direction, discharge of air therefrom causing said plenum means to float above the sheet stack; indexing means adapted for vertically indexing said base plate; and, switch means adapted for contact by said plenum means when the height of the sheets in the stack causes said plenum means to float above a predetermined level, said switch means being adapted to energize said indexing means to lower said base plate and the sheets stacked theron to provide space above the stack for receipt of subsequent sheets presented thereto.