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Unknown system dynamics estimator-based impedance control for lower limb exoskeleton with enhanced performance

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Abstract

In this article, an unknown system dynamics estimator-based impedance control method is proposed for the lower limb exoskeleton to stimulate the tracking flexibility with the terminal target position when suffering parametric inaccuracies and unexpected disturbances. To reinforce the robust performance, via constructing the filtering operation-based dynamic relation, i.e., invariant manifold, the unknown system dynamics estimators are employed to maintain the accurate perturbation identification in both the hip and knee subsystem. Besides, a funnel control technique is designed to govern the convergence process within a minor overshoot and a higher steady-state precision. Meanwhile, an interactive complaint result can be obtained with the aid of the impedance control, where the prescribed terminal trajectory can be adjusted into the interaction variable-based target position by the force–position mapping, revealing the dynamic influence between the impedance coefficient (stiffness and damping) and the adjusted position magnitude. A sufficient stability analysis verifies the ultimately uniformly bounded results of all the error signals, and even the angle errors can be regulated within the predefined funnel boundary in the whole convergence. Finally, some simulations are provided to demonstrate the validity and superiority including the enhanced interaction flexibility and robustness.

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The data supporting the findings of this study are available within the article.

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Authors and Affiliations

  1. Northwest Institute of Mechanical and Electrical Engineering, Xianyang, 712099, Shaanxi, China

    Wenhao Zhang, Peng Song, Mingying Wu, Qiang Li, Xinmin Mo & Pingxin Ji

  2. Xi’an Exo-Smart Dynamics Technology Ltd., Xi’an, 712046, Shaanxi, China

    Wenhao Zhang, Peng Song, Qiang Li, Xinmin Mo & Pingxin Ji

  3. Department of Mechanical and Engineering, Beijing Institute of Technology, Beijing, 100081, China

    Pingxin Ji

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  1. Wenhao Zhang
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Correspondence to Wenhao Zhang.

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This work was supported in part by the Young Talent Fund of Association for Science and Technology in Shaanxi, China (No. 20230126).

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Zhang, W., Song, P., Wu, M. et al. Unknown system dynamics estimator-based impedance control for lower limb exoskeleton with enhanced performance. Control Theory Technol. 22, 56–68 (2024). https://doi.org/10.1007/s11768-023-00189-0

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