Ultrasonic motors, as one kind of actuators, have attracted a lot of attention since it was proposed more than 20 years ago. In such kind of motors, the sliders (for linear motors) or the rotors (for rotary motors) are driven by the frictional forces between the sliders (rotors) and the stators when ultrasonic waves are propagating on the stators. Since then, the ultrasonic motors have been dev...