Patent ID: 6445903
Filing Date: 2002-09-03
Classification: B65H,G03G

Abstract:
An image forming apparatus having a sheet reversing device, said sheet reversing device comprising:a pull-in passage which is provided on the way of a first sheet transporting passage connecting a fixing device and an after treatment device to each other, and into which a sheet transported from the first sheet transporting passage is pulled; a reversal roller pair that is provided on the pull-in passage and provided so that it can rotate forward and reversely in order to reverse the advance direction of the sheet; a nip release member adapted to release a nip of the reversal roller pair; a first roller pair adapted to transport the sheet to a reversal passage that diverges from the pull-in passage at a divergent point located upstream of the reversal roller pair and to the pull-in passage; and a second roller pair adapted to transport the sheet transported from the reversal passage by reverse rotation of the reversal roller pair, and said sheet reversing device feeding out the sheet from the reversal passage in such a manner that a rear end of the sheet transported on the first transporting passage becomes a leading end in the transporting direction; wherein there are provided said sheet reversing device so constituted that the following expression is satisfied, and a controller which, in case of a sheet having a length in the transporting direction of at least 8.5 inch or less, causes the sheet to reverse without the nip release of said reversal roller pair: Y>L1>S>{8.5 (inch)âˆ’X}/2+VÂ·tY>L2, where Y (inch) is the smallest length in the transporting direction of a sheet used in the image forming apparatus, X (inch) is a distance between a rear end of the preceding sheet and a leading end of the succeeding sheet during sheet transportation, L1 (inch) is a length of the transporting passage between the first roller pair and the reversal roller pair, L2 (inch) is a length of the transporting passage between the reversal roller pair and the second roller pair, S (inch) is a length of the transporting passage between the divergent point and the reversal roller pair, V(inch/sec.) is a sheet transporting velocity in the first sheet transporting passage, and t(sec.) is a time necessary for a deceleration/stop/acceleration step when the rotation of the reversal roller is switched from the forward rotation to the reverse rotation or from the reverse rotation to the forward rotation.