A hierarchical framework for manufacturing systems scheduling: A two-machine example

A hierarchical framework for understanding manufacturing systems is described. It provides guidance for the development of algorithms for real-time decision-making in a manufacturing enterprise in which such disruptive events as machine failures, material absences, expedited items, engineering changes, fluctuations of demand, and setups play a role. The hierarchy is divided into a set of levels that correspond to events that occur at very different frequencies. At each level, decisions are made in a way that satisfies the capacity constraints that are appropriate to that level and that meets objectives determined at higher levels. These decisions are either actions, such as the loading of a part or the initiation of a setup, or objectives to be issued to lower levels. The application of the scheduling hierarchy to a simple, two-machine manufacturing system is presented. The goal is to meet a specified production plan as closely as possible. The scheduler must compensate for random failures, and must choose times to initiate set-ups and load parts. Simulation results are presented.