A real-time feedback control algorithm is developed for scheduling manufacturing systems in which there are three important classes of activities: operations, failures, and starvation or blockage. The scheduling objectives are to keep the actual production as close to the demand as possible, and to keep the level of work-in-process (WIP) inventory as low as possible. The processing time for each operation is deterministic. Failure and repair times are random. Whenever a machine fails or is starved or blocked, the scheduling system recalculates the short term production rates. Using the relationship between system capacity and starvation or blockage, desirable buffer levels and buffer sizes are found. Consequently, the WIP distribution in the system is defined. The production control policy is determined to meet the system performance requirements concerning low WIP inventory and tardiness. The results from the simple case are extended to multiple-part type and then reentrant systems.
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