Sphere Drive and Control System for Haptic Interaction With Physical, Virtual, and Augmented Reality
A system for haptic interaction with physical, virtual, and augmented realities, founded on drive and measurement elements (DMEs), is considered. The system consists of eight DME rolls equipped with linear actuators, able to measure their angular velocity, drive the sphere, and adjust downforce (pressing the roll against the sphere). Two modeling issues are addressed. Special effort is put in to compensate for various technical issues. Analytic derivation of the relation between the angular velocities of the rolls and the sphere is presented. On this basis, the importance of control over the downforce applied to an individual roll is indicated with the aim of minimizing the wear of the roll. The selection of the proper downforce for each specific position (angle) of a DME roll can extend its life cycle by reducing its grinding on the sphere. The issue of modeling the relation between the angular velocity of a given DME and the sphere is addressed. In a simplified case, such a relation can be obtained analytically. However, for a nonuniform distribution of reaction forces on the contact area, a numerical approach is necessary. Two numerical methods for the estimation of the angular velocity of the DME roll are presented and discussed. Moreover, an algorithm for the estimation of the sphere's rotational motion parameters is described and implemented, proving the usefulness of the presented method.
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