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A composite position control of flexible lower limb exoskeleton based on second-order sliding mode

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Abstract

Aiming at the problem that the trajectory tracking error of flexible lower limb exoskeleton robot is too large under the condition of external disturbance and parameters uncertainty, a composite position control method based on second-order sliding mode control was proposed. Firstly, the flexible lower limb exoskeleton robot is modeled by Lagrange function. Secondly, considering that the system is affected not only by matched disturbance but also by unmatched disturbance, two finite time state observers are used to observe and compensate the two disturbances in real time. The super-twisting method is employed in the position control section to ensure that the trajectory tracking error of the knee joint converges to zero in finite time. Finally, the Lyapunov function proves the stability of the suggested control technique. The experimental findings reveal that the suggested control approach has a better trajectory tracking effect and resilience than classic PD control and sliding mode control, indicating its superiority.

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Acknowledgements

This work was supported by National Natural Science Foundation of China (Grant No. 61903186) and Natural Science Foundation of Jiangsu Province, China (Grant No. BK20190665).

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Authors and Affiliations

  1. School of Electrical Engineering and Control Science, Nanjing Tech University, Nanjing, 211816, China

    Zhenxing Sun, Jiaxin Qiu & Jinghao Zhu

  2. School of Electronic and Optical Engineering, Nanjing University of Science and Technology Zijin College, Nanjing, 210000, China

    Shenghui Li

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  1. Zhenxing Sun
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  2. Jiaxin Qiu
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Correspondence to Zhenxing Sun.

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Sun, Z., Qiu, J., Zhu, J. et al. A composite position control of flexible lower limb exoskeleton based on second-order sliding mode. Nonlinear Dyn 111, 1657–1666 (2023). https://doi.org/10.1007/s11071-022-07910-9

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