Position sensorless control for ultrasonic motors based on input voltage information

Abstract

This paper presents a method of position sensorless control of ultrasonic motors (USM). The position sensorless control method is useful for reducing the cost and size of drive system. The position estimation method is based on the input voltage information of the ultrasonic motor. The characteristic of input voltage versus rotor position is expressed by a quadratic function which is used to estimate a rotor position based on input voltage information. This estimation method, which uses only the drive voltage of the ultrasonic motor, is a very simple algorithm and shows good estimation ability. The parameters of the quadratic function are adjusted by using the recursive least squares method and are obtained on-line. Since it can correspond to parameter change, the estimated rotor position shows good agreement with the measured rotor position against load torque and motor temperature changes. Sensorless position control is achieved by using the estimated rotor position instead of the measured rotor position. The validity of the proposed method is confirmed by experimental results. © 2008 Wiley Periodicals, Inc.