High capacity sheet stacking system with variable height input and stacking registration

A high capacity sheet stacking apparatus for stacking output copy sheet sets received from the sheet output of a reproduction machine comprising:

• an output sheet stacking tray providing a sheet stacking surface inclined at a substantial angle to the horizontal for receiving sheets to be stacked thereon from said reproduction machine;
• a sheet input system for feeding sheets into said sheet stacking tray to provide an increasing stack height thereon;
• a stack edge registration unit providing an upstanding sheet edge registration surface against which the edges of said output sheets being stacked in said stacking tray are registered by sliding down said inclined angle to abut against said sheet edge registration surface;
• and an elevator system for vertically repositioning said sheet input system relative to said stacking tray above said stack height so as to accommodate the stacking of multiple output copy sheets of said increasing stack height on said sheet stacking surface without interfering with said feeding of further output sheets from said sheet input system into said stacking tray;
• wherein said stack edge registration unit is automatically adjusted in coordination with said increasing stack height to increase the height of said sheet edge registration surface above said stack height in said stacking tray.