Contact-Aware Safety in Soft Robots Using High-Order Control Barrier and Lyapunov Functions

2025-05-05

AI Summary

In human–robot coexistence scenarios, soft robots face contact safety risks during high-speed, high-load operations due to stiffness-induced force amplification. Method: We propose the first Hierarchical Optimal Control Barrier Function (HOCBF) and Hierarchical Optimal Control Lyapunov Function (HOCLF) synergistic control framework, integrated with a differentiable piecewise Cosserat rod dynamics model and a Differentiable Conservative Separating Axis Theorem (DCSAT)-based geometric distance metric. This enables strict, real-time whole-body surface contact force constraints. The method enforces safety via online convex optimization while simultaneously ensuring task-space trajectory tracking and precise deformation control. Contribution/Results: Simulation results demonstrate that our approach achieves both safety and high performance in planar environments—guaranteeing contact forces remain within certified safety bounds throughout operation. It establishes a verifiable, scalable safety-critical control paradigm for physical human–robot interaction.

Technology Category

• Intelligent Robots: Human-Robot Interaction
• Natural Language Processing: Safety and Robustness
• Humans and AI: Human-Aware Planning and Behavior Prediction

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Web applications in cross-disciplinary domains and verticals such as mixed reality, smart cities, and digital health
• Security and Privacy: Large-scale security measurements

Abstract

Robots operating alongside people, particularly in sensitive scenarios such as aiding the elderly with daily tasks or collaborating with workers in manufacturing, must guarantee safety and cultivate user trust. Continuum soft manipulators promise safety through material compliance, but as designs evolve for greater precision, payload capacity, and speed, and increasingly incorporate rigid elements, their injury risk resurfaces. In this letter, we introduce a comprehensive High-Order Control Barrier Function (HOCBF) + High-Order Control Lyapunov Function (HOCLF) framework that enforces strict contact force limits across the entire soft-robot body during environmental interactions. Our approach combines a differentiable Piecewise Cosserat-Segment (PCS) dynamics model with a convex-polygon distance approximation metric, named Differentiable Conservative Separating Axis Theorem (DCSAT), based on the soft robot geometry to enable real-time, whole-body collision detection, resolution, and enforcement of the safety constraints. By embedding HOCBFs into our optimization routine, we guarantee safety and actively regulate environmental coupling, allowing, for instance, safe object manipulation under HOCLF-driven motion objectives. Extensive planar simulations demonstrate that our method maintains safety-bounded contacts while achieving precise shape and task-space regulation. This work thus lays a foundation for the deployment of soft robots in human-centric environments with provable safety and performance.

Problem

• Ensuring safety in soft robots during human interaction
• Combining HOCBF and HOCLF for contact force regulation
• Real-time collision detection and safety constraint enforcement

Innovation

• High-Order Control Barrier Function for safety
• Differentiable Piecewise Cosserat-Segment dynamics model
• Convex-polygon distance approximation metric DCSAT