Sheet sorting device

A sheet sorting device comprising:

• a sheet receiving tray configured to stack sheets sequentially discharged and falling from an image forming device alternately at a first sheet stacking position and at a second sheet stacking position offset downstream of the first sheet stacking position by a predetermined amount in a sheet discharging direction;
• a pair of side fence plates provided in parallel with the sheet discharging direction above the sheet receiving tray, to face each other at an interval and to be movable in a sheet width direction orthogonal to the sheet discharging direction, the side fence plates being configured to align both side ends, in the sheet width direction, of the sheets stacked on the sheet receiving tray;
• a side fence plate opening-closing unit configured to selectively open and close the pair of side fence plates between a position where the pair of side fence plates are away from the both side ends, in the sheet width direction, of the sheets stacked on the sheet receiving tray and a position where the pair of side fence plates are in contact with the both side ends, in the sheet width direction, of the sheets stacked on the sheet receiving tray;
• an offset guide plate movably installed at a position above the sheet receiving tray and configured to align rear ends, in the sheet discharging direction, of the sheets stacked on the sheet receiving tray;
• an offset guide plate moving unit configured to offset the offset guide plate to locations for the first sheet stacking position and the second sheet stacking position;
• an end fence plate provided above the sheet receiving tray to face the offset guide plate at an interval equal to a length of the sheets in the sheet discharging direction and to be movable in the sheet discharging direction, the end fence plate being configured to align front ends, in the sheet discharging direction, of the sheets stacked on the sheet receiving tray;
• an end fence plate moving unit configured to offset the end fence plate to locations for the first sheet stacking position and the second sheet stacking position;
• a sheet receiving tray lifting unit configured to liftably support the sheet receiving tray;
• and
• a controller configured to control the side fence plate opening-closing unit, the offset guide plate moving unit, the end fence plate moving unit, and the sheet receiving tray lifting unit, wherein
• the controller is configured to:
• (a) while the sheets are discharged from the image forming device and are stacked on the sheet receiving tray at the first and second sheet stacking positions, drive the sheet receiving tray lifting unit to lower the sheet receiving tray downward to keep a constant falling height of a top sheet stacked on the sheet receiving tray;
• (b) after each time when stacking of the sheets at the first sheet stacking position is completed and when the second sheet stacking position is completed, drive the side fence plate opening-closing unit to temporarily open the pair of side fence plates under a prescribed condition to move the pair of side fence plates away from the both side ends, in the sheet width direction, of the sheets;
• (c) after the step (b), drive the sheet receiving tray lifting unit to temporarily lower the sheet receiving tray downward;
• (d) after the step (c), drive the offset guide plate moving unit to offset the offset guide plate and drive the end fence plate moving unit to offset the end fence plate;
• (e) after the step (d), drive the sheet receiving tray lifting unit to lift the sheet receiving tray up;
• and
• (f) after the step (e), drive the side fence plate opening-closing unit to close the pair of side fence plates to bring the pair of side fence plates into contact with the both side ends, in the sheet width direction, of the sheets again.