Lyapunov-Stable Orientation Estimator for Humanoid Robots
This work addresses the challenge of stable orientation estimation for humanoid robots, which is crucial for reliable locomotion and whole-body control, representing an incremental improvement with specific stability proofs.
The paper tackles the problem of estimating a humanoid robot's floating base orientation by introducing a Lyapunov-stable observer that uses velocity-aided attitude estimation, leveraging contact information, IMU, and joint encoders, and demonstrates its effectiveness in simulations and closed-loop stabilization for HRP-5P and HRP-2KAI robots during locomotion tasks.
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.