Stiffness optimization based on muscle fatigue and muscle synergy for passive waist assistive exoskeleton
Robotic Intelligence and Automation
ISSN: 2754-6969
Article publication date: 4 April 2023
Issue publication date: 23 June 2023
Abstract
Purpose
This paper aims to optimize the stiffness coefficient of the elastic element for a passive waist assistive exoskeleton (WAE). There is a tradeoff between stiffness coefficient of elastic element of the exoskeleton and work efficiency of the wearer, because elastic element affects original bending motion of the wearer and the force requirement of erector spinae is compensated by the other muscles. However, there is no accepted conclusion on how to determine the proper stiffness coefficient, especially with respected to the effort of groups of muscles, not only erector spinae.
Design/methodology/approach
In this study, a consumption indicator based on muscle fatigue of seven muscles is proposed and a Bayesian-based human-in-the-loop optimization approach is adopted to optimize the stiffness coefficient. Pneumatic artificial muscles are used to replace the mechanical elastic part to adjust the assistive force automatically. The proposed optimization method is verified by the way of load-lifting experiments with three different conditions: without exoskeleton, with fixed air pressure and with optimized air pressure. Six subjects participated in the experiment and each experiment is performed in different day.
Findings
Compared with No-Exo condition and static assistance condition, the parameter-optimized waist exoskeleton averagely reduces muscle fatigue of the six subjects by 45.30 ± 29.14% and 30.94 ± 30.29%, respectively. The experimental results indicate that the proposed method is effective to reduce muscle fatigue during stoop lifting task.
Originality/value
This paper provides a novel cost function construction method based on muscle fatigue and muscle synergy for passive WAE stiffness optimization.
Keywords
Acknowledgements
This work was supported in part by the National Natural Science Foundation of China under Grant No. 61603284, 61903286 and 62203341, in part by the Fundamental Research Funds for the Central Universities under Grant WUT: 2022IVA044.
Citation
Pang, M., Li, R., Ding, Y., Tang, B., Luo, J. and Xiang, K. (2023), "Stiffness optimization based on muscle fatigue and muscle synergy for passive waist assistive exoskeleton", Robotic Intelligence and Automation, Vol. 43 No. 3, pp. 209-224. https://doi.org/10.1108/RIA-08-2022-0221
Publisher
:Emerald Publishing Limited
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