Position tracking of linear piezoelectric motor using sliding mode control with closed-loop filtering

Piezoelectric motors are used for high precision positioning applications. It is quite difficult to get an exact model of the motor as non-linear phenomenon of inverse piezoelectric effect and friction are involved. Using linear controllers for precision positioning does not result good tracking performance. A sliding mode control based on simplified model of the motor is used. Due to modelling error and external disturbance such control suffers from chattering resulting in wear and tear. Thus a sliding mode control with closed-loop filtering is proposed for position tracking. This scheme has reduced chattering while maintaining robustness property of variable structure control. In this scheme a low pass filter is used to extract the equivalent control from the switching control signals and concurrently a second low pass filter is used to reduce the switching gain. With the extraction or equivalent control or disturbance and reduction of switching gain the chattering is kept at lower level. Experimental results are shown for position tracking of linear piezoelectric motor with and without disturbance. Tracking results observed proves the scheme is effective in extracting equivalent control, reduce chattering and robust to bounded disturbances.