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Process flow scheduling (PFS) is a general framework for scheduling flow manufacturing plants. PFS provides an alternative to the scheduling logic employed in closed-loop material requirements planning (MRP) systems. Process flow scheduling is not a specific scheduling technique, but an integrative paradigm which describes the scheduling logic used by many flow manufacturing plants. Like MRP systems, most state-of-the-art PFS systems employ vendor software. Accordingly, the information in this article relies heavily on information provided by the PFS systems vendors which are acknowledged at the end of this article. Readers not familiar with process flow scheduling terminology and principles may want to begin by reading the brief PFS overview in the Appendix.
PFS ORIGINS
The origins of PFS are obscured. We know from personal experience that PFS concepts were used in proprietary systems over 20 years ago. The first commercial package using PFS concepts appeared in 1982 and vendor offerings expanded to include several packages by 1987. In 1988, following years of business experience and academic research on flow manufacturing scheduling systems, we finally stumbled on the rather simple ideas underlying the PFS framework.
Several articles on PFS have been published in this journal [2, 3, 7, 8, 9] and presentations have been made at over 20 APICS conferences, seminars, and meetings. The PFS literature was summarized and expanded in a 1994 book published by APICS [10]. PFS terminology now appears in the APICS Dictionary [1] and a chapter on PFS is included in the third edition of the Production and Inventory Control Handbook [4].
CURRENT ENVIRONMENT
Today, there are at least seven software vendors that employ PFS concepts. Their software is used in over 800 flow manufacturing plants on six continents. Industry groups using PFS software include petroleum, chemical, paper, plastics, rubber, food, textile, pharmaceutical, beverage, and semiconductors.
Although the use of PFS concepts appears to be quite high, many PFS users are not familiar with the PFS framework and its terminology. These PFS users are aware that several vendors offer a type of finite capacity scheduling system quite different from MRP, but are simply unaware that a general framework exists for these scheduling systems. Instead, most users tend to think in terms of the particular system they are using. This is not surprising...