Design and Mechanical Characterization of a Variable Stiffness ESR Foot Prosthesis

In this article, MyFlex- epsilon , an ESR foot prosthesis equipped with a light and manually adjustable mechanism that allows for varying its stiffness in the sagittal plane, and a systematic approach to calculate its rotation-stiffness curves are presented. Through a design of experiment conducted numerically using a two-dimensional (2D) finite element (FE) model, calibrated experimentally, a geometric parameter whose variation alters the sagittal plane stiffness of a prosthesis originally designed with invariable stiffness, MyFlex- delta , was determined. After building the mechanism and integrating it into MyFlex- delta to obtain MyFlex- epsilon , the displacement-force curves of the latter through tests equivalent to the static tests specified in ISO 10328 were determined. Based on the experimental results, the 2D FE model of MyFlex- epsilon was built and calibrated to determine its rotation-stiffness curves in the sagittal plane. Comparing the rotation-stiffness curves obtained with the most compliant setting to the stiffest setting, stiffness variations of 119%, 122%, 138%, and 162% at plantarflexion angles of -5 degrees and -2.5 degrees, and dorsiflexion angles of 7.5 degrees and 15 degrees, respectively, were found.