Patent ID: 8229342

Claim:
An image forming apparatus, comprising: an image forming section for transferring a toner image onto a sheet; a fixing section for fixing the toner image transferred onto the sheet; a reversing section for reversing facing directions of front and back sides of the sheet that has had the toner image formed on the front side to enable double sided image formation; a reversing conveying passage formed under the reversing section and disposed for putting the sheet back to the image forming section; a first pair of rollers provided above the reversing section and including first and second unit rollers forming a first nip portion for feeding toward the reversing section the sheet, which bears the toner image transferred onto a front side in the image forming section and fixed in the fixing section; a second pair of rollers including third and fourth unit rollers forming a second nip portion, the third unit roller having on its outer peripheral surface an arc-shaped surface and a non-arc-shaped surface receding inwardly from a circle drawn continuously from the arc-shaped surface, the third unit roller adapted for feeding the sheet, which has been fed toward the reversing section by the first pair of rollers, to the reversing section by rotation in a first direction and pulls out the sheet, which is temporarily transferred to the reversing section, from the reversing section by rotation in a second direction opposite to the first direction; and a third pair of rollers including fifth and sixth unit rollers forming a third nip portion, the third pair of rollers transferring the sheet to the reversing conveying passage, so that an image forming is performed with respect to the back side of the sheet pulled out by the second pair of rollers from the reversing section; and a rotational controller for controlling the rotating operation of the third unit roller; wherein the first, second and third pairs of rollers are disposed substantially adjacent to one another along a conveying route along which the sheet is conveyed to the reversing conveying passage via the reversing section; the following mathematical relation is met: x>y<z where x=a distance between the first nip portion and the second nip portion, y=an arc length of the third unit roller, and z=a distance between the second nip portion and the third nip portion, and the rotational controller causes the third unit roller to start rotating at a time immediately after a rear end of the sheet in a sheet conveying direction is out of the first nip portion, subsequently to stop after one rotation of the third unit roller so that the sheet is stopped in a state where the rear end of the sheet does not arrive at the second nip portion.