A Comparison of Spring Stiffness Profiles for Use in a Passive-Elastic Leg Exoskeleton

Graduate Thesis Or Dissertation

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/kk91fm07q

Abstract

Several research groups have pursued the development of a device capable of improving a human’s running ability. In 2009, Grabowski and Herr developed a passive-elastic leg exoskeleton that reduced the metabolic demand of hopping (an analogue to running) by 19 to 28% across a range of hopping frequencies. They implemented bow springs that had a nonlinear, decreasing stiffness. No study has addressed if other spring behaviors could be more effective. In the present study, three exoskeleton spring types were developed with linear, progressively increasing, and progressively decreasing stiffness profiles. The effort of hopping in place was studied for each profile and compared to hopping with no exoskeleton in three subjects. It was hypothesized that a linear profile that matches the stiffness of the leg would result in the lowest metabolic power. Instead, the gradually decreasing stiffness was most effective, reducing metabolic power for one subject by up to 32%.

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