Creating the haptic information

A fundamental part of the PURE-FORM system is the subsystem which creates the force-feedback information on the basis of the position data coming from the interfaces and the environment model stored into the system.

The generation of the force information is realized by means of a coherence algorithm. To the user, exploring a piece of art, it is associated a digital subject inside the VE, commonly known as avatar. The association is realized such that the user can really think of being the animated subject created in the virtual space.

The association between the user and his/her avatar greatly simplifies the generation of the feedback forces. In this way, the forces result as they were naturally generated into the VE by means of the avatar-environment interactions. The forces felt by the avatar can then be mapped on the user by means of the haptic display. The avatar is modeled to feel a wide set of interaction sensations. Among all haptic information which can be shared during an exploitation session, only data concerned with force information are considered in the following:

• contact forces which appears during a contour following procedure, i.e. exploration of a shape, or a grasping of a virtual object;
• contact forces appearing during a fix contact for evaluating stiffness;
• gravity forces related to the weight of grasped objects;
• friction forces generated during a contour following procedure.

All these kinds of forces are intrinsically related to the contact between the user-avatar and the virtual object. The generation of the force is based on the local geometry near the contact point.

This geometry is used to rapidly compute the amount of penetration of the contact point within the surface and consequently generate a reaction force to counterbalance the penetration. As a result a virtual constraint is created to the user’s movements, that produces the feeling of being in touch with a surface.

The feeling of touch, which is realized in this way, relies almost only on the stimulation of kinesthetic sense, so it cannot reach the same richness of stimuli that elicit from the skin of a fingert sliding over a real surface, where cues are spatially distributed over the fingerpad. Nevertheless, by opportunely generating local high frequency vibrations of the applied force, it is possible to a lesser extent to elicit the sensation of textures, generating in this way specific sensations for different materials.