Design of Ankle Exoskeleton Based on Analysis on Energy Cost of Human Walking

doi:10.3901/JME.2021.19.008

Abstract

Abstract: A new type of active unpowered ankle exoskeleton is designed based on the analysis on the energy cost of human walking. Firstly, dynamical equations of swing phase of human walking are built based on a coupled pendulum model and shooting method is used to solve the equations. Energy cost rate of knee-lock, heel-strike and joint friction of the swing leg are calculated based on the principle of momentum conservation. The calculation results show that the energy cost rate of heel-strike is much greater than the energy cost rate resulted from knee-lock and joint friction. Then, based on the results of analysis of the energy cost, an plantar elastic storage mechanism is designed to store the energy cost of heel-strike, which is released during the plantar flexion push-off phase. Pressure signals from forefoot are used to control the clutch mechanism driven by electromagnet, the clamping and releasing states switching of assistive spring is achieved. Experimental results of the prototype shown that plantar energy storage mechanism can increase the output torque and power of the ankle exoskeleton, enhance the ability of assisting walking. The maximum output torque is 19Nm. The muscle activity of the triceps surae is reduced by 8.6% when wearing the exoskeleton compared with the state without wearing the exoskeleton. The measurement results of ankle joint angle show that the exoskeleton rarely interferes with the normal range of motion of the wearer’s ankle during swing phase.

Key words: exoskeleton, ankle joint, clutch mechanism, energy recycle, coupled pendulum

CLC Number:

TP24

WANG Cunjin, DONG Linjie, LI Jie, WANG Xingsong, DING Ye. Design of Ankle Exoskeleton Based on Analysis on Energy Cost of Human Walking[J]. Journal of Mechanical Engineering, 2021, 57(19): 79-92.

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