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.