Institute for Systems Research
Permanent URI for this communityhttp://hdl.handle.net/1903/4375
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Item A Class of Conflict Free Petri Nets Used for Controlling Manufacturing Systems(1992) Harhalakis, George; Levantopoulos, Marios M.; Lin, Chang-Pin; Nagi, R.; Proth, J.M.; ISRThis paper is devoted to the behavior, evaluation and management of non-cyclic discrete systems in general and manufacturing systems in particular. We introduce a special type of Petri nets called CFIOs (Conflict-Free nets with Input and Output transitions). It is shown that CFIOs are live, reversible if consistent, and can be kept bounded under certain conditions. We also develop reduction rules which facilitate the computation of the t-invariants of CFIOs. We then take advantage of the qualitative properties of CFIOs to perform planning in manufacturing systems. Numerical examples illustrate these approachesItem Hierarchical Modeling Approach for Production Planning(1992) Harhalakis, George; Nagi, R.; Proth, J.M.; ISRProduction management problems are complex owing to large dimensionality, wide variety of decisions of varying scope, focus and time-horizon, and disturbances. A hierarchical approach to these problems is a way to address this complexity, wherein the global problem is decomposed into a series of top-down sub- problems. We advocate that a single planning architecture cannot be employed for all planning problems. We propose a multi-layer hierarchical decomposition which is dependent on the complexity of the problem, and identify the factors influencing complexity. A systematic stepwise design approach for the construction of the hierarchy and inputs required are presented. The subsequent operation of the hierarchy in an unreliable environment is also explained. Aggregation schemes for model reduction have been developed and blended with a time-scale decomposition of activities to provide the theoretical foundation of the architecture. It is also hoped that this methodology can be applied to other such large-scale complex decision making problems.Item Event Graphs for Modeling and Evaluating Modern Production Systems(1990) Harhalakis, George; Laftit, S.; Proth, J.M.; ISRVery few Mathematical Tools are available to study the dynamics of discrete manufacturing systems. Petri Nets, and in particular a special type of Petri Nets called Timed Event Graphs, seem to be of special interest for studying discrete manufacturing systems. In this paper, we define Timed Event Graphs and emphasize the properties which are of interest for out purpose. Modeling job-shop systems as well as assembly systems using event graphs is then explained. The model obtained is a strongly connected event graph whose properties are presented in the first part of the paper. These properties are used to derive the properties of the manufacturing system. In particular, it can be shown that the productivity of the manufacturing system is defined by the cycle time of the critical circuit in its event graph model. Blocking conditions of the system are also studied.Finally, we show how to use the previous results to maximize the productivity with a minimal in-process inventory when the sequences of product types are fixed at the entrance of each machine.
Item Manufacturing Cell Design Using Simulated Annealing: an Industrial Application(1990) Harhalakis, George; Proth, J.M.; Xie, X.L.; ISRIn this paper, we give a brief summary of simulated annealing procedures used to solve combinatorial optimization problems. We then present the manufacturing cell design problem which consists of designing cells of limited size in order to minimize inter- cell traffic. We show how to use a SA approach to obtain a good, if not optimum, solution to this problem. Finally, we apply this approach to an industrial problem and compare the results to the ones obtained using the so-called twofold heuristic algorithm.