Sheet processing apparatus and image forming system incorporating the sheet processing apparatus

A sheet processing apparatus comprising:

• a conveyance passage configured to convey a two-ply sheet having two sheets overlapped and bonded together at a bonding portion in a conveyance direction,
• the conveyance passage including
• a first branched conveyance passage branched in a first direction, and
• a second branched conveyance passage branched in a second direction different from the first direction;
• a sheet separation device configured to
• separate a non-bonding portion of the two-ply sheet,
• convey a first sheet of the two sheets separated from each other to the first branched conveyance passage, and
• convey a second sheet of the two sheets separated from each other to the second branched conveyance passage, and
• the sheet separation device including a conveyance roller pair having two rollers,
• the two rollers being configured as separable from each other and contactable with each other, and the two rollers being disposed on at least one of the first branched conveyance passage or the second branched conveyance passage;
• and
• circuitry configured, in response to a passage of a leading end in one of the first direction and the second direction, of one of the first sheet and the second sheet conveyed to a corresponding one of the first branched conveyance passage and the second branched conveyance passage, over a position of the conveyance roller pair, to control the conveyance roller pair to
• change a state of the two rollers from a separated state in which the two rollers are separated from each other to a contact state in which the two rollers are in contact with each other to grip the one of the first sheet and the second sheet, and
• convey the one of the first sheet and the second sheet, conveyed to the corresponding one of the first branched conveyance passage and the second branched conveyance passage, in the one of the first direction and the second direction.