Precision motion control of a linear piezoelectric ultrasonic motor stage

An piezoelectric ultrasonic motor (USM) is a kind of motor which offers high precision and fast response. It is widely used in industrial and medical applications and precision engineering in the forms of micromanipulator, surgical instruments and robots, etc. This paper presents a control strategy for a linear USM stage. The model of the USM is built and its parameters are identified. The PID controller is used and a LQR-assisted approach is developed and applied in order to help to find optimal PID parameters and achieve the advantages of optimal control. A nonlinear compensation including a sign function and sliding mode control is designed to compensate the nonlinear dynamics including friction and hysteresis. The control system is implemented on a dSPACE control card. The experimental results show that the LQR-assisted PID tuning achieves a performance better than the traditional tuning method such as relay-based PID tuning. Moreover, the nonlinear compensation is capable of improving the system performance significantly.