ULTRASONIC MOTOR

PURPOSE:To reduce the vibration of an ultrasonic motor propagated to the outside through a rotor so as to improve the silentness and efficiency of the motor by setting a vibrating condition so that the outer end of the rotor and a second resonator can become nodes of resonant vibrations. CONSTITUTION:A rotor 101, first resonator 104a, and second resonator 104b are arranged in this order in the direction of axis of rotation and an ultrasonic vibrator 105 which generates vibrations in the direction of the axis of rotation is held between the resonators 104a and 104b so that a rotational driving force can be given to the rotor 101 from vibrations produced at the contacting section between the resonator 104a and rotor 101. In such an ultrasonic motor, a vibrating condition is set so that the outer ends of the rotor 101 and resonator 104b can become nodes of resonant vibrations. In order to create a rigidity difference among the resonators 104a and 104b and rotor 101, the resonator 104a is constituted of an aluminum material and the resonator 104b and rotor 101 are made of steel.