CAREER: Recovering and Enhancing Natural Locomotion in Changing Conditions with Powered Lower-Limb Prostheses and Orthoses

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This Faculty Early Career Development (CAREER) project will investigate new ways to control powered prosthetic and orthotic (P&O) devices to assist lower-limb amputees and stroke survivors with the mobility activities needed to navigate their homes and communities. With existing P&O devices, mobility is often limited by stairs, slopes, and uneven terrains. State-of-the-art powered P&O devices are capable of overcoming these obstacles, but most current advanced control methods are specialized to a limited set of specific pre-defined motions -- for example, walking, running, and ascending or descending stairs. Existing approaches must infer the user's intention and switch to the most closely matching pre-defined activity. Even if user intention is correctly interpreted, the desired motion may not match any of the pre-determined options. In contrast, the P&O devices enabled by this project will provide mobility for a continuously changing variety of tasks, including the ability to respond to changing and unanticipated slope and footing conditions. In addition to restoring natural function, the investigated control approach can also adjust the physical environment as experienced by the user. For example, the apparent weight and mass of the user could be reduced to provide increased stability during physical therapy, or even to enhance natural capabilities. This work will significantly improve quality of life and productivity for nearly a million lower-limb amputees, and even more stroke survivors, in the US alone. The integrated education plan will have broad impact by 1) promoting disability awareness and increasing interest in STEM among K-12 and college students, 2) fostering mutual understanding between engineering and P&O students through joint education and research, and 3) educating P&O students in STEM concepts that will be needed to utilize the projected P&O technologies in their future clinical practice.This project supports a paradigm shift from task-specific, kinematic control approaches to task-invariant, energetic control approaches for powered P&O devices that can assist lower-limb amputees and stroke survivors across varying activities. This project will advance knowledge in the control of powered P&O devices through energy shaping, where the parameters and/or formula for the human body's energy are altered in closed loop to achieve more desirable dynamics. In this approach, wearable actuators could reduce mass/inertia parameters in body energetics to dynamically offload the weight of a stroke patient who otherwise would be supported by multiple therapists during gait rehabilitation. Powered prosthetic legs could provide support and propulsion during amputee locomotion by shaping the momentum of the human body. Accordingly, the goals of this project are to 1) understand how to use wearable actuators to shape the energetics of the human body during locomotion, 2) determine specific changes to body energetics that lead to effective control strategies for powered prosthetic legs and powered leg orthoses (i.e., exoskeletons), and 3) understand how different gaits (i.e., kinematic patterns) emerge from body energetics in order to design task-invariant controllers for powered P&O devices. This innovation in dynamics and control will enable P&O devices to assist humans in a continuum of locomotor activities, which cannot be achieved with state-of-art control strategies based on pre-defined, task-specific joint kinematics.