Fast and fine position control of an ultrasonic motor is generally difficult because its rotational speed is nonlinear to voltage, frequency or phase shift input. This paper shows both theoretically and experimentally that the motor has an approximate first-order transfer function between phase shift input and rotational speed output in the case of coarse motion to a command position. This paper also shows experimentally that the rotor moves finely and intermittently in the neighborhood of the command position. A linear position control system which applies integral control action was developed. A fast response of about 50ms and fairly high positioning accuracy up to a rotary encoder resolution were both realized.
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