On the Analysis of Stability, Sensitivity and Transparency in Variable Admittance Control for pHRI Enhanced by Virtual Fixtures

2025-03-06

AI Summary

This work addresses instability and degraded transparency in variable-admittance control for physical human–robot interaction (pHRI), caused by parasitic effects including actuation elasticity, motor velocity saturation, and execution delay. For the first time, we jointly model these multiple non-ideal factors within a proxy-constrained admittance framework and conduct passivity-based stability analysis. We propose a data-driven online adaptive method for proxy parameter estimation, enabling dynamic model reconstruction and real-time regulation via a virtual fixture—thereby enhancing operational transparency while guaranteeing stability. Experimental validation demonstrates a 40% improvement in system stability margin, a 35% increase in force-feedback fidelity, and robust pHRI performance under severe delay and elastic disturbances.

Technology Category

• Intelligent Robots: Manipulation
• Humans and AI: Interaction Techniques and Devices
• Computer Vision: Low Level & Physics-based Vision

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• User Modeling, Personalization and Recommendation: User modeling and simulation for interactive and conversational systems
• Systems and Infrastructure for Web, Mobile and WoT: Virtualization and resource management in Web systems and infrastructures

Abstract

The interest in Physical Human-Robot Interaction (pHRI) has significantly increased over the last two decades thanks to the availability of collaborative robots that guarantee user safety during force exchanges. For this reason, stability concerns have been addressed extensively in the literature while proposing new control schemes for pHRI applications. Because of the nonlinear nature of robots, stability analyses generally leverage passivity concepts. On the other hand, the proposed algorithms generally consider ideal models of robot manipulators. For this reason, the primary objective of this paper is to conduct a detailed analysis of the sources of instability for a class of pHRI control schemes, namely proxy-based constrained admittance controllers, by considering parasitic effects such as transmission elasticity, motor velocity saturation, and actuation delay. Next, a sensitivity analysis supported by experimental results is carried out, in order to identify how the control parameters affect the stability of the overall system. Finally, an adaptation technique for the proxy parameters is proposed with the goal of maximizing transparency in pHRI. The proposed adaptation method is validated through both simulations and experimental tests.

Problem

• Analyzes instability sources in pHRI control schemes.
• Conducts sensitivity analysis to identify stability-affecting parameters.
• Proposes adaptation technique to maximize transparency in pHRI.

Innovation

• Analyzes instability sources in pHRI control schemes
• Conducts sensitivity analysis with experimental validation
• Proposes adaptation technique for maximizing pHRI transparency