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research-article

An Ankle Exoskeleton Using Lightweight Motor to Create High Power Assistance for Push-off

[+] Author and Article Information
Jiazhen Liu

A843-2 Lee Shau Kee Building, Tsinghua University Beijing, Beijing 100084 China liujz1991@qq.com

Caihua Xiong

Room B207, East building, Advanced Manufacturing Park 1037 Luoyu Road, Hongshan District Wuhan, Hubei 430074 China chxiong@hust.edu.cn

Chenglong Fu

Innovation Park 7-604 Southern University of Science and Technology Guangdong, Shenzhen 518055 China fucl@sustech.edu.cn

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanisms and Robotics. Manuscript received October 12, 2017; final manuscript received March 29, 2019; published online xx xx, xxxx. Assoc. Editor: Xilun Ding.

ASME doi:10.1115/1.4043456 History: Received October 12, 2017; Accepted April 03, 2019

Abstract

Active exoskeletons have capacity to provide biologically equivalent levels of joint mechanical power, but high mass of actuation units may lead to uncoordinated walking and extra metabolic consumption. Active exoskeletons normally have a power burst during push-off, and the requirements on power of motors are high which is the main reason for the high mass. However, in muscle-tendon system, the strategy of injecting energy slowly and releasing quickly is utilized to obtain higher peak power than that of muscle alone. Application of this strategy of peak power amplification in exoskeleton actuation might lead to reductions of input power and device mass. This paper presents an ankle exoskeleton which can accumulate the energy injected by motor during swing and mostly stance phase, then release it quickly during push-off. An energy storage and release system was developed by using a four-bar linkage clutch. In addition, evaluation experiments on the exoskeleton were carried out. Results show that the exoskeleton could provide a high power assistance with a low power motor and reduced the requirement on motor power by 4.73 times. Besides, when walking with the exoskeleton, the ankle peak power was reduced by 25.8% compared to the normal condition. The strategy which imitates working pattern of muscle-tendon system leads to a lightweight and effective exoskeleton actuation, and it also supplies ideas for the designs of lightweight actuators that work discontinuously in other conditions.

Copyright © 2019 by ASME
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