The Kinetics Observer: A Tightly Coupled Estimator for Legged Robots

TL;DR

The paper introduces the Kinetics Observer, a real-time estimator for legged robots that combines contact and force estimation with kinematic tracking using a Kalman filter, improving robustness and accuracy.

Contribution

It presents a novel tightly coupled estimator based on a Multiplicative Extended Kalman Filter for simultaneous contact, force, and kinematic estimation in legged robots.

Findings

Effective in real-time on humanoid robots

Improves robustness and accuracy of state estimation

Performs well in complex multi-contact scenarios

Abstract

In this paper, we propose the "Kinetics Observer", a novel estimator addressing the challenge of state estimation for legged robots using proprioceptive sensors (encoders, IMU and force/torque sensors). Based on a Multiplicative Extended Kalman Filter, the Kinetics Observer allows the real-time simultaneous estimation of contact and perturbation forces, and of the robot's kinematics, which are accurate enough to perform proprioceptive odometry. Thanks to a visco-elastic model of the contacts linking their kinematics to the ones of the centroid of the robot, the Kinetics Observer ensures a tight coupling between the whole-body kinematics and dynamics of the robot. This coupling entails a redundancy of the measurements that enhances the robustness and the accuracy of the estimation. This estimator was tested on two humanoid robots performing long distance walking on even terrain and non-coplanar multi-contact locomotion.