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Research paper : Toward the integrated optimization of steel plate production process (K. Nishioka et al.)−106−Synthesiology - English edition Vol.5 No.2 (2012) scale hierarchical structure, and conceptualize it as a multi-scale hierarchically structured model for production control.In the field of material researches for steels having a complex structure, Olson proposed a spatial multi-scale hierarchically structured model and demonstrated that the model is capable of specifying comprehensively the property extending from the millimeter level to the meter level of commercial steels, by organically combining physical models developed for each hierarchy.[23] We apply this spatial multi-scale hierarchically structured model to the description of time-wise multi-scale structure, namely, we propose dividing the time scale of production control into three levels, and to each level, the efficiency model, required time/ in-process stock model and manufacturing lead time model are assigned respectively together with a time-wise multi-scale hierarchically structured model for the integrated production control that links them organically (see Fig. 6). This is an integrated model that determines the multi-scale nature for time in plate manufacturing and enables the quantitative evaluation of decision-making from the micro (processing in individual processes) to the macro (control of manufacturing lead time) level and the search for the optimal point. This model made it possible to search for the optimal schedule for achieving well balanced coordination of two types of needs difficult to satisfy at the same time, i.e., the optimization of process conditions in the upstream processes based on the push-type production control methodology and the shortening of manufacturing lead time in the downstream processes that anticipate the application of the pull-type production control.The difficulty of the production control model lies with the multi-leveled time scale, but specifying complex physical phenomena having hierarchical structure is one of the most fundamental research themes of R & D in ferrous metallurgy. One of the authors learned and assimilated the knowledge as his own during his pre-doctoral researches in the USA that it is effective to simplify matters by dividing structures into every level when developing the model of a mechanism that elicits physical phenomena. This engineer, in addition to studying theories, was moved to the manufacturing shop floor, and it can be said that the knowledge of the existing lean production system and his already acquired know-how for advancing his researches were amalgamated through such on-site activities, enabling him to analyze complex phenomena as hierarchical structure.6.2 Significance of the multi-scale hierarchically structured modelThe routine practices of the production control of iron and steel manufacturing is broken down into each task level from the viewpoint of pursuing work efficiency. Therefore, even if the skill for each process is acquired, it is extremely difficult to picture the total view of the production control system in manufacturing. The main significance of the multi-scale hierarchically structured model lies in its ability to provide a framework that enables detailed technical examination of the management issues of integrated optimization via the production control at the level of individual plants by providing an overview of the overall picture of the system. From the very beginning, the basic premise for engineers, when performing work whose mission is to realize continual improvement by designing and redesigning manufacturing systems, is to have an overview of the overall picture of the production control system, and the role played by the proposed model is important.However, the model proposed at this time does not possess the optimization evaluation function that realizes overall optimization, and does not guarantee the overall optimization theoretically and quantitatively. To realize the optimization, the existence of various models is essential, but compared with the assembly industries represented by the automobile industry, in the steel industry, the fluctuation of daily production and operation in the upstream of iron making and steel making processes is extremely marked and moreover, plans are frequently changed. In such an environment, because the model is developed based on past records that contain also external disturbances, it is difficult to make a highly accurate estimate and its reliability is naturally limited. It is evident that the deterministic approach that seeks optimal answers assuming full-information is available does not fit, and it is not realistic time-wise and from the viewpoint of effectiveness to conduct a complex and large volume of calculation by integrating a model obtained through a top-down analysis.In contrast, reviewing the history of the development of the proposed models, in the production control system covered by this research, we understand that (i) the individual elements constituting the system are locally organized and the structure that realizes the functions required by the system is sequentially decided through trial and error (hypothesis formation and verification), and (ii) the derived adaptive solution (even if it is not the optimum solution) provides an answer beyond expectation, to complex problems and supports effectively the decision-makings on the shop floor working in a dynamic environment. Our observation strongly suggests that the processes constituting the proposed model were emergent processes.[24]So, how were the emergent phenomena witnessed in this case example induced? Business scholars who interpret the strategic development of an organization as an emergent process claim that by setting an appropriate “place” (environment) for business activities, it is possible to promote the induction of emergent phenomena among individual persons constituting the organization.[25]-[27] We believe, as mentioned in chapter 4, in this case example, thanks to the management innovation at the level of the head office and under the leadership of middle

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