The digital twin is making it easier to create simulation models for complex systems. A recent joint research project between Volkswagen and Siemens shows how this approach improves efficiency in production lines.
As industrial robots assemble passenger vehicles at Volkswagen production facilities, worker safety is paramount. A software error could cause serious accidents and material losses. Virtual commissioning helps reduce the downtime required for real-world commissioning — but it takes around six weeks. Siemens and Volkswagen therefore set about reducing the time required, as part of the completed EU grant project Maya.
The existing simulation models were based on different, domain-specific tools. Using the Maya Simulation Framework, Volkswagen can now combine models from different simulators.
The co-simulation models combine existing models for the safety door, rotary indexing table and manufacturing robot to form a virtual tailgate assembly system.
Almost 70 percent of users and pilot testers at Volkswagen are convinced that co-simulation will greatly reduce the costs of virtual commissioning.
A safety door, rotary indexing table and robot are three components needed for tailgate assembly. The robot picks up the tailgate from the rotary indexing table, which first tips into the correct position, and then conveys it to the next station. The closed safety door protects people in the factory, but must be opened when a new tailgate is placed on the table.
“A production line like the one at VW is complex,” says simulation expert Veronika Brandstetter, of the Siemens research and development unit Corporate Technology (CT). “The individual components may be in-house developments or bought-in products. In most cases, paperwork and development documentation is already available, as well as models that come in different degrees of detail and use a range of notation systems.”
Virtual commissioning is nothing new for VW: “Before we commission the real production plant, or even individual new components, we always perform virtual commissioning,” explains Volkswagen project manager Torben Meyer. “That means we test the functions first using a virtual model of the system, which ensures that the real commissioning, which involves stopping the plant at great cost, proceeds as fast as possible.”
Heads of production must budget around six weeks to virtually commission a production line. About two-thirds of that is needed to create the virtual commissioning model in the first place.
“The process of creating a model like this can be made much faster and more efficient if the people in charge are able to use existing and well-maintained sources,” Brandstetter observes.
One labor-intensive and error-prone stage is reverse engineering. Here, the behavior model of existing components is recreated by working backwards from the original. “The people in charge of virtual commissioning face the error-prone and laborious challenge of gathering all this material from many different co-workers in multiple departments,” says Brandstetter.
The ideal vision is to make simulation models and associated information available in a library, enabling these elements to be drawn together quickly to create a complete, virtual system. “We already have library elements for many system components,” says Brandstetter. “But this is still an exception for bought-in products. The goal is to establish the Digital Testing Twin as a standard
The challenge lies in creating a comprehensive virtual system from these digital components, which have many different sources, degrees of detail, and environments — and usually can’t be directly combined with each other.
This is where the Siemens experts come in: “It’s especially difficult when the simulation models are based on different, domain-specific tools. For our research project, we concentrated on achieving a solution for this problem,” Brandstetter explains. “For the tailgate assembly, for example, we had to accommodate three separate environments (Process Simulate, Amesim, and PLCSIM Advanced), which simulate or emulate 3D kinematic
“The Maya Simulation Coordinator orchestrates the workflows of the individual simulators to create a single comprehensive system,” says Brandstetter. “Comparable approaches were already in place in the area of automobile development, but for the development of manufacturing plant, like our pilot project for VW, it’s a new process.”
The control software for tailgate assembly was piloted using co-simulation. Workable simulation models already existed for 3D kinematic behavior and electrical behavior of the three components, but for differing simulation environments and with specific features. In the Maya Simulation Framework, they were combined with the control software to form a virtual tailgate assembly system, which they were then able to verify.
The users and pilot testers at Volkswagen were impressed by this example. Almost 70 percent of them are convinced that co-simulation will greatly reduce the costs of virtual commissioning. Volkswagen’s Torben Meyer is also happy: “We think that co-simulation offers major potential for reducing the time needed for commissioning in our production lines.”
We think that co-simulation offers major potential for reducing the time needed for commissioning in our production lines.