US Patent 7242131 Ultrasonic motor

An ultrasonic motor includes rotors and an annular stator, which are integrated in the rotational direction, a rectangular parallelepiped multilayer piezoelectric transducer, a support shaft, and a transducer with drivers. The support shaft is attached to the outer circumference of the stator and arranged along the radial direction, and the drivers are abutted by a spring urging force to the rotors arranged on both sides of the stator in the axial direction, and are clamped with the rotors. When the transducer is driven so as to excite an elliptical movement produced by combining a bending standing-wave vibration with a longitudinal vibration with the drivers, the rotors are rotated relatively to the stator. Since the drivers are clamped with the integrated rotors, the ultrasonic motor can be driven with small frictional loss and improved conversion efficiency.