Lyapunov-Stable Orientation Estimator for Humanoid Robots

TL;DR

This paper introduces a Lyapunov-stable orientation estimation scheme for humanoid robots that combines velocity-based attitude estimation with contact and kinematic data, ensuring stability and robustness during locomotion.

Contribution

It presents a novel, Lyapunov-stable observer for humanoid orientation estimation that integrates velocity aided attitude estimation with contact-based kinematic data.

Findings

Proven Lyapunov stability with almost global asymptotic convergence.

Demonstrated effectiveness in simulation and real robot tasks.

Enhanced robustness for locomotion and whole-body control.

Abstract

In this paper, we present an observation scheme, with proven Lyapunov stability, for estimating a humanoid's floating base orientation. The idea is to use velocity aided attitude estimation, which requires to know the velocity of the system. This velocity can be obtained by taking into account the kinematic data provided by contact information with the environment and using the IMU and joint encoders. We demonstrate how this operation can be used in the case of a fixed or a moving contact, allowing it to be employed for locomotion. We show how to use this velocity estimation within a selected two-stage state tilt estimator: (i) the first which has a global and quick convergence (ii) and the second which has smooth and robust dynamics. We provide new specific proofs of almost global Lyapunov asymptotic stability and local exponential convergence for this observer. Finally, we assess its performance by employing a comparative simulation and by using it within a closed-loop stabilization scheme for HRP-5P and HRP-2KAI robots performing whole-body kinematic tasks and locomotion.