To make the speed control function of a driving source effectively act on an image carrier by detecting the rotating state of a rotary output shaft and controlling the rotation of the rotary output shaft based on a detection signal.
When an ultrasonic motor is actuated, a signal from a pulse detection part 45c is transmitted to a motor driving part and impressed voltage on a piezoelectric element 53 stuck to a stator 51 is changed in accordance with circumstances while confirming the conditions of the output shaft 45 (whether speed variation occurs or not) so as to obtain desired rotational accuracy. As for the revolving speed at such a case, the rotation of the motor is not high-speed rotation as a DC motor but low-speed rotation because the rotary shaft 45 is always brought into press-contact, that is, a rotor 50 is always brought into press-contact with the stator 51 by energizing force of a leaf spring 48. Therefore, a photoreceptor drum is driven in a state where a drum shaft and the output shaft 45 are directly connected by coupling, that is, in a state where a deceleration means (timing belt and pulley) is not required.
MATSUI TAKAO
SUGIMOTO SHIGETO
