ITI-Symposium 2014

Model based Systems Engineering using SimulationX and ModelCenter

Gerhard Pregitzer1, Alexander Blumör1, Dr. Sven Kleiner2, Dr. Marcus Krastel2, Michael Neubert2

1 KARL MAYER Textilmaschinenfabrik GmbH, Brühlstraße 2, 63179 Obertshausen www.karlmayer.com, [email protected]

2 :em engineering methods AG, Rheinstr. 97, 64295 Darmstadt, www.em.ag, [email protected]

Summary: The introduction of Systems Engineering (SE) for the mechatronic product development is important even in classic engineering companies and shall be discussed. Therefore, companies are asking the question, what added value is offered by the integration of SE with respect to their conventional and established development process as well as what benefits will arise with respect to a shortening of the development time, cost savings such as an increase in productivity, quality and innovation. Rightly so, the question must also be asked, how high the investments in Systems Engineering processes, methods and IT- Tools are to be expected for a company. In the following contribution the challenges and benefits of SE will be presented. The deliberate introduction of “Model Based Systems Engineering” (MBSE) can aid in the conversion from a document-centered approach to a model-based development methodology in order to exploit the desired potential benefits. This paper presents the experience of the introduction and adaptation of MBSE based on the example of machine development.

Zusammenfassung: Die Einführung von Systems Engineering (SE) für die mechatronische Produktentwicklung gewinnt auch in den klassischen Maschinen- bauunternehmen an Bedeutung und wird diskutiert. Unternehmen stellen sich dabei die Frage, was Ihnen der Einsatz von SE bezogen auf ihre konventionellen und etablierten Entwicklungsprozesse an Mehrwert bietet und welcher Nutzen hinsichtlich Verkürzung der Entwicklungszeit, Kosteneinsparung sowie Steigerung von Produktivität, Qualität und Innovation daraus entsteht. Zu Recht muss auch die Frage gestellt werden, wie sich die Investitionen in Systems Engineering Prozesse, Methoden und IT-Werkzeuge für ein Unternehmen rechnen. Im vorliegenden Beitrag werden dazu Herausforderungen und Nutzen von SE dargestellt. Die gezielte Einführung von „Model Based Systems Engineering“ (MBSE) kann dabei helfen von der dokumentenzentrierten Vorgehensweise zu einer modellbasierten Entwicklungsmethodik zu gelangen, um die gewünschten Nutzenpotentiale auszuschöpfen. Der vorliegende Beitrag zeigt die Erfahrung aus der Einführung und Erstanwendung von MBSE am Beispiel der Maschinenentwicklung auf.

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1 Quick introduction to Systems Engineering

The Gesellschaft für Systems Engineering (GfSE e.V. which is the german chapter of INCOSE, International Council of Systems Engineering) describes Systems Engineering (SE) as a comprehensive engineering activity, which is necessary for the development of complex products [GfSE14]. The tasks associated with SE are varied and start with requirements engineering and system analysis and range to system development to safeguarding and testing. Due to the variety of disciplines involved in today’s innovative product development processes, such as mechanics, electronics, and software, the mastery of SE is increasingly becoming a real competitive advantage for companies. With the requirements for solutions in the context of Industrie 4.0 and the development of so-called cyber physical products presents new challenges. A competitive development of these products and systems without the introduction of a SE- Methodology is not feasible [MCP14].

A large number of companies currently fear a high methodological, organizational and financial expense in the introduction of SE: there is a lack in both the procedural and organizational basis as well as in experience and competencies for a successful introduction of SE in practice. The idea of an overall concept and presentation of the benefits of the introduction of SE in companies are critical in convincing the decision- makers to carry out such measures.

2 Benefits of Systems Engineering

Companies face a legitimate question when considering and implementing SE, what SE offers with regard to value-added based on their conventional and established development processes. Therefore, the question must be asked whether and when the investment in SE methods and IT tools will pay off for a company.

In the work „Systems Engineering Return on Investment“ by Eric C. Honour from the year 2013 a wide-ranging study of the return on investment (ROI) was calculated for Systems Engineering [HON13]. Thereby 51 development programs from 16 companies in the aerospace and the defense industry were analyzed. A key finding was that the optimal cost for SE lies at around 14.4% of the total development costs for an average development program (approximately 14 million EUR development budget). For smaller or larger programs and depending on other characteristics (depth of system integration, size of the system, Technological risk, etc.) the value may vary between 8% and 19%. For an average sized program the calculated SE-ROI was 3.5:1.

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Figure 1: Benefits linked to the use of systems engineering components

Figure 1 shows the points at which the benefit of SE can be generated. Through SE the transition from today’s numerous trial and prototype-driven functional verification to virtual system verification is made possible (1). Additionally both the development time (3) as well as the development costs (2) can be reduced.

The benefits of SE are therefore combination of several effects [KK14]:

SE helps to master the complexity of a system: The networking of the systems will grow massively through current and future innovations and the control of these cross-domain dependencies and relationships can only be mastered with SE methods. The transparency and traceability of dependencies are an integral part of increasing the efficiency of the development process. Through the use of SE methods interdisciplinary change processes can be introduced and implemented.

SE enables interdisciplinary quality management and validation: The conformity of the system properties to the requirements (e.g. customer requirements, standards, certifications or country regulations) with respect to individual components and the overall system must be ensured during the development process. This is where the SE method comes into play, as it provides an assessment of the degree of fulfillment of requirements based on the total system throughout the development process.

SE reduces Hardware and Prototypes: In particular, in the established experimental and calculation disciplines the number of real hardware tests has been significantly reduced by use of simulation, thus saving development time and cost. This development experiences your continuation in the increasing virtualization of validation - that is, in a

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transition from hardware- (HiL) via software- (SiL) to model-in-the-Loop (MiL) tests. To the same extent, through SE multidisciplinary system behavior can be integrated in early stages of development by networking behavior simulations from different disciplines. The presence of appropriate tool interface allows the re-use of behavior models for virtual testing in all Model granularities and thus in all phases of the development process. Thus, the number of hardware prototypes will be reduced by the early virtual validation.

SE enables cooperative development processes: Cooperation with suppliers and development partners as well as OEM / OEM cooperation is in the design sector and in particular the exchange of CAD data has long been standard practice. With SE-methods the integration of suppliers for requirements definition, system design and optimization solution can also be made possible in the early stages of product development. This is supported by the increasing standardization of interfaces for tool coupling. An example of this is the Functional Mock-up Interface reference, a tool-independent standard for the exchange functional behavior models. [FMI14].

The overarching goal of SE is to increase the efficiency in the development of mechatronic systems by providing model-based methods and formulate the continuous networking of heterogeneous development tools.

3 Challenges in Systems Engineering

The development process is characterized by constant decisions between different concepts and solution alternatives in order to achieve the best solution for the product. As a rule, there is a trade-off between the number of possible solutions and the amount of time available for the project development in order to evaluate all solution alternatives and make decisions early.

An approach for the systematic development of solution concepts, system architectures and components based on the model-based systems engineering (MBSE), for example, provides the so-called FAS method [FAS14]. The method "Functional Architecture for Systems" (FAS) is understood as a communication tool and can be used to derive architecture decisions. The FAS method is independent of modeling languages and modeling tools. Modeling tools based on the SysML language support the model-based analysis and synthesis of systems from the perspective of the system engineer [Wei08]. At the same time, among other things requirement, functional and architectural models are developed, which are supplemented by the first parameter and behavior models in the design phase to the system level. Through which the so-called system model is created.

CAD systems support the description of the mechanical or electrical system structure and product shape. CAE tools help in the prediction of physical properties or in the simulation of the behavior of subsystems based on models in the context of virtual product development. However, the optimization of the overall system is often a time- consuming and experience-based process that is complemented using test rigs or prototypes for testing under real conditions. In order to carry out the optimization of a

4 ITI-Symposium 2014 mechatronic system, the interdisciplinary and automated coupling of different CAx tools and models is necessary. In the process parameters, properties, input and result information, variants and calculation alternatives must be consistently available in the interdisciplinary development process as a link between the models.

Figure 2: Links between System Models and physical Models in the disciplines

Many challenges are present which need to be overcome, such as:

• ability to check at any time if the requirements are met for the entire system across all disciplines,

• integration of the different calculation processes of existing CAx tools and to exchange parameters and results between the tools,

• ensure a reproducible computation process which will be comprehensible even years later,

• integration of information from different disciplines, such as, mechanics, electronics or software into the simulation of the complete system,

• to understand and assess the impact of changes made to the individual models on the overall system or

• despite heterogeneity in the tool environment and the lack of interconnection of the existing, highly optimized calculation and simulation tools, to provide reliable and reproducible results for the considered system as a whole.

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4 System Modelling as a solution

Especially in the SE, it is crucial to describe the requirements of different disciplines in a system model and to handle them in an integrated manner. The pure integration of data describing the system model, into a database is not sufficient and effective. This is especially true when established and existing IT tools will continue to be used in the development process. Rather, the federal approach to integration is the appropriate solution when data must be linked between heterogeneous development tools [Kle03].

The model-based SE approach (Model-Based Systems Engineering - MBSE) in this case provides the link between the physical models of the individual disciplines to a higher- level system model. The use of the MBSE approach allows system engineers or system architects to consider and optimize all aspects of a multidisciplinary system. During the development process one is constantly faced with the challenge to verify, to what extent are the system design and the behavior of the system within the defined requirements. At the same time, the detailed control of all necessary authoring tools through the system architect is contrary to the goal of increased efficiency both in terms of handling the demanding environments and in terms of the associated licensing costs.

MBSE development tools that support the graphical modeling language SysML, will be increasingly used for system modeling. They are when it comes to the possibilities of linking the system model with the actual physical behavior and simulation models, however, limited. This linkage is necessary to make forecasts as to the compliance with requirements of shape and behavior of the system or the cost. The transparent presentation of alternative solutions and decision support should be possible via the push of a button [F4M14]. In addition, the use of exported behavior models in the form of royalty-free artifacts, e.g. as Functional Mock-up Units, is an approach for "push-button" solutions with a view of the optimization of administrative costs.

5 Practical experience for a federal MBSE approach in machine development with ModelCenter

Model-based systems engineering will now be described using the following application example. It involves the design of a mechatronic functional support. The functional support is a sub-system of a textile machine, which is responsible for the creation of patterns in industrially manufactured textiles. The sub-system consists of a pneumatic cylinder (1), the actual functional support (2), a servo motor (3) and the controller (4). The controller determines the traversing curve of the functional carrier (see Figure 3).

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Figure 3: Conception of the functional carrier as a sub-system of a textile machine

The aim of the model-based development is the design and validation of alternative drive concepts to meet the performance requirement for increased speed and thus increasing the amount of material produced in a certain amount of time. In the following, the approach, methods and tools in model-based systems engineering with are applied are summarized.

To model process of the functional architecture proceeded as follows: the system context was identified, requirements analysis, use cases and their refinement through activities, create functional block diagrams, development of functional models to the logical architecture as well as identification of the active principles of the system, extraction of CAD models based on the recognized principles of action, creation of a multidisciplinary simulation model and completion of investigations in the simulation. At the same time, based on the requirements as well as the system context, requirements models, use cases, as well as various system models (system architecture, functional structure, etc.) the system is modeled with the language SysML.

The system context shown in Figure 4 describes the systems involved in the project using the description in SysML. In addition, requirements and use cases of the system in SysML are described based on the system context. Using the method Functional Architecture for System (FAS) results in a solution-neutral function-oriented system structure. This is finally converted into the target system architectures for alternative solutions and also documented in SysML using the authoring system CAMEO Systems Modeler from NoMagic. An example of the system context for the functional support is shown in a SysML diagram in Figure 4.

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Figure 4: Description of the system context for the mechatronic functional support

Based on the requirements, during the conception phase the solution alternatives based on the selected components for the target architecture and the drive concept could be described with the help of the modeling language in a behavioral model and the multi-physical properties in multidisciplinary simulation tool SimulationX could also be simulated.

This requires that the professional discipline-specific properties of the system model and partial models from different tools be linked together. With the use of existing tools in a heterogeneous IT environment for product development, the link is based on the federal integration approach.

The combination of the data from the partial models and the federation of tools Excel for the preliminary design, SimulationX for simulation, Matlab to evaluate the results and CAMEO Systems Modeler for comparison of results and requirements is realized through the development platform ModelCenter MBSEPak for model-based systems engineering. In the so-called dashboard based on ModelCenter, the simulation results are shown and compared with the requirements of the SysML model (see Figure 5).

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Figure 5: Dashboard in ModelCenter MBSE Analyzer for the presentation of the results

Since essential parameters of the system and especially critical geometrical parameters are formulated in the requirements, interdisciplinary communication was supported by means of simulation in the early design phase. The simulation results obtained here had a high degree of accuracy and have not only enabled early decision making, but also created acceptance for the procedure. As a result of the pilot project, the model-based system development is to be introduced across the company.

5 Process Integration and System Optimization with ModelCenter

ModelCenter is a platform with which both the integration of processes as well as the development of complete systems design optimization can be carried out. It is of critical importance that the existing design, simulation and calculation tools in the company can continue to be used.

With the help of ModelCenter CAx workflows can be quickly and easily defined, which ensures automated and repeatable simulations. Through the execution of workflows, results can be recorded from different tools, design alternatives evaluated, tested against defined requirements and behavior can be visualized. Thus, decisions that mean a local optimum for the development, are reviewed with respect to the best solution for the

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entire system, verified and if necessary discarded. In a few cases the optimization is one variable in the system applicable for the total system view.

Figure 6 shows an example of the tools used in the model-based system development for a mechatronic functional support in a textile machine.

Figure 6: ModelCenter as an information hub for parameters and results for process integration and system optimization for the interaction of various development tools and the maturity assessment with help of a dashboard

6 Summary - Experiences and recommendations

The introduction of systems engineering for mechatronic product development is also gaining importance in classical engineering companies and is currently being discussed intensively. Companies are asking the question, what does the use of SE provides in terms of value added with respect to its conventional and established development processes and benefits with regard to reducing development time, cost savings as well as increased productivity, quality and innovation which arises from it.

The benefits of SE is only revealed by the holistic view of the entire system across all disciplines and development phases. For this purpose, we recommend to conduct an initial assessment of the approach, methods and tools for model-based systems engineering with a pilot project. At first the topic MBSE sounds for those involved in machine development theoretical and abstract and is then made understandable and comprehensible only through a practical application. In addition, within the framework of the evaluation methods and tools can be tried, evaluated and selected for later use and based on the first experience make necessary adjustments to the specifications for the introduction.

The user support in the introduction through MBSE-experts is required in order to transfer knowledge in the sense of know-that, know-why, and know-how and thus

10 ITI-Symposium 2014 fundamentally to empower developers and achieve direct benefits through the use of MBSE. An individual, modular deployment strategy (e.g. project-based first use) is recommended after sensitization and training of the personnel involved. Once the initial hurdles are overcome, once unachievable efficiency potentials in the development process can be revealed and realized.

System complexity in will continue to rise –the variety and customization of products accelerates this process further. Therefore, the timely planning and implementation of SE methods is essential for the competitiveness of future machines and thus indirectly also for the medium and long-term success of the company.

Bibliography

[Hon13] Eric C. Honour: Systems engineering return on investment, Dissertation, University of South Australia, 2013 [F4M14] www.fasform.org, aufgerufen am 03.07.2014 [FAS14] www.fas-method.org, aufgerufen am 03.07.2014 [FMI14] www.fmi-standard.org, aufgerufen am 22.07.2014 [GfSE14] www.gfse, aufgerufen am 03.07.2014 [KK14] Sven Kleiner, Marcus Krastel: Modellbasiertes Systems Engineering: Einführung und Einsatz von MBSE für die Fahrzeugentwicklung und im Maschinenbau, Deutschsprachige NAFEMS Konferenz 2014, Bamberg [Kle03] Sven Kleiner: Föderatives Informationsmodell zur Systemintegration für die Entwicklung mechatronischer Produkte, Shaker, 2003 [MCP14] www.mecpro.de, aufgerufen am 03.07.2014 [Wei08] Weilkiens, T.: Systems Engineering mit SysML / UML. dpunkt.verlag, 2008

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