Position control of ultrasonic motors using MRAC with dead-zone compensation

The ultrasonic motor has a heavy nonlinearity, which varies with driving conditions and possesses variable dead zone in the control input associated with applied load torque. This dead zone is a problem as an accurate positioning actuator for industrial applications and it is important to eliminate the dead zone in order to improve the control performance. This letter proposes a new position control scheme for ultrasonic motors, to overcome the load-torque-dependent dead zone employing model reference adaptive control with dead-zone compensation. The dead zone is compensated by an observer, whereas model reference adaptive control performs accurate position control. Mathematical models are formulated and experimental results are given to validate the proposed position control scheme.