Abstract
Programmable Logic Controllers (PLCs) are widely used for control and automation of machines and processes, so the quality of PLC software has a direct impact on production efficiency. This paper describes a PLC program for a food production line that was completely rewritten using a different software architecture and framework. The PLC hardware and the production line equipment were not changed, so this project provides an opportunity to quantify the impact of different PLC software architecture on production efficiency. The average number of cases of products produced per production hour during the first ten months with the new program was 6.1% higher than the average during the previous ten months with the old program. PLC software, unlike most other software, is often used by the end-user for troubleshooting. In this case, a relatively simple architecture and framework that favors the end-user significantly improved production efficiency over a more sophisticated architecture and framework that favors the software developer. Suggestions for further research on software architecture and framework are given.
Highlights
Programmable Logic Controllers (PLCs) are special-purpose computers that are widely used in industry for control and automation of machinery and processes
The cost of rewriting the PLC program was recovered through increased efficiency after just a few months, and continues to pay dividends every production run going forward
One benefit is that PID loops are updated much faster, which is important for several speed, flow, pressure, and continuous blending loops in the production line
Summary
Programmable Logic Controllers (PLCs) are special-purpose computers that are widely used in industry for control and automation of machinery and processes. The quality of PLC software has a direct impact on production efficiency [2]. PLC software may sequence equipment differently than intended by the equipment designer, or interlocked equipment may hold in a wait state longer than necessary. Such software may still produce products correctly, but waste time and/or energy unnecessarily. This work has had little impact on PLC programming practice because it is too complex for most PLC programmers to apply. Some work has been done to apply software engineering principles to PLC software development, such as recognizing design patterns [4], using an object-oriented approach [5] and proposing new, high-level graphical
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