Hierarchical real-time scheduling of a semiconductor fabrication facility

A hierarchical framework for manufacturing system scheduling and planning and its experimental implementation in a semiconductor research laboratory are described. Its purpose is to aid 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 meet objectives determined at higher levels. These decisions are either actions, such as the loading of a part of the initiation of a setup, or objectives to be issued to lower levels. The integration of the scheduler with the systemwide database, the structure of the scheduler as determined by the time constants and process flows in the system, and the use of the scheduler are described