• 제목/요약/키워드: Shewhart Control Chart

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Properties of VSI CUSUM Chart for Monitoring Dispersion Matrix

  • Chang, Duk-Joon;Shin, Jae-Kyoung
    • Journal of the Korean Data and Information Science Society
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    • 제15권4호
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    • pp.1003-1010
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    • 2004
  • Properties of the variable sampling interval(VSI) CUSUM chart for monitoring dispersion matrix of related quality characteristics are investigated. Performances of the proposed charts are evaluated for matched fixed sampling interval(FSI) and VSI charts in terms of average time to signal(ATS) and average number of samples to signal (ANSS). Average number of swiches(ANSW) of the proposed VSI Shewhart and CUSUM charts are also investigated.

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가변추출간격을 이용한 c 관리도의 최적설계 (Optimal Design of c Control Chart using Variable Sampling Interval)

  • 박주영
    • 대한안전경영과학회지
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    • 제9권2호
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    • pp.215-233
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    • 2007
  • Even though the ad hoc Shewhart methods remain controversial due to various mathematical flaws, there is little disagreement among researchers and practitioners when a set of process data has a skewness distribution. In the context and language of process control, the error related to the process data shows that time to signal increases when a control parameter shifts to a skewness direction. In real-world industrial settings, however, quality practitioners often need to consider a skewness distribution. To address this situation, we developed an enhanced design method to utilize advantages of the traditional attribute control chart and to overcome its associated shortcomings. The proposed design method minimizes bias, i.e., an average time to signal for the shift of process from the target value (ATS) curve, as well as it applies a variable sampling interval (VSI) method to an attribute control chart for detecting a process shift efficiently. The results of the factorial experiment obtained by various parameter circumstances show that the VSI c control chart using nearly unbiased ATS design provides the smallest decreasing rate in ATS among other charts for all experimental cases.

두 개의 이상원인이 존재하는 공정에 대한 VSSI $\bar{X}$ 관리도의 통계적 효율성 (Statistical Efficiency of VSSI $\bar{X}$ Control Charts for the Process with Two Assignable Causes)

  • 이호중;임태진
    • 품질경영학회지
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    • 제32권4호
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    • pp.156-168
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    • 2004
  • This research investigates the statistical efficiency of variable sampling size & sampling interval(VSSI) $\bar{X}$ charts under two assignable causes. Algorithms for calculating the average run length(ARL) and average time to signal(ATS) of the VSSI $\bar{X}$ chart are proposed by employing Markov chain method. States of the process are defined according to the process characteristics after the occurrence of an assignable cause. Transition probabilities are carefully derived from the state definition. Statistical properties of the proposed chart are also investigated. A simple procedure for designing the proposed chart is presented based on the properties. Extensive sensitivity analyses show that the VSSI $\bar{X}$ chart is superior to the VSS or VSI $\bar{X}$ chart as well as to the Shewhart $\bar{X}$ chart in statistical sense, even tinder two assignable causes.

WTO/TBT 협정에 따른 KS 규격의 부합화에 관한 연구 (A Study on the Conformity of KS Standards according to Agreement on WTO/TBT)

  • 김진규
    • 산업경영시스템학회지
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    • 제26권4호
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    • pp.12-22
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    • 2003
  • The purposes of this study are to investigate the conformity of Korean Standards(KS) according to agreement on WTO/TBT, and to propose systematic frameworks of preparation, adoption, and application for KS in our enterprises. Significant changes in this establishment, revision, and abrogation include the following divisions; i) statistics-vocabulary and symbols, ii) Shewhart control chart, iii) statistical interpretation of data, iv) sampling procedures for inspection by attributes, v) sequential sampling plans for inspection.

개별 관측치에서 지수변환을 이용한 EWMA 관리도 적용기법 (EWMA chart Application using the Transformation of the Exponential with Individual Observations)

  • 지선수
    • 산업경영시스템학회지
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    • 제22권52호
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    • pp.337-345
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    • 1999
  • The long-tailed, positively skewed exponential distribution can be made into an almost symmetric distribution by taking the exponent of the data. In these situations, to use the traditional shewhart control limits on an individuals chart would be impractical and inconvenient. The transformed data, approximately bell-shaped, can be plotted conveniently on the individuals chart and exponentially weighted moving average chart. In this paper, using modifying statistics with transformed exponential of the data, we give a method for constructing control charts. Selecting method of exponent for individual chart is evaluated. And consider that smaller weight being assigned to the older data as time process and properties and taking method of exponent($\theta$), weighting factor($\alpha$) are suggested. Our recommendation, on the basis result of simulation, is practical method for EWMA chart.

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다변량 공정관리 기술과 추세알고리즘의 연계에 관한 조사연구 (A Study on the Relation between Multivariate Process Control Techniques and Trend Algorithm)

  • 정해운
    • 대한안전경영과학회지
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    • 제13권4호
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    • pp.225-235
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    • 2011
  • Autoregressed Controller, which have trend algorithm, seeks to minimize variability by transferring the output variable to the related process input variable, while multivariate process control techniques seek to reduce variability by detecting and eliminating assignable causes of variation. In the case of process control, a very reasonable objective is to try to minimize the variance of the output deviations from the target or set point. We also investigate algorithm with relevant Shewhart chart, Theoretical control charts, precontrol and process capability. To help the people who want to make the theoretical system, we compare the main techniques in "a study on the relation between multivariate process control techniques and trend algorithms".

Switching properties of bivariate Shewhart control charts for monitoring the covariance matrix

  • Gwon, Hyeon Jin;Cho, Gyo-Young
    • Journal of the Korean Data and Information Science Society
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    • 제26권6호
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    • pp.1593-1600
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    • 2015
  • A control chart is very useful in monitoring various production process. There are many situations in which the simultaneous control of two or more related quality variables is necessary. We construct bivariate Shewhart control charts based on the trace of the product of the estimated variance-covariance matrix and the inverse of the in-control matrix and investigate the properties of bivariate Shewart control charts with VSI procedure for monitoring covariance matrix in term of ATS (Average time to signal) and ANSW (Average number of switch) and probability of switch, ASI (Average sampling interval). Numerical results show that ATS is smaller than ARL. From examining the properties of switching in changing covariances and variances in ${\Sigma}$, ANSW values show that it does not switch frequently and does not matter to use VSI procedure.

Control Charts Based on Self-critical Estimation Process

  • Won, Hyung-Gyoo
    • 품질경영학회지
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    • 제25권1호
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    • pp.100-115
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    • 1997
  • Shewhart control chart is a basic technique to monitor the state of a process. We observe samples of size four or five and plot some statistic(e.g., mean or range) of each sample on the chart. When setting up the chart, we need to obtain u, pp.r and lower control limits. It is common practice that those limits are calculated from the preliminary 20-40 samples presumed to be homogeneous. However, it may ha, pp.n in practice that the samples are contaminated by outlying observations caused by various reasons. The presence of outlying observations make the control limits wider and hence decrease the sensitivity of the charts. In this paper, we introduce robust control charts with tighter control limits when outlying observations are present in the preliminary samples. Examples will be given via simulation study.

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Switching performances of multivarite VSI chart for simultaneous monitoring correlation coefficients of related quality variables

  • Chang, Duk-Joon
    • Journal of the Korean Data and Information Science Society
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    • 제28권2호
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    • pp.451-459
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    • 2017
  • There are many researches showing that when a process change has occurred, variable sampling intervals (VSI) control chart is better than the fixed sampling interval (FSI) control chart in terms of reducing the required time to signal. When the process engineers use VSI control procedure, frequent switching between different sampling intervals can be a complicating factor. However, average number of samples to signal (ANSS), which is the amount of required samples to signal, and average time to signal (ATS) do not provide any control statistics about switching performances of VSI charts. In this study, we evaluate numerical switching performances of multivariate VSI EWMA chart including average number of switches to signal (ANSW) and average switching rate (ASWR). In addition, numerical study has been carried out to examine how to improve the performance of considered chart with accumulate-combine approach under several different smoothing constant and sample size. In conclusion, process engineers, who want to manage the correlation coefficients of related quality variables, are recommended to make sample size as large and smoothing constant as small as possible under permission of process conditions.