TimeSpace Network Model and MILP Formulation of the ConflictFree Routing Problem of a Capacitated AGV system Abstract   Automated guided vehicles (AGVs) are used to transport materials in flexible manufacturing systems. This paper addresses an AGV routing problem known as the dispatch and conflictfree routing problem of a capacitated AGV system (DCFRPC). In the problem, we consider the additional constraints of collision avoidance, AGV capacities, and capacities of the machine buffers. We use a timespace network (TSN) to model the DCFRPC and formulate it as a mixedinteger linear programming (MILP) problem. In the TSN, we consider the flows of the AGVs and materials separately and then synchronize these flows considering the constraints in the formulation. This approach allows us to formulate the DCFRPC as a MILP problem. The experimental results demonstrate that our proposed approach can find optimal solutions to the majority of instances examined in a previous study.

Routing a Fleet of Automated Vehicles in a Capacitated Transportation Network Routing of a fleet of automated unitoccupancy vehicles in a capacitated transportation network is an emerging problem that needs to be addressed to realize largescale automated transportation systems. We adopt an existing networkflowbased model for the problem and present a new reformulation based on DantzigWolfe decomposition. This reformulation allows us to apply the column generation solution technique which, in turn, enables us to solve largescale problem instances with tens of thousands of requests on networks with thousands of links. We empirically compare our method to the stateoftheart approach on several standard benchmark instances and find that the computational time of our solution approach scales qualitatively better in all tested problem instance parameters: namely, in the size of the transportation network, in the magnitude of demand intensity, and in the number of demand flows.