A sheet folder includes a conveyor conveying a sheet, a first folding roller and a second folding roller that form a first nip, a third folding roller forming a second nip with the second folding roller, a first guide movable between a first guide posture and a first retracted posture, a second guide movable between a second guide posture and a second retracted posture, and a motor. The motor rotates the second folding roller forward to convey the sheet toward the first nip, reverse to convey the sheet toward the second nip, moves the first guide to arrange in the first guide in the first guide posture or the first retracted posture, and moves the second guide to arrange the second guide in the second guide posture or the second retracted posture.

A sheet folding device includes first and second folding rollers as a pair arranged on a sheet transfer path located downstream of a printing unit and configured to form a fold on a printed sheet. At least the first folding roller includes a small-diameter portion formed at a position corresponding to a range of a width of a separating roller in the sheet width direction, and a large-diameter portion formed at a position other than the position of the small-diameter portion.

A collation folding device comprising one or more fold rollers mounted in fixed positions. Below and adjacent to the fold rollers are adjustable nip rollers to form nip spacing between the rollers. The adjustable nip roller is mounted on a nip axis shaft. An adjustment mechanism is used for moving the nip axis shaft to adjust the nip spacing. The nip adjustment mechanism includes a bearing block cam follower on which the nip axis shaft is fixedly mounted and supported. An eccentric cam in operative contact with the bearing block cam follower. Rotation of the eccentric cam on the eccentric cam axis drives the bearing block cam follower in its linear motion to adjust the nip spacing.

A postprocessing device performs postprocessing on sheets received from an image forming apparatus. The postprocessing device includes a pair of folding rollers, a folding blade, a transport device, a drive portion, and a drive controller. The drive controller controls the drive portion to match moving speed of a tip portion of the folding blade with moving speed of a circumferential surface of the folding rollers, at a time point that the sheaf of the sheets makes contact with the circumferential surface of the folding rollers, when the image forming apparatus forms the image by ink jet printing, and to match the moving speed of the tip portion of the folding blade with the moving speed of the circumferential surface of the folding rollers, at a time point that the sheaf of the sheets reaches the nip region between the folding rollers.

A sheet is nipped and held by first and second bend forming rollers of which rotation axes are in a direction perpendicular to a sheet conveying direction, the conveying speed of the held portion is made lower than a sheet conveying speed on the upstream side so that a bend is formed on the sheet, the sheet is conveyed toward the bend forming rollers such that the sheet conveying direction to the bend forming rollers passes through a line segment from the rotation axis of the first bend forming roller to a predetermined position on a surface of the first bend forming roller, and the bend formed on the conveyed sheet is pressed from the surface of the sheet in a position on the opposite side of the second bend forming roller with respect to the position where the sheet is in contact with the first bend forming roller.

A sheet is nipped and held by first and second bend forming rollers of which rotation axes are in a direction perpendicular to a sheet conveying direction, the conveying speed of the held portion is made lower than a sheet conveying speed on the upstream side so that a bend is formed on the sheet, the sheet is conveyed toward the bend forming rollers such that the sheet conveying direction to the bend forming rollers passes through a line segment from the rotation axis of the first bend forming roller to a predetermined position on a surface of the first bend forming roller, and the bend formed on the conveyed sheet is pressed from the surface of the sheet in a position on the opposite side of the second bend forming roller with respect to the position where the sheet is in contact with the first bend forming roller.

A folding machine comprises a blade folding unit having a first and a second folding roller, the folding roller axes thereof defining a folding roller plane, and having a folding blade which is oriented and is movable in a folding blade plane which is oriented perpendicularly to the folding roller plane and intersects the folding roller plane in an intersection line. The folding blade is arranged in a retracted position in or below a horizontal plane which comprises the intersection line.

A sheet folder includes a conveyor conveying a sheet, a first folding roller and a second folding roller that form a first nip, a third folding roller forming a second nip with the second folding roller, a first guide movable between a first guide posture and a first retracted posture, a second guide movable between a second guide posture and a second retracted posture, and a motor. The motor rotates the second folding roller forward to convey the sheet toward the first nip, reverse to convey the sheet toward the second nip, moves the first guide to arrange in the first guide in the first guide posture or the first retracted posture, and moves the second guide to arrange the second guide in the second guide posture or the second retracted posture.