Adaptive Control for High-fidelity Haptic Interaction with Virtual Environments

An adaptive nonlinear controller is proposed that can couple impedance-type haptic devices with admittance-type virtual environments. The controller, which takes into account the nonlinear dynamics of the haptic device and parametric uncertainty in the user's arm dynamics, replaces the natural dynamics of the interface with that of a mass-type virtual tool. The transparency and stability of the proposed haptic control system is investigated using a Lyapunov analysis. Low-pass filtering of the hand force measurement in a discrete-time implementation of the controller is shown to significantly reduce the lower bound on achievable synthesized inertia. The theoretical results are supported by experiments in which the proposed adaptive controller exhibits a far superior performance by reducing the haptic device interfering dynamics and rendering highly rigid contacts, when compared to a conventional spring-damper coupler.