A medium transport unit includes an upstream route in which a print sheet is transported, a first switchback route, a second switchback route, a first guide route, a second guide route, a guide flap configured to switch the route so that the print sheet in the upstream route is transported either toward the first guide route or toward the second guide route, a first discharge route from which the print sheet in the first switchback route is discharged, a second discharge route from which the print sheet in the second switchback route is discharged, and a downstream route passing between the first switchback route and the second switchback route and having an upstream end connected to a junction of downstream ends of the first discharge route and the second discharge route.

A preheating device includes two first inverting members disposed at different positions while obliquely intersecting a feeding direction of a continuous recording medium on which an unfixed image is formed, the first inverting members inverting the recording medium by passing a back surface of the recording medium, on which the unfixed image is not formed, therealong before a fixing operation, and at least one heating rotating body disposed at a position further on an outside than a side edge portion of the recording medium in the feeding direction to preheat the recording medium before the fixing operation by passing a portion of the back surface of the recording medium present between the two first inverting members so that the portion of the back surface is wound around the heating rotating body.

A method for heat treatment of mixed media sheets in an image reproduction apparatus having an image forming station, a heat treatment station, a conveying path for conveying the sheets one by one through the image forming station and the heat treatment station, and a duplex loop for looping sheets back from the heat treatment station to the image forming station includes pre-heating a sheet before an image is formed thereon in the image forming station. The pre-heating includes the sub-steps of passing the sheet through the image forming station while the image forming station is idle, passing the sheet through the heat treatment station for pre-heating, and looping the sheet back to the image forming station.

A sheet post-processing apparatus includes a sheet introducing unit, a first sheet discharge unit, a second sheet discharge unit, a sheet processing unit, a sheet conveyance unit, and a control unit. The first and the second sheet discharge unit are configured to be able to discharge a sheet to an outside. The sheet conveyance unit includes a sheet conveyance path arranged between the first sheet discharge unit and the second sheet discharge unit. The control unit controls the sheet conveyance unit to convey the sheet along the sheet conveyance path toward the first sheet discharge unit to a predetermined position at which the sheet is not discharged from the first sheet discharge unit to the outside, then convey the sheet along the sheet conveyance path in an opposite direction toward the second sheet discharge unit, and discharge the sheet from the second sheet discharge unit.

A medium transport unit includes an upstream route in which a print sheet is transported, a first switchback route, a second switchback route, a first guide route, a second guide route, a guide flap configured to switch the route so that the print sheet in the upstream route is transported either toward the first guide route or toward the second guide route, a first discharge route from which the print sheet in the first switchback route is discharged, a second discharge route from which the print sheet in the second switchback route is discharged, and a downstream route passing between the first switchback route and the second switchback route and having an upstream end connected to a junction of downstream ends of the first discharge route and the second discharge route.

A medium transport unit includes an upstream route in which a print sheet is transported, a first switchback route, a second switchback route, a first guide route, a second guide route, a guide flap configured to switch the route so that the print sheet in the upstream route is transported either toward the first guide route or toward the second guide route, a first discharge route from which the print sheet in the first switchback route is discharged, a second discharge route from which the print sheet in the second switchback route is discharged, and a downstream route passing between the first switchback route and the second switchback route and having an upstream end connected to a junction of downstream ends of the first discharge route and the second discharge route.

A sheet transfer device for transferring a sheet between two sheet processing devices comprising a switch for directing sheets from a first transport path coming from the first sheet processing device onto a two-way transport path or for directing sheets from the two-way transport path onto a second transport path for feeding sheets to the second sheet processing device. A transport pinch is provided along the two way transport path for reversing a sheet on the two-way transport path. When in use, the two-way transport path extends downward in a vertically extending free-hanging chamber wherein the sheet engaged by the transport pinch is allowed to hang freely under the influence of gravity. Thereby, a compact device is formed which is able to adjust the sheet to a suitable orientation for the second processing device. The device further prevents forces from the first processing device to disrupt the sheet's orientation in the second processing device.

A medium transport unit includes an upstream route in which a print sheet is transported, a first switchback route, a second switchback route, a first guide route, a second guide route, a guide flap configured to switch the route so that the print sheet in the upstream route is transported either toward the first guide route or toward the second guide route, a first discharge route from which the print sheet in the first switchback route is discharged, a second discharge route from which the print sheet in the second switchback route is discharged, and a downstream route passing between the first switchback route and the second switchback route and having an upstream end connected to a junction of downstream ends of the first discharge route and the second discharge route.

An image forming apparatus includes a paper reading section, a similarity judgment section, and a control section. Between a downstream side in a paper conveyance direction of the paper feed section and a position where image formation is performed, the paper reading section reads an existing image already formed on a surface opposite to a formation surface of a new image newly formed on paper by an image formation section. Based on image data of the new image and image data of the existing image obtained by the image formation section, the similarity judgment section judges similarity between the both images. The control section, upon judging that the similarity is high, causes a pattern image to be formed on a surface of the paper where the existing image is formed, and upon judging that the similarity is not high, does not cause the pattern image to be formed.

An image forming apparatus includes a paper reading section, a similarity judgment section, and a control section. Between a downstream side in a paper conveyance direction of the paper feed section and a position where image formation is performed, the paper reading section reads an existing image already formed on a surface opposite to a formation surface of a new image newly formed on paper by an image formation section. Based on image data of the new image and image data of the existing image obtained by the image formation section, the similarity judgment section judges similarity between the both images. The control section, upon judging that the similarity is high, causes a pattern image to be formed on a surface of the paper where the existing image is formed, and upon judging that the similarity is not high, does not cause the pattern image to be formed.