Recognizing and handling the livelock problem in AGV systems

The paper concerns AGV systems (automated guided vehicle systems or AGVS) with bidirectional guide path network, unidirectional vehicles, zone control for avoiding collisions, and dynamic route planning. An AGVS is represented with a DES that models the feasible system dynamics. We study the liveness problem of the system and associate this property with the permanent ability of the vehicles to attain any edge in the network. The paper is a continuation of our earlier work, where we established necessary and sufficient conditions for a state of AGVS to be live, for each possible case except a singularity case, where (unlike in the other cases) the occurrence of livelocks is possible. We define the notion of a livelock with respect to the AGVS model and conduct the analysis that results in a necessary and sufficient condition for the occurrence of this phenomenon.