An image forming apparatus includes a sheet separation device, a first sheet feeder, a second sheet feeder, an image forming device, and circuitry. The sheet separation device is configured to separate a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at a bonding portion of the two-ply sheet. The first sheet feeder is configured to feed the two-ply sheet. The second sheet feeder is configured to feed an inner sheet to be inserted between the two sheets. The image forming device is configured to form an image on a surface of the inner sheet. The circuitry is configured to cause the first sheet feeder to feed the two-ply sheet, perform a sheet separating operation on the two-ply sheet and cause the second sheet feeder to start feeding the inner sheet before completion of the sheet separating operation on the two-ply sheet.

A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at one end of the two-ply sheet. The sheet separation device includes a separator that includes a first separator and a second separator. The first separator is inserted into a gap between the two sheets of the two-ply sheet. The second separator is inserted between the two sheets at said another end of the two-ply sheet that is opposite to the one end of the two-ply sheet and moves in a width direction of the two-ply sheet after the first separator is inserted into the gap and relatively moves from the one end to said another end.

A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at a bonding portion of the two-ply sheet. The sheet separation device includes a winding roller, a conveyance roller pair, and a separation claw. The winding roller rotates and winds the two-ply sheet. The conveyance roller pair conveys the two-ply sheet toward the winding roller. The separation claw is inserted into a gap between the two sheets at a position between the winding roller and the conveyance roller pair. The separation claw is disposed in a space that is bounded by an imaginary plane and includes the winding roller. The imaginary plane passes through a nip of the conveyance roller pair and a winding start position at which the two-ply sheet starts to be wound around the winding roller.

A sheet processing apparatus is configured to sandwich one or more sheet media in a two-ply sheet in which two sheets are overlaid and bonded together at a portion of the two-ply sheet. The sheet processing apparatus includes circuitry configured to control insertion processing to insert the one or more sheet media into the two-ply sheet based on a length of the two-ply sheet in a conveyance direction, a length of one of the one or more sheet media in the conveyance direction, and a number of the one or more sheet media.

A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at one end of the two-ply sheet. The sheet separation device includes a separator that includes a first separator and a second separator. The first separator is inserted into a gap between the two sheets of the two-ply sheet. The second separator is inserted between the two sheets at said another end of the two-ply sheet that is opposite to the one end of the two-ply sheet and moves in a width direction of the two-ply sheet after the first separator is inserted into the gap and relatively moves from the one end to said another end.

A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at a bonding portion of the two-ply sheet. The sheet separation device includes a winding roller and a gripper. The winding roller rotates and winds the two-ply sheet to separate the two-ply sheet. The gripper is disposed in the winding roller and configured to grip a gripped portion of the two-ply sheet at one end of the two-ply sheet without abutting a tip of the gripped portion at the one end of the two-ply sheet on a member.

A sheet separation device includes a sheet separator and a conveyor. The sheet separator separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at a bonding portion of the two-ply sheet. The conveyor conveys the two-ply sheet toward the sheet separator while bending the two-ply sheet in a direction that intersects a conveyance direction of the two-ply sheet.

A sheet processing device sandwiches a sheet-shaped medium in a two-ply sheet in which two sheets are overlaid and partially bonded. The sheet processing device includes a separator, a conveyor, and a switching member. The separator separates the two sheets of the two-ply sheet. The conveyor is disposed downstream from the separator in a sheet conveyance direction and conveys the two-ply sheet. The switching member is disposed downstream from the conveyor in the sheet conveyance direction. The switching member switches a conveyance path of the two-ply sheet to convey the two-ply sheet to a fixing path on which fixing processing is performed on the two-ply sheet or a non-fixing path on which no fixing processing is performed on the two-ply sheet.

An image forming system includes an image forming apparatus, a sheet processing device, and control circuitry. The image forming apparatus forms an image on a sheet. The sheet processing device performs post-processing on the sheet. The sheet processing device includes a first conveyance path through which the sheet is conveyed and subjected to the post-processing and a second conveyance path through which the sheet is conveyed without the post-processing. In response to an instruction of print jobs including both a print job of one or N copies subjected to the post-processing and a print job not subjected to the post-processing, the circuitry executes the job not subjected to the post-processing during execution of an M-th copy of the job subjected to the post-processing and causes the sheet to be conveyed through the second conveyance path, where N is two or greater and M satisfies 1≤M<N.

A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at a bonding portion of the two-ply sheet. The sheet separation device includes a separator, an abnormality detection device, and circuitry. The separator is configured to move to be inserted into a gap formed between the two sheets of the two-ply sheet. The abnormality detection device is configured to detect an abnormal state in which the gap larger than a predetermined size is not formed between the two sheets before the separator is inserted into the gap. The circuitry is configured to control movement of the separator based on a result detected by the abnormality detection device.