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Controlling knee swing initiation and ankle plantarflexion with an active prosthesis on level and inclined surfaces at variable walking speeds

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Improving lower-limb prostheses is important to enhance the mobility of amputees. The purpose of this study was to introduce an impedance-based control strategy (consisting of four novel algorithms) for an active knee and ankle prosthesis and test its generalizability across multiple walking speeds, walking surfaces and users. The four algorithms increased ankle stiffness throughout stance, decreased knee stiffness during terminal stance, as well as provided powered ankle plantarflexion and knee swing initiation through modifications of equilibrium positions of the ankle and knee, respectively. Seven amputees (knee disarticulation and transfemoral levels) walked at slow, comfortable and hurried speeds on level and inclined (10º) surfaces. The prosthesis was tuned at their comfortable level ground walking speed. We further quantified trends in prosthetic knee and ankle kinematics and kinetics across conditions. Subjects modulated their walking speed by ±25% (average) from their comfortable speeds. As speed increased, increasing ankle angles and velocities as well as stance phase ankle power and plantarflexion torque were observed. At slow and comfortable speeds, plantarflexion torque was increased on the incline. At slow and comfortable speeds, stance phase positive knee power was increased and knee torque more flexor on the incline. As speed increased, knee torque became less flexor on the incline. These algorithms were shown to generalize well across speed, produce gait mechanics that compare favorably with non-amputee data, and display evidence of scalable device function. They have the potential to reduce the challenge of clinically configuring such devices and increase their viability during daily use.
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Authors

See complete bios of the authors in the full version of this article.
N FeyN Fey
Dr. Fey is currently a Post-Doctoral Research Fellow with the Center for Bionic Medicine, Rehabilitation Institute of Chicago, Chicago, IL, USA. He also has an appointment with the Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago. His overall research interest is to identify how given task demands and lower-limb assistive devices contribute to human motor control and biomechanics.

A SimonA Simon
Dr. Simon is a Biomedical Engineering Manager in the Center for Bionic Medicine at the Rehabilitation Institute of Chicago, and a Research Assistant Professor in the Department of Physical Medicine and Rehabilitation at Northwestern University. Her research interests include overcoming clinical challenges associated with the application of advanced pattern recognition myoelectric control systems for both upper- and lower-limb amputees.

A YoungA Young
Mr. Young is currently working toward the Ph.D. degree at Northwestern University in the Center for Bionic Medicine at the Rehabilitation Institute of Chicago. His research interests include neural signal processing and pattern recognition using advanced machine learning techniques for control of myoelectric prosthesis for the upper and lower limb.

L HargroveL Hargrove
Dr. Hargrove is Director of the Neural Engineering for Prosthetics and Orthotics Laboratory at CBM. He is also a Research Assistant Professor in the Department of Physical Medicine and Rehabilitation at Northwestern University. His research interests include pattern recognition, biological signal processing and myoelectric control of powered prostheses.

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