Sheet post-processing apparatus and image forming system including the apparatus

A sheet post-processing apparatus, comprising:

• a first conveying member which is configured to convey a sheet, the sheet including a plurality of sheets;
• a processing tray on which the sheets that are carried in along a predetermined carry-in direction by the first conveying member are stacked;
• a first processing unit which is configured to execute a predetermined post process onto the sheets that are stacked on the processing tray;
• a reference plate which aligns the sheets in the carry-in direction by abutting against a downstream edge of the sheets in an alignment direction that is opposite to the carry-in direction of the sheets that are carried in onto the processing tray;
• an alignment member having:
• a shaft which is arranged above the processing tray and rotates, and
• one or more alignment paddles which protrude in a radial direction of the shaft and which make contact with the sheets having been carried in on the processing tray;
• the alignment member rotating in the alignment direction on a surface facing the processing tray to move the sheets having been carried in on the processing tray in the alignment direction, thereby assisting in aligning the sheets;
• a home-position detection unit which is configured to detect the alignment paddle being at a reference position;
• a drive unit which is configured to drive the alignment member;
• and
• a control portion which is configured to control the drive unit,
• wherein,
• the control portion
• calculates a contact assumed interval in which a trailing end of the sheets carried in in the alignment direction may make contact with the alignment paddle based on output information of the sheets,
• calculates an interference timing at which the alignment paddle interferes with a carry-in path of the sheets based on a result of detection by the home-position detection unit, and
• if the interference timing falls within the contact assumed interval, the control portion temporarily changes a rotation speed of the alignment member from a reference speed to shift a phase of the alignment paddle so that the interfere timing falls outside the contact assumed interval.