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

The ultrasonic motor has a heavy nonlinearity, which varies with driving co nditions and possesses variable dead zone in the control input associated w ith applied load torque. This dead zone is a problem as an accurate positio ning actuator for industrial applications and it is important to eliminate the dead zone in order to improve the control performance. This letter prop oses a new position control scheme for ultrasonic motors, to overcome the l oad-torque-dependent dead zone employing model reference adaptive control w ith dead-zone compensation. The dead zone is compensated by an observer, wh ereas model reference adaptive control performs accurate position control. Mathematical models are formulated and experimental results are given to va lidate the proposed position control scheme.