The communication module described in this paper combines the simulation system MOSYS, developed at the Fraunhofer-Institute for Production Systems and Design Technology (IPK Berlin), with the CAD system GDS, which is in widespread use in factory planning. Being familiar with CAD environment and applying CAD operational drawings the planner can easier and faster implement transfer paths and the resources locations. The practicality of different system configurations and control concepts for an available layout may be examined as well as the effects of different layout variants on the dynamics of production.
Simulation technology assists for designing manufacturing systems regarding capacity and structure as well as to optimizing and testing their operational capability. The layout, which today is predominantly developed with CAD systems, documents the planning results in concentrated form. In industrial practice CAD and simulation are tools, that are usually applied separately even though in some degree they use the same data. Rationalization potentials for factory planning remain unused. The factory simulation system MOSYS was therefore connected with a CAD system. In simulation studies of manufacturing systems special attention may now be driven to spatial arrangement of resources and transport paths.
The simulation system MOSYS supports the layout planning of manufacturing systems. MOSYS was applied in several industrial projects, in the planning of transfer lines, flexible manufacturing systems and islands of automation as well as in the evaluation of teamwork concepts (Gddigk and Rabe 1994).
MOSYS analyzes the system behavior with discrete, event-oriented simulation; the simulation time advances with the beginning and the ending of processes. Simulation models are developed module-oriented (Hanisch et al.1993). The modelling process takes place graphic-interactively. MOSYS supports the hierarchical development of models by the way of enabling planners to use each model as a subsystem of another model. To model the functions of a manufacturing system as well as spatial information the simulation model MOSYS is equipped with functional and topological means of description. The topological description is independent of the functional description and may be developed before or afterwards.
Therefore, the same manufacturing system might, for example, be simulated with different transport paths or different machine locations (Mertins et al.1993). Figure 1 illustrates the structure of the simulation system.
The functional description portrays the productions technical, organizational and personnel-related features. With the function-based model a manufacturing system may be examined, for example in the rough planning stage, without knowing the spatial arrangement of the technical installations. Time demands of the material flow are either disregarded or displayed with average values.
The functional behaviour of a system is described by using the five buildings blocks Manufacture, Transport, Store, Assemble and Test (figure 1). These building blocks can be combined freely to each other and thus allows the modelling of every thinkable sequence. Each building block has a distinguished behavior to make it easy for the user to decide which block he wants to use. By use of parameters they are customized to the specific applications (Mertins et al.1992).
In addition to the functional description, the topological description enables the registration of the technical installations spatial arrangement in the simulation model. In many systems the exact position of equipment and transport paths effects, for example, transport and blocking times. Waiting for means of transport again effects parts of the manufacturing structure, for example buffer sizes or the number of pallets. Therefore, production and transport cannot be evaluated separately (Rabe 1988). They have to be investigated as a whole. Thus provides the possibility to add topological information to the functional model. The position of equipment and the routes of transport devices can be described in the model. The topological description includes a simple layout of the production system with positions of resources and material flow tracks. The topological description can be executed independently from the functinal description. The topological information contains data on the location of all technical installations, particulars of conveyor routes and detailed information on vehicles and their characteristics.
With this information MOSYS can model the real behavior of conveyor systems in the model. An example is shown in figure 2. The model consist of nodes and lines. The nodes represent positions of production equipment. They are connected with lines, which represent transport paths.
The topological description of the simulator results in a very abstract description of the material flows and in an uncomfortable data entry. To eliminate planning errors the topological description is supported with a realistic CAD layout. For this purpose, the simulator MOSYS is connected with the CAD system GDS, which has often been applied in factory planning projects.
GDS was developed by McDonnell Douglas and is distributed by Graphic Data Systems Ltd.
It is used in two- and three-dimensional CAD applications. GDS is mainly used in factory planning projects (planning, layout, facility management etc.).
GDSs External Program Interface (EPI) provides interfaces to the programming languages FORTRAN, PASCAL and C. EPI enables the communication between an external program and GDS
The integration of simulation and CAD takes place by the way of a mutual communication module. In contrast to a connection via passive data interfaces the online integration enables the mutual use of data files and the program-technical connection of the two software systems.
To enable the future coupling of additional, common CAD software the communication module is divided into a general and a CAD-specific program part.
MOSYS is constructed modularly and is implemented in the simulation language Simula. Simula enables the embedding of external FORTRAN procedures, that can be connected with the External Program Interface on the FORTRAN interface. The CAD system GDS is treated just like an additional MOSYS module.
When designing the user interface of the communication module great emphasis was placed on retaining the existing user interfaces, which experienced simulation and CAD users knew. The user may apply each and every CAD function of GDS to enter spatial data into the simulator and to edit the layout plans.Figure 5 illustrates the screen display of a CAD layout developed with GDS with transport paths and machine symbols.
The design of the topological model is based on an operational floor space plan which in the CAD system is faded in to the background and which serves the planning engineer as an orientation when determining the transportation connection. Inversely, a topology optimized during simulation experiments may also be described in the CAD system. Based on this, the spatial arrangement of the manufacturing system could be determined or revised.
MOSYS nodes and the CAD symbol are connected with object parameters This insures the possibility to restore the consistency of data after changing the layout or the topology drawing. In contrast to a rigid connection of the two drawings the CAD layout may be edited independently of simulation applications and the topology drawings may be changed independently of the CAD layout.
Important effects of the integration of CAD and simulation include the reduction of coordination and transfer errors in the planning process as well as faster modeling. The use of internal CAD drawings improves the acceptance of simulation. In contrast to the application of three-dimensional animation modules, which is planned as well, additional graphic datas are not required.
When implementing the communication module the future expandability was kept in mind. Modularization supports portability as well as expansions of functions.It is planned to transfer the data of the simulations results to the CAD system and to combine them with the graphic objects connected to the MOSYS functional module. Relations of the material flow may then be represented in the layout, for example as Sankey diagrams.
Gddigk, G.; Rabe, M. 1994. "Simulationsgestuetzte Investitionsminimierung bei der Produktion von Fahrzeugteilen". ZWF 89 (1994)1-2, S. 43-45
Hanisch. S.; Koop, D.; Rabe, M.; Reinhardt, A.; Rottbeck, B. 1993. "Modellierung und Implementierung". ASIM Arbeitskreis fuer Simulation in der Fertigungstechnik (Hrsg.): Simulationsanwendungen in Produktion und Logistik.Wiesbaden, Braunschweig: Vieweg 1993
Mertins, K.; Furgac, I.; Rabe, M.1993. "Planungssicherheit durch Simulation".Technica 42 (1993) 9, S. 12-18
Mertins, K.; Rabe, M.; Bergmann, M. 1992: "Hierarchical Modelling of Production Systems". In: Computational Systems Analysis 1992, S. 641-646. Amsterdam, London, New York, Tokyo: Elsevier 1992.
Rabe, Markus 1988. "Materialfluss und Layoutplanung", Proceedings of the LOG88,Hamburg 1988
Dr.-Ing. Kai Mertins is the Director of the Planning Technology Department at the Institute for Production Systems and Design Technology (IPK) headed by Prof. Dr. h.c. mult. Dr.-Ing. G. Spur in Berlin. His doctoral thesis was entitled "Production Control of Flexible Manufacturing Systems". His research interests are design and planning of flexible automated systems in manufacturing and assembly. In addition to heading the Planning Technology department, he is actively involved in teaching "Production Informatics" to graduate students at the Technical University of Berlin.