Patent ID: 8774703

Claim:
A sheet stacking apparatus comprising: a stacking unit which accommodates sheets stacked thereon and is capable of moving upward and downward within an operation range between an upper limit and a lower limit; a sheet detection unit which detects an uppermost sheet of the sheets stacked on the stacking unit; a lower-limit detection unit that detects that the stacking unit has reached the lower limit; a determination unit which determines that the stacking unit has been fully loaded with sheets when the lower-limit detection unit detects that the stacking unit has reached the lower limit; and a moving unit which moves the stacking unit upward after the determination unit determines that the stacking unit has been fully loaded with sheets, and stops moving the stacking unit upward when the sheet detection unit detects the uppermost sheet, wherein the moving unit is configured to start moving the stacking unit upward if the sheet detection unit no longer detects the uppermost sheet after the determination unit determines that the stacking unit has been fully loaded with sheets, wherein if an elapsed time from when the stacking unit starts moving upward to when the sheet detection unit detects the uppermost sheet is shorter than or equal to a first threshold time, the determination unit is configured to maintain the determination that the stacking unit has been fully loaded with sheets, and wherein if the elapsed time from when the stacking unit starts moving upward to when the sheet detection unit detects the uppermost sheet is longer than the first threshold time, the determination unit is configured to release the determination that the stacking unit has been fully loaded with sheets.