Modified VRFT and its application to ultrasonic motors

In this study, we propose a virtual reference feedback tuning (VRFT) method that can take into account a dead-zone. To this end, we first modify the performance index to be minimized in VRFT by focusing on the control error. We then present optimality conditions and their related filters in the modified VRFT method. Next we propose a VRFT method under dead-zone compensation by combining the modified VRFT method and the dead-zone compensation technique proposed in the previous work. The proposed VRFT method is then applied to an experimental ultrasonic motor control system, and its effectiveness is verified.