ABSTRACT

There are currently 2 million Americans living with an amputation; the majority of those amputations are of the lower limbs. Leg amputation is a significant life-altering event that has an overwhelmingly negative effect on many aspects of life, even years after the injury. Leg amputation can cost in excess of $1.8 million per individual. Most available prostheses are designed to replicate some aspects of normal ankle function during level-ground walking. These prostheses allow many individuals with below-knee amputation to return to basic daily activities. However, these devices are best suited for level-ground walking and many users experience difficulties during other important tasks, such as walking on slopes, stairs, or different terrains. Therefore, the general aim of this project is to address this gap in the design of existing powered ankle-foot prostheses by enabling new prosthetics that adapt to different environmental conditions commonly found in daily life. The proposed ankle-foot mechanism significantly enhances the customizability of lower leg-powered prostheses by introducing a new design approach. This project will study how the human ankle stiffness changes during different walking scenarios. The research team will use this information to design a powered ankle-foot prosthesis with properties more similar to the human ankle. In order to do so, a lightweight and modular prosthesis that uses programmable material will be developed. The modular mechanical design and control approach generates human-like characteristics and enables a larger set of users with different lengths of amputated legs to use this prosthesis. Moreover, the prosthesis' performance will be evaluated during real-world activities in dynamic environments. The focus of this project is on amputees' well-being. The resulting agile ankle foot prosthesis will help amputees improve their physical function, ability to work, and recreation, thus helping individuals return to the activities and quality of life they had prior to injury. The research findings from this project can also be applied to advance functions of exoskeletons, orthotics, and rehabilitation robots. In addition to advancing research, undergraduate and graduate students will be involved in research activities and will receive interdisciplinary education/innovation/outreach experiences. Outreach activities will allow the project team to engage diverse middle and high school students in science and engineering, especially those from underrepresented groups and low-income families.

This project plans a new class of customizable agile ankle-foot prosthesis that is modular in design and has its impedance modulation decoupled from its torque control. This will be achieved by equipping a novel and recently developed powered 2-degrees of freedom (DOF) ankle-foot prosthesis with an augmented mechanism built from soft programmable material. The primary outcomes of this project will be a comprehensive understanding of how to 1) reduce the complexity of the control of ankle-foot prostheses, as observed in clinical trials, and 2) enhance prosthesis performance in real-world activities, such as walking and running on surfaces with different profiles, stiffness, and lateral inclinations. The planned work aims to address customizability issues of robotic ankle foot prostheses and address societal impact by improving amputees' quality of life and work. The main goal of this study is to consolidate the impedance control of the ankle to a mechanical module comprised of programmable material to follow the 2-D human ankle impedance. The effort will further integrate the impedance modulation with 2-DOF torque control of the ankle to provide the customizability required for tailoring an agile prosthesis to each user's need in parallel to the torque control tuning. The project researchers hypothesize that real-time control of the two-dimensional ankle impedance in a robotic ankle-foot prosthesis can improve the performance and the agility of the user during walking on surfaces with different profiles, stiffness, and inclinations. The interconnected research thrusts will provide the opportunity to offer a new solution through 1) modeling the ankle dynamics in different gait scenarios, 2) equipping a 2-DOF robotic ankle-foot prosthesis with a programmable material module, and 3) performing extensive evaluation experiments with amputees. Understanding the effect of the control and adaptation of the 2-D ankle impedance during walking with a lower extremity prosthesis will be significantly beneficial for the field of assistive robotics because it can provide guidelines for the design and control of powered prostheses, exoskeletons, and rehabilitation devices. In addition to advancing research, undergraduate and graduate students will be involved in research activities and will receive interdisciplinary education/innovation/outreach experiences. Outreach activities will allow the project team to engage diverse middle and high school students, especially those from underrepresented groups and low-income families. The findings from this project will be disseminated through publications, software sharing, and technology commercialization.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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