Safety-Critical Reactive Motion Using Constrained Variable Admittance Control with Dual-Type Proximity Sensors

Abstract

We present a method that enhances the safety and responsiveness of robotic manipulators through constrained Variable Admittance Control (VAC) combined with proximity perception. Recent studies have demonstrated that manipulators equipped with proximity sensors can avoid close obstacles in real-time. However, unavoidable collisions still remain a significant challenge in human-robot interaction (HRI). As a safety fallback, conventional reactive motion algorithms aim to avoid obstacles but often suffer from inefficient avoidance and don't consider collision. Our approach integrates proximity-based pre-contact detection and VAC with QP-based motion constraints to proactively adjust the robot’s impedance parameters while maintaining stable and controlled motion. By dynamically modulating stiffness and damping based on sensor feedback, the system improves both obstacle avoidance efficiency and smooth contact handling. Additionally, a passivity-preserving energy tank mechanism prevents instability caused by parameter variations, ensuring robust and adaptive behavior. Furthermore, experiments involving HRI demonstrate that the proposed method ensures both safe avoidance and smooth contact handling. These findings suggest that the proposed approach is well-suited for safety-critical applications in collaborative and industrial robotics.