Power-based Safety Layer for Aerial Vehicles in Physical Interaction using Lyapunov Exponents

TL;DR

This paper introduces a safety layer for aerial vehicles that uses Lyapunov exponents to detect unstable dynamics and prevent dangerous behaviors during physical interactions, enhancing autonomous system safety.

Contribution

It presents a novel safety mechanism combining Lyapunov exponents with control barrier functions to limit power flow and ensure stability in aerial vehicles during interactions.

Findings

Successfully detects unstable dynamics in real-time

Prevents dangerous behaviors during flight and interaction

Enhances safety without compromising control performance

Abstract

As the performance of autonomous systems increases, safety concerns arise, especially when operating in non-structured environments. To deal with these concerns, this work presents a safety layer for mechanical systems that detects and responds to unstable dynamics caused by external disturbances. The safety layer is implemented independently and on top of already present nominal controllers, like pose or wrench tracking, and limits power flow when the system's response would lead to instability. This approach is based on the computation of the Largest Lyapunov Exponent (LLE) of the system's error dynamics, which represent a measure of the dynamics' divergence or convergence rate. By actively computing this metric, divergent and possibly dangerous system behaviors can be promptly detected. The LLE is then used in combination with Control Barrier Functions (CBFs) to impose power limit constraints on a jerk controlled system. The proposed architecture is experimentally validated on an Omnidirectional Micro Aerial Vehicle (OMAV) both in free flight and interaction tasks.