The digital factory

The digital factory is defined in VDI Guideline 4499 (drafted with the participation of KUKA) as a “[…] generic term for a comprehensive network of digital models and methods, including simulation and 3D visualization. Its purpose is the integrated planning, implementation, control and on-going improvement of all important factory processes and resources relating to the product.”
Important contents of the digital factory thus include the provision of models of the products and systems and the integration of all these models to form a continuous process chain. KUKA paved the way for this at an early stage with the three-dimensional design and simulation of the systems in which the required 3D data and models are generated. Today, these data are integrated into a systematic PLM workflow, supported by solutions such as our PLM system, our weld data management and our global data exchange platform that is integrated to a neutral data model via the KUKA InfoBus.
Up to this point, we have been looking at the integrated management and provision of the information required for system building and control of the corresponding information flow. Another important approach is use of this information to bring forward the real commissioning to the world of the digital model. Virtual commissioning deals with precisely this aspect of the digital factory.

Hybrid commissioning

System building in the automotive sector is more and more characterized by model and successor-flexible systems in order to react quickly to new market requirements and allow as many vehicle type derivatives as possible to be manufactured on a single system. To reduce downtime and thus loss of production by retooling such systems, the conversion times are also reduced accordingly. The high complexity of such systems, coupled with reduced installation and commissioning times, requires the use of new technologies to relocate part of the commissioning process to the digital planning process. This is where virtual commissioning comes in. It combines the real PLC with the digital model of the system in order to be able to test the control programs in the virtual system. KUKA Systems goes a step further here by additionally taking the real robot controller and the real bus system (Safety Bus) into consideration. Only in this way can genuinely realistic commissioning conditions be assured. What we are talking about here is hybrid commissioning, as real and digital components are integrated into a single system. Figure 1 gives a schematic representation of a work station for hybrid commissioning of robotic cells for body-in-white production and illustrates implementation on the basis of the Delmia Automation simulation system. During implementation, we place great importance on working with the standard systems of our customers and our own development process to ensure compatibility with future customer projects.

Advantages / uses of hybrid commissioning

Since hybrid commissioning is not used until the PLC and robot programs are created, i.e. very late in the planning and development process, the basic concept of the system and the manufacturing process used can no longer be influenced. Figure 2 shows an example of such a system. There is none-theless a range of potential uses, particularly in terms of the quality of program development and the real commissioning itself. These are:

• Purely digital verification is now a standard process in the design of robotic cells. Investigation of the interplay between several robots and the higher-level system controller is still difficult in the digital world. Robots are often packed close together and hinder one another. Frequently, this is first noticed at the installation site. Modifications at this stage are time-consuming and expensive. The use of hybrid commissioning should enable significant improvements here.
• In this context, early verification of the PLC and robot programs, particularly in the case of in-tegration of modifications in running systems, plays an important role.
• The integration of new components and their interaction with the existing system should be checked and optimized in the virtual system. Only then should the real system be stopped briefly, in order to minimize production loss.
• A further topic is the indexing of the systems. The indexing should be defined and optimized using the virtual image of the system.

In order to maximize these potential benefits, and to ensure that the simulation results can be trans-ferred to the real system, the mechatronic system model must correspond so exactly to the real system that the bus system, PLC and robot controller cannot detect a difference between the model and reality. The digital model must be constantly adapted to the real system configuration. Furthermore, it has to be possible for the real control programs and robot programs to be used for hybrid commissioning.

Test scenarios implemented for hybrid commissioning

Status and outlook

The simulation systems Delmia Automation (Dassault Système) and Process Simulate Commissioning (Siemens PLM Software) are currently being subjected to detailed tests. These systems have their origins in the creation of digital product and system models rather than in the development of the corresponding automation technology.
For this reason, considerable effort is still required to optimize the system models with the corresponding automation behavior models (mechatronic models). In the absence of vast libraries of mechatronic components, cost-effective use is only conceivable in complex scenarios in which the risk of errors outweighs the additional effort required in creating models. Precisely this task is being investigated as a subproject of the AVILUS project funded by the German Federal Ministry of Education and Research (BMBF). The aim here is to devise an initial approach for the neutral representation of mechatronic components.
Moreover, there are still major limitations in the real-time capability of the virtual machine sequence (especially in the graphics and the logic processing). KUKA’s approach here is based on a virtual time management system that is intended to equalize the performance problems in a kind of “slow motion”, thereby relativizing the real-time problem.
In order to resolve these tasks and establish hybrid commissioning in practical applications, KUKA is continuing to work on in-house research as well as participating in funded research projects.
Figure 3 shows test scenarios already implemented at KUKA Systems.