Adaptive Control of Haptic Interaction with Impedance and Admittance Type Virtual Environments

Adaptive nonlinear controllers have been proposed to improve the stability and transparency in haptic rendering. Through a separation of control and dynamic simulation, the proposed controllers can couple impedance-type haptic devices with impedance and admittance-type virtual environment simulators. The intervening dynamics of the interface, subject to stability constraints, can be replaced with an adjustable mass-damper tool within the proposed framework. Nonlinear dynamics for haptic device and parametric uncertainty in user´s arm dynamics are considered in the design of controllers which require position, velocity and force measurements. The transparency and stability of the proposed haptic control systems are investigated using a Lyapunov analysis. The controllers are implemented on a two-axis impedance-type haptic device for interacting with impedance and admittance-type virtual environments. In the impedance-type environment, interaction with a virtual wall is modeled by a spring-damper coupler. This model along with an alternative constraint-based rigid wall model are employed in the admittance-type simulations. Although the two controllers behave similarly in free motion, the controller for admittance-type environments is capable of rendering markedly stiffer rigid contacts.