Identification of contact properties of the foot in the stance phase of walking

In the study of biped walking, when using forward dynamics analysis, the description of the contact between the feet and the ground is of fundamental importance. The aim of this work is to build a foot model that is capable of describe the foot-ground contact during the stance phase in a simulation. Hyper ellipsoids are used as the contact elements between the foot and the ground and an optimization procedure is used to identify the material and geometric properties of the ellipsoids for the model to simulate human walking. The optimal problem is the minimization of a function relating the predicted ground reaction forces with the forces measured experimentally for a given trial and their application points. Several optimization methods were tested. In the end, a combination of a genetic algorithm and the Sequential Quadratic Programming method was used. There is a good correlation between the solution obtained by the model and experimental data acquired. The model presented is able to simulate the same task as the one captured experimentally and reliable enough to be used in a biomechanical model of the human locomotor system.