Adaptive linearization of hysteresis for enhanced positional accuracy of robotic arm

Precision control of multi-axis piezo actuated micro / nanopositioning stages suffers not only from the inherent nonlinearities but also from parametric variations and uncertainties. In order to effectively implement any real-time control theory to mitigate the effects of nonlinearity, an adaptive mechanism to update the control system is a prerequisite. This paper investigates the effects of hysteretic nonlinearity in a second order Dahl model based piezoelectric manipulator. The plant performance is known to improve with injection of a suitable dose of noise called “dither”. The concept of dither based control is interwoven with the conventional PID controller to introduce a novel adaptive dither control strategy. A double axis piezo stage is considered for controller design and validation. The controller performance is ascertained using three specific tests - a) Tracking Error Test, b) Multi-frequency, multi-amplitude tracking test and c) Two-axis Circular Contour Tracking Test. Results show an enhanced positioning accuracy of the manipulator in the presence of proposed control scheme than without it. The proposed control transpires as an effective control to improve tracking accuracy and resist external disturbances.