A thesis submitted to the faculty of Northwestern University in
partial fulfillment of the requirements for the degree of Master of
Science in Mechanical Engineering, March 1995.
Abstract:
This thesis addresses some of the issues that come up in the
implementation of virtual environments for haptic display. In
particular, the concept of "Z-width", or dynamic range of achievable
impedances, will be used to evaluate the performance of different
device configurations. We suggest that an impedance is achievable if
it satisfies a robustness property such as passivity. Several factors
affecting Z-Width - sample-and-hold, inherent interface dynamics,
displacement sensor quantization, and velocity filtering - are
discussed. A set of human subject experiments designed to evaluate
these factors are described, and experiemental results are presented.
A striking result is that inherent interface damping exerts an
overwhelming influence on Z-width. Finally, we discuss the practical
difficulties of implementing low impedances with a damped haptic
display, introducing the concept of "frequency-dependent damping."
