Sheet stacking apparatus with vertically movable tray

A sheet stacking apparatus comprising:

• a sheet discharge tray configured to move up and down and hold a sheet that is discharged thereto;
• and
• a sheet discharge roller located above said sheet discharge tray and rotatable to discharge the sheet to said sheet discharge tray, wherein
• said sheet discharge tray receives the sheet from said sheet discharge roller at a standard sheet receiving position which is located at a predetermined downward distance away from said sheet discharge roller, and
• said sheet discharge tray moves down to a lower position than said standard sheet receiving position by a predetermined distance and receives at least a next sheet at said lower position, when a stacked amount of sheets on said sheet discharge tray reaches a predetermined stacking amount;
• a plurality of sensors configured to identify a top of the stacked amount of sheets;
• and
• a lever configured to cooperate with said plurality of sensors to control a movement of said sheet discharge tray by moving said lever to a sensing position of at least one of said plurality of sensors corresponding to an operating mode of said apparatus.