• 제목/요약/키워드: Use of Control Charts

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Comparison of the Efficiencies of Variable Sampling Intervals Charts for Simultaneous Monitoring the means of multivariate Quality Variables

  • Chang, Duk-Joon
    • 통합자연과학논문집
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    • 제9권3호
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    • pp.215-222
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    • 2016
  • When the linear correlation of the quality variables are considerably high, multivariate control charts may be a more effective way than univariate charts which operate quality variables and process parameters individually. Performances and efficiencies of the multivariate control charts under multivariate normal process has been considered. Some numerical results are presented under small scale of the shifts in the process to see the improvement of the efficiency of EWMA chart and CUSUM chart, which use past quality information, comparing to Shewart chart, which do not use quality information. We can know that the decision of the optimum value of the smoothing constant in EWMA structure or the reference value in CUSUM structure are very important whether we adopt combine-accumulate technique or accumulate-combine technique under the given condition of process.

Comparisons of Multivariate Quality Control Charts by the Use of Various Correlation Structures

  • Choi, Sung-Woon;Lee, Sang-Hoon
    • 한국경영과학회지
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    • 제20권3호
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    • pp.123-146
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    • 1995
  • Several quality control schemes have been extensively compared using multivariate normal data sets simulated with various correlation structures. They include multiple univariate CUSUM charts, multivariate EWMA charts, multivariate CUSUM charts and Shewhart T$^{3}$ chart. This paper considers a new approach of the multivariate EWMA chart, in which the smoothing matrix has full elements instead of only diagonal elements. Performance of the schemes is measured by avaerage run length (ARL), coefficient of variation of run length (CVRL) and rank in order of signaling of off-target shifts in the process mean vector. The schemes are also compared by noncentrality parameter. The multiple univariate CUSUM charts are generally affected by the correlation structure. The multivariate EWMA charts provide better ARL performance. Especially, the new EWMA chart shows remarkable results in small shifts.

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가변추출구간을 이용한 계수치 관리도의 수행도 평가 (Evaluation of Performance on Attribute Control Chart using Variable Sampling Intervals)

  • 송서일;이보근
    • 한국산업경영시스템학회:학술대회논문집
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    • 한국산업경영시스템학회 2002년도 춘계학술대회
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    • pp.359-364
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    • 2002
  • In case of pn control chart often used in mass production system of plant industry and so on, we could evaluate it's performance by the approximation to normal distribution. It has many differences according to sample sizes and defective fraction, and have disadvantage that needs much samples to use the normal distribution approximation. Existent control charts can not detect the cause of process something wrong because it is taking the sampling intervals of fixed length about all times from the process. Therefore, to overcome this shortcoming we use VSI(variable sampling intervals) techniques in this paper. This technique takes a long sampling interval to have the next sampling point if the sample point is in stable state, and if the sample point is near control lines, it takes short sampling interval because the probability to escape control limit is high. To analyze performance of pn control charts that have existent fixed sampling intervals(FSI) and that use VSI technique, we compare ATS of two charts, and analyze the performance of each control chart by the sample sizes, process fraction defective and control limits that Ryan and Schwertman had proposed.

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An Improvement on Target Costing Technique

  • Wu, Hsin-Hung
    • International Journal of Quality Innovation
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    • 제4권1호
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    • pp.191-204
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    • 2003
  • The target costing technique, mathematically discussed by Sauers, only uses the $C_p index along with Taguchi loss function and $\bar{X}$-P control charts to setup goal control limits. The new specification limits derived from Taguchi loss function is linked through the $C_p value to $\bar{X}$-P control charts to obtain goal control limits. Studies have shown that the point estimator of the $C_p index, $C_p, could vary from time to time due to the sampling error. The suggested approach is to use confidence intervals, especially the lower confidence intervals, to replace the point estimator. Therefore, an improvement on target costing technique is presented by applying the lower confidence interval of the $C_p index and using both Taguchi and Spiring's loss functions together with $\bar{X}$-P charts to make this technique more robust in practice. An example is also provided to illustrate how the improved target costing technique works.

VSI EWMA 관리도의 경제적 통계적 설계 (An Economic Statistical Design of the EWMA Control Charts with Variable Sampling Interval)

  • 송서일;박현규;정혜진
    • 품질경영학회지
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    • 제32권1호
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    • pp.92-101
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    • 2004
  • Tris paper present an economic statistical design which have statistically constraints for the optimal design of an EWMA control charts with variable sampling interval. Cost function use that proposed by Lorenzen and Vance, and the optimal design parameters include the sample size, control limit width, sampling interval, EWMA weight value. Comparisons between VSI EWMA control charts optimal economic design and optimal economic statistical designs show the following fact. Although have demerits which are more costly than economic design, have merits which to detect shifts more efficiently and to improve statistical performance.

VSI EWIMA 관리도의 경제적 설계 (An Economic Design of the EWMA Control Charts with Variable Sampling Interval)

  • 송서일;정혜진
    • 품질경영학회지
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    • 제30권4호
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    • pp.1-14
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    • 2002
  • Traditional SPC techniques are looking out variation of process by fixed sampling interval and fixed sample size about every hour, the process of in-control or out-of-control couldn't be detected actually when the sample points are plotted near control limits, and it takes no notice of expense concerned with such sample points. In this paper, to overcome that, consider VSI(variable sampling interval) EWMA control charts which VSI method is applied. The VSI control charts use a short sampling internal if previous sample points are plotted near control limits, then the process has high probability of out-of-control. But it uses a long sampling interval if they are plotted near centerline of the control chart, since process has high possibility of in-control. And then a comparison and analysis between FSI(fixed sampling interval) and VSI EWMA in the statistical aspect and economic aspect is studied. Finally, we show that VSI EWMA control chart is more efficient than FSI EWMA control chart in the both aspects.

이미지 데이터를 모니터링하는 관리도에서 이미지와 ROI 크기 조정의 영향 (Resizing effect of image and ROI in using control charts to monitor image data)

  • 이주형;윤형욱;이성민;이재헌
    • 응용통계연구
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    • 제30권3호
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    • pp.487-501
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    • 2017
  • 최근 산업의 생산공정에서는 머신비전시스템을 통하여 제품의 품질특성치에 대한 정보를 이미지 데이터로 제공하는 경우가 많다. 따라서 산업과 의학 현장에서 이미지 데이터의 모니터링을 위해 관리도 절차의 필요성이 많이 대두되고 있다. 이미지 데이터를 모니터링하는 관리도 절차는 전통적으로 사용하는 관리도 절차와 유사한 점도 있지만, 데이터의 구조를 비롯하여 각 이미지에서 ROI를 설정하여 관리도 절차를 적용하는 등 서로 다른 점도 많이 있다. 이 논문에서는 생산공정에서 제공되는 이미지 데이터에 대해 관리도를 사용하는 절차를 소개하고, 이미지 또는 ROI 크기의 확대와 축소가 제품의 이상원인을 탐지하는데 어떠한 영향이 주는지를 모의실험을 통하여 알아보았고 각 관리도의 성능 또한 비교하였다.

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.

시공간 탐지 정확성을 고려한 다변량 누적합 관리도의 비교 (Comparison of Multivariate CUSUM Charts Based on Identification Accuracy for Spatio-temporal Surveillance)

  • 이미림
    • 품질경영학회지
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    • 제43권4호
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    • pp.521-532
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    • 2015
  • Purpose: The purpose of this study is to compare two multivariate cumulative sum (MCUSUM) charts designed for spatio-temporal surveillance in terms of not only temporal detection performance but also spatial detection performance. Method: Experiments under various configurations are designed and performed to test two CUSUM charts, namely SMCUSUM and RMCUSUM. In addition to average run length(ARL), two measures of spatial identification accuracy are reported and compared. Results: The RMCUSUM chart provides higher level of spatial identification accuracy while two charts show comparable performance in terms of ARL. Conclusion: The RMCUSUM chart has more flexibility, robustness, and spatial identification accuracy when compared to those of the SMCUSUM chart. We recommend to use the RMCUSUM chart if control limit calibration is not an urgent task.

자기상관 공정에 대한 누적합관리도에서 설계모수 값의 결정 (A note on CUSUM design for autocorrelated processes)

  • 이재준;이종선
    • 품질경영학회지
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    • 제36권4호
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    • pp.87-92
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    • 2008
  • It is common to use CUSUM charts for detecting small level shifts in processes control, in which reference value(k) and decision interval(h) are the design parameters to be determined. To control process with autocorrelation, CUSUM charts could be applied to residuals obtained from fitting ARIMA models. However, constant level shifts in processes lead to varying mean shifts in residual processes and thus standard CUSUM charts may need to be modified. In this paper, we study the performance of CUSUM charts with various design parameters applied to autocorrelated processes, especially focussing on ARMA(1,1) models, and propose how they can be determined to get better performance in terms of the average run length.