Ultrasonic motor having a plate-shaped vibrating body

Abstract

An ultrasonic motor is provided with increased torque without an increase in size. The ultrasonic motor includes a stator having a plate-shaped vibrating body including first and second main surfaces and a piezoelectric element on the first main surface; and a rotor in contact with the second main surface. The piezoelectric element is disposed along a circumferential direction of a traveling wave so as to generate the traveling wave circulating around an axial direction Z by vibrating the vibrating body. The piezoelectric element vibrates the vibrating body in a vibration mode including a nodal line extending in the circumferential direction. A mass addition portion is provided along the circumferential direction on at least one of the first and second main surfaces of the vibrating body, and the mass addition portion is located outside the nodal line in a direction perpendicular to the axial direction Z.