Author: Robert Trott
Trott, Robert, 2022 Novel Control for a Post-Stroke Gait Rehabilitation Exoskeleton, Flinders University, College of Science and Engineering
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Stroke is the second highest cause of death worldwide and the third leading cause of adult disability across all age brackets. Recovering gait following stroke is a major goal of patients, and hence rehabilitation, as it is central to many activities of daily living. Of the different treatment modalities, robotic assisted gait training is growing in popularity, but is still considered complementary to, and not substitute for conventional therapies comprising physiotherapy, overground walking and body weight supported treadmill training. The potential advantages that lower limb robotics bring to neurorehabilitation over conventional therapies include, higher dosage, specificity, improved consistency, and duration, though these benefits have been slow to manifest. Exoskeletons are well placed to provide these benefits, as well as environmental variation and task salience if they can be used away from outpatient settings. Control strategies that may be enhancing of recovery are often confined to stationary exoskeletons, and the control of mobile exoskeletons is only loosely related to gait, if at all, which limits rehabilitation outcomes.
The primary aim of this PhD thesis was to develop an adaptive, user-initiated gait Controller that aims to target a novel neural recovery pathway. The Controller would use a robotic exoskeleton, with the intention of developing novel neuroplasticity that is beneficial for gait and would be permissive of simultaneous control of hip and knee posture. A theoretical framework based on the principles of neuroplasticity was proposed that seeks to bring higher engagement, task variance, and volition to gait rehabilitation. This framework considers stroke and rehabilitation timelines and the interaction of the proposal with existing theory, how beneficial neuroplasticity may manifest, and how the proposal may be detrimental. A comprehensive survey of candidate lower limb devices followed (164 devices), to understand exactly what features are compatible, complementary, or contradictory to the proposed control method, and to understand the implications the various specifications have. Specifically, it was found that ambulating exoskeletons that can move around the environment were preferred for their ability to be used in the community and the home, and that extended joint range of motion will be permissive of activities that are supportive of gait such as sit-to-stand and stair ascent/descent. Of the various control systems that have been implemented with exoskeleton devices, trajectory control, where motion is enforced on the limb by the exoskeleton, is preferred.
The method of control was assessed for suitability as a gait controller through a participant study (n = 21). Participants were asked to reproduce the motion required for the controller, and with minor modification to participant motion it was shown that reliable control signals can be obtained. The remainder of the thesis applies the learnings of the previous stages in the development of the Controller and an accompanying Sensor. The custom Sensor was designed with a small form factor to be applied on the Controller. The thesis concludes with an implementation of the Controller and a successful demonstration of the proposed concept, where the control signals are reproduced on a scale lower limb exoskeleton. The full technical detail and specification of the Controller, and the custom position Sensor developed specific for this application, are presented as part of this work.
This work has added a new theoretical framework for gait control following stroke and has added technological capability to implement the proposal. It is the primary recommendation of this PhD that the novel control method be tested further with participant studies and that the component hardware be developed further. Therapies targeting novel recovery mechanisms breathe fresh air into rehabilitation and may inspire other new treatments, and future funded work originating from this PhD will see the concept tested with a chronic stroke population, using an ambulating exoskeleton and the Controller.
Keywords: Exoskeleton, Gait, Stroke, Rehabiliation, Robotics, Sensors
Subject: Engineering thesis
Thesis type: Doctor of Philosophy
Completed: 2022
School: College of Science and Engineering
Supervisor: David Hobbs