| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which does not cause color shift even when using cardboard by adjusting the rotational speed of a secondary transfer roller in a transfer nip part N in accordance with the thickness of a recording medium. <P>SOLUTION: The transfer nip part N is formed by press-contacting an intermediate transfer belt 17 wound round a drive roller 15 with the secondary transfer roller 18. The surface speed S of the recording medium P in the transfer nip part N is S=v1×2πär1+(t/2)} assuming that the radius of the drive roller 15 is r1 (including the thickness (t) of the intermediate transfer belt 17) and the rotational speed thereof is v1. The surface speed M of the secondary transfer roller 18 in the transfer nip part N is M=v2×(2π×r2) assuming that the radius of the secondary transfer roller 18 is r2 and the rotational speed thereof is v2. By setting S=M (uniform speed), the color shift is not caused in the transfer nip part N. If the recording medium is cardboard, the surface speed M becomes low to cause the color shift. Then, the rotational speed of the secondary transfer roller is adjusted to be increased in accordance with the thickness (t) of the recording medium, whereby the color shift is prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT |
