Navigation of multi-robot formation in unstructured environment using dynamical virtual structures

In this paper, the control problem for a group of mobile robots keeping a geometric formation is considered. The proposed architecture of control allows to each robot to avoid obstacles and to rejoin the desired formation. To not complicate the control of such a system, it is proposed to divide the overall complex task into two basic tasks: attraction to a dynamical target, and obstacle avoidance. Thus, a desired geometric shape is defined and each robot has to track one node of this mobile shape. Each robot has to be autonomously able to avoid disturbing obstacles and to rejoin the formation in a reactive manner. Moreover, it chooses the optimal avoidance side thanks to limit-cycle method in order to reach as rapidly as possible its virtual target. The proposed control architecture is implemented in a distributed manner. In addition, this architecture uses the same control law (Lyapunov stable) for the two elementary tasks, and the switching from one task to another occurs only by changing the set-points. Experimental results validate the proposed control architecture.