At the 2001 AAAI Conference in Seattle, WA, the
demonstrated the ability of a team of seven robots to locate and form a perimeter around a water spill using ambient chirping as a means to initiate convergence to the spill and orchestrate the formation of a perimeter around it. This behavior was demonstrated both within the NIST Urban Search and Rescue test bed and within an exhibition arena. After release, the robots began to disperse using their social potential fields to implicitly divide the environment.
The length of time necessary for the first robot to locate and identify the spill differed significantly during the tests, since the robots initially perform a random search. Once one robot found the spill and began to emit an audible signal, congregation and perimeter formation occurred quickly as the other robots were drawn to the “come hither” chirp. With the repulsive field in place, an incoming robot would be forced away by the robots already on the spill and must eventually find its own place to roost along a less populated stretch of the spill perimeter. In this manner, we are able to accomplish perimeter formation in an entirely reactive manner.
Due to the additive properties of sound, the attractive force of the robots that have already found the spill extends as more robots find it. One effect that we had not expected was that the repulsive arm of the social potential fields also grew as robots began to form a perimeter, making it increasingly difficult for each additional robot to get onto the spill. When two separate small spills were used, the combined repulsive field of the robots that had already formed a perimeter around the first spill prevented excess robotic resources being spent on the already marked spill. Instead, the strong repulsive arm pushed the remaining robots away from the first spill, allowing them to seek out the second. When there is only one large spill, all the robots were able to find a place around the perimeter of the spill.