A hierarchical system for dynamically solving planning and scheduling problem in a flexible manufacturing system

A system with a two-level structure (high and low level) for dynamically solving the problem of planning and scheduling in an FMS (flexible manufacturing system) is presented. The problem is first formulated as the determination of an optimal routing assignment of p automated guided vehicles (AGVs) among m workstations to accomplish N tasks, facing several possible dynamical situations, e.g. change of due date or breakdown of some workstation(s). A hierarchical system is then built to solve this optimization problem in a dynamical manner. The low-level structure aims to solve the AGV routing problem among workstations given a set of AND/OR graphs which represent tasks to be processed. On the other hand, the high-level structure, using a rule-based system, provides necessary data for low-level use and simultaneously determines principles concerning how to respond to the occurrence of some unexpected events. It is shown that a near-optimal solution can be derived with moderate computation time that allows operation in an FMS to be more flexible