کمک به قابلیت استفاده مجدد و خاصیت پیمانه ای مدل های شبیه سازی سیستم های تولید : برنامه برای شبیه سازی کنترل توزیع شده در زمینه DFT

Requirements for manufacturing control evolve from traditional centralised approaches where decision making is hierarchically broadcasted to more complex distributed control architectures involving autonomous entities and processes. Moreover, manufacturing processes are facing standardisation and globalisation such as promoted by the demand flow technology (DFT) concepts. In order to evaluate these new architectures, discrete-event simulation seems the most appropriate tool. However, complexity of distributed architectures and DFT standardisation requires introducing modularity and reusability in the modelling process. This paper deals with a methodological approach, based on ASDI (analysis-specification-design-implementation), to develop a library of generic simulation components that can be, as automatically as possible, instantiated into a modular simulation model. This approach is illustrated using an industrial case study where simulation aims at evaluating the impact of operator's flexibility induced by DFT context.

Today manufacturing systems need to be adapted to the internal (e.g., machine breakdown) as well as the external disturbances (e.g., changes in demands or product specifications). Consequently, research in manufacturing system control has moved away from traditional centralised approaches where decision making was hierarchically broadcasted from the higher decisional levels down to the operational units to more distributed architectures. In this way, heterarchical architectures promote production control by distributing every decision capacities in autonomous entities, without any centralised view of the shop floor status. To ensure the consistency of a decision making, more pragmatic approaches are based on hybrid control which combines the predictability of the centralised control with the agility and robustness against disturbances of the heterarchical control. Holonic Manufacturing Systems (HMS) has been suggested as a concept for these future manufacturing systems (Koestler, 1967). In order to evaluate these new manufacturing systems or to choose a management production organisation rather than another, Law and Kelton (1991) showed that discrete-event simulation is the more adaptable method (in the following, the term simulation will always be related to discrete-event simulation). While simulation has much strength, it is difficult to identify in a given model the different flows that are processed by the system. Consequently, decisional and physical systems cannot be separated in the model which is a serious limitation for evaluation of several control policies without a complete simulation model redesign. It emphasises the need for an underlying modelling discipline or structured approach (Douglas et al., 2002) to guarantee modularity and thus facilitate modification on the model. Moreover, nowadays the majority of companies are evolving towards a standardisation of their various physical and decisional processes to ensure coherence and interoperability of their processes. In this way, Trane Company, which is our industrial case study, chose to implement the demand flow technology (DFT) principles (Costanza, 1996) to standardise all its 29 production sites. DFT methodology is a particular implementation of Just-in-Time concepts, where all production lines are structured in the same way in every shop floor. Consequently, all shop floor production lines have to be modelled in a similar way. This fact justifies the need of reusability of process models to be used in simulation. Effectively, it is obvious that the time savings in simulation model design can be obtained if it is possible to reuse some simulation model modules to construct new assembly line models. In this paper, we propose a structured approach (ASDI-dc) to build reusable and modular simulation models for manufacturing systems with distributed control. This approach is based on the ASDI (analysis-specification-design-implementation) Kellert and Force, 1998a and Kellert and Ruch, 1998b methodology, which implements the object-oriented concepts and a systemic modelling framework to the simulation techniques. The main goal of our study will be to give a framework to generate automatically specific models from generic ones by using standards objects and automated functions in DFT context. According to the Trane objectives, this framework could be used by a person who is not necessarily an expert in software tools. The remainder of this paper is organised as follows. In Section 2, we highlight the reusability and modularity challenges in distributed control context. Section 3 presents the proposed methodological approach. Section 4 describes an industrial application related to an assembly line manufacturing. In Section 5 we will discuss the credibility of the reuse and the modularity. Conclusions and open issues for future research will be presented in Section 6.

The study of different simulation methodologies enabled us to answer limitations that must be addressed to improve their effectiveness in a distributed control context. The ASDI methodology enables to answers formalisation, modularity and “reuse” problems. But it does not take into account the distribution aspect. Our contribution concerns all ASDI life cycle phases in the definition of autonomous processes and their conceptual model. In design and implementation, we used Arena and Visual Basic software for application to develop a generic component for control. The question of model validity cannot be ignored. It seems widely accepted in the simulation community that models or modelling approaches cannot be fully validated. It makes sense to have some form of model quality insurance to ensure that the model is fit for its intended purpose. In the future research, we are interested on the following two objectives: The first one is to give a more formal setting for this approach and propose a simulation platform to build simulation model in DFT context. The second one deals within the scope of our laboratory research team; this scope concerns product-driven manufacturing systems. In this project, we consider that the product can store its own information and can be an actor of its own transformations. This fact deals with intelligent products resulting from HMS architecture. In the DFT context, the concept of product-driven control is very developed. For example, the signal of work is given by the product state. However, physical flow and information flow synchronisation are not assured. To resolve this problem, new technologies of identification like RFID have appeared. The goal of our next work will be to use simulation as a tool to integrate this technology in Trane company legacy systems. In our current case, autonomous process concerned labour on the shop floor. Nevertheless, it would be interesting to analyse how to adapt the autonomous process concept to intelligent product concept.