Speed Adaptable Prosthetic Foot: Concept Description, Prototyping and Initial User Testing

• Published in: IEEE transactions on neural systems and rehabilitation engineering 2020-12, Vol.28 (12), p.2978-2986
• Main Authors: Tryggvason, Heimir, Starker, Felix, Armannsdottir, Anna L., Lecomte, Christophe, Jonsdottir, Fjola
• Format: Article
• Language: English
• Subjects: Adaptability; Adaptive equipment; Adaptive systems; Ankle; Body kinematics; Coupling; Couplings; Damping; Design; Design modifications; discontinuous shear thickening; Energy storage; Feet; Foot; Force; Gait; Kinematics; Legged locomotion; Material properties; Motivation; Prostheses; prosthetic foot; Prosthetics; Prototypes; Prototyping; quasi-stiffness; Springs; Stiffness; variable stiffness; Walking; Working fluids
• ISSN: 1534-4320; 1558-0210
• DOI: 10.1109/TNSRE.2020.3036329

This article presents a novel design of a prosthetic foot that features adaptable stiffness that changes according to the speed of ankle motion. The motivation is the natural graduation in stiffness of a biological ankle over a range of ambulation tasks. The device stiffness depends on rate of movement, ranging from a dissipating support at very slow walking speed, to efficient energy storage and return at normal walking speed. The objective here is to design a prosthetic foot that provides a compliant support for slow ambulation, without sacrificing the spring-like energy return beneficial in normal walking. The design is a modification of a commercially available foot and employs material properties to provide a change in stiffness. The velocity dependent properties of a non-Newtonian working fluid provide the rate adaptability. Material properties of components allow for a geometry shift that results in a coupling action, affecting the stiffness of the overall system. The function of an adaptive coupling was tested in linear motion. A prototype prosthetic foot was built, and the speed dependent stiffness measured mechanically. Furthermore, the prototype was tested by a user and body kinematics measured in gait analysis for varying walking speed, comparing the prototype to the original foot model (non-modified). Mechanical evaluation of stiffness shows increase in stiffness of about 60% over the test range and 10% increase between slow and normal walking speed in user testing.