Abstract: A control unit calculates a difference between a displacement of a belt detected by an encoder and a predetermined target value, calculates a pulse frequency of a driving pulse signal based on a feedback control based on the difference and a feed-forward control based on a reference driving pulse frequency, sets a control range of the feedback control to be equal to or smaller than a frequency of one rotation of a driven roller, and controls driving of a pulse motor such that the belt moves at a constant speed.

Abstract: A control unit calculates a difference between a displacement of a belt detected by an encoder and a predetermined target value, calculates a pulse frequency of a driving pulse signal based on a feedback control based on the difference and a feed-forward control based on a reference driving pulse frequency, sets a control range of the feedback control to be equal to or smaller than a frequency of one rotation of a driven roller, and controls driving of a pulse motor such that the belt moves at a constant speed.

Abstract: For a conventional image forming apparatus, since a waveform in a phase opposite that of a rotation change waveform is applied to a drive motor to rotate a photosensitive member, a correction to cancel the rotation change is also performed for a sudden rotation change of the photosensitive member, or for a high frequency change in the noise component generated by a rotation detector. As a result, since the drive motor can not be smoothly rotated, and since the drive torque of the drive motor is not stabilized, small vibrations always occur in the photosensitive member and cause image deterioration, such as a jitter or banding. Therefore, according to the invention, cycling due to the eccentricity of the photosensitive member is represented by using a continuous repetition function, and the waveform in the opposite phase is employed as a drive instruction value for the driving unit. With this arrangement, smooth rotation of the driving unit can be obtained, and the offsetting of the change is performed.