Sheet stacking apparatus

A sheet stacking apparatus comprising:

• a discharge unit configured to discharge a sheet;
• a stacking tray on which the sheet to be discharged by the discharge unit is stacked;
• an alignment unit configured to align the sheet stacked on the stacking tray in a width direction which is orthogonal to a direction in which the sheet is discharged, wherein the alignment unit includes first and second alignment members configured to move in the width direction and to come into contact with side ends in the width direction of the sheet stacked on the stacking tray to align the sheet, and wherein one of the first and second alignment members is placed on a first sheet in a case where a subsequent second sheet to be shifted in the width direction and stacked on the first sheet stacked on the stacking tray is aligned;
• and
• a control unit configured to prohibit, if a length of the second sheet is smaller than a length of the first sheet in the width direction, an alignment operation by the alignment unit on the second sheet in a case where the second sheet is shifted in the width direction and stacked on the first sheet on the stacking tray, and configured to cause, if the length of the second sheet is larger than the length of the first sheet in the width direction, the alignment unit to perform the alignment operation on the second sheet.

An image forming apparatus comprising:

• an image forming unit configured to perform image formation on a sheet;
• a discharge unit configured to discharge the sheet subjected to the image formation by the image forming unit;
• a stacking tray on which the sheet to be discharged by the discharge unit is stacked;
• an alignment unit configured to perform an alignment operation to align the sheet stacked on the stacking tray in a width direction which is orthogonal to a direction in which the sheet is discharged, wherein the alignment unit includes first and second alignment members operable to move in the width direction and to contact side ends in the width direction of the sheet stacked on the stacking tray to align the sheet, and wherein one of the first and second alignment members is placed on a first sheet in a case where a subsequent second sheet to be shifted in the width direction and stacked on the first sheet stacked on the stacking tray is aligned;
• and
• a control unit configured to prohibit, if a length of the second sheet in the width direction is different from a length of the first sheet in a case where the second sheet is shifted in the width direction and stacked on the first sheet on the stacking tray, an alignment operation by the alignment unit on the second sheet.

An image forming apparatus comprising:

• an image forming unit configured to perform image formation on a sheet;
• a discharge unit configured to discharge the sheet subjected to the image formation by the image forming unit;
• a stacking tray on which the sheet to be discharged by the discharge unit is stacked;
• an alignment unit configured to perform an alignment operation to align the sheet stacked on the stacking tray in a width direction which is orthogonal to a direction in which the sheet is discharged, wherein the alignment unit includes first and second alignment members operable to move in the width direction and to contact side ends in the width direction of the sheet stacked on the stacking tray to align the sheet, and wherein one of the first and second alignment members is placed on a first sheet in a case where a subsequent second sheet to be shifted in the width direction and stacked on the first sheet stacked on the stacking tray is aligned;
• and
• a control unit configured to prohibit, if a length of the second sheet is smaller than a length of the first sheet in the width direction in a case where the subsequent second sheet is shifted in the width direction and stacked on the first sheet stacked on the stacking tray, the alignment operation by the alignment unit on the second sheet, and configured to cause, if the length of the second sheet is larger than the length of the first sheet in the width direction, the alignment unit to perform the alignment operation on the second sheet.