The design, validation, and performance evaluation of an untethered ankle exoskeleton

Orekhov, Grigoriy (2022) The design, validation, and performance evaluation of an untethered ankle exoskeleton. Doctoral thesis, Northern Arizona University.

Text Orekhov_2022_design_validation_performance_evaluation_untethered_ankle.pdf - Published Version Download (7MB)

Abstract

Individuals with neuromuscular impairment from conditions like cerebral palsy face reduced quality of life due to diminishing mobility and independence. Lower-limb exoskeletons, particularly ankle exoskeletons, have potential to aid mobility in impaired populations and augment performance in unimpaired populations and have been extensively researched for the past decade. Few untethered ankle exoskeletons exist due to the difficulty of providing enough mechanical power to offset the weight of the exoskeleton on top of improving human biomechanics and metabolic efficiency. Short battery life is also an obstacle to widespread adoption of untethered ankle exoskeletons in the clinic and at home. In this work, we assess the efficacy of our prototype devices during over-ground walking, design new exoskeleton controllers, develop a new ankle exoskeleton device from the ground up, and evaluate the potential for parallel elasticity to improve the performance of our refined exoskeleton platform. In the first study, we observed that our ankle exoskeleton prototype improved metabolic economy, increased walking speed, and lowered plantarflexor muscle activity in a small cohort of individuals with cerebral palsy during over-ground walking – a significant obstacle to the adoption of exoskeletons in free-living settings. In the second study, we presented a framework for developing adaptive, torque sensor-less open-loop controllers that were competitive with our standard closed-loop controllers in mechanical terms while reducing motor energy consumption and noise. The shortcomings of our prototypes in the first and second chapters inspired a third study to develop new lightweight and modular ankle exoskeleton design with a significantly higher torque and power output and joint-level sensing that improved metabolic economy in both unimpaired and impaired cohorts – our device is the second ever to improve metabolic economy in unimpaired adults. We also presented the first-ever lower-limb exoskeleton usability study. In the final study, we use our new hardware platform to design, validate, and demonstrate that a simple parallel elastic element can significantly improve the performance and battery life of our device. Together, these studies establish our untethered ankle exoskeletons as effective and versatile tools for rehabilitation and human augmentation and support the continued research of exoskeletons in clinical and at-home settings.

Item Type:	Thesis (Doctoral)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	ankle joint; cerebral palsy; design and validation; electromechanical efficiency; exoskeleton; human performance; prosthetic devices;
Subjects:	T Technology > TJ Mechanical engineering and machinery
MeSH Subjects:	J Technology,Industry,Agriculture > J01 Technology, Industry, and Agriculture
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of Engineering, Informatics, and Applied Sciences > Mechanical Engineering
Date Deposited:	26 May 2023 17:00
Last Modified:	27 May 2023 08:30
URI:	https://openknowledge.nau.edu/id/eprint/5915

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