Progress in Industrial Automation Programming and Design: From a Primitive to a Simple Solution. Forty years after its introduction into the automotive industry ...
Guest Editorial by Alexander Fay and Richard Zurawski
Progress in Industrial Automation Programming and Design: From a Primitive to a Simple Solution
F
orty years after its introduction into the automotive industry as a replacement for inflexible relay logic, programmable logic controllers (PLCs) have still retained their importance to industrial automation. The market continues to rise, with approximately US$9.0 billion worth of PLCs sold in 2007. What has made PLCs so useful that they are today the most prevalent implementation platform for automation systems in various industries?
IEC 61131 and 61499 One success factor is the International Electrotechnical Commission (IEC) 61131 standard Programmable Controllers, especially its Part 3 Programming Languages. Published in 1993 and incrementally adopted by PLC manufacturers, it has helped automation application engineers to develop a common understanding of PLC functioning and programming by allowing or even enforcing wellstructured top-down or bottom-up programming, strong data typing, full execution control, flexible language selection, and vendor-independent software development, among others. Since 1992, the vendor-independent association PLCopen has fostered the propagation and application of the concepts standardized in IEC 61131 (see ‘‘PLCopen’’). Furthermore, PLCopen created working groups to develop further concepts to extend the capabilities of IEC 61131.
Digital Object Identifier 10.1109/MIE.2009.934792
The first three articles of this special section deal with the latest results of the mentioned PLCopen established working groups. In their article ‘‘IEC 61131: A General Overview and Emerging Trends,’’ Andreas Otto and Klas Hellmann give an overview of the standard and its evolution, including an introduction to motion-control function blocks, which allow integration of motion-control functionality with PLC programs, and safety function blocks which ease the programming of safety-relevant applications. In the article ‘‘XML Exchange of Control Programs,’’ Marga Marcos, Elisabet Estevez, Federico Perez, and Eelco van der Wal report on the potential approaches to exchange PLC programs written in graphical programming languages between different engineering tools. Bernhard Werner outlines how features of object-oriented programming can be added to IEC 61131 in his article ‘‘Object-Oriented Extensions for IEC 61131-3.’’ Although IEC 61131 has proven its suitability for the programming of stand-alone PLC applications, it does not provide convenient support for the design and implementation of distributed automation applications. In these applications, several controllers (and, in addition, sensors and actuators with built-in control capabilities) are interconnected, and timely communication between them must be guaranteed. As a consequence, the IEC 61499 standard was conceived in anticipation of the growing demand for distributed automation. It is not
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intended to replace IEC 61131 programming but proposes a system-level design language for distributed automation systems, thus bridging the gap between the PLC programming languages supported by the IEC 61131 standard and design requirements of distributed systems. In his article, ‘‘The IEC 61499 Standard and Its Semantics,’’ Valeriy Vyatkin discusses the semantic problems of the standard and outline the solutions. The Oooneida association (see ‘‘Oooneida’’) has been a driving force behind the evolution of the IEC 61499 standard and its arising implementations.
Presentations and Discussions The 13th IEEE International Conference on Emerging Technologies and Factory Automation (ETFA) held its Industry Day in Hamburg, Germany, in September 2008. The focus was on these two standards, their applications in industrial automation, and their further prospects. The aforementioned four articles are extensions and aggregations of presentations given at that event. The presentation slides of all presentations can be downloaded from the conference Web site at http://www.etfa2008. org/ETFA_2008/Industry_Day.html. As pointed out during the plenary discussion, combinations of IEC 61131 and 61499 can be devised for the benefit of easier design and implementation of distributed automation systems. This is the topic of the fifth article ‘‘Is IEC 61499 in Harmony with IEC 61131-3?’’ by Alois Zoitl, Thomas Strasser, Christoph Su ¨ nder, and Thomas Baier.
PLCopen by Eelco van der Wal What Is PLCopen? PLCopen is an independent organization founded in 1992 for providing efficiency in industrial automation based on the needs of users. Its members, representing various industries, focus on the harmonization of control programming and application and interfacing engineering. They have concentrated on the technical specifications around International Electrotechnical Commission (IEC) 61131-3, creating specifications and implementations to reduce cost in industrial engineering. The outcome, for example, is standardized libraries for different application fields, harmonized language conformity levels, and engineering interfaces for exchange. The experts of the PLCopen who are members of the technical committees together with end users define such open standards.
Why Was PLCopen Founded? PLCopen was founded in 1992 just after the programming standard IEC 61131-3 was published. The controls market at that time was a very heterogeneous market with different types of programming methods for many different PLCs. The IEC 61131-3 is a standard defining the programming languages for PLCs, embedded controls, and industrial PCs, harmonizing applications independent from specific dialects, but still based on known methods such as textual programming languages instruction list and structured text, the graphical programming languages function block diagram and ladder diagram, and the structuring tool sequential function chart. Today, IEC 61131-3 is a highly accepted programming standard, and many industrial software and hardware companies offer products based on this standard, which in the end, are used in many different machinery and other application fields.
What Does PLCopen Do Today? Today’s technical challenges in the industrial control market are very different, and PLCopen follows the demands of the market requirements, with the main focus of driving efficiency in automation by defining general standards.
Today, PLCopen makes major contributions to the industrial automation market. By merging the logic and the motion control in one development environment, a large variety of motion control systems, all with their own proprietary technology, languages, dialects, buses, and development environment, were harmonized toward the user. The user can include the programmer, the operator, and the maintenance personnel. Currently, the motion control specifications contain five parts, ranging from single axis and synchronized motion to coordinated motion and homing building blocks. The activity that is new here is the inclusion of the mobile fluid world. Before one starts to move the machines, the safety aspects, especially with the new regulations in place, have to be remembered. For this, PLCopen has created a specification for safety at the software level. With more and more usage of digital-field buses that incorporate the safety functionality and more and more mechatronic design, this safety functionality is a natural extension to logic and motion. The PLCopen extensible markup language (XML) specification provides an interface toward the engineering tool, and as such provides a data-exchange format of IEC projects in software systems. With benchmarking, we provide a sophisticated benchmark standard, while the cooperation with open connectivity unified architecture (OPC UA) provides data exchange at run time. In the future, practical automation tasks will be challenged by new industry demands and products, and PLCopen will remain focused on global harmonization.
How Can PLCopen Help You? By PLCopen’s activities of standardizing base functions, your efficiency in automation control technology is increased, costs are reduced, and core competence can be focused. The PLCopen organization offers a solid base for harmonizing principle technological challenges and a platform for members to work on these. If you are active in industrial control, think about joining this organization.
Digital Object Identifier 10.1109/MIE.2009.934799
Although IEC 61499 provides methods to address some of the most demanding problems in the design of distributed automation systems, it also adds complexity to the engineering of automation systems. Some peculiarities are not clarified yet, and many suppliers and users are hesitant to adopt it. Further research
and, subsequently, standardization will be necessary to arrive at design and implementation solutions that allow for easy and accurate engineering. To quote Werner von Braun: ‘‘Progress is the way from the primitive via the complicated to the simple solution.’’ The ultimate goal is not yet
reached. As pointed out by Rolf Ernst at ETFA 2008, embedded systems research has addressed similar issues with significant success. The transfer of those solutions into the world of PLCs and distributed automation seems to be a rewarding field for further research in industrial automation.
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