We describe real-time, physically-based simulation algorithms for haptic interaction with elastic objects. Simulation of contact with elastic objects has been a challenge, due to the complexity of physically accurate simulation and the difficulty of constructing useful approximations suitable for real time interaction. We show that this challenge can be effectively solved for many applications. In particular global deformation of linear elastostatic objects can be efficiently solved with low run-time computational costs, using pre-computed Green's functions and fast low-rank updates based on Capacitance Matrix Algorithms. The capacitance matrices constitute exact force response models, allowing contact forces to be computed much faster than global deformation behavior. Vertex pressure masks are introduced to support the convenient abstraction of localized scale-specific point-like contact with an elastic and/or rigid surface approximated by a polyhedral mesh. Finally, we present several examples using the CyberGlove TM and PHANToM TM haptic interfaces.

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(MS 2000-01, submitted 7-Oct-2000)

This paper describes an experiment, conducted to investigate the benfits of force feedback for virtual reality training of a real task. Three groups of subjects received different levels of training before completing a manual task, the construction of a LEGO biplane model. One group trained on a Virtual Building Block (VBB) simulation whcih emulated the real task in a virtual environment, including haptic feedback. A second group also trained on the VBB system, but without the benefit of force feedback. The last group received no virtual assembly training. Completion times were compared for these different groups in building the actual biplane model in the real world. ANOVA analysis showed a signficant change in performance due to training level.

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(MS 1999-06, submitted 19-Aug-99)

Cutting a deformable body may be viewed as an interchange between three forms of energy:the elastic energy stored in the deformed body, the work done by a sharp tool as it moves against it, and the irreversible work spent in creating a fracture. The work dissipated by friction can optionally also be considered. The force applied can be found by evaluating the work done by a tool which is suffciently sharp to cause local deformation only. To evaluate this work, we propose a computational model that reduces cutting to the existence of three modes of interaction: deformation, rupture, and cutting, each of which considers the exchange between two forms of energy. During deformation, the work done by a tool is recoverable. During rupture, this work is zero. During cutting, it is equal to the irreversible work spent by fracture formation. The work spent in separating the sample is a function of its fracture toughness and of the area of a crack extension. It is in principle necessary to compute the deformation caused by a sharp tool in order to recove the force. This is in general an unsolved problem. However, for the case of a sharp interaction, measurements from tests performed on samples used in conjunction with analytical approximations to the contact problem, make it possible to propose a model which is applicable to haptic rendering. The technique is then compared to experimental results which conffirms the model hypotheses. The paper also describes a model implementation that yields realistic results.

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(MS 2001-01, submitted 27-Aug-01)