摘要:

AbstractThis article considers a particular printed circuit board (PCB) assembly system employing surface mount technology. Multiple, identical automatic placement machines, a variety of board types, and a large number of component types characterize the environment studied. The problem addressed is that of minimizing the makespan for assembling a batch of boards with a secondary objective of reducing the mean flow time. The approach adopted is that of grouping boards into production families, allocating component types to placement machines for each family, dividing of families into board groups with similar processing times, and the scheduling of groups. A complete setup is incurred only when changing over between board families. For the environment studied, precedence constraints on the order of component placement do not exist, and placement times are independent of feeder location. Heuristic solution procedures are proposed to create board subfamilies (groups) for which the component mounting times are nearly identical within a subfamily. Assignment of the same component type to multiple machines is avoided. The procedures use results from the theory of open‐shop scheduling and parallel processor scheduling to sequence boards on machines. Note that we do not impose an open‐shop environment but rather model the problem in the context of an open shop, because the order of component mountings is immaterial. Three procedures are proposed for allocating components to machines and subsequently scheduling boards on the machines. The first two procedures assign components to machines to balance total work load. For scheduling purposes, the first method groups boards into subfamilies to adhere to the assumptions of the open‐shop model, and the second procedure assumes that each board is a subfamily and these are scheduled in order of shortest total processing time. The third procedure starts by forming board subfamilies based on total component similarity and then assigns components to validate the open‐shop model. We compare the performance of the three procedures using estimated daily, two‐day, and weekly production requirements by averaging quarterly production data for an actual cell consisting of five decoupled machines. © 1994 John Wiley

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<587::AID-NAV3220410502>3.0.CO;2-Q

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe use of a single vendor for each inventoried item is usually assumed in most of the inventory models. However, there are situations where the use of more than one vendor should be considered, especially when lead times are stochastic. This research presents a theoretical investigation of the effect of cost structures on the relative performance of sole‐sourcing versus dual‐sourcing inventory control policies. We show that except for cases where the ordering cost is high, the lead‐time variability is low, or the customer service level is low, dual sourcing performs better than sole sourcing under the normally distributed demand and shifted‐exponential lead times. Moreover, the computational results indicate the dual sourcing provides a better service level than sole sourcing at the optimal solutions, and that dual sourcing results in larger order quantities than sole sourcing, which suggests that attractive quantity discounts may not be in jeopardy when dual sourcing is employed. Finally, because it is generally known that multiple sourcing can enhance the competition among suppliers, material managers should consider splitting purchase orders when two equally qualified suppliers are available. © 1994 John Wiley&S

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<609::AID-NAV3220410503>3.0.CO;2-7

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractMethodology for the optimal selection of a mixture of components for the attainment of a required performance level is developed. This accommodates both cost and stochastic variation and is applied to gasoline blending. © 1994 John Wiley&Sons, Inc

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<625::AID-NAV3220410504>3.0.CO;2-2

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis article examines the applicability of acceptance sampling and the effectiveness of Deming'skprule in relation to the degree of process stability achieved through statistical process control techniques. A discrete‐event simulation model is used to characterize the correlation between the number of defective units in a randomly drawn sample versus in the remainder of a lot, in response to a number of system and control chart parameters. The model reveals that such correlation is typically present when special causes of variation affect the production process from time to time, even though the process is tightly monitored through statistical process control. Comparison of these results to an analogous mixed binomial scenario reveals that the mixed binomial model overstates the correlation in question if the state of the process is not necessarily constant during lot production. A generalization of thekpanalysis is presented that incorporates the possibility of dependence between a sample and the unsampled portion of the lot. This analysis demonstrates that acceptance sampling is generally ineffective for lots generated by a process subject to statistical process control, despite the fact that the number of defectives in the sample and in the remainder of the lot are not strictly independent. © 1994 John Wiley&Sons, I

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<635::AID-NAV3220410505>3.0.CO;2-X

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractFor the loss system with time‐varying intensities and a finite number of identical servers we derive formulas for the expected number of refused customers in a given time interval and for the expected number of servers busy at a given time instant. © 1994 John Wiley&Sons, I

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<653::AID-NAV3220410506>3.0.CO;2-Q

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractVarious mathematical models for multistate systems have been proposed in the literature. Among them the model introduced by Barlow and Wu is the one most intimately related to that of binary systems; hence the Barlow‐Wu class possesses many nice properties inherited from the binary systems. In this article we obtain several characterization results for multistate systems, which closely relate the Barlow‐Wu class to other classes of multistate systems. The characterizations we obtained originate from the invariance properties of the Barlow‐Wu functions, and are easy to apply in verifying whether a particular model is of the Barlow‐Wu type. © 1994 John Wiley&S

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<661::AID-NAV3220410507>3.0.CO;2-M

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractAssume the payoffs of a matrix game are concave in the index of the maximizing player. That player is shown to have an optimal strategy which uses at most two consecutive pure strategies, identifiable through approximate solution of a related continuous game. Generalizations are given, and the results are applied to a motivating hidden‐target model due to Shapley. © 1994 John Wiley&Sons, I

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<669::AID-NAV3220410508>3.0.CO;2-B

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe problem of scheduling n jobs on m parallel machines is considered when the machines are subject to random breakdowns and job processing times are random variables. An objective function of mean flow time is developed for a general parallel machine system, and an expression of its expected value is derived. The problem is transformed into a deterministic unrelated parallel machine scheduling model with modified processing times when the number of breakdowns is modeled as a generalized Poisson process. © 1994 John Wiley&Sons, Inc

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<677::AID-NAV3220410509>3.0.CO;2-7

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractBoland, Proschan, and Tong [2] used the notion of criticality of nodes in a coherent system to study the optimal component arrangement of reliability structures. They also provided a sufficient minimal cut (path) based criterion for verifying the criticality ordering of two nodes. We develop a necessary and sufficient condition for two nodes to be comparable and provide specific examples illustrating our result's applicability. As a corollary, certain optimal arrangement properties of well‐known systems are derived. © 1994 John Wiley&Sons, I

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<683::AID-NAV3220410510>3.0.CO;2-Y

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0894-069X    

DOI:10.1002/1520-6750(199408)41:5<::AID-NAV3220410501>3.0.CO;2-J

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY