Design and validation of a quasi-passive knee exoskeleton with clutched elastic actuators for human walking assistance

Abstract

Human legs exhibit spring-like behavior during the walking stance phase, motivating the development of lightweight passive lower extremity exoskeletons with elastic energy storage. While such designs offer promise in improving gait economy and reducing muscular effort, they often compromise swing-phase kinematics. Here, we propose a quasi-passive knee exoskeleton equipped with Clutched Elastic Actuators (CEAs) to assist human walking. The CEA on the knee joint comprises a magnetorheological fluid (MRF) bearing unit that serves as a clutch mechanism and a torsional spring for energy recycling. When the spring is engaged, the CEA stores energy during knee flexion and releases it during knee extension. Then, the spring is disengaged to permit unrestricted limb motion and maintain natural gait kinematics during the swing phase. Benchtop tests confirm that the MRF bearing unit delivers sufficient locking torque and enables smooth, rapid engagement and disengagement of the spring. Furthermore, with the assistance of the knee exoskeleton, treadmill walking experiments demonstrate notable reductions in muscle activity. Our approach paves the way for developing lightweight, inexpensive, and quasi-passive exoskeletons that reduce muscular effort and make recreational walking more enjoyable.

Keywords

Knee exoskeletons / Magnetorheological technologies / Mechanism design / Walking assistance / Clutched elastic actuators

CRediT authorship contribution statement

Wenpan Wang: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Zirui Chen: Writing – original draft, Visualization, Validation, Software, Methodology, Formal analysis, Data curation. Linghao Yu: Validation, Software, Data curation. Lei Li: Visualization, Validation, Investigation. Shengfeng Zhu: Visualization, Validation, Data curation. Shiwu Zhang: Writing – review & editing, Resources, Project administration, Funding acquisition, Conceptualization. Weihua Li: Writing – review & editing, Methodology, Conceptualization. Shuaishuai Sun: Writing – review & editing, Supervision, Resources, Project administration, Investigation, Funding acquisition, Formal analysis, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (U21A20119, 52105081), Anhui’s Key R&D Program of China (202104a05020009), USTC, China start-up funding (KY2090000067), Major Project of An-hui Province’s Science and Technology Innovation Breakthrough Plan, China (202423h08050003) and the Fundamental Research Funds for the Central Universities, China . The authors would like to thank all participants involved in the experiments, as well as the exoskeleton team members.

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