Heterogeneous fleet vehicle routing and scheduling subject to mesh-like route layout constraints

Abstract

The behavior of a Material Transportation System (MTS) encompassing movement of various transport modes has to be admissible, i.e. collision-and congestion-free, as to guarantee deadlock-free different flows of concurrently transported goods. Since the material flows following possible machining routes serviced by MTS determine its behavior the following questions occur: what kind of MTS structure can guarantee a given behavior, and what admissible behavior can be reachable in a given MTS structure? These questions are typical for vehicle routing problems which are computationally hard. Their formulation within the framework of mesh-like and fractal-like structures enables, however, to get a significant reduction on the size. Such structures enable to evaluate admissible routings and schedules following flow-paths of material transportation in a polynomial time. Considered in the paper production routes followed by MTS are serviced by operations subsequently executed by AGVs and machine tools. The transport operations performed by AGVs are arranged in a streaming closed-loops network where potential conflicts are resolved by priority dispatching rules assigned to shared resources. The main problem boils down to the searching for sufficient conditions guaranteeing MTS cyclic steady state behavior. Implementation of proposed conditions is illustrated through multiple examples.