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Design and preliminary validation of a compatible lower limb exoskeleton with variable stiffness actuation

Published online by Cambridge University Press:  10 April 2025

Yufeng Zhou ,
Yixin Shao Open the ORCID record for Yixin Shao [Opens in a new window] ,
Di Shi ,
Yanggang Feng ,
Xilun Ding  and
Wuxiang Zhang
Yufeng Zhou
Affiliation:
School of Mechanical Engineering and Automation, Beihang University, Beijing, China
Yixin Shao*
Affiliation:
School of Mechanical Engineering and Automation, Beihang University, Beijing, China Ningbo Institute of Technology, Beihang University, Ningbo, China
Di Shi
Affiliation:
School of Mechanical Engineering and Automation, Beihang University, Beijing, China
Yanggang Feng
Affiliation:
School of Mechanical Engineering and Automation, Beihang University, Beijing, China
Xilun Ding
Affiliation:
School of Mechanical Engineering and Automation, Beihang University, Beijing, China Ningbo Institute of Technology, Beihang University, Ningbo, China
Wuxiang Zhang
Affiliation:
School of Mechanical Engineering and Automation, Beihang University, Beijing, China Ningbo Institute of Technology, Beihang University, Ningbo, China
*
Corresponding author: Yixin Shao; Email: [email protected]
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Abstract

Compliant and safe human–robot interaction is an important requirement in lower limb exoskeleton design. Motivated by this need, this paper presents the design of a compatible lower limb exoskeleton with variable stiffness actuation and anthropomorphic joint mechanisms, for walking assistance and gait rehabilitation. A novel variable stiffness actuator (VSA) based on a guide-bar mechanism was designed, to provide force and impedance controllability. By changing the crank length of the mechanism, the stiffness of the actuator is adjusted in a wide range (from 0 to 1301 Nm/rad), at fast speed (about 2582 Nm/rad/s), and with low-energy cost. These features make it possible for online stiffness adjustment during one gait cycle, to change the human–robot coupling behavior and improve the performance of the exoskeleton. An anthropomorphic hip joint mechanism was designed based on a parallelogram linkage and a passive joint compensation approach, which absorbs misalignment and improves kinematic compatibility between the human and the exoskeleton joint. Furthermore, a torque control-based multimode control strategy, which consists of passive mode, active mode, and hybrid mode, was developed for different disease stages. Finally, the torque control performance of the actuator was verified by benchtop test, and experimental validations of the exoskeleton with a human subject were carried out, which demonstrate that compliant human–robot interaction was achieved, and stiffness variation benefits for control performance improvement when the control mode changes.

Keywords

exoskeletonsmechatronic systemsvariable stiffness actuatorforce controlman-machine systems
Type
Research Article
Information
Robotica , First View , pp. 1 - 16
Copyright
© The Author(s), 2025. Published by Cambridge University Press

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