Time-domain adaptive control scheme for a new passivity condition including the human arm impedance

The new passivity condition including the human arm impedance shows that the achievable maximum stiffness at each sampling period depends on the local minimum viscosity of the human arm during the sampling period. Based on the analytical results and the characteristics of the human arm, a new control scheme is proposed to improve the performance of the haptic system, when the human arm impedance varies largely. We present a method to predict the local minimum of the human arm viscosity at every sampling period and design an adaptive virtual coupling that maximizes the performance of the system while guaranteeing the passivity of the system. The newly defined Passivity Margin Tracker (PMT) tracks how much more conservative the haptic system is than the ideal mass-spring system in the aspect of the passivity. These results are verified through experiments to affirm that the proposed method is shown to usefully improve the performance of a haptic system if the human arm viscosity is initially calibrated.