Speed control of ultrasonic motors by adaptive control with a simplified mathematical model

The ultrasonic motor is a new type of motor. In recent years, some mathematical models for the ultrasonic motor have been reported. However, these models are very complex to apply to control of the motor, and therefore speed or position controllers for this type of motor have been designed based on proportional and integral controllers or fuzzy controllers. Since these controllers cannot take account of the motor’s dynamics, a simple and convenient mathematical model of the ultrasonic motor is necessary in order to achieve high control performance. The authors propose a simpliFied mathematical model for the ultrasonic motor, which is expressed by a difference equation, and they then design a speed controller based on adaptive control theory. Adaptive control is attractive for controlling the ultrasonic motor because its speed characteristics vary with drive conditions. The effectiveness of the proposed control scheme is demonstrated by experiments. Furthermore, the paper indicates the influence of control delay and model orders on the mathematical model experimentally.