Nonlinear virtual coupling for stable haptic interface

Abstract

This thesis develops a new model to analyze stability of a haptic interface interacting with a stiff virtual environment, and proposes that the human arm property be characterized by a Linear Time-Invariant 2nd order impedance model and a response model of the human reaction to a simulated force. This thesis suggests a nonlinear virtual coupling to adjust the human response for guaranteeing high performance while maintaining the system stability based on the analysis of the new model including the human arm characteristic. A new and general stability condition is derived and compared with a passivity condition and a linear virtual model theoretically and empirically. Property of the stiff virtual wall dramatically changes around the wall surface. The force generated inside the wall is quite different from the force generated outside the wall. Since the human arm has a delay in corresponding with this variation, the human arm cannot keep up with this unexpected force variation. This leads to high frequency vibration at the wall surface. Many researches have focused more on the passivity concept than the stability itself to analyze these problems. This is because the human arm is quite nonlinear and time variant. This thesis divides the human arm property into a passive impedance term and an active response term. This thesis compares the proposed stability condition with the passivity condition or linear model and verifies a superiority of the proposed condition and the nonlinear model through theoretical analysis, simulation, and experiments.