Estimating the Center of Mass and the Angular Momentum Derivative for Legged Locomotion—A Recursive Approach

Estimating the center of mass position and the angular momentum derivative of legged systems is essential for both controlling legged robots and analyzing human motion. In this letter, a novel recursive approach to concurrently and accurately estimate these two quantities together is introduced. The proposed method employs kinetic and kinematic measurements from classic sensors available in robotics and biomechanics, to effectively exploit the accuracy of each measurement in the spectral domain. The soundness of the proposed approach is first validated on a simulated humanoid robot, where ground truth data are available, against an extend Kalman filter. The results demonstrate that the proposed method reduces the estimation error on the center of mass position with regard to kinematic estimation alone, whereas at the same time, it provides an accurate estimation of the derivative of angular momentum. Finally, the effectiveness of the proposed method is illustrated on real measurements, obtained from walking experiments with the HRP-2 humanoid robot.

I. Introduction

The precise estimation of both the center of mass (CoM) position and the angular momentum derivative is an important issue for legged robots control [1], [2]. It also has various applications in humans for motion analysis in biomechanics or for disorders diagnosis in medicine. The main challenge of this estimation problem lies in the fact that these two quantities are not directly measurable, and depend at the same time on fixed parameters (e.g. mass distribution of the system, dimensions of the limbs, etc.) as well as on varying quantities (e.g. joints configurations).