PLCopen adds independent schemes to IEC 61131-3
Opening up the development environments
by specifying XML formats for IEC 61131-3
Background informationSince the release of the IEC 61131-3 programming standard, users want to be able to exchange their programs, libraries and projects between development environments. Although this was not the intent of the standard itself, it was a task that the independent organization PLCopen committed itself to. IEC 61131-3 is focused on the software development environment. As such it is just a part of a total solution. The other parts are a structure of tools like: network tools, debug tools, simulators, documentation tools, etc. Therefore PLCopen decided to realize interfaces towards these support tools. This resulted in a workgroup named TC6 for XML (eXtensible Markup Language). This committee defined an open interface between all different kinds of software tools, which provides the ability to transfer the information that is on the screen to other platforms. This screen information does not only contain textual information, but also graphical information, like where the blocks are and how they are connected.
User PespectivePLCopen wanted to accomplice that, without much additional effort, a project can be transferred from one development environment to another, without loosing information, even when it is incomplete, e.g. not compilable without errors. This of course is also valid for the POUs, and especially for User Derived Function Block libraries. This means that the program itself has to remain the same, so not be altered during this transfer. The big variety of possibilities has to be brought under one umbrella. And XML provides the right technology for this. The result of the PLCopen XML work opens the development environment by providing interfaces to other software tools. As such it is more than an export / import tool from one development environment to another. From the moment onwards that this format was available, it was just a small step to feed for instance a documentation tool with the information. Actually, it is not important where this XML-code is coming from as long as it is recognizable and useable. So it could be generated by other tools like simulation and modeling tools, and consumed by verification, documentation, and version control tools. In principle all relevant information will be exported. The importing tool has to be intelligent in filtering which parts of this information is useful and needs to be imported and used. With this PLCopen creates a complete new market, in which the focus is on reusability of software developments up to whole projects.
Short introduction into XMLXML stands for eXtensible Markup Language, providing the basis for the well known HTML (Hyper Text Markup Language) which is used extensively on the internet.
XML has several advantages:
PLCopen MissionThe work as done by the PLCopen Technical Committee 6 fits well into the PLCopen mission: We want to be the leading association resolving topics
related to control programming to support the use of international standards in this field.
Programming in its environmentAs mentioned before, the programming tools are just a part of the whole suite of software tools that can be used to make an application work. The results of the PLCopen XML work opens the development environment by providing interfaces to other software tools. In the figure below, one can identify the interfaces at the end of the blue circle.
Definition of use casesThe participants identified 4 areas where the specification fits ideal:
What is includedWith the scope of whole projects, a lot of information needs to be stored in the XML format. And since we do not know upfront which tool will be the consumer of the information, we have to export all potential relevant information. These include items like:
This means that the exported file contains everything, including supplier specific information. The consumer side, with the parsing function during input, must contain the intelligence to select the relevant information, and to check on the consistency of this data. For this the tool can use a different scheme. Combining both schemes provide the possibility to check the incompatibilities, and get the relevant information more easily. This clearly shows the benefits of using XML schemes.
Status of the PLCopen TC6 XML workPLCopen first published the XML schema and documentation in June 2005 as version 1.01. The PLCopen specification is implemented by suppliers in Japan and Germany.
With a new initiative called AutomationML we came to a new
phase. The companies Daimler, ABB, KUKA, Rockwell, Siemens, netAllied
and Zühlke together with the University of Karlsruhe and the University
of Magdeburg jointly defined and standardized the Automation Markup
Language as an intermediate format for the Digital
Factory. For more information check www.automationML.org.
Version 2.01 of the PLCopen specification (published in May 2009) includes general feedback as well as the requirements for the format of the sequencing as output of their Automation Markup Language (AutomationML™) as an intermediate format for the Digital Factory. In connection with AutomationML this exchange was also integrated in the engineering work flows and there it has priority in the exchange of logic information.
In 2014 we entered a new phase for this document. Through the German
DKE, PLCopen handed over its intellectual property rights on the schema,
specification and documentation to IEC. Based on this a New Work Item
Proposal (NWIP) was started in January 2014.