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research-article

Passive Prosthetic Foot Shape and Size Optimization Using Lower Leg Trajectory Error

[+] Author and Article Information
Kathryn Olesnavage

Global Engineering and Research (GEAR) Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
kolesnav@mit.edu

Victor Prost

Global Engineering and Research (GEAR) Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
vprost@mit.edu

Brett Johnson

Global Engineering and Research (GEAR) Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
wbj@mit.edu

Amos G. Winter, V

Global Engineering and Research (GEAR) Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
awinter@mit.edu

1Corresponding author.

ASME doi:10.1115/1.4040779 History: Received November 06, 2017; Revised June 11, 2018

Abstract

A method is presented to optimize the shape and size of a passive, energy-storing prosthetic foot using the Lower Leg Trajectory Error (LLTE) as the design objective. The LLTE is defined as the root-mean-square error between the lower leg trajectory calculated for a given prosthetic foot's deformed shape under typical ground reaction forces, and a target physiological lower leg trajectory obtained from published gait data for able-bodied walking. Using the LLTE as a design objective creates a quantitative connection between the mechanical design of a prosthetic foot (stiffness and geometry) and its anticipated biomechanical performance. The authors' prior work has shown that feet with optimized, low LLTE values can accurately replicate physiological kinematics and kinetics. The size and shape of a single-part compliant prosthetic foot made out of nylon 6/6 was optimized for minimum LLTE using a wide Bezier curve to describe its geometry, with constraints to produce only shapes that could fit within a physiological foot's geometric envelope. Given its single part architecture, the foot could be cost effectively manufactured with injection molding, extrusion, or 3D printing. Load testing of the foot showed that its maximum deflection was within 0.3 cm (9%) of FEA predictions, ensuring the constitutive behavior was accurately characterized. Prototypes were tested on six below-knee amputees in India - the target users for this technology - to obtain qualitative feedback, which was overall positive and confirmed the foot is ready for extended field trials.

Copyright (c) 2018 by ASME
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