Journal
MECHANISM AND MACHINE THEORY
Volume 161, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.mechmachtheory.2021.104323
Keywords
Ankle exoskeleton; Compliant actuator; Nonlinear spring; Energy efficiency
Categories
Funding
- National Natural Science Foundation of China (NSFC) [91848104]
- National Key RAMP
- D Program of China [2016YFE0105000]
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A novel load-adaptive actuator with variable stiffness has been proposed to enhance the energy efficiency of ankle exoskeletons. This actuator adjusts the stiffness of the exoskeleton based on external load and joint angle through an inverted slider-crank mechanism, improving energy efficiency during load and angle variations.
To overcome the limitations of linear series elastic actuators (SEAs) with constant stiffness, a novel load-adaptive actuator with variable stiffness is proposed for actuating ankle exoskeletons through an inverted slider-crank mechanism. Using the proposed actuator, the stiffness of the exoskeleton can be adjusted passively based on the external load and joint angle. To achieve compactness, a novel nonlinear spring mechanism with user-defined load-deflection behaviour is designed by combining a cam mechanism with parabolic beams; this proposed mechanism is used as the series elastic element of the proposed actuator. Dimensional optimisation of the ankle exoskeleton, including the actuator, is subsequently performed for maximising the energy efficiency based on gait biomechanics and considering the constraints of the inverted slider-crank mechanism, electric motor, and the nonlinear spring mechanism. Simulation and experimental results show that the energy efficiency is improved by using the proposed load-adaptive actuator-powered ankle exoskeleton compared with using an exoskeleton driven by linear SEAs. (c) 2021 Elsevier Ltd. All rights reserved.
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