Research Papers

Theoretical Analysis and Numerical Optimization of a Wearable Spring-Clutch Mechanism for Reducing Metabolic Energy Cost During Human Walking

[+] Author and Article Information
Roee Keren

Faculty of Mechanical Engineering,
Technion—Israel Institute of Technology,
Haifa 3200003, Israel
e-mail: roeekeren@gmail.com

Yizhar Or

Faculty of Mechanical Engineering,
Technion—Israel Institute of Technology,
Haifa 3200003, Israel
e-mail: izi@technion.ac.il

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received August 30, 2017; final manuscript received August 20, 2018; published online September 17, 2018. Assoc. Editor: K. H. Low.

J. Mechanisms Robotics 10(6), 061004 (Sep 17, 2018) (9 pages) Paper No: JMR-17-1276; doi: 10.1115/1.4041262 History: Received August 30, 2017; Revised August 20, 2018

There is a growing interest in assistive wearable devices for laden walking, with applications to civil hiking or military soldiers carrying heavy loads in outdoor rough terrains. While the solution of powered exoskeleton is known to be heavy and energy consuming, recent works presented wearable light-weight (semi-)passive elements based on elastic springs engaged by timed clutches. In this work, we theoretically study the dynamics of a five-link model of a human walker with point feet, using numerical simulations. We propose a novel mechanism of a spring and two triggered clutches, which enables locking the spring with stored energy while the device's length can change freely. For a given gait of joint angles trajectories, we numerically optimize the spring parameters and clutch timing for minimizing the metabolic energy cost. We show that a cleverly designed device can, in theory, lead to a drastic reduction in metabolic energy expenditure.

Copyright © 2018 by ASME
Topics: Optimization , Springs
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Fig. 1

(a) The five-link model with notation, (b) schematics of the proposed spring-clutches mechanism, and (c) the five-link model with the spring-clutches mechanism on the stance leg

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Fig. 2

The chosen gait from Ref. [39] for the five-link model: (a) joint angle trajectories and (b) motion snapshots

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Fig. 3

(a) Torques at the joints during motion τi(t) and (b) Mechanical power at the joints during motion Pi(t)

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Fig. 4

(a) Contour plot of metabolic energy expenditure as a function of spring parameters k, lo and (b) comparison of mechanical (solid curves) and metabolic (dashed) power at the knee joint for the five-link model, with and without spring

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Fig. 5

(a) Mechanical power at the knee joint P2(t) as a function of time and (b) device length d(t) as a function of time. Decomposition into four time intervals I1…I4 according to signs of P2(t) and d˙(t).

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Fig. 6

Mechanical (solid) and metabolic (dashed) power at the knee joint P2(t) as a function of time for: (a) naive selection of clutch timing, and (b) optimized spring and timing parameters, both compared with the nominal case without spring. Shaded regions correspond to energy saving. Small dotted region denotes excessive expended energy.

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Fig. 7

(a) Mechanical (solid) and metabolic (dashed) power at the knee joint P2(t) as a function of time, under optimized geometry, spring and timing parameters, compared with the nominal case without spring. Shaded regions correspond to energy saving. Small dotted region denotes excessive expended energy. (b) Sketch of the five-link model with the energy-optimal device geometry.



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