A patent pending, energy based, method is presented for controlling a haptic interface system to ensure stable contact undes a wide variety of operating conditions. System stabili9 is analyzed in terms of the time -domain definition of passivity We define a "Passivity Observer" (PO) wliich nzeasures enevgy flow in and out of one or more subsystems in real-time software. Active behavior is indicated bjj a negative value ofthe PO at any time.We also define the "Passivity Controller" (PC), an adaptive dissipative element which, at each time sample, absorbs exactly the net energy output (ifany) measured by the PO. The method is tested with simulation and implementation in the "Ekcalibur " haptic interface system. Totally stable operation was achieved under conditions such us stifJizess > 100 N/mm or time delays of 15ms. The PO/PC method requires very little additional computation and does not require a dynamical model to be identified.

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A patent-pending, energy-based method is presented for controlling a haptic interface system to ensure stable contact under a wide variety of operating conditions. System stability is analyzed in terms of the time-domain definition of passivity. We define a "Passivity Observer" (PO) which measures energy flow in and out of one or more subsystems in real-time software. Active behavior is indicated by a negative value of the PO at any time. We also define the "Passivity Controller" (PC), an adaptive dissipative element which, at each time sample, absorbs exactly the net energy output (if any) measured by the PO. The method is tested with simulation and implementation in the Excalibur haptic interface system. Totally stable operation was achieved under conditions such as stiffness 100 N/mm or time delays of 15 ms. The PO/PC method requires very little additional computation and does not require a dynamical model to be identified.Index Terms-Haptic interface, passivity controller, passivity observer, time-domain passivity.

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We propose a new time-domain passivity observer (PO) and passivity controller (PC) which removes the constant-velocity assumption during one sample time, which was used in our previous PO/PC approach. A new sampled-time definition of passivity is introduced, and this new definition is compared with the previous sampled-time definition of passivity. Through this comparison, we propose the more accurate PO/PC approach. The proposed new PO/PC approach is applied to the "Excalibur" haptic interface system with very high stiffness ( = 120 kN m) virtual environment, and stable contact is demonstrated. Index Terms-Haptic interface, passivity controller (PC), passivity observer (PO), time-domain passivity.