Model Predictive Control with Environment Adaptation for Legged Locomotion

TL;DR

This paper presents a real-time nonlinear model predictive control method for legged robots that enhances terrain adaptation and mobility, enabling dynamic and robust locomotion across various terrains.

Contribution

The work introduces a novel NMPC with a mobility-based cost function and real-time re-planning at 25 Hz, tailored for legged robots to improve terrain adaptation and dynamic walking.

Findings

Successfully tested in simulations on diverse terrains.

Demonstrated real-world omni-directional walking and terrain adaptation.

Achieved real-time re-planning at 25 Hz with a 2-second horizon.

Abstract

Re-planning in legged locomotion is crucial to track the desired user velocity while adapting to the terrain and rejecting external disturbances. In this work, we propose and test in experiments a real-time Nonlinear Model Predictive Control (NMPC) tailored to a legged robot for achieving dynamic locomotion on a variety of terrains. We introduce a mobility-based criterion to define an NMPC cost that enhances the locomotion of quadruped robots while maximizing leg mobility and improves adaptation to the terrain features. Our NMPC is based on the real-time iteration scheme that allows us to re-plan online at $25\,\mathrm{Hz}$ with a prediction horizon of $2$ seconds. We use the single rigid body dynamic model defined in the center of mass frame in order to increase the computational efficiency. In simulations, the NMPC is tested to traverse a set of pallets of different sizes, to walk into a V-shaped chimney,and to locomote over rough terrain. In real experiments, we demonstrate the effectiveness of our NMPC with the mobility feature that allowed IIT's $87\, \mathrm{kg}$ quadruped robot HyQ to achieve an omni-directional walk on flat terrain, to traverse a static pallet, and to adapt to a repositioned pallet during a walk.