Safe Consensus of Cooperative Manipulation with Hierarchical Event-Triggered Control Barrier Functions

TL;DR

This paper introduces a distributed control framework using hierarchical event-triggered control barrier functions for safe, coordinated manipulation by multiple robots, reducing computation and communication while ensuring safety.

Contribution

It presents a novel hierarchical event-triggered safety architecture integrated with a consensus protocol for multi-robot manipulation with safety guarantees.

Findings

Successfully validated on real-world hardware with two Franka manipulators.

Achieved higher precision cooperation under safety constraints.

Significantly reduced computational cost and communication frequency.

Abstract

Cooperative transport and manipulation of heavy or bulky payloads by multiple manipulators requires coordinated formation tracking, while simultaneously enforcing strict safety constraints in varying environments with limited communication and real-time computation budgets. This paper presents a distributed control framework that achieves consensus coordination with safety guarantees via hierarchical event-triggered control barrier functions (CBFs). We first develop a consensus-based protocol that relies solely on local neighbor information to enforce both translational and rotational consistency in task space. Building on this coordination layer, we propose a three-level hierarchical event-triggered safety architecture with CBFs, which is integrated with a risk-aware leader selection and smooth switching strategy to reduce online computation. The proposed approach is validated through real-world hardware experiments using two Franka manipulators operating with static obstacles, as well as comprehensive simulations demonstrating scalable multi-arm cooperation with dynamic obstacles. Results demonstrate higher precision cooperation under strict safety constraints, achieving substantially reduced computational cost and communication frequency compared to baseline methods.