High accuracy tracking of ultrasonic motor based on PID operation of sliding surface plus inverse system compensation

Ultrasonic motor as a actuator of control system is widely used in the equipment driven for the precision manufacturing. In this brief, for the selection of the ultrasonic motor, an approximate time-domain mathematical model was established according to the physical mechanism of the ultrasonic motor. The parameters of the model were identified by using the least square method. Responses of the obtained model to the pulse width signal and the triangular wave signal are approximate consistent with those of the actual system respectively, which show the accuracy of the model. Then, the approach of PID operation of the sliding surface plus the inverse system compensation is proposed, the stability of the controlled system and the selection of the proposed approach parameters were discussed. The conventional PI control method with large gain and the proposed control approach were used to track the same signal. Then, the robustness of the proposed control method was tested, a 0.3 kg load was added to the system while keeping the two controller parameters and tracking signals unchanged, and the tracking effects of the two control methods were obtained. The results show that the proposed control approach has a superior performance compared to the conventional PI control approach.