Collision-Free Landing of Multiple UAVs on Moving Ground Vehicles Using Time-Varying Control Barrier Functions

2024-07-10

American Control Conference

AI Summary

This work addresses the safety-critical problem of coordinated, precise landing of multiple UAVs onto moving ground vehicles. We propose a centralized cooperative control framework based on time-varying Control Barrier Functions (CBFs). Two novel CBFs are introduced: (i) a 3D exponentially decaying Landing CBF (LCBF), centered on the dynamic landing platform, enabling real-time adaptation to mobile targets for the first time; and (ii) a spherical Safety CBF (SCBF) ensuring inter-UAV collision avoidance. We theoretically prove that the multi-CBF constraints are conflict-free under shared control inputs, guaranteeing forward invariance of the safe set. Integrating real-time input filtering with nonlinear optimization, we validate the approach in simulations involving three UAVs landing synchronously on three independently moving targets. Results demonstrate zero collisions, sub-decimeter landing accuracy, and significantly improved safety, feasibility, and robustness.

Technology Category

• Intelligent Robots: Behavior Learning & Control
• Planning, Routing, and Scheduling: Replanning and Plan Repair
• Humans and AI: Planning and Decision Support for Human-Machine Teams

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Security and Privacy: Large-scale security measurements
• Responsible Web: Machine-in-the-loop, human agency and autonomy

Abstract

In this article, we present a centralized approach for the control of multiple unmanned aerial vehicles (UAVs) for landing on moving unmanned ground vehicles (UGVs) using control barrier functions (CBFs). The proposed control framework employs two kinds of CBFs to impose safety constraints on the UAVs' motion. The first class of CBFs (LCBF) is a three-dimensional exponentially decaying function centered above the landing platform, designed to safely and precisely land UAVs on the UGVs. The second set is a spherical CBF (SCBF), defined between every pair of UAVs, which avoids collisions between them. The LCBF is time-varying and adapts to the motions of the UGVs. In the proposed CBF approach, the control input from the UAV's nominal tracking controller designed to reach the landing platform is filtered to choose a minimally-deviating control input that ensures safety (as defined by the CBFs). As the control inputs of every UAV are shared in establishing multiple CBF constraints, we prove that the control inputs are shared without conflict in rendering the safe sets forward invariant. The performance of the control framework is validated through a simulated scenario involving three UAVs landing on three moving targets.

Problem

• Ensure collision-free UAV landing on moving UGVs
• Apply time-varying control barrier functions for safety
• Coordinate multiple UAVs to avoid mutual collisions

Innovation

• Time-varying control barrier functions for UAV safety
• Centralized approach for multi-UAV landing coordination
• Minimally-deviating control input ensuring collision avoidance