Robotic group formation with phosphorescent trails

Abstract In swarm robotics, stigmergy (indirect communication through changes to the environment) offers an alternative to direct communication and centralised control when these are unavailable. We investigate whether stigmergy alone can solve a group-formation task, namely controlling the number of robots that gather into a group. To this end, a leader robot lays a phosphorescent trail by exciting the arena surface with ultraviolet light; the brightness of the trail decays over time, and its initial intensity encodes the target group size. Following robots join the trail and leave it once the measured brightness falls below a threshold, so that the group size is regulated without any direct inter-robot communication. We demonstrate this mechanism as a proof of concept on real hardware, using a swarm of small Dezibot robots, and show that groups of a specified size form and are maintained over an extended period of time.