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  > Home > Activities > VIDET Project > Control Algorithms
 
 
 

Team's members:

The currently devised solution

During the free space movements, the wires are maintained tensed, so that a correct measure of the finger's position can be carried out. This tension is, anyway, weak enough to allow the user a full freedom of movements.
When the thimble is "in contact" with the virtual surface, a force, perpendicular to the surface itself, is computed. Its intensity is proportional to the penetration of the finger through the surface. This is the desired force, which would best realize the correct feeling. But this force can be generated at the thimble only if its vector lies inside the infinite pyramid having the edges along the wires. All other vectors have negative components along some of the wires, so they cannot be realized; in these cases, the interested wires are put under a minimum pre-defined tension. The net feeling - as results from experiment - is all the same realistic, and pushing against the surface yields a sliding motion along it.

The control software is developed under RTAI-Linux, the real-time variant of Linux made by Politecnico of Milan. The software is organized in two main modules: the first one is the real-time one, which is executed at a 400Hz frequency and implements the effective control algorithm, reading informations from the position and force sensors and writing the torque values for the motors calculated in according with the fact that the user is touching or not the virtual environment. The second module is the user part, which provides the interface with the user. A communication channel between these two part was clearly developed. The following figure can give an idea of the software architecture.

VIDET software architecture

Alternative solutions

A setup with only one active wire is under study.

 
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