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Adaptive Control of Lower-Limb Exoskeletons for Walking Assistance Based on Inter-Joint Coordination

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Abstract

Unilateral motor impairment can disrupt the coordination between the joints, impeding the patient’s normal gait. To assist such patients to walk normally and naturally, an adaptive control algorithm based on inter-joint coordination was proposed in this work for lower-limb exoskeletons. The control strategy can generate the reference trajectory of the affected leg in real time based on a motion coordination model between the joints, and adopt an adaptive controller with virtual windows to track the reference trajectory. Long Short-Term Memory (LSTM) network was also adopted to establish the coordination model between the joints of both lower limbs, which was optimized by preprocessing angle information and adding gait phase information. In the adaptive controller, the virtual windows were symmetrically distributed around the reference trajectory, and its width was adjusted according to the gait phase of the auxiliary leg. In addition, the impedance parameters of the controller were updated online to match the motion capacity of the affected leg based on the spatiotemporal symmetry factors between the bilateral gaits. The LSTM coordination model demonstrated good accuracy and generality in the gait database of seven individuals, with an average root mean square error of 3.5\(^\circ\) and 4.1\(^\circ\) for the hip and knee joint angle estimation, respectively. To further evaluate the control algorithm, four healthy subjects walked wearing the exoskeleton while additional weights were added around the ankle joint to simulate an asymmetric gait. From the experimental results, it was shown that the algorithm improved the gait symmetry of the subjects to a normal level while exhibiting great adaptability to different subjects.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. The data are not publicly available due to privacy or ethical restrictions.

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Funding

This work was supported by the Graduate Scientific Research and Innovation Foundation of Chongqing, China (CYB19062), and the China Scholarship Council (CSC202206050121).

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Author notes

  1. Chaoyang Li and Lincong Luo contributed equally to this work.

Authors and Affiliations

  1. School of Mechanical Engineering, Chongqing University, Chongqing, 400044, China

    Chaoyang Li, Zhi Liu, Tianchi Chen, Ye He & Xiaoan Chen

  2. Rehabilitation Research Institute of Singapore, Singapore, 308232, Singapore

    Lincong Luo & Lei Li

  3. Department of Orthopedics, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China

    Songxiang Liu

  4. School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore, 639798, Singapore

    Wei Tech Ang

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  1. Chaoyang Li
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Correspondence to Ye He.

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Approval of all ethical and experimental procedures and protocols was granted by Chongqing University Cancer Hospital Ethics Committee under Application No. CZLS2021070-A.

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Li, C., Luo, L., Liu, Z. et al. Adaptive Control of Lower-Limb Exoskeletons for Walking Assistance Based on Inter-Joint Coordination. J Bionic Eng (2024). https://doi.org/10.1007/s42235-024-00537-z

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