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Plug and Play Measurement Technology Is Within Reach

Innovations in measurement technology are increasingly linked to data. Standardized communication channels are required to organize the exchange of data from different machines efficiently and without errors. The manufacturers of measurement and testing technology rely on standards for seamless integration into the smart factory.

In the first of a three-part series providing an insight into the diverse activities of the VDMA for standardization in measurement technology. More and more machines and systems in mechanical engineering are communicating via the OPC UA communication standard. An important step towards interoperability in metrology was recently achieved with the companion specification for geometric measuring systems (GMS). Member companies of the VDMA have brought the development of the interface to industrial maturity in an extremely short time.

Dr. Karl-Dietrich Imkamp, ​​Chairman of the OPC UA Working Group Geometric Measurement Systems at VDMA and Head of Metrological Qualification at ZEISS IQS (Industrial Quality Solutions), explains in an interview what improves the interface in digital data communication and what is the reason for his great commitment to the standardization of measurement technology.

Q: Geometric measuring systems are a prerequisite in mechanical in order to manufacture parts and components within defined tolerances. Even if there has been great progress in the transfer of data from the design in the form of CAD data with tolerances, other data has so far often been transferred manually. What does the OPC UA interface to geometric measurement systems enable?

A: In the VDMA working group, we specifically looked at the field of geometric measuring systems. The spectrum of devices ranges from vernier calipers to multipoint, form and surface measuring devices to coordinate measuring systems. In production, these devices are often found in the area of ​​processing machines. In this environment, we considered five application areas (use cases): provision of static and dynamic machine data, parts and order data management, and the provision of measurement results.

Q: When will the OPC UA communication standard find the necessary acceptance?

A: Efficient implementation can only take place if similar processes – examples are the system status or a loading process – on different systems such as processing machines and measuring systems are mapped in the same way in the standard. With regard to OPC UA, this is achieved through standards that build on one another. The specification for cutting tools will be based on the specification for geometric measuring systems. The OPC UA specification for geometric measuring systems, in turn, builds on the specification for machine tools. As a result, implementing the standard for a system also requires knowledge of the definitions for the systems in the environment. However, this also means that systems can be seamlessly integrated. This has a decisive influence on acceptance.

Q: What is the status of the development of the OPC UA interface for geometric measuring systems?

A: We started in 2019 and are pleased that after the presentation of the 2022 draft, the final version is now being published. As with the presentation last year, we will use the Control trade fair in Stuttgart in May for the presentation. I hope that even more systems there will be linked to the revised umati dashboard on on the internet to show the potential for integration. The release of the OPC UA Companion Specification for geometric measurement systems, GMS for short, has thus been adopted and published just three years after the start of work. The task set by the working group has thus been fulfilled. We’re awaiting feedback on the release to see if corrections are needed.

Q: When the final version is out, there is great joy. Until then, it will probably require a great deal of time and energy?

A: The preparatory work is complex. They have to be funded. Someone has to write the documents. You have to be familiar with the formats for this. Then not only is a piece of paper written on, but the document is also published in machine-readable form. This is an XML file that contains the entire data structure. The OPC UA Foundation not only requires the standard to be written, but also requires a prototype to be presented. In our case, this was implemented by the Institute for Control Technology and Machine Tools (ISW) at the University of Stuttgart as a simulation of a measuring system and visualized on the umati dashboard. We will thus present the work to a considerable extent during the Control trade fair.

Q: With the initiative for standardization, you rely on the support of the VDMA. What is your conclusion of the cooperation? 

A: The cooperation with the VDMA has paid off. The main manufacturers are represented in the VDMA and can therefore participate in the creation of the standard. This results in a constructive cooperation very quickly. The length measurement technology in the VDMA organized the financing and controlled the cooperation with the OPC Foundation. This work is also important for Germany as a business location in order to remain competitive. Nevertheless, we would have wished for more international participation. In principle, however, all representatives in the working group are also on the move globally. Efficient cooperation has resulted. This can also be seen in the speed with which the standard was developed. Within three years it was finished and on the road. Many standardization organizations fail to do this. Of course, this is not the solution to all problems, but it has proven itself. In the development for OPC UA Cutting Tools, I believe it will continue. 

Q: Is this the end of the first phase of development for geometric measuring systems?

A: You could say that. It is now documented which use cases we want to cover. It is essentially about information about the device status, i.e. what the device is currently doing and all information that describes the operational capability. Furthermore, automations can be supported by the parts and order data management. There is still a need for further development here in order to control the automation via OPC UA. Finally, the provision of the measurement results provides the basis for the closed loop.

Q: Is it mainly about looking at the current status of the measuring system?

A: In contrast to other specifications, we do not control the measurement process. We provide information about which measuring process is currently taking place, but we do not give the measuring system any commands to move and take measuring points. That’s not part of the specification. The I++-DME interface is suitable for this and is dealt with in another part of this series.

Q: Knowing the system status of the measuring machine is the starting point. Then the question follows, what did the machine learn from the measurement?

A: There is another use case in the Companion Specification. It’s about the measurement results. We need to unify access to measurement results, but we don’t want to develop a new format for measurement results. That is why we inform that there are measurement results and we also inform where the measurement results can be found, but – with one exception – we do not give out individual measurement results. We didn’t see that as our job.

Are users satisfied with the formal information that data is available?

Q: We have planned to a small extent to output measurement results for realizing so-called closed-loop implementations. This means when processing has to be controlled directly from the measuring device. Then we can, to a limited extent, pass on information that is needed for the correction. However, how a correction is to be handled is determined by the processing machine and not the measuring machine. This results in the frequent misunderstanding that a correction value is expected from the measuring machine. We called it Correction Value because the value is the basis for a correction. However, it is only the provision of the information for the correction itself, which in turn has to be carried out by the processing machine.

Q: What does the interface to OPC UA do?

A: With this interface it will be possible for each device to provide at least its basic information. For example, the device reports that it is a coordinate measuring machine that works with a specific sensor system and has a specific measurement volume. I suspect that providing information of this kind will become standard in the years to come. Every measuring device today is connected to at least one company-internal network and can make information available in the network. Based on this, you can then also create customer-specific extensions with OPC UA. There are already measuring devices that communicate via OPC UA in digital production. But they don’t communicate according to a standard.

Q: What is the perspective?

A: If you continue this standardization and store the information in a uniform way, then hopefully you will reach a status that allows plug-and-play. Then the coordinate measuring system can be automatically integrated into the digital production. With certain basic information, which is part of the mandatory scope of the Companion Specification, it will probably already be possible today. Building on this, one can imagine that one can obtain a great deal of information from a measuring device without having to configure it and that this information can be used for other applications. This means that the measuring system can work productively in a short time and can be continuously optimized. Furthermore, there is the potential for the provider of the OPC UA implementation to develop standard modules that are reusable and continuously expandable.

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