Ultimate Passivity: Balancing Performance and Stability in Physical Human–Robot Interaction

Abstract

Haptic interaction is critical in physical human–robot Interaction (pHRI), given its wide applications in manufacturing, medical and healthcare, and various industry tasks. A stable haptic interface is always needed while the human operator interacts with the robot. Passivity-based approaches have been widely utilized in the control design as a sufficient condition for stability. However, it is a conservative approach which therefore sacrifices performance to maintain stability. This article proposes a novel concept to characterize an ultimately passive system, which can achieve the boundedness of the energy in the steady-state. A so-called ultimately passive controller (UPC) is then proposed. This algorithm switches the system between a nominal mode for keeping desired performance and a conservative mode when needed to remain stable. An experimental evaluation on two robotic systems, one admittance-based and one impedance-based, demonstrates the potential interest of the proposed framework compared to existing approaches. The results demonstrate the possibility of UPC in finding a more aggressive tradeoff between haptic performance and system stability, while still providing a stability guarantee.