Position Sensorless Control for Ultrasonic Motors Based on Input Voltage Information

This paper presents a method of position sensorless control of ultrasonic motor (USM). The rotor position of USM is estimated based on the input voltage information. The characteristic of input voltage versus rotor position is expressed by a quadratic function. Since the parameters of quadratic function are adjusted on-line, estimated rotor position agrees well with actual rotor position against load torque and motor temperature changes. Position sensorless control is achieved by using estimated rotor position instead of measured rotor position. The validity of the proposed method is confirmed by experimental results.