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 Similarity Measures for Process Planning and Design Evaluation(1997) Herrmann, Jeffrey W.; Singh, Gurdip; ISRDesign engineers and process planners need to search for similar designs. Design engineers use similar designs to estimate a new design's manufacturability. Like process planners, who need to generate process plans before production begins, design engineers can use an existing, similar design's plan to create a new process plan. Then, they can evaluate the new design. Variant process planning, a common process planning approach, uses a design similarity measure to identify the most similar design and retrieve a useful process plan. However, standard design similarity measures do not explicitly consider the production process. This paper presents an approach for developing a new class of plan-based design similarity measures. Such a measure explicitly exploits process plan similarity and thus improves the variant process planning approach. An example illustrates the approach and compares the new measure and a traditional group technology code-based approach.Item A Generative Approach for Design Evaluation and Partner Selection for Agile Manufacturing(1996) Minis, Ioannis; Herrmann, Jeffrey W.; Lam, Giang; ISRAn agile manufacturing firm forms partnerships with other manufacturers as necessary to design and manufacture a product quickly in response to a market opportunity. In order to form a successful partnership, the firm needs to create a superior design and select the partners that best fit the partnership's scope. In this paper we consider the intrinsic relationship between design evaluation and partner selection. The paper presents a generative approach that a design team can use to obtain feedback about a new product embodiment based on high- level process plans and on the manufacturing capabilities and performance of potential partners. Using this information, the design team can improve their design and identify the potential partners that best fit its manufacturing requirements. The primary application of this work is to certain types of mechanical and electronic products.Item Hierarchical Production Planning for Job Shops(1995) Mehra, Anshu; Minis, I.; ISRProduction management and control of job shops is an important and complex problem. This dissertation proposes a two-level hierarchical method for tactical production planning in such environments. We first develop a scheme to design the planning hierarchy by aggregating parts into families and resources into manufacturing cells; a priori aggregation of elementary time periods into aggregate time periods is assumed. Based on the results of the design stage, the medium- and short- term production planning problems are formulated. The objective of the production planning problems consists of minimizing the holding costs for the work-in-process and finished goods inventory and the backlogging costs for unfulfilled demand. The formulations are complemented by capacity constraints, inventory state equations, and constraints that ensure feasibility of the aggregate production plan. We decompose the global production planning problem such that the short-term planning sub-problems can be computed in parallel. An efficient solution algorithm is developed to solve the optimization problems of the hierarchy. The algorithm has been shown to converge to near-optimal solutions in a finite number of iterations. Furthermore, the algorithm provides optimal solutions for a special case of the planning problem. The hierarchical approach is evaluated with respect to computational complexity, memory requirements, and the quality of the resulting production plans. The hierarchical approach is also tested on an industrial case and the resulting plan is compared with the one obtained from the company's Manufacturing Resource Planning system.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 Development of Variant Designs in ISO 9000 Certification(1993) Woo, M.; Zhang, G.M.; ISRThis paper will present the research results from developing a computer database system using a variant design approach to assist in the preparation of quality manuals. The basic principle is "the most common one of design assignments modifies or uses an existing design to make a 'new' component." Such an information flow mainly relies on a database, which stores all the information about ISO 9000 certification requested by a desired company. Integration of system architecture and communication protocol allows to accommodate different types of business (electronics, mechanical, etc.). A case study is presented to illustrate the process of generating quality manuals through an intelligent user-interface and to demonstrate a new and unique business strategy to enhance quality improvement and management.Item Manufacturing Cell Formation by State-Space Search(1993) Ghosh, Subrata; Mahanti, Ambuj; Nagi, Rakesh; Nau, Dana; ISRThis paper addresses the problem of grouping machines in order to design cellular manufacturing cells, with an objective to minimize intercell flow. This problem is replaced to one of the major aims of group technology (GT): to decompose the manufacturing system into manufacturing cells that are as independent as possible.This problem is NP-hard. Thus, nonheuristic methods cannot address problems of typical industrial dimensions because they would require exorbitant amounts of computing time, while fast heuristic methods may suffer from sub-optimality.
We present a branch-and-bound state-space search algorithm that attempts to overcome both these deficiencies. One of the major strengths of this algorithm is its efficient branching and search strategy. In addition, the algorithm employs the efficient Inter-Cell Traffic Minimization Method to provide good upper bounds, and computes lower bounds based on a relaxation of merging.
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 Implementation of an Integrated CAD and CAM System(1992) Chen, A.T.; Zhang, G.M.; ISRThis is a progress report on a joint research project between the University and the M.S. Willett, Inc. The research focus is on the integration of a CAD system and a CAM system currently being used at the Willett.The development of CAD systems has revolutionized the process of preparing engineering designs and drawings. Likewise, CAM systems have significantly impacted the stop floor production process. Numerically controlled machines have improved accuracy and productivity in many applications. Integration of these two systems would tie the design phase of a project to the production process, and if done efficiently, could result in significant cost reduction and quality improvement.
In this project, two computer programs have been developed to automate NC code generation directly from a CAD file, either in DXF format or in IGES format. These two programs have been successful in identifying the important elements of an integrated CAD and CAM system. The initial results also indicated how the Willett could shorten the time of product development cycle, low the production cost, and improve the quality of end products.
This project has been supported by the Center for Manufacturing on the College Park campus.
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.