Background: Ultrasonic motor is a typical nonlinear system with significant time-varying
characteristics. In this paper, the position control of ultrasonic motor is comprehensively studied.
Method: Firstly, a Hammerstein model is established to obtain the characteristic form of the motor
operation, followed by the establishment of an inverse control model aiming to handle the nonlinear
characteristic of the ultrasonic motor. By canceling the nonlinear component, the motor is modeled as a
linear system and the controller is also designed linearly. The direct multi-step predictive control strategy is
then designed and used to realize the precise position control on the basis of stable motor operation.
Conclusion: The experimental results show that the proposed control algorithm has superior tracking
behavior and small steady-state error when the structure or parameters of the controlled object change.