Gert Zülch

Hierarchical simulation of complex production systems by coupling of models

Abstract The simulation of production systems usually requires rather detailed data, concerning the duration of the modelled activities, which determine the quality and reliability of simulation results. Application in industry has shown that these data are usually available for manufacturing. However, for non-manufacturing tasks, only rough data are available as expert guesses. Therefore, in order to simulate complex production systems which include manufacturing functions as well as pre- and post-manufacturing functions, it is often necessary to combine simulation models with different levels of detail. Therefore, an adequate approach is needed in order to avoid inconsistencies in results. Such inconsistencies may be connected with different levels of detail and occur if i.e. a highly detailed manufacturing model is combined with a more global simulation model for the winding-up of customer orders. The solution until now has been to define a simulation model with only one unique level of detail. If highly specific results are needed, the user is forced to build a very detailed model of the whole production system. Often, this turns out to be either impossible or connected with too much effort. If more global models are used instead, the obtained results may be insufficient to render an answer to the users questions. At the ifab-Institute of the University of Karlsruhe, a new simulation tool OSim, which allows for the integration of variously detailed submodels into an overall global model of the investigated production system, is under development. The consistency of different models is guaranteed by a specific method of coupling the models. In this hierarchical way, the global simulation model can be combined with various submodels which contain more detailed processes. These detailed processes are then synchronised with the processes of the global model. For this purpose, the global model initiates an underlying process which then delivers its result to the global process. This combination of variously detailed models can be extended hierarchically. Following the description of this new simulation concept, a practical example for application will be given. This example is derived from an aluminium factory. It concerns the simulation of the overall winding-up of customer orders with their underlying manufacturing processes. The consistency of this simulation approach will be demonstrated by evaluating logistical key data at various levels of detail.

Indicators for the Evaluation of Organizational Performance

Due to increasing international competition, productive enterprises are currently searching for measures to improve their order processing. As the major potentialities for further improvements are strongly connected to the organization of production systems, the organizational performance has to be investigated and evaluated.

Computer-supported competence management: Evolution of industrial processes as life cycles of organizations

The examination of human performance within industrial processes increasingly extends beyond the matter of resource implementation. In addition to traditional approaches to personnel assignment planning, new management methods for the preservation and further development of personnel are becoming established. The following paper discusses the effects and challenges related to computed-aided competence management. For this purpose it is indispensable to examine the notion of competence more in depth as well as the resulting competence management. Since as of yet no universally valid definition of competence exists, the following article discusses various facets of competence management and illustrates these by considering individual simulation-aided decision and planning tools for industrial process optimization.

Simulation-supported change process for product customization - A case study in a garment company

Due to the increasing competition in global markets, many European garment manufacturers have had to undergo significant restructuring and were forced to create leaner value-adding processes. As a result, the majority of the manufacturing operations have been outsourced to low labor cost countries. At the same time, production logistics as well as information and communication technologies have gained importance, in order to keep job functions requiring higher qualifications within Europe. Another challenge concerns the introduction of customized products into the production processes which previously had been designed for manufacturing of large volumes. Prior to implementing such changes, the consequences with respect to production logistics as well as the financial impacts should be examined. The case study presented in this paper uses a simulation tool for these purposes. Different scenarios developed for a garment company were analyzed. Based on the results, recommendations for the further development of the regarded company were deduced.

An integrated object model for activity network based simulation

This paper describes an object-orientated simulation approach towards an integrated planning of production systems. The main obstacle for an integrated use of simulation over different planning areas and stages are the different views on a production system. Therefore, an object model is developed, which enables the co-existence of different views and levels of detail in the same simulation model while maintaining its consistency. This is achieved by combining object-orientated technology with a network based simulation approach. The prevailing idea is to offer the opportunity to re-use existing models for the investigation of different aspects of a production system. The approach is abstractly described as a conceptual object model and is thus, independent from a concrete simulation language, tool or environment. The last part of this paper introduces the simulation tool OSim, that implements this object model and demonstrates its usage through an example.

Dynamic analysis of changes in decisional structures of production systems

Abstract In the realm of enterprise reorganization, terms such as process orientation, group work, segmentation, and de-layering of hierarchical structures are frequently discussed. Growing needs of support, before and during enterprise reorganization, calls for methods to assist the change process to the highest possible degree. During recent years, several methodologies and tools for modelling and designing enterprises were developed. This paper describes an approach using the GRAI-methodology for modelling the functional, physical, and decisional structure of production systems, respectively. Upon completion, the created enterprise models are transferred into the simulation system FEMOS for dynamical analysis. After describing the theoretical background, the paper demonstrates the effects of decisional adaptations using two case studies completed during the ESPRIT project REALMS (re-engineering application integrating modeling and simulation). The first case looks into the impact of decreasing the number of hierarchical layers with respect to a one-of-a-kind production system. The second case shows the effects of re-engineering a function-oriented production system with several department interfaces to a process-oriented organization.

Editorial: The Digital Factory: An instrument of the present and the future

In a time of shortened product life cycles and the consequential product changes, increasing product variety and shrinking delivery times, survival in the market demands an enterprise to possess agility and flexibility. One route taken by many enterprises is that of shortened planning times and the flexible configuration of the planning process, which in turn influence the production in such a way that a quicker adaptation to changing circumstances is possible and the time needed to bring a product onto the market is shortened drastically. In this scenario, the ‘‘Digital Factory’’ is seen as the planning instrument of the future. A large part of the factory planning, productionand product-planning is already supported by digital tools. These various planning phases are not integrated and thus are generally carried out in isolation. The VDI (Association of German Engineers) defines the Digital Factory as ‘‘a comprehensive network of digital models, methods and tools, including simulation and 3D/VRvisualization, which are integrated through continuous data management.’’ The goal is to achieve a holistic planning, evaluation and continuous improvement of all significant processes and resources in the factory in connection with the product. All elements within the production should be modelled during planning by means of computer-supported methods, in such a way that the physical manufacturing of the product meets all quality, time and costs goals [1]. The computer-supported models within the Digital Factory must document and visualize all the elements of the future factory as well as describe their interplay. Only when the digital product has successfully passed through the Digital Factory, the product is released into the real factory. This digital safeguarding leads to

Shaping the organization of order processing with the simulation tool FEMOS

Abstract Having been forced by the development of international markets, producing enterprises are presently searching for possibilities to improve their order processing. Besides technical means, new organizational concepts which can be characterized by a process orientation are under consideration. Examples for such concepts which consider the entire order processing from order entry to delivery are order centers, production segments or the concepts of lean production. In connection with the realization of new forms of organizational structures, an enterprise has to decide which form of structure tends to produce the best system behavior in given circumstances. Up to now, general statements concerning the suitability of different forms of structure have not been available. Therefore, specially adapted solutions must be developed according to the given production conditions. As the evaluation of their suitability requires the examination of the dynamical system behavior, a simulation tool has to be used in order to completely evaluate the effects of the different possible solutions. A simulation-aided approach will be presented for the design of the organizational structure of production systems by using a case study as an example. In a mechanical engineering enterprise which produces conveying systems the production situation can be characterized by a strong customer-orientation. Each order refers to a special conveying system consisting of different components which are arranged individually. With the help of the simulation tool FEMOS, a suitable structure for the winding-up of orders in the pre-productive functions will be developed. This case study results in a proposal for the reorganization of the departments for design and operations planning.

Modelling and simulation of human decision-making in manufacturing systems

The simulation of manufacturing processes mainly focuses on the structure of machinery resources and the flow of material, but the inclusion of the personnel in the simulation model is only slowly gaining in importance. When personnel resources are modelled, merely the operative tasks are represented. However, as a result of modern manufacturing concepts, worker decisions at a workshop level are becoming more and more important. This article deals with various concepts for the modelling of human decisions in manufacturing systems, namely from human decision makers as passive resources over the modelling of decisions based on global rules to the modelling of active decision makers with individual, locally valid decisionmaking rules. Each of these various types of modelling will be elucidated using an application example.

Simulating alternative organizational structures of production systems

Abstract Changes in international competition lead to changes of the requirements on production enterprises. The introduction of new production technologies does not seem to be exclusively an adequate reaction to the increasing problems. Therefore tools of computer-integrated production lCIMr and new organizational concepts have to be conceived. Because these organizational and technical means are linked on the one hand with severe changes in the production system and, on the other hand, with rather higher economic risks in their realization, the effects have to be estimated in advance in the planning stage. Consideration of dynamical system behaviour plays an important part because the main goal is the improvement of order processing. This paper presents a simulation program, which can be used during the design phase of the organizational structure of production systems as a powerful tool for predicting the effects of new computer-aided tools and structures.