Sheet stacking apparatus

An image forming apparatus comprising:

• an image forming unit configured to form an image on a sheet;
• a determination unit configured to determine a type of a sheet;
• an overlapping unit configured to overlap a sheet to be conveyed with a following sheet and convey the overlapped sheets;
• a stacking tray onto which a sheet bundle conveyed as overlapped sheets by the overlapping unit, or a sheet conveyed without being overlapped with a following sheet by the overlapping unit, is discharged, and moves up and down according to the stacked amount of the discharged sheets;
• an alignment unit configured to align sheets stacked on the stacking tray;
• and
• a control unit configured to discharge the sheet onto the stacking tray by overlapping with a following sheet by the overlapping unit if the sheet which is determined by the determination unit is a first type sheet, and discharge the sheet onto the stacking tray without overlapping with the following sheet by the overlapping unit if the sheet which is determined by the determination unit is a second type sheet,
• wherein the first type sheet is lighter that the second type sheet.

A sheet stacking apparatus comprising:

• an overlapping unit configured to overlap a sheet conveyed with another sheet and convey the overlapped sheets;
• a stacking tray onto which a sheet bundle conveyed as overlapped sheets by the overlapping unit, or a sheet conveyed without being overlapped with another sheet by the overlapping unit, is discharged, and moves up and down according to the stacked amount of the discharged sheets;
• an alignment unit configured to align sheets stacked on the stacking tray;
• and
• a control unit configured to discharge the first type sheet onto the stacking tray by overlapping with another sheet by the overlapping unit, and discharge the second type sheet onto the stacking tray without overlapping with another second type sheet by the overlapping unit,
• wherein the first type sheet is lighter that the second type sheet.