Towards Terrain-Aware Safe Locomotion for Quadrupedal Robots Using Proprioceptive Sensing

TL;DR

This paper presents a terrain-aware safety control system for quadrupedal robots using only proprioceptive sensors, improving safety and estimation accuracy over uneven terrain.

Contribution

It introduces a novel terrain estimation framework and integrates it with safety-critical control using control barrier functions, solely based on proprioceptive sensing.

Findings

Reduces base position estimation error by 64.8%

Decreases estimation variance by 47.2%

Enhances safety by preventing collisions and hazardous area entry

Abstract

Achieving safe quadrupedal locomotion in real-world environments has attracted much attention in recent years. When walking over uneven terrain, achieving reliable estimation and realising safety-critical control based on the obtained information is still an open question. To address this challenge, especially for low-cost robots equipped solely with proprioceptive sensors (e.g., IMUs, joint encoders, and contact force sensors), this work first presents an estimation framework that generates a 2.5-D terrain map and extracts support plane parameters, which are then integrated into contact and state estimation. Then, we integrate this estimation framework into a safety-critical control pipeline by formulating control barrier functions that provide rigorous safety guarantees. Experiments demonstrate that the proposed terrain estimation method provides smooth terrain representations. Moreover, the coupled estimation framework of terrain, state, and contact reduces the mean absolute error of base position estimation by 64.8%, decreases the estimation variance by 47.2%, and improves the robustness of contact estimation compared to a decoupled framework. The terrain-informed CBFs integrate historical terrain information and current proprioceptive measurements to ensure global safety by keeping the robot out of hazardous areas and local safety by preventing body-terrain collision, relying solely on proprioceptive sensing.