Time-domain passivity control of haptic interfaces

TLDR

The paper proposes a patent‑pending, energy‑based method to control haptic interfaces for stable contact across diverse operating conditions. The approach uses a time‑domain passivity observer to measure real‑time energy flow and an adaptive passivity controller that absorbs excess energy, enabling stable operation without a dynamical model and requiring minimal computation. Stable operation was achieved for stiffness >100 N/mm and time delays up to 15 ms, with negligible computational overhead.

Abstract

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.