Conception of a digital twin for Kroenert GmbH & Co. KG

In order to drive forward the development of the simulation model, all those involved first sat down together. It quickly became apparent that the normal procedure with a top-down model and a firmly defined specification sheet would not lead to success. If, for example, minor details are overlooked or system concepts have to be changed, the engineering process repeatedly goes through cost-intensive iterations and errors creep in, which may only be discovered during commissioning. The development team therefore opted for agile development and broke down the complex project into many small sub-steps with a scheduled time and a defined function. The resulting transparency was used to review the overall project and adapt it based on new findings. The basis was therefore a strictly modularised, object-oriented cooperation development based on project and driver generators.

The coronavirus crisis that began in March 2020 demanded additional creativity from the development team. At times, the development and validation of the modules took place in parallel across three locations throughout Germany. To this end, the hardware-in-the-loop test setup was duplicated and the software versions were repeatedly synchronised via update mechanisms. As these are systems in which the paper, foil or film flow is coupled, the processes had to be modelled and developed extremely realistically in a simulative environment. This is because the control processes can only be validated if the entire machinery is also modelled in a real-time simulation. However, it had to be taken into account that the process-related control cycle of the Kroenert systems is one millisecond. This means that each simulation step had to take place within a maximum time span of one millisecond. According to the Refa process principle, this performance can only be achieved if all other modules - and there are up to twelve modules here - are simulated with each other in a cycle of one millisecond. At the same time, it should be possible to parameterise the simulation in real time in order to do justice to the high variability of the machinery.

This presented the specialists at HEITEC with new challenges, as it was necessary to develop a machine model that could be parameterised in real time for the drives as well as for other machine components and for the process simulation. This allowed parameters to be adjusted both manually and automatically while the simulation was running, without having to stop and restart the simulation. This controller-based real-time simulation is the latest development from HeiVM. It uses validated mechatronic modules and communication modules that have been tested during real commissioning and implements them in dedicated real-time-capable controllers and controller emulations. This has two advantages: Firstly, it gives the high-level language-based modules a PLC interface that the PLC programmers know and can use as their familiar working and development environment. Secondly, HeiVM adopts the architecture of the controllers, which facilitates signal exchange according to the Refa principle. However, this also means that the virtual machine model speaks the same language as the control project.

Modern controllers are now so advanced in their computing power that, thanks to their multi-core and thread capability, they can not only describe the drive, behaviour and controller models deterministically, but can also define simulation tasks specifically according to priority and cycle time. This made it possible to process the complete behavioural model externally and thus relieve the real-time simulation tool suitable for the task during virtual commissioning. In addition, the controller performance was still sufficient to integrate the complex material flow into the simulation. All in all, this resulted in a decisive performance gain, thanks to which we were able to create a simulation that met Kroenert's performance requirements.

Customer benefits

In our joint work with Kroenert, we were able to validate the feasibility and use of digital twins for in-depth process tasks, as is standard at Kroenert. By duplicating the hardware-in-the-loop test setup and synchronising the software versions via an update mechanism, it was possible to simultaneously test the functionality and performance of the newly created modules at Kroenert, while at the same time the HEITEC team in Erlangen and in the home office successively added to the modules and further developed other modules.

This meant that up to three developers were successfully working on different functions at different locations in parallel. This resulted in a considerable boost in development efficiency. The new concept for success, which has matured through close collaboration, is now to be extended to the entire modularised machine park. The modules will be further honed and finally validated. The aim is for the newly developed simulation methodology to be fully mapped to the entire machine park in controller real time - on a single simulation unit, without the use of additional hardware.