Patent ID: 7800335

Claim:
An image forming apparatus, comprising: an image forming section; and a sheet transfer device, the sheet transfer device comprising: a transfer belt carried by a plurality of rollers, including a drive roller and a detector roller, and configured to rotate around at least two target rotational speeds; a drive motor configured to drive the transfer belt via the drive roller in an excitation mode set according to a target rotational speed of the at least two target rotational speeds; a detector configured to detect a current rotational speed of the transfer belt via the detector roller and configured to output the current rotational speed as a detector pulse signal; and a controller configured to receive the detector pulse signal from the detector, calculate a difference between the current rotational speed and the target rotational speed, calculate a control value based on the difference, and calculate a pulse rate of a drive pulse signal by multiplying the control value with a gain coefficient after having adapted the gain coefficient according to the excitation mode, and control the drive motor based on the pulse rate.