Guarding Force: Safety-Critical Compliant Control for Robot-Environment Interaction

TL;DR

This paper introduces a novel safety-critical control method for robots that ensures strict adherence to interaction force constraints during physical contact with unknown environments, enhancing safety and reliability.

Contribution

The paper presents a new force-constrained control barrier function and a quadratic programming approach to enforce safety constraints in robot-environment interactions.

Findings

Successfully enforced force constraints in experiments

Validated stability of the control system

Demonstrated effectiveness in unknown environments

Abstract

In this study, we propose a safety-critical compliant control strategy designed to strictly enforce interaction force constraints during the physical interaction of robots with unknown environments. The interaction force constraint is interpreted as a new force-constrained control barrier function (FC-CBF) by exploiting the generalized contact model and the prior information of the environment, i.e., the prior stiffness and rest position, for robot kinematics. The difference between the real environment and the generalized contact model is approximated by constructing a tracking differentiator, and its estimation error is quantified based on Lyapunov theory. By interpreting strict interaction safety specification as a dynamic constraint, restricting the desired joint angular rates in kinematics, the proposed approach modifies nominal compliant controllers using quadratic programming, ensuring adherence to interaction force constraints in unknown environments. The strict force constraint and the stability of the closed-loop system are rigorously analyzed. Experimental tests using a UR3e industrial robot with different environments verify the effectiveness of the proposed method in achieving the force constraints in unknown environments.