共查询到20条相似文献，搜索用时 15 毫秒
1.
Aamir Saghir Yousaf Ali Khan Subha Chakraborti 《Quality and Reliability Engineering International》2016,32(5):1807-1823
Multivariate control charts are usually implemented in statistical process control to monitor several correlated quality characteristics. Process dispersion charts are used to determine the stability of process variation (which is typically done before monitoring the process location/mean). A Phase‐I study is generally used when population parameters are unknown. This article develops Phase‐I |S| and |G| control charts, to monitor the dispersion of a bivariate normal process. The charting constants are determined to achieve the required nominal false alarm probability (FAP0). The performance of the proposed charts is evaluated in terms of (i) the attained false rate and (ii) the probability of signaling for out‐of‐control situations. The analysis shows that the proposed Phase‐I bivariate charts correctly control the FAP (the false alarm probability) and detect a shift occurring in the bivariate dispersion matrix with adequate probability. An example is given to explain the practical implementation of these charts. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
2.
Saddam Akber Abbasi Muhammad Riaz Arden Miller Shabbir Ahmad 《Quality and Reliability Engineering International》2015,31(8):1705-1716
Control charts are usually implemented in two phases: the retrospective phase (phase I) and the monitoring phase (phase II). The performance of any phase II control chart structure depends on the preciseness of the control limits obtained from the phase I analysis. In statistical process control, the performance of phase I dispersion charts has mainly been investigated for normal or contaminated normal distributions of the quality characteristic of interest. Little work has been carried out to investigate the performance of a wide range of possible phase I dispersion charts for processes following non‐normal distributions. The current study deals with the proper choice of a control chart for the evaluation of process dispersion in phase I. We have analyzed the performance of a wide range of dispersion control charts, including two distribution‐free structures. The performance of the control charts is evaluated in terms of probability to signal, under normal and non‐normal process setups. These results will be useful for quality control practitioners in their selection of a phase I control chart. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
Saddam Akber Abbasi Muhammad Riaz Arden Miller Shabbir Ahmad Hafiz Zafar Nazir 《Quality and Reliability Engineering International》2015,31(8):1691-1704
Process monitoring through control charts is a quite popular practice in statistical process control. This study is planned for monitoring the process dispersion parameter using exponentially weighted moving average (EWMA) control chart scheme. Most of the EWMA dispersion charts that have been proposed are based on the assumption that the parent distribution of the quality characteristic is normal, which is not always the case. In this study, we develop new EWMA charts based on a wide range of dispersion estimates for processes following normal and non‐normal parent distributions. The performance of all the charts is evaluated and compared using run length characteristics (such as the average run length). Extra quadratic loss, relative average run length, and performance comparison index measures are also used to examine the overall effectiveness of the EWMA dispersion charts.Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
This article designs and studies the approximate performance of robust dispersion charts, namely, MAD chart, Sn chart, and Qn chart, in Phase I analysis (recently developed in the literature). The proposed limits are based on false alarm probability for monitoring the dispersion of a process in Phase I analysis. The charting constants are determined to achieve the required nominal FAP (FAP0). The performance of these structures is evaluated in (i) the attained false alarm rate and (ii) the probability of signals for out‐of‐control situations. The analysis shows that the proposed design of Phase I robust dispersion charts correctly controls the FAP and shows a good performance in detecting the shifts in the process variation. An illustrative example is used to explain the practical implementation of these limits. 相似文献
5.
6.
Jyh‐Jen Horng Shiau Jian‐Huang Sun 《Quality and Reliability Engineering International》2010,26(5):475-486
The Phase I analysis in statistical process control usually includes a task of filtering out out‐of‐control data in the historical data set via control charting. The conventional procedure for this is an iterative procedure that first uses all the samples to set up initial trial control limits and discards all the ‘out‐of‐control’ samples accordingly, and then iteratively repeats the screening step on the remaining samples until no more ‘out‐of‐control’ samples are detected. For simplicity, the ‘out‐of‐control’ samples here refer to the samples with their monitoring statistics exceeding the trial control limits. It is found in this study that this procedure throws away too many useful in‐control samples. To overcome this drawback, we propose and study a new iterative procedure that discards only one ‘out‐of‐control’ sample (i.e. the most extreme one) at each iteration. Our simulation study, using the Shewhart X Chart for illustration, demonstrates that the new one‐at‐a‐time procedure reduces dramatically the occurrences of false alarms. For cost‐saving, we further suggest a new strategy on when to stop and inspect the process to look for assignable causes for samples signaling out‐of‐control alarms. To determine the control limits, both the traditional method that controls the individual false‐alarm‐rate and the Bonferroni method that controls the overall false‐alarm‐rate are considered. The performances of the proposed schemes are evaluated and compared in terms of the false‐alarm rate and the detecting power via simulation studies. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
7.
Muhammad Riaz Rashid Mehmood Muhammad Rizwan Iqbal Saddam Akber Abbasi 《Quality and Reliability Engineering International》2016,32(3):837-854
Shewhart control charts are very popular in a variety of disciplines such as industry, agriculture and medical science. The design structure of the usual Shewhart charts depends on normality and one point decision rule. This makes the scope of these charts quite limited and not very efficient for small shifts. This study comes up with an intermediate solution by implementing runs rules schemes and adjusting the limits' coefficients for non‐normality using the idea of skewness correction. We have covered some commonly used location and dispersion charts, namely , R and S charts. We have investigated the performance of the proposals in terms of false alarm rate and signalling probability. We have observed that the proposals serve the dual purpose in terms of robustness and efficiency. The study also provides an application example using numerical dataset. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
8.
Sepehr Fathizadan Seyed Taghi Akhavan Niaki Rassoul Noorossana 《Quality and Reliability Engineering International》2017,33(8):2075-2087
Functional data and profiles are characterized by complex relationships between a response and several predictor variables. Fortunately, statistical process control methods provide a solid ground for monitoring the stability of these relationships over time. This study focuses on the monitoring of 2‐dimensional geometric specifications. Although the existing approaches deploy regression models with spatial autoregressive error terms combined with control charts to monitor the parameters, they are designed based on some idealistic assumptions that can be easily violated in practice. In this paper, the independent component analysis (ICA) is used in combination with a statistical process control method as an alternative scheme for phase II monitoring of geometric profiles when non‐normality of the error term is present. The performance of this method is evaluated and compared with a regression‐ and PCA‐based approach through simulation of the average run length criterion. The results reveal that the proposed ICA‐based approach is robust against non‐normality in the in‐control analysis, and its out‐of‐control performance is on par with that of the PCA‐based method in case of normal and near‐normal error terms. 相似文献
9.
Philippe Castagliola Fugee Tsung 《Quality and Reliability Engineering International》2005,21(2):131-161
The importance of statistical process control (SPC) techniques in quality improvement is well recognized in industry. However, most conventional SPC techniques have been developed under the assumption of independent, identically and normally distributed observations. With advances in sensing and data capturing technologies, large volumes of data are being routinely collected from individual units in manufacturing industries. These data are often autocorrelated and skewed. Conventional SPC techniques can lead to false alarms or other types of poor performance monitoring of such data. There is a great need for process control techniques for variation reduction in these environments. Much recent research has focused on the development of appropriate SPC techniques for autocorrelated data, but few studies have considered the impact of non‐normality on these techniques. This paper investigates the effect of skewness on conventional autocorrelated SPC techniques, and provides an effective approach based on a scaled weighted variance approach to improve SPC performance in such an environment. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
10.
Recently there has been an increasing interest in techniques of process monitoring involving geometrically distributed quality characteristics, as many types of attribute data are neither binomial nor Poisson distributed. The geometric distribution is particularly useful for monitoring high‐quality processes based on cumulative counts of conforming items. However, a geometrically distributed quantity can never be adequately approximated by a normal distribution that is typically used for setting 3‐sigma control limits. In this paper, some transformation techniques that are appropriate for geometrically distributed quantities are studied. Since the normal distribution assumption is used in run‐rules and advanced process‐monitoring techniques such as the cumulative sum or exponentially weighted moving average chart, data transformation is needed. In particular, a double square root transformation which can be performed using simple spreadsheet software can be applied to transform geometrically distributed quantities with satisfactory results. Simulated and actual data are used to illustrate the advantages of this procedure. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
11.
Yuhui Yao Subhabrata Chakraborti 《Quality and Reliability Engineering International》2021,37(3):1244-1265
Phase I is crucial for the success of the overall statistical process control (SPC) and monitoring regime. Shewhart-type charts are recommended in this phase because of their broader shift detection ability. In this paper, a Phase I Shewhart-type
12.
David Gilliam Stefan Leigh Andrew Rukhin William Strawderman 《Journal of research of the National Institute of Standards and Technology》2009,114(3):195-199
Performance standards for detector systems often include requirements for probability of detection and probability of false alarm at a specified level of statistical confidence. This paper reviews the accepted definitions of confidence level and of critical value. It describes the testing requirements for establishing either of these probabilities at a desired confidence level. These requirements are computable in terms of functions that are readily available in statistical software packages and general spreadsheet applications. The statistical interpretations of the critical values are discussed. A table is included for illustration, and a plot is presented showing the minimum required numbers of pass-fail tests. The results given here are applicable to one-sided testing of any system with performance characteristics conforming to a binomial distribution. 相似文献
13.
Richard Osei-Aning Saddam Akber Abbasi 《Quality and Reliability Engineering International》2020,36(1):247-267
To ensure high quality standards of a process, the application of control charts to monitor process performance has become a regular routine. Multivariate charts are a preferred choice in the presence of more than one process variable. In this article, we proposed a set of bivariate exponentially weighted moving average (EWMA) charts for monitoring the process dispersion. These charts are formulated based on a variety of dispersion statistics considering normal and non-normal bivariate parent distributions. The performance of the different bivariate EWMA dispersion charts is evaluated and compared using the average run length and extra quadratic loss criteria. For the bivariate normal process, the comparisons revealed that the EWMA chart based on the maximum standard deviation (SMAXE) was the most efficient chart when the shift occurred in one quality variable. It also performed well when the sample size is small and the shift occurred in both quality variables. The EWMA chart based on the maximum average absolute deviation from median (MDMAXE) performed better than the other charts in most situations when the shift occurred in the covariance matrix for the bivariate non-normal processes. An illustrative example is also presented to show the working of the charts. 相似文献
14.
F. S. Haddad S. S. Syed‐Yahaya J. L. Alfaro 《Quality and Reliability Engineering International》2013,29(4):583-593
Hotelling's T2 chart is a popular tool for monitoring statistical process control. However, this chart is sensitive in the presence of outliers. To alleviate the problem, this paper proposed alternative Hotelling's T2 charts for individual observations using robust location and scale matrix instead of the usual mean vector and the covariance matrix, respectively. The usual mean vector in the Hotelling T2 chart is replaced by the winsorized modified one‐step M‐estimator (MOM) whereas the usual covariance matrix is replaced by the winsorized covariance matrix. MOM empirically trims the data based on the shape of the data distribution. This study also investigated on the different trimming criteria used in MOM. Two robust scale estimators with highest breakdown point, namely Sn and Tn were selected to suit the criteria. The upper control limits for the proposed robust charts were calculated based on simulated data. The performance of each control chart is based on the false alarm and the probability of outlier's detection. In general, the performance of an alternative robust Hotelling's T2 charts is better than the performance of the traditional Hotelling's T2 chart. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
15.
William H. Woodall 《Quality Engineering》2017,29(1):2-15
ABSTRACTSome issues are discussed relative to the gap between theory and practice in the area of statistical process monitoring (SPM). Among other issues, it is argued that the collection and use of baseline data in Phase I needs a greater emphasis. Also, the use of sample ranges in practice to estimate process standard deviations deserves reconsideration. A discussion is given on the role of modeling in SPM. Then some work on profile monitoring and the effect of estimation error on Phase II chart performance is summarized. Finally, some ways that researchers could influence practice more effectively are discussed along with how SPM research could become more useful to practitioners. 相似文献
16.
《Quality Engineering》2012,24(3):400-403
ABSTRACT To evaluate the performance of the sequential probability ratio test (SPRT) for radiation detection, we present an algorithm based on simulation and local regression smoothing to find thresholds that achieve specified false alarm probabilities. An example is given to illustrate the use of the algorithm. 相似文献
17.
Y. Yao C.W. Hilton S. Chakraborti 《Quality and Reliability Engineering International》2017,33(8):2667-2672
Control charts play an important role in Phase I studies, which are conducted to establish process control and generate reference data for parameter estimation and calculation of prospective (Phase II) control limits. Researchers have tabulated the necessary charting constants for the normal theory–based Phase I Shewhart chart for the process mean to achieve a desired nominal false alarm probability given the number of Phase I subgroups, m, up to 15. However, in practice, when parameters are estimated, the currently recommended number of Phase I subgroups is much larger than covered by their tables. Recognizing the need and taking advantage of some recently available software and computing resources, an extension to these tables is provided for m = 3(1)10 , 15(5)30 , 50(25)300 and n = 3 , 5 , 7 , 10. In addition to the tables, an R program is provided to calculate the charting constant, on demand, for user‐given values of nominal false alarm probability, m, and n. An appendix shows the details of how the program should be used. 相似文献
18.
L. Macorini B. A. Izzuddin 《International journal for numerical methods in engineering》2011,85(12):1584-1608
This paper presents a novel interface element for the geometric and material non‐linear analysis of unreinforced brick‐masonry structures. In the proposed modelling approach, the blocks are modelled using 3D continuum solid elements, whereas the mortar and brick–mortar interfaces are modelled by means of the 2D non‐linear interface element. This enables the representation of any 3D arrangement for brick‐masonry, accounting for the in‐plane stacking mode and the through‐thickness geometry, and importantly it allows the investigation of both the in‐plane and the out‐of‐plane responses of unreinforced masonry panels. A co‐rotational approach is employed for the interface element, which shifts the treatment of geometric non‐linearity to the level of discrete entities, and enables the consideration of material non‐linearity within a simplified local framework employing first‐order kinematics. In this respect, the internal interface forces are modelled by means of elasto‐plastic material laws based on work‐softening plasticity and employing multi‐surface plasticity concepts. Following the presentation of the interface element formulation details, several experimental–numerical comparisons are provided for the in‐plane and out‐of‐plane static behaviours of brick‐masonry panels. The favourable results achieved demonstrate the accuracy and the significant potential of using the developed interface element for the non‐linear analysis of brick‐masonry structures under extreme loading conditions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
19.
An R chart is often used to monitor shifts in the process variability. However, the range, , statistics from a sampling distribution are highly skewed. Hence, the classical R chart based on the control limits will not give an in‐control average run length of approximately 370, or equivalently a type I error, . In this paper, an approach is shown to obtain the control limits of an improved R chart based on a desired type I error from the density function of the Ri statistics. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
20.
Nasir Abbas Muhammad Riaz Ronald J. M. M. Does 《Quality and Reliability Engineering International》2011,27(6):821-833
Control charts are extensively used in processes and are very helpful in determining the special cause variations so that a timely action may be taken to eliminate them. One of the charting procedures is the Shewhart‐type control charts, which are used mainly to detect large shifts. Two alternatives to the Shewhart‐type control charts are the cumulative (CUSUM) control charts and the exponentially weighted moving average (EWMA) control charts that are specially designed to detect small and moderately sustained changes in quality. Enhancing the ability of design structures of control charts is always desirable and one may do it in different ways. In this article, we propose two runs rules schemes to be applied on EWMA control charts and evaluate their performance in terms of the Average Run Length (ARL). Comparisons of the proposed schemes are made with some existing representative CUSUM and EWMA‐type counterparts used for small and moderate shifts, including the classical EWMA, the classical CUSUM, the fast initial response CUSUM and EWMA, the weighted CUSUM, the double CUSUM, the distribution‐free CUSUM and the runs rules schemes‐based CUSUM. The findings of the study reveal that the proposed schemes are able to perform better than all the other schemes under investigation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献