A passivity criterion for real-time haptic simulation of viscoelastic soft tissues

Passivity analysis provides a convenient measure to assess the stability of haptic systems interacting with virtual environments. Passivity analysis of haptic sampled-data systems coupled with virtual environments requires knowledge of parameters of the employed environment model. Kelvin–Voigt models have been popularly used to describe viscoelastic behavior of soft tissues being simulated in a virtual environment. This paper employs a standard linear solid model that has been recently shown to be better suited to represent the behavior of the actual soft tissues, and provides passivity analysis of the haptic systems interacting with virtual viscoelastic soft tissues based on the standard linear solid model. The analysis results in a new criterion for design and control of passive haptic interfaces. The effect of the employed discretization method on passivity is also discussed. Experimental results show that the new passivity criterion is less conservative. This criterion increases the domain of soft-tissue environments that can be interacted with passively by the haptic interface.