Institute for Systems Research Technical Reports

Permanent URI for this collectionhttp://hdl.handle.net/1903/4376

This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.

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Author: search.filters.author.Harhalakis, George

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Now showing 1 - 10 of 46
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    A Practical Method for Design of Hybrid-Type Production Facilities
    (1994) Harhalakis, George; Lu, Thomas C.; Minis, Ioannis; Nagi, R.; ISR
    A comprehensive methodology for the design of hybrid-type production shops that comprise both manufacturing cells and individual workcenters is presented. It targets the minimization of the material handling effort within the shop and comprises four basic steps: (1) identification of candidate manufacturing cells, (2) evaluation and selection of the cells to be implemented, (3) determination of the intra-cell layout, and (4) determination of the shop layout. For the cell formation step the ICTMM technique has been enhanced to cater for important practical issues. The layout of each significant cell is determined by a simulated annealing (SA)-based algorithm. Once the sizes and shapes of the selected cells are known, the shop layout is determined by a similar algorithm. The resulting hybrid shop consists of the selected cells and the remaining machines. The methodology has been implemented in an integrated software system and has been applied to redesign the shop of a large manufacturer of radar antennas.
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    Temporal Aggregation in Production Planning
    (1993) Harhalakis, George; Mehra, Anshu; Nagi, R.; Proth, J.M.; ISR
    In this paper, the problem of temporal aggregation in production planning is addressed. A single facility with multiple part types is considered. The planning horizon consists of a sequence of elementary time periods, and the demand for all part types is assumed to be known over these periods. The production planning problem consists of minimizing the holding and backlogging cost for all part types. Due to usual errors in demand forecasting, and due to the large size of the linear programming problem commonly encountered in such problems, there is a need for aggregating the production variables over the time horizon (typically, for weekly to monthly) to result in a hierarchical structure. We consider a two-level hierarchy composing a sub- problem at each level, and we propose an iterative technique which solves these sub-problems in sequence. A posteriori bounds are developed, which are useful in evaluating the performance of the iterative algorithm. Quick lover and upper bounds of the original problem are also developed. Finally, numerical results for numerous test cases are presented.
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    Manufacturing Cell Formation Under Random Product Demand
    (1993) Harhalakis, George; Minis, Ioannis; Nagi, R.; ISR
    The performance of cellular manufacturing systems is intrinsically sensitive to demand variations and machine breakdowns. A cell formation methodology that addresses, during the shop design stage, system robustness with respect to product demand variation is proposed. The system resources are aggregated into cells in a manner that minimizes the expected inter-cell material handling cost. The statistical characteristics of the independent demand and the capacity of the system resources are explicitly considered. In the first step of the proposed approach the expected value of the feasible production volumes, which respect resource capacities, are determined. Subsequently, the shop partition that results in near optimal inter cell part traffic is found. The applicability of the proposed approach is illustrated through a comprehensive examples.
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    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.; ISR
    This 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 approaches
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    Single Machine Scheduling with Discrete Earliness and Tardiness
    (1992) Harhalakis, George; Nagi, R.; Proth, J.M.; ISR
    This paper considers the problem of scheduling a given set of jobs on a single machine in order to minimize the total weighted earliness and tardiness costs. The scheduling horizon is divided into elementary periods; jobs have due-dates at the end of these periods. All jobs are assumed initially available. Jobs have unique (weighted) early and tardy staircase penalty functions. No preemption of jobs is permitted. and idle time may be inserted. We prove that this problem is NP-complete. Some results relating to job priorities and completion times in an optimal solution are presented. A Mixed Integer Linear Programming (MILP) formulation of this problem is developed. A branch-and-bound scheme that solves the above problem optimally is also presented. Heuristics, derived from simple priority rules, provide an initial upperbound to the search. We develop two lower bound procedures for the remaining jobs to be scheduled at any partial solution state. Numerical results relating to the performance of the branch-and- bound scheme are also presented.
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    UPN: A Petri Net Based Graphical Representation of Company Policy Specifications in CIM
    (1992) Harhalakis, George; Lin, Chang-Pin; ISR
    A graphical representation schema - Updated Petri Nets (UPN) - has been developed to model rule based company policy specifications, in the context of computer integrated manufacturing systems. UPN facilitates the modeling of relationships between operations of various related application systems and the database updates and retrievals among various CIM databases. Based on this representation, a hierarchical modeling technique which includes refining and aggregating rules has also been developed. Application of the UPN is demonstrated in designing rule based systems for controlling and integrating the information between manufacturing applications, including Computer Aided Design, Computer Aided Process Planning, Manufacturing Resources Planning, and Shop Floor Control.
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    INformation Systems for Integrated Manufacturing (INSIM)
    (1992) Harhalakis, George; Lin, Chang-Pin; Mark, Leo; ISR
    A mechanism with the potential to control the information flow among all of the manufacturing application systems, in order to streamline factory activities, based on company-specific and company-wide policies and procedures is proposed here. The goal is to achieve a fully integrated manufacturing management system. The INformation Systems for Integrated Manufacturing (INSIM) reflects a design methodology to build a knowledge base to serve as the control mechanism.
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    Hierarchical Modeling Approach for Production Planning
    (1992) Harhalakis, George; Nagi, R.; Proth, J.M.; ISR
    Production 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.
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    A Step-Wise Specification of a Manufacturing System Using Petri Nets
    (1992) Claver, J.F.; Harhalakis, George; Proth, J.M.; Savi, V.M.; Xie, X.L.; ISR
    Our experience, mainly based on two recently conducted real-life studies for some European companies, reveals that a natural way to proceed with the modeling and specification of large manufacturing system is to decompose the model of the entire system into sub-systems (referred to as modules). Models for modules are developed, and then integrated to model the entire system. Several problems arise in this process. If we express these problems from the users' point of view, they can be summarized by the following two issues: (i) how to decompose the whole system into sub-systems modules in order to have tractable (thus small) models exposing "good" properties? (ii) how then to integrate the module models in order to reach a global model also exposing "good" properties?
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    Implementation of Rule Based Information Systems for Integrated Manufacturing
    (1992) Harhalakis, George; Lin, Chang-Pin; Mark, Leo; Muro-Medrano, P.R.; ISR
    This paper focuses on the development of a methodology within a software environment for automating the rule based implementation of specifications of integrated manufacturing information systems. The specifications are initially formulated in a natural language and subsequently representted in terms of a graphical representation by the system designer. A new graphical representation tool is based on Updated Petri Nets (UPN) which we have developed as a specialized version of Colored Petri Nets (CPN). The rule based implementation approach utilize the similarity of features between UPN and the general rule specification language used in the implementation. The automation of the translation of UPN to the rule specification language reduces considerably the life cycle for design and implementation of the system. The application presented here deals with the control and management of information flow between Computer Aided Design, Process Planning, Manufacturing Resource Planning and Shop Floor Control databases. This provides an integrated information framework for Computer Integrated Manufacturing (CIM) systems.

    Index Terms - Rule base, information system, computer integrated manufacturing, system modeling, knowledge verification, Petri nets, rule specification language, reasoning, language translation.