Safe Flocking in Spite of Actuator Faults

The safe flocking problem requires a collection of N mobile agents to (a) converge to and maintain an equi-spaced lattice formation, (b) arrive at a destination, and (c) always maintain a minimum safe separation. Safe flocking in Euclidean spaces is a well-studied and difficult coordination problem. Motivated by real-world deployment of multi-agent systems, this paper studies one-dimensional safe flocking, where agents are afflicted by actuator faults. An actuator fault is a new type of failure that causes the affected agent to be stuck with an arbitrary velocity. In this setting, first, a self-stabilizing solution for the problem is presented. This relies on a failure detector for actuator faults. Next, it is shown that certain actuator faults cannot be detected, while others may require O(N) time for detection. Finally, a simple failure detector that achieves the latter bound is presented. Several simulation results are presented for illustrating the effects of failures on the progress towards flocking.