HYSTERESIS MODELLING AND COMPOSITE CONTROL OF PNEUMATIC MUSCLE ACTUATOR BASED ON PRANDTL–ISHLINSKII MODEL

Kai Liu, Yining Chen, Yang Wu, Haozhi Liu, and Yangwei Wang

Keywords

Pneumatic muscle actuator, hysteresis characteristics, Prandtl–Ishlinskii model, dynamic position tracking, composite control

Abstract

To improve the dynamic position tracking control accuracy of pneu- matic muscle actuator (PMA), a Prandtl–Ishlinskii (P–I) model which is accurate and controllable is proposed. Meanwhile, a composite control strategy is presented by combining the P–I in- verse model and PID control algorithm. The force/length and length/pressure hysteresis characteristics of PMA are captured through static and dynamic tests. On the basis, the P–I model is established to describe the dynamic length/pressure hysteresis loop. Furthermore, to improve the modelling accuracy and enable the P–I inverse model applicable to different loads, the model is multiplied by a correction factor of load. Compared with the classical P–I inverse model, the error can be reduced by 5%–8%. Practicability of the model under feed-forward open-loop control is verified. Finally, to further improve the dynamic control accuracy, a composite control strategy combining the P–I inverse model and incremental PID is proposed. Comparative tests demonstrate that the proposed strategy can greatly reduce the influence of hysteresis characteristics on accuracy, which is also adaptable under different loads in a certain range. The maximum tracking error is less than 0.5 mm and the mean error is less than 0.08 mm, which satisfies the requirements of dynamic control accuracy.

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