Date of Award

Spring 2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biomedical Engineering - (Ph.D.)

Department

Biomedical Engineering

First Advisor

Richard A. Foulds

Second Advisor

William Corson Hunter

Third Advisor

Sergei Adamovich

Fourth Advisor

Gail Forrest

Fifth Advisor

I-Jy Steven Chien

Abstract

Maintaining stable posture is important for humans, even though it is challenging because of our bipedal structure. One of the main balance related disorders is paraplegia due to spinal cord injury. People with a complete spinal cord injury have motor and sensory impairment that greatly reduces the ability to move their lower extremities. In recent years, lower extremity exoskeletons that apply torques generated by motors to the joints of the person have helped to them stand and walk.

This research is a part of an extended project to build a new exoskeleton for use by individuals with paraplegia due to motor complete spinal cord injury. The goal of the project is to develop a device with an intuitive control mechanism capable of generating real time gait and balance. Commercial exoskeletons have achieved great steps regarding restoring ambulation. On the other hand, most of them do not actively support bipedal balance. In addition, commercially available exoskeletons except the REX need crutches to balance for people with motor complete paraplegia. The NJIT TREKKER, our laboratory’s research exoskeleton, suggests a novel, human-robot interface strategy that allows users to completely control and feel the trajectories of their exoskeleton-assisted feet, and be able to walk with considerably greater independence. The first study to develop TREKKER was performed before where a trekking pole was attached to each foot of a biped robot. Subjects controlled the trajectory of the foot of the biped by applying small forces to the trekking poles. The study proved that hands can produce trajectories similar to human foot trajectories when provided with haptic and visual feedback.

If the hands and arms are effective surrogates for expressing ambulation, can they also be surrogates for natural balance in quiet standing? This is the main question that this dissertation answers. Importantly, this dissertation considers the ability of the arms and hands to make rapid adjustments to the center of pressure (COP) that will follow the center of mass (COM) and allow the person to retain balance to achieve this aim a perturbing system was constructed to study human body response to perturbations. Special shoes with small blocks attached to their soles were designed to study the capability of human body to adapt to base of support (BOS) reduction, and two special platforms with shoes on Pivots and two trekking poles attached to them were designed to study the effectiveness of using trekking poles. The pivots were used to eliminate the use of ankle strategy to retain balance by non-disabled subjects. In this study, subjects were asked to stand in front of the perturbing system and within the motion capture system’s field of view, then they were perturbed with at seven different forces with and without visual feedback in three different experiments: using regular shoes, the shoes with small blocks attached to their soles, and the shoes with pivots and trekking poles. Biomechanical parameters were studied to assess balance in A/P plane in each of the three experiments. The results suggest that the use of trekking poles is a viable approach to maintain balance during quiet standing.

The main conclusion of this study is that using trekking poles is a good approach to maintain balance in quiet standing and as a response to small perturbations. Statistical analysis of SI, error signal peaks, and correlations comparing Pivots experiment to Regular experiment support this hypothesis. In addition, the high correlation coefficients between COM and COP of quiet standing on Pivots and in Pivots experiment with perturbations, and the high correlation coefficients of the correlation between COP and the trekking poles trajectories indicates that the trekking poles are working as a surrogate to the ankle joint. It is concluded that using the trekking poles, though the response to perturbations does not match the biological response, is good enough to maintain balance in quiet standing and perturbed quiet standing especially for small perturbations.

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