Patent ID: 7300055

Claim:
An image forming apparatus comprising: a pair of rollers consisting of a rigid roller which is a metal roller or a roller with resin material wound on the periphery thereof and diameter of which is defined as G, and an elastic roller having rubber of hardness of JIS-A Hs65 to 90 wound around the periphery thereof to be depressed with the rigid roller and diameter of which after depression is defined as R; a group of gears, at least one of which is connected to each of the pair of rollers, each roller's gear engaging the other roller's gear, the group of gears having a gear ratio defined as B/A so that the peripheral velocities of each of the pair of rollers are approximately equal to each other, such that (B/A)×(G/R)≈1; and a roller system for transferring a copy sheet by pinching the copy sheet between the pair of rollers by pressing the pair of rollers, with each of the pair of rollers being rotated with approximately the same peripheral velocity by the gear mechanism; wherein the diameter R′ of said elastic roller before depression, from which R is calculated with a reduction rate Q due to the depression by the rigid roller, is set in the range of R 1 <R'<R 2 ; wherein R 1 is a criterial value of a virtual maximum diameter of the elastic roller calculated such that the peripheral velocity of the elastic roller at the part depressed due to the pressing of the elastic roller against the rigid roller coincides with the peripheral velocity of the rigid roller, such that R 1 ={(B/A)×(G)}/Q; and wherein R 2 is a criterial value of a virtual minimum diameter of the elastic roller calculated such that the peripheral velocity of the elastic roller at the part depressed due to the pressing of the elastic roller against the rigid roller with increased diameter defined as G+P, where P is the thickness of the copy sheet, coincides with the peripheral velocity of the rigid roller such that R 2 ={(B/A)×(G+P)}/Q.