Patent ID: 8145105

Claim:
A belt drive control device, comprising: a first detection device to detect one of rotational angular displacement and rotational angular velocity of a driven supporting rotary member included in a plurality of supporting rotary members over which a circular belt is extended and not contributing to transmission of torque; a second detection device to detect one of the rotational angular displacement and the rotational angular velocity of a drive supporting rotary member included in the plurality of supporting rotary members and receiving the torque from a drive source; an extraction device to extract, from a difference between a detection result of the first detection device and a detection result of the second detection device, amplitude and phase of a belt alternating current component of one of a rotational angular displacement and a rotational angular velocity having a frequency corresponding to a cyclical variation in thickness of the belt; a control device to control the driving of the belt by controlling the rotation of the drive supporting rotary member based on the amplitude and the phase of the belt alternating current component extracted by the extraction device; a first holding device to hold the amplitude and the phase extracted by the extraction device: a first feedback device to feed back the amplitude and the phase held by the first holding device to rotation control of the drive supporting rotary member; a second holding device to set and hold respective normal ranges of the amplitude and the phase; and a second feedback device to perform, if any of the amplitude and the phase is out of the normal range thereof, a feedback operation using a substitution value substituted for the any of the amplitude and the phase fed back by the first feedback device, wherein if any of the amplitude and the phase is out of the normal range thereof, the second feedback device uses, as the substitution value, the average value of a plurality of past values of the any of the amplitude and the phase held by the first holding device.