SoftNash: Entropy-Regularized Nash Games for Non-Fighting Virtual Fixtures

TL;DR

This paper introduces Soft-Nash Virtual Fixtures, a parameterized control policy that balances accuracy and user comfort in teleoperation by softening traditional virtual fixtures through entropy regularization, improving user experience without sacrificing performance.

Contribution

The paper presents a novel entropy-regularized Nash game approach for virtual fixtures, enabling adjustable controller assertiveness and improved user comfort in teleoperation tasks.

Findings

Moderate softness maintains tracking accuracy.

Soft-Nash reduces controller-user conflict.

Increases perceived agency and reduces workload.

Abstract

Virtual fixtures (VFs) improve precision in teleoperation but often ``fight'' the user, inflating mental workload and eroding the sense of agency. We propose Soft-Nash Virtual Fixtures, a game-theoretic shared-control policy that softens the classic two-player linear-quadratic (LQ) Nash solution by inflating the fixture's effort weight with a single, interpretable scalar parameter $\tau$. This yields a continuous dial on controller assertiveness: $\tau=0$ recovers a hard, performance-focused Nash / virtual fixture controller, while larger $\tau$ reduce gains and pushback, yet preserve the equilibrium structure and continuity of closed-loop stability. We derive Soft-Nash from both a KL-regularized trust-region and a maximum-entropy viewpoint, obtaining a closed-form robot best response that shrinks authority and aligns the fixture with the operator's input as $\tau$ grows. We implement Soft-Nash on a 6-DoF haptic device in 3D tracking task ($n=12$). Moderate softness ($\tau\approx 1-3$, especially $\tau=2$) maintains tracking error statistically indistinguishable from a tuned classic VF while sharply reducing controller-user conflict, lowering NASA-TLX workload, and increasing Sense of Agency (SoAS). A composite BalancedScore that combines normalized accuracy and non-fighting behavior peaks near $\tau=2-3$. These results show that a one-parameter Soft-Nash policy can preserve accuracy while improving comfort and perceived agency, providing a practical and interpretable pathway to personalized shared control in haptics and teleoperation.