A Mechanical Descriptor of Human Locomotion and its Application to Multi-Contact Walking in Humanoids

This work aims at experimentally identifying a new mechanical descriptor of human locomotion and demonstrating that it can be exploited for the generation of multi-contact motions for humanoids. For this purpose, an experimental setup was built on which five different experiments were carried out by 15 human volunteers. Experimental results show that the distance between the center of mass and the so-called central axis of the external contact wrench significantly varies as a function of locomotion phases and environmental constraints. This finding is combined with a theoretical reasoning in mechanics in order to exhibit how this distance is linked to the whole body's angular acceleration and thus constitutes an interesting parameter to control. Finally, we illustrate the relevance of this result for humanoid robot motion generation by embedding the minimization of the distance between the center of mass and the central axis of the external contact wrench in an optimal control formulation in order to generate multi-contact locomotion in simulation.

I. Introduction

Humanoid robotics and biomechanics share a common interest in the study of principles involved in human locomotion. Researchers from both fields have widely used the Zero Moment Point (ZMP) to describe and evaluate several properties of locomotion on horizontal walkways. This particular point is the intersection between the ground and the axis along which the moment of contact forces under the feet is collinear to the normal of the ground [1].