Safe Flocking in Spite of Actuator Faults using Directional Failure Detectors

The safe flocking problem requires a collection of 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 wellstudied and difficult coordination problem. In this paper, we study one-dimensional safe flocking in the presence of actuator faults and directional failure detectors (DFDs). Actuator faults cause affected agents to move permanently with arbitrary velocities, and DFDs detect failures only when actuation and required motion are in opposing directions. First, assuming existence of a DFD for actuator faults, we present an algorithm for safe flocking. Next, we show that certain actuator faults cannot be detected with DFDs, while detecting others requires time that grows linearly with the number of participating agents. Finally, we show that our DFD algorithm achieves the latter bound.