Design and feedforward control of a two-degree-of-freedom positioning stage with bidirectional piezoelectric drive

The positioning stage composed of piezoelectric stacks and flexible mechanisms is highly competitive in the field of micro/nanomanipulation. Driving stroke and positioning accuracy are the two most important factors to evaluate the positioning stage. However, the attenuation of the driving stroke caused by the stiffness load of the flexible mechanism is an important but neglected problem. On the other hand, the hysteresis of piezoelectric ceramics directly affects the positioning accuracy of the platform. In this study, a two-degrees-of-freedom positioning stage with low displacement attenuation and hysteresis is proposed. Static and dynamic models of the positioning stage were established to derive analytical models of the displacement amplification ratio, structural stiffness, and natural frequency. The displacement transfer coefficient was introduced to establish an equivalent physical model for structural stiffness and displacement attenuation. Genetic algorithms were used to optimize the structural parameters. Finite element analysis is performed to verify the accuracy of the analytical model. The hysteresis is suppressed by the combination of bidirectional piezoelectric driving and inverse Bouc-Wen model feedforward compensation. The measurement results indicated that the proposed positioning stage had a displacement transfer coefficient of 0.82, which was 95.89% lower than the hysteresis of the piezoelectric stack.