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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Item Design of Material Flow Networks in Manufacturing Facilities(1994) Herrmann, Jeffrey W.; Ioannou, George; Minis, Ioannis; Nagi, R.; Proth, J.M.; ISRIn this paper we consider the design of material handling flow paths in a discrete parts manufacturing facility. A fixed-charge capacitated network design model is presented and two efficient heuristics are proposed to determine near-optimal solutions to the resulting NP- hard problem. The heuristics are tested against an implicit enumeration scheme used to obtain optimal solutions for small examples. For more realistic cases, the solutions of the heuristics are compared to lower bounds obtained by either the linear programming relaxation of the mixed integer program, or an iterative dual ascent algorithm. The results obtained indicate that the heuristics provide good solutions in reasonable time on the average. The proposed methodology is applied to design the flow paths of an existing manufacturing facility. The role of the flow path network problem in the integrated shop design is also discussed.Item A Practical Method for Design of Hybrid-Type Production Facilities(1994) Harhalakis, George; Lu, Thomas C.; Minis, Ioannis; Nagi, R.; ISRA 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.Item Temporal Aggregation in Production Planning(1993) Harhalakis, George; Mehra, Anshu; Nagi, R.; Proth, J.M.; ISRIn 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.Item Manufacturing Cell Formation Under Random Product Demand(1993) Harhalakis, George; Minis, Ioannis; Nagi, R.; ISRThe 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.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 Single Machine Scheduling with Discrete Earliness and Tardiness(1992) Harhalakis, George; Nagi, R.; Proth, J.M.; ISRThis 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.Item 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 Design and Operation of Hierarchical Production Management Systems(1991) Nagi, R.; Harhalakis, G.; ISRProduction Planning Management and Control of a production system subject to random events are challenging problems. A multi-layer hierarchical approach to tactical and aggregate production planning problems is proposed, wherein the architecture is strongly based on the specific physical system, applicable controls and the complexity of the decision making problem at hand. We address the design and operation of such Hierarchical production Management Systems (HPMS). Regarding the design aspect, we start by developing schemes for product, machine and temporal aggregation; consistency and controllability issues in the hierarchy have been addressed in the aggregation/disaggregation schemes. These three aggregation schemes for model reduction have been developed and incorporated to the time-scale decomposition of activities, in order to provide a solid theoretical foundation of the architecture. We then proceed to a systematic stepwise design approach for the construction of the hierarchy. It provides the appropriate number of layers and an associated Model as well as Decision Making Problem (DMP) at each level. A model is defined by entities, attributes, links and domains, while a DMP is defined by a set of possible controls (decisions), constraints, and optimality criteria to be optimized over a planning horizon. The operation of the hierarchy consists of a topdown computation of controls, which calls for the resolution of an optimization problem at each level of the hierarchy. The solution of any problem in sequence determines some parameters in the subsequent problem. We detail the mechanism for top-down constraint propagation, which is important in ensuring consistency of criteria and feasibility. The execution then involves the bottom-up feedbacks, and a revision in the plan is carried out if necessary. In particular, the rolling horizon mechanism, and the reaction of the hierarchy to random events has been detailed. A generic job-shop example has been employed to present the design and operation of the HPMS. It is hoped that this methodology can be applied to other types of large-scale complex decision making problems.Item Multiple Routings and Capacity Consideration in Group Technology Applications.(1989) Harhalakis, George; Nagi, R.; Proth, J.M.; ISRThis paper addresses the problem of manufacturing cell formation, given multiple part routings, and multiple functionally similar work-centers. The suggested choice of part routings favors the decomposition of the manufacturing system into manufacturing cells in a way that minimizes part traffic, along with satisfying the part demand and work-center capacity constraints. The proposed heuristic, iteratively solves two independent problems: (i) routing selection, and (ii) cell formation. The common objective is to minimize the inter-cell traffic in the system. The first problem is formulated as a linear-programming problem, while the latter is approached by an existing bottom-up aggregation procedure, known as Inter-Cell Traffic Minimization Method (ICTMM), enhanced appropriately. Applications of the proposed system include: (i) the design of a manufacturing facility with respect to machine layout, (ii) selection of part routings for changing product mixes, and (iii) assignment of new parts to part families, given the initial layout.Item Development and Application of a Knowledge Based System for Cellubr Manufacturing.(1989) Harhalakis, George; Minis, Ioannis; Nagi, R.; ISRThe Inter Class Traffic Minimization Method (ICTMM) that arranges the production equipment of a machine shop into manufacturing cells in order to minimize the inter cell trafflc of parts is presented in this paper. All quantitative tasks of this method are performed by algorithms that are embedded in a knowledge base. The aggregation rules and the problem constraints form the core of this knowledge base. Two other methods of factory flow analysis are also presented in order to compare their criteria and objectives to the ICTMM. Finally, all three systems are applied to a large size industrial project and the results obtained are presented and evaluated. We conclude by suggesting further research directions for a most comprehensive solution to the layout of a cellular manufacturing facility.