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Achieving Near-Natural Locomotion in Transfemoral Amputees - A Control Theoretic Approach
Date
2024Type
DissertationDepartment
Electrical Engineering
Degree Level
Doctorate Degree
Abstract
Amputation of the lower limb is prescribed to address conditions such as trauma, vascular issues, tumors, neuropathy, frostbite, and complications from diabetes. Post-surgery, the individual has to be fitted with a prosthetic limb to regain mobility. While a good-fitting, well-designed prosthetic device can help support body weight and locomotion, the loss of lower limb muscles profoundly impacts body support, and stability and often results in asymmetrical gait patterns.Traditionally, prosthetic limbs were designed primarily to support weight and mimic the appearance of natural limbs. However, modern prosthetic devices aim for active functionality, striving to replicate near-natural human locomotion. However, achieving such functionality is not an easy task as the control of the prosthetic limb has to determine the user’s intent while adapting to unknown nonlinear dynamics, and varying terrain and environmental conditions.
Among lower limb amputations, transtibial amputations are the most common. The loss of the ankle joint for transtibial amputees causes several constraints during gait, such as lower walking speed, increased metabolic energy expenditure, and reduced power in the amputated limb during the push-off phase. For above-knee amputations, where the individual loses both the knee and ankle joints, the effects are more severe. Losing multiple joints leads to significant asymmetry in gait, which can affect musculoskeletal health in the long run.
This dissertation addresses the critical challenges encountered in controlling above-knee prosthetic limbs to promote a symmetrical gait and natural movement in transfemoral amputees. Traditional control methods often fall short due to the inherent uncertainty in user intent and prosthetic dynamics. To overcome these limitations, two intelligent controllers are designed for above-knee prostheses.
A pivotal component of this dissertation is a comparative case study conducted to analyze muscle activity and gait asymmetry in individuals with osteomyoplastic transfemoral amputation (OTFA) compared to able-bodied counterparts. The findings reveal significant muscle activity in residual muscles during various gait types among OTFA subjects, emphasizing notable asymmetries in their gait patterns. This empirical insight underscores the critical need to address gait asymmetry in both prosthetic limb design and control strategies.
A radial basis function neural network-based controller has been designed and developed to reduce gait asymmetry. The controller showed significant improvement from the traditional PD controller which is mostly used for prosthetic leg systems. The designed controller is stable and shows promising results in optimizing the gait asymmetry cost function.
The second intelligent control strategy for the prosthetic leg is a novel neuro-dynamic approach, leveraging actor-critic networks to learn and adapt control actions dynamically. The primary objective is to minimize long-term gait asymmetry between the intact and amputated sides, thereby enabling a gait closer to natural human locomotion. Stability analysis confirms the method's robustness and its capacity to adapt to varying user gaits. Further validation through numerical simulations and Monte Carlo analysis underscores the controller's efficacy across diverse dynamics and user requirements.
By synthesizing findings from the proposed control strategies and the empirical case study, this dissertation significantly contributes to the advancement of prosthetic limb technology and rehabilitation practices for transfemoral amputees. It is known that, minimizing gait asymmetry not only enhances user safety but also reduces metabolic energy consumption and musculoskeletal strain. Moreover, it mitigates the risk of long-term health issues such as cardiovascular complications associated with persistent asymmetrical gait patterns.
In conclusion, this dissertation presents a comprehensive analysis and control approach dedicated to achieving natural human locomotion in transfemoral amputees. Through innovative control strategies and empirical studies, it sheds light on the complexities of gait asymmetry and offers practical solutions to enhance prosthetic limb functionality and user well-being. Moving forward, continued research efforts should explore and refine these approaches to further improve the mobility and overall quality of life for individuals with above-knee amputations.
Permanent link
http://hdl.handle.net/11714/12209Additional Information
Committee Member | Park, Jeongwon; Xu, Hao; Shen, Yantao; Zhang, Jun |
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Rights | Creative Commons Attribution-NonCommercial 4.0 United States |
Rights Holder | Author(s) |