Title:  Tool-Based Haptic Interaction with Dynamic Physical Simulations
        using Lorentz Magnetic Levitation 

Author:  Peter Berkelman

Abstract:
For my robotics dissertation I have designed and built a
high-performance six degree-of-freedom magnetic levitation haptic
interface device and integrated it with graphically displayed realtime
three-dimensional simulated dynamic physical environments.

An ideal haptic interface would enable simulated objects to be sensed
and manipulated in the same manner as real physical objects, at the
same level of detail and responsiveness that the user is capable of
sensing.  To approach this level of performance requires stiff
lightweight moving parts, powerful and responsive actuators, high
resolution sensors, and a fast control system.

In tool-based haptic interaction, the user feels and interacts with
the simulated environment through a rigid tool rather than directly
with the hand and fingers.  Tool-based tasks such as pushing,
screwing, probing, and insertion can all be simulated with the new
device.  Lorentz levitation technology is well suited to tool-based
haptic interaction because it provides motion and force feedback in 6
DOF with high control bandwidths and sensitivity due to non-contact
actuation and position sensing and only one moving part.  The range of
the new magnetic levitation haptic interface is 25 mm in translation
and 15-20 degrees in rotation to accomodate fingertip motions for fine
haptic tasks.  The device has a closed-loop position bandwidth of at
least 100 Hz in each DOF, a maximum stiffness of 25.0 N/mm, and a
position resolution of 5-10 um.

Detailed surface texture and friction effects have also been emulated
using the new haptic interface device.  Virtual coupling and
intermediate representation methods were developed and implemented to
provide realistic and stable haptic interaction with simulations using
the haptic device and to maintain consistency between the fast device
controller and the slower updates of the physical simulation.
Additional user interface features such as rate control and variable
scaling and offsets have been implemented to enable the user to move
the virtual tool easily over arbitrarily large distances and rotations
in the simulated environment using the limited motion range of the
haptic device.  The effectiveness of the haptic interface system has
been demonstrated with interactive simulations of sample tasks.