摘要:

Roberts (1959) first introduced the exponentially weighted moving average (EWMA) control scheme. Using simulation to evaluate its properties, he showed that the EWMA is useful for detecting small shifts in the mean of a process. The recognition that an EWMA control scheme can be represented as a Markov chain allows its properties to be evaluated more easily and completely than has previously been done. In this article, we evaluate the properties of an EWMA control scheme used to monitor the mean of a normally distributed process that may experience shifts away from the target value. A design procedure for EWMA control schemes is given. Parameter values not commonly used in the literature are shown to be useful for detecting small shifts in a process. In addition, several enhancements to EWMA control schemes are considered. These include a fast initial response feature that makes the EWMA control scheme more sensitive to start-up problems, a combined Shewhart EWMA that provides protection against both large and small shifts in a process, and a robust EWMA that provides protection against occasional outliers in the data that might otherwise cause an out-of-control signal. An extensive comparison reveals that EWMA control schemes have average run length properties similar to those for cumulative sum control schemes.

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484583

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484584

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484585

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484586

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484587

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484588

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484589

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Consider a sequence of lots from a manufacturing process that is put through an acceptancesampling inspection program, the accepted lots being shipped to a customer. Taken together. the accepted lots form a population whose overall quality, called theoutgoing quality, is of importance to the customer. This article describes a method for estimating this outgoing quality using data from both the accepted and rejected lots. The method is based on a very general definition of outgoing quality and on the quality measurement plan (QMP)—a hierarchical Bayes model of the underlying process. Our estimator is the only one known to us that works when sample sizes and acceptance numbers vary from lot to lot and the acceptance-sampling rules are sometimes broken—a practical reality. In the case of fixed sample size, the QMP estimator of outgoing quality has a very simple form. It is the weighted average of two naive estimators—the sample qualities observed in the incoming and outgoing lots, respectively. The weight on the observed incoming quality is monotonically increasing with [sampling variance]/[process variance].

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484590

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Acceptance control charts provide control limits for processes in which the natural dispersion is small and the process mean may be permitted to vary. These control limits are based on specification limits and on permitted probabilities of making incorrect decisions of “acccptance” or “rejection.” This article deals with acceptance control charts in which two processes, or two characteristics of a product. are controlled for simultaneous conformance to specitication limits or standards. The proccsscs can be positively or negatively correlated. Sample sizes and control limits are derived for each chart, using cost minimization or maximumsample-size minimization as criteria. The analysis is also applicable to acceptance sampling.

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484591

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The monitoring of deformations is a very important task in engineering surveying. The object to be investigated is represented by a cluster of points, whose positions are fixed by geodetic observations at different epochs of time. If deformations occur. they cause distortions of the cluster. resulting in position differences hetween epochs. These differences are typically of the same order of magnitude as the observational errors, so statistical methods arc needed to reasonably make inferences on the true behavior of the object. The field of deformation vectors is approximated by linear models that are designed to estimate rigid body displacements and distortions of the object separately. This article presents several robust methods of parameter estimation as alternatives to the conventional least squares approach. They are based on special loss functions that are independent of the reference system. The application of these robust estimators to a real example indicates that for deformation analyses abounded infuence modified Huber estimator yields results that nicely agree with experience.

ISSN:0040-1706    

DOI:10.1080/00401706.1990.10484592

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor