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1.
This article proposes a new control chart (called the ABS SPRT chart) for Statistical Process Control (SPC) based on Sequential Probability Ratio Test (SPRT). This chart is able to monitor the mean and variance of a variable x simultaneously by inspecting the absolute sample shift |xμ0| (where μ0 is the in-control mean or target value of x). The ABS SPRT chart is designed by an optimization algorithm, aiming at minimizing the Average Extra Quadratic Loss (AEQL) over the process shift domain. The results of intensive performance studies show that the ABS SPRT chart not only uniformly outperforms the CUSUM chart with a Variable Sample Size (VSS) feature, but is also more effective than a 2-SPRT scheme which incorporates a lower-sided SPRT chart and an upper-sided one. From a holistic viewpoint, the ABS SPRT chart detects process shifts in mean and variance faster than the VSS CUSUM chart and 2-SPRT scheme by more than 30% and 13%, respectively. Noteworthily, the design of an ABS SPRT chart is relatively easier than that of a VSS CUSUM chart, and much simpler than the design of a 2-SPRT scheme.  相似文献   

2.
The aim of this paper is to present an economical design of an X chart for a short-run production. The process mean starts equal to μ0 (in-control, State I) and in a random time it shifts to μ1>μ0 (out-of-control, State II). The monitoring procedure consists of inspecting a single item at every m produced ones. If the measurement of the quality characteristic does not meet the control limits, the process is stopped, adjusted, and additional (r-1) items are inspected retrospectively. The probabilistic model was developed considering only shifts in the process mean. A direct search technique is applied to find the optimum parameters which minimizes the expected cost function. Numerical examples illustrate the proposed procedure.  相似文献   

3.
近年来环境污染问题日益严重,其中电力企业在NOx排放方面对环境的污染尤为突出。为减少环境污染,针对某电厂原有锅炉进行燃烧器的改造,以降低电厂NOx的排放。依据设计方案,以基于炉膛空间尺度和煤粉燃烧过程尺度的双尺度低NOx燃烧技术,对电厂燃烧器进行改造。改造结果表明:基于双尺度低NOx燃烧技术改造后的电站锅炉,其NOx的排放显著降低。  相似文献   

4.
For many types of equipment whose maintenance requires skilled labor or whose random failure may have serious consequences, such as aircraft engines, medical equipment and others, customers generally prefer to entrust maintenance activities to the manufacturer or any of its representatives. The latter must, in turn, provide the customer with a maintenance program that is economically viable for both parties. In this study, the customer and the manufacturer agree on what follows regarding a non-self-announcing failure equipment whose state is only known through inspection: during the warranty period, the manufacturer inspects the equipment according to a specified schedule which he establishes taking into account that the costs incurred for inspections and replacements are supported by him during the warranty period. After the expiration of the warranty, inspections and replacements are performed by the manufacturer and billed to the customer. Moreover, penalties related to inactivity periods between failures and their detection are always supported by the manufacturer. The warranty is applicable to any equipment replaced during the validity period of the service contract. This type of contract generates a profit for the manufacturer. In this paper, an analytical model taking into account the commitments of both parties has been developed. The model allows generating the instants (x1, x2,…, xn) at which the inspections must be performed and the corresponding expected profit for the manufacturer while considering the warranty period offered on the market for similar equipment. An algorithm has also been developed to generate the inspection instants given the costs structure and the lifetime probability distribution of the equipment. In a context where business models argue for a greater implication of suppliers towards their customers, the proposed decision model may be relevant and very useful.  相似文献   

5.
The magnitude of the effect of government-sponsored enterprise purchases on primary mortgage market rates has been a difficult research question with differing data and competing methodologies producing varying results. Here we present a new approach using loan level data and controlling for credit risk differentials between conforming and nonconforming loans. Our method also addresses econometric problems of endogeneity and sample selection bias. We find that conforming loans have yield spreads about 5.5% lower compared to other loans on a risk-adjusted basis. This is lower than previous estimates appearing in the literature.  相似文献   

6.
An economic model including the labor resource and the process stage configuration is proposed to design charts allowing for all the design parameters to be varied in an adaptive way. A random shift size is considered during the economic design selection. The results obtained for a benchmark of 64 process stage scenarios show that the activities configuration and some process operating parameters influence the selection of the best control chart strategy; to model the random shift size, its exact distribution can be approximately fitted by a discrete distribution obtained from a relatively small sample of historical data. However, an accurate estimation of the inspection costs associated to the SPC activities is far from being achieved. An illustrative example shows the implementation of the proposed economic model in a real industrial case.  相似文献   

7.
8.
The classical Shewhart NP control chart is used widely in industrial and service practice for the relative simplicity of handling attribute quality characteristics. However, the static strategies become less and less adequate for today's highly competitive industrial society because of their low efficiency to detect slight process changes promptly. To improve the capability of control charts, some adaptive schemes, such as variable sample size (VSS), variable sample interval (VSI), and variable control limits (VCL), have been extensively studied in the recent decade. In this paper, we propose a new VSS NP control chart with adjusting sampling inspection (called ASI-NP chart) and give the performance analysis using Markov chain. As the optimal model is related to an integer nonlinear program, genetic algorithms (GAs) are involved and Taguchi experiments are applied to configure the parameter of the GAs in numerical examples. The comparison study between classical NP chart and ASI-NP chart is conducted, and the result shows that ASI-NP chart's performance characteristics are significantly better than those of classical NP charts in all situations, especially, in processes with slight shift and high quality.  相似文献   

9.
This article proposes the best bounds for e?x ?l+x subject to some constraints. With these bounds for e?x ?l+x, the better bounds for the optimal cycle time can be developed such that the bisection algorithm locates the optimal cycle time more accurately. Finally, an example is given to illustrate all results obtained by this article.  相似文献   

10.
To remain competitive in customer-oriented economics, the major parties in the supply chain should be integrated and managed effectively to respond to customer needs. Thus, the efficiency of the entire supply chain is a main concern, and is determined by the members of that supply chain. Partner selection thus becomes one of the key steps in supply chain construction. Given buyer–supplier information asymmetry, obtaining complete information from suppliers is difficult, since some supplier attributes cannot be definitely and quantitatively measured. This study establishes a suppliers capability and price analysis chart (SCPAC) focused on the case where the specification limits are symmetric about the target for evaluating supplier performance which applies the process incapability index Cpp introduced by Greenwich and Jahr-Schaffrath (International Journal of Quality & Reliability Management 12 (1995) 58) to measure supplier quality performance and the price index Ip is proposed here to display the difference between budget and component price. Practitioners can instantly and visually obtain information based on the locations of suppliers and price indices on SCPAC. SCPAC also provides clear directions for quality improvement, such as process accuracy and precision. SCPAC thus is an effective and efficient method for evaluating suppliers, which can simplify supplier evaluation, facilitate their effective visual selection, and provide insights into the process situation of suppliers who can become technological innovation partners.  相似文献   

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