paper decurling is achieved at the output of a printer or other paper handling machine by discharging sequential sheets of the paper into an angled tray . upon sensing of the paper at a predetermined height , paper curling is presumed and the tray is caused to drop . this causes the sheets to slide against an end stop and drop down with the tray . the tray then returns back upward , whereupon the sheets , which are sliding against the end stop are decurled at an end of the tray facing the discharge portion of the paper handling machine . the movement of the tray is further controlled so as to establish the stack at a uniform predetermined height at the end of each print job .