In this thesis, we have addressed some of the issues that come up in the
implementation of virtual environments for haptic display. In particular, we
have used the concept of "Z-width" to evaluate the performance of different
device configurations, and conducted human subject experiments that verify, at
least qualitatively, these results. Specifically, we make the following
recommendations towards improving the Z-width of a haptic display :
- Maximize inherent damping. In our experience, this is the least
expensive and highest payoff measure available. Negative virtual damping may
be used to extend the lower limit of impedance.
- Maximize sensor resolution. This is particularly important if
position measures will be differentiated to provide a velocity estimate.
- Maximize sampling rate (with the caveat that faster sampling
exacerbates the velocity estimation problem unless appropriate filtering is
used).
- Filter the velocity signal. A first order low pass filter improves
subject impressions of wall quality. We have not yet attempted to design an
"optimal" filter.
We've also included a section addressing the practical difficulties
encountered in attempting to implement low impedances with a damped haptic
display. In particular, we recommend the use of torque-based damping
cancellation at low frequencies, resulting in frequency-dependent damping of
the haptic display. To achieve the desired performance level, careful
attention must be paid to the electro-mechanical design of the torque sensor.
Future work will address the implementation of more complex virtual
environments with a multi-DOF haptic display. We hope to design a haptics
programming language which allows complex virtual environments to be rapidly
assembled and modified, while providing stable, realistic interaction. Such a
language would hopefully build upon the results presented in this thesis,
extending them to more general usage.
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