April 1997 € Volume 7 € Number 4
April 1997 € Volume 7 € Number 4
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This department is provided to answer technical questions regarding problems in production and inventory control. Readers are invited to contact George Johnson, APICS National Research Committee, Rochester Institute of Technology |
Dear APICS: What is a manufacturing execution system? Is it the same as what used to be known as a shop floor control system? I am confused about this concept, having read and heard several different things about it.
Reply: Don't feel alone. I've had that reaction from many people. One of the reasons the concept is not clear is that it is relatively early in its life cycle and still evolving. To illustrate: In 1992, after some years of MES software development, the trade association MESA (Manufacturing Execution Systems Association) International was formed to foster advancement of the concept and related systems. Since that time, MESA has developed a series of white papers to explore and document: (a) the benefits of MES (paper #1, 1994); (b) the functionalities of MES and its relationship to MRP (paper #2, 1994); (c) the relationship of MES to the controls layer of systems (paper #3, 1995); (d) a process for evaluating and selecting MES software (paper #4, 1996); and (e) a buyers' guide and resource directory (updated 1996). In parallel with these developments, MES have been the subject of various magazine and proceedings articles and of conference presentations.
Recently, a MESA International spokesperson noted that, "The formal description of the area served by manufacturing execution systems and the many other technologies and products involved in bringing successful management of the plant floor to customers is still in the formation stages. It is expanding, changing, and still presents a somewhat unfocused aspect to prospective users of MES technology." MESA is examining the current body of knowledge concerning MES and is "spearheading the development of a new model to describe today's rapidly changing shop floor as a singular environment serving the enterprise through the fairly intricate integration of a wide range of systems -- from the traditional MES system through the smallest data generating solenoid on the manufacturing floor. The original three-tier model including MRP but separating MES and controls no longer describes what is actually happening on the plant floor." (MES Supplement to APICS--The Performance Advantage, February 1997, pg. 1)
A general statement often heard about MES is that they are systems that bridge the long-standing gap between shop floor control systems and resource planning systems such as MRP II or enterprise resource planning (ERP). It may be more accurate to characterize MES as systems which perform functions that occur between the time frames and levels of detail involved in planning systems such as MRP II or ERP, and those of shop controls systems which direct and control technical processes. MES are also interdependent with the other systems. This view is portrayed in an enterprise data flow diagram in MESA White Paper #3, page 10; but as noted above, this may be an insufficient model.
So, given the obvious presence of evolution and confusion, what are MES? I think it is safe to say they "are not your father's shop floor control systems." Credit for this is due to rapid and far-reaching advancements in automation; to the total quality management movement, which focused us on the nature of processes and their improvement; to ongoing developments in finite scheduling; to acquiring in-depth understanding of the ingredients of successful lean manufacturing; to the emerging/developing concepts of agile manufacturing and object-orientation; and to myriad entrepreneurial approaches to operating the shop floor.
The APICS Definition of an MES is: "A factory floor information and communication system with several functional capabilities. It includes functions such as resource allocation and status, operation/detailed scheduling, dispatching production units, document control, data collection and acquisition, labor management, quality management, process management, maintenance management, product tracking and genealogy, and performance analysis. It can provide feedback from the factory floor on a real-time basis. It interfaces with and complements accounting-oriented, resource planning systems." (APICS Dictionary, Eighth Edition, pg. 47)
Reading and information about MES are available from or contained in the following:
1. Hess, U., "A Plan that Works," APICS--The Performance Advantage, August 1995, pp. 36-40.
2. Layden, J., "Getting Along," APICS--The Performance Advantage, May 1995, pp. 40-43.
3. MES Supplements to the February Issues of APICS--The Performance Advantage, Lionheart Publishing Company, 1995, 1996, 1997.
4. MESA International (Trade Association: Manufacturing Execution Systems Association), 303 Freeport Road, #1, Pittsburgh, PA 15215. Phone: (412)781-9511;
5. MESA International, White Paper #1, "The Benefits of MES: A Report from the Field," 1994.
6. MESA International, White Paper #2, "MES Functionalities and MRP to MES Data Flow Possibilities," 1994.
7. MESA International, White Paper #3, "The Controls Layer: Controls Definition and MES to Controls Data Flow Possibilities," 1995.
8. MESA International, White Paper #4, "MES Software: Evaluation/Selection," 1996.
9. MESA International, "Buyers' Guide & Resource Directory," Updated 1996.
10. Suri, R., "MRP+Q=QRM," APICS--The Performance Advantage, August 1996, pp. 68-71.
11. Trino, J., "Real-time Management Software for Performance-Driven Manufacturers," APICS--The Performance Advantage, January 1995, pp. 28-31.