摘要:

Since mathematical models based on component reliabilities are frequently used for prediction of system reliability, it stands to reason that cost-effective inferences on the reliability of a system could be made on the basis of tests of its constituent components. Prior research in the area of system-based component testing has for the most part addressed the development of plans that test only the components. From a practitioner's point of view, this is an issue of concern since system failures are often caused by imperfect interfaces and other causes that are not directly attributable to component failures. The exclusion of system tests may thus be an erroneous approach. This paper addresses the development of test plans that explicitly consider the possibility of interface failures. The paper analyzes a series system to determine when testing should be performed on the system alone, on the components only, and on both, depending on test costs and interface reliabilities. Optimum test plans are: derived by solving a two-stage mathematical program.

ISSN:0740-817X    

DOI:10.1080/07408179908969851

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this paper, we develop an integrated model for the joint optimization of the economic production quantity, the economic design of X¯-control chart, and the optimal maintenance level. This is done for a deteriorating process where the in-control period follows a general probability distribution with increasing hazard rate. In the proposed model, Preventive Maintenance (PM) activities reduce the shift rate to the out-of-control state proportional to the PM level. Compared to the case with no PM, the extra cost of maintenance results in lower quality control cost which may lead to lower overall expected cost. These issues are illustrated using an example of a Weibull shock model with an increasing hazard rate.

ISSN:0740-817X    

DOI:10.1080/07408179908969852

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We consider the common SQC problem of estimating a process standard deviation based on several sample ranges or sample standard deviations. Simple, well-known facts that are used to produce “control chart constants” can also provide guidance in the combining of such ranges or standard deviations for normal processes. Root mean squared errors for both unbiased linear estimators common in the literature and some (biased) optimal estimators are shown to be simple functions of these constants.

ISSN:0740-817X    

DOI:10.1080/07408179908969853

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

It is a common practice to monitor the fractionpof non-conforming units to detect whether the quality of a process improves or deteriorates. Users commonly assume that the number of non-conforming units in a subgroup is approximately normal, since large subgroup sizes are considered. Ifpis small this approximation might fail even for large subgroup sizes. If in addition, both upper and lower limits are used, the performance of the chart in terms of fast detection may be poor. This means that the chart might not quickly detect the presence of special causes. In this paper the performance of several charts for monitoring increases and decreases inpis analyzed based on their Run Length (RL) distribution. It is shown that replacing the lower control limit by a simple runs rule can result in an increase in the overall chart performance. The concept of RL unbiased performance is introduced. It is found that many commonly usedpcharts and other charts proposed in the literature have RL biased performance. For this reason new control limits that yield an exact (or nearly) RL unbiased chart are proposed.

ISSN:0740-817X    

DOI:10.1080/07408179908969854

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An integrated design methodology has been developed for a run-to-run PID controller and SPC monitoring for the purpose of process disturbance rejection. In the paper, the process disturbance is assumed to be an ARM A (1,1) process. A detailed procedure is developed to design a PID controller which minimizes process variability. The performance of the PID controller is also discussed. A joint monitoring of input and output, using Bonferroni's approach, is then designed for the controlled process. The ARL performance is studied. One major contribution of the paper is to develop a complete procedure and design plots, which serve as tools to conduct all the aforementioned tasks. An example is provided to illustrate the integrated design approach.

ISSN:0740-817X    

DOI:10.1080/07408179908969855

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this paper we study the performance ofX2control limits onT2control charts during on-line process monitoring. We make recommendations on the minimum number of subgroups necessary for control charts based on estimated parameters to perform similar to control charts based on true parameters when theX2control limit is used. We discuss an exact procedure for constructingT2control charts using estimated parameters that perform similar to control charts based on true parameters regardless of the number of preliminary subgroups. Furthermore, we suggest an implementation approach for using Alt's control limit onT2control charts until the accumulation of recommended minimum number of subgroups.

ISSN:0740-817X    

DOI:10.1080/07408179908969856

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We consider a production inventory system that produces a single product type, and inventory is maintained according to an (S, s) policy. Exogenous demand for the product arrives according to a random process. Unsatisfied demands are not back ordered. Such a make-to-stock production inventory policy is found very commonly in discrete part manufacturing industry, e.g., automotive spare parts manufacturing. It is assumed that the demand arrival process is Poisson. Also, the unit production time, the time between failures, and the repair and maintenance times are assumed to have general probability distributions. We conjecture that, for any such system, the down time due to failures can be reduced through preventive maintenance resulting in possible increase in the system performance. We develop a mathematical model of the system, and derive expressions for several performance measures. One such measure (cost benefit) is used as the basis for optimal determination of the maintenance parameters. The model application is explained via detailed study of 21 variants of a numerical example problem. The optimal maintenance policies (obtained using a numerical search technique) vary widely depending on the problem parameters. Plots of the cost benefit versus the system characteristic parameters (such as, demand arrival rate, failure rate, production rate, etc.) reveal the parameter sensitivities. The results show that the actual values of the failure and maintenance costs, and their ratio are significant in determining the sensitivities of the system parameters.

ISSN:0740-817X    

DOI:10.1080/07408179908969857

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Quality Function Deployment (QFD) is a multi-disciplinary team process in which team member preferences are often in conflict with respect to varied individual objectives. Successful applications of QFD, thus, rely on: (1) effective communication among team members to reach a consensus; (2) assigning importance levels that reflect each individual member's preferences; and (3) mutual interaction of these two factors. No previous paper in the QFD literature has attempted to aggregate team members' opinions in the case where each individual has his or her own criteria. In this study, we consider both agreed criteria, if any, and individual criteria, simultaneously; whereas A HP, MAUT, and others are based only on an agreed set of criteria. Specifically, we modify the nominal group technique to obtain customer requirements, and integrate agreed and individual criteria methods to assign customer's importance levels in general situations where some members in a team have an agreed criteria set while others prefer individual criteria sets. By using voting and linear programming techniques, the proposed approaches consolidate individual preferences into a group consensus in situations starting with or without (partial) agreed criteria sets. This integrated group decision-making system minimizes inconsistency over group and individual preferences and provides preference ordering for alternatives through iterative communication and the resolution of any inconsistencies that exist between the group and individuals, and amongst the individuals themselves.

ISSN:0740-817X    

DOI:10.1080/07408179908969858

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We consider several control charts for monitoring normal processes for changes in dispersion. We present comparisons of the average run length performances of these charts. We demonstrate that a CUSUM chart based on the likelihood ratio test for the change point problem for normal variances has an ARL performance that is superior to other procedures. Graphs are given to aid in designing this control chart.

ISSN:0740-817X    

DOI:10.1080/07408179908969859

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0740-817X    

DOI:10.1080/07408179908969923

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor