• 산업경영시스템학회지
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• 제33권3호
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• pp.146-153
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• 2010

When the production run is short and process parameters change frequently, it is difficult to monitor the process using traditional control charts. In such a case, the coefficient of variation (CV) is very useful for monitoring the process variability. The CV control chart is an effective tool to control the mean and variability of process simultaneously. The CV control chart, however, is not sensitive at small shifts in the magnitude of CV. The CV-EWMA(exponentially weighted moving average) control chart which was developed recently is effective in detecting a small shifts of CV. Since the CV-EWMA control chart scheme can be viewed as a weighted average of all past and current CV values, it is very sensitive to small change of mean and variability of the process. In this paper, we propose an FIR(Fast initial response) CV-EWMA control chart to improve the sensitivity of a CV-EWMA scheme at process start-up or out-of-control process. Moreover, we suggest the values of design parameters and show the results of the performance study of FIR CV-EWMA control chart by the use of average run length(ARL). Also, we compared the performance of FIR CV-EWMA control chart with that of the CV-EWMA control chart and we found that the CV-EWMA control chart gives longer in-control ARL and much shorter out-of-control ARL.

• 한국건설관리학회논문집
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• 제5권5호
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• pp.135-142
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• 2004

본 연구에서는 바차트(bar chart) 기법과 CPM 기법의 장점을 결합한 CPM bar chart(CBC) 기법을 제시한다. CBC는 기존의 fenced bar chart(FBC)의 장점을 유지하면서 단점을 보완한 것으로, 작업 관계를 나타내는 fence에 방향성을 부여함으로써, 기존 FBC에서 상당한 혼란을 유발하는 fence의 분리과정 없이 작업들의 관계를 표현할 수 있다. 또한, fence의 분리를 파악하기 위해 더미작업(dummy activity)을 확인하는 과정이 생략되어 보다 손쉽게 작성할 수 있는 장점도 있다. 바차트의 간결성을 유지하면서 CPM의 네트워크 논리 표현이 가능해짐에 따라, CBC는 다양한 프로젝트 참여자들 간의 원활한 의사소통에 기여하리라 예상된다. 또한, resource constrained scheduling, resource leveling, 작업 분리가 고려된 일정 조정, 공기 지연 분석 등의 CPM 기법에 기초한 다양한 일정 계획 및 관리에도 적용이 용이하여, 실무뿐만이 아니라 공정관리 교육과정에서도 활용성이 높으리라 기대된다.

• 한국안광학회지
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• 제13권4호
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• pp.115-119
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• 2008

목적: 노안에서 십자와 적록을 조합한 시표를 사용하여 얻어진 잠정가입도와 최종가입도를 비교하기 위해 실시하였다. 방법: 대상자는 41~60세(평균연령 51.7세) 사이의 노안이 있는 60명으로 하였다. 잠정가입도는 십자시표(CG), 적록시표(RG) 및 두 가지 시표를 조합하여 만든 적록십자시표(RGCG)를 사용하여 결정하였으며, 최종가입도는 검사거리 40 cm에서 각 대상자에 맞게 잠정가입도를 조정하여 결정하였다. 결과: 측정 방법별 잠정가입도와 최종가입도 사이의 유의한 차이가 있었으며, 적록십자시표에 의한 방법이 높은 신뢰도(repeatability)를 나타냈다. 결론: 적록 십자시표(RGCG)는 노안 가입도 결정에 필요한 적절한 데이터를 얻을 수 있으며, 양안시 임상에서 가입도 처방의 진단 평가에 유용할 것이다.

• 대한산업공학회지
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• 제38권4호
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• pp.237-243
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• 2012

This paper proposes quantitative investment strategies for KOSPI200 index futures using VKOSPI and control chart. Stochastic control chart is employed to decide when to take a position as well as what position out of long and short should be taken by monitoring whether VKOSPI or difference of VKOSPI touches the control limit lines. The strategies include 4 approaches, which are traditional control chart and 2-Area control chart coupled with VKOSPI and its difference, respectively. Computational experiments using real KOSPI200 futures index for recent 3 years are conducted to show the excellence of the proposed investment strategies under control chart framework.

• 대한인간공학회:학술대회논문집
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• 대한인간공학회 1995년도 추계학술대회논문집
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• pp.268-279
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• 1995

The purpose of this study is to suggest a brassiere sizing chart for elderly women. It is found that there is no direct linear relationship between cup size and under bust girth from the analsis of breast measurements. These 2 factors(under bust girth and cup size) were chosen as 2 axes of brassiere size chart. A loss function was used to determined intervals of bust girth and cup size of size chart, because the loss function introduces the concept of frequency to size chart for better customer's satisfaction. From the dual distribution table whose intervals had been determinde by a loss function. The 15 sizes, which had more than 2% of appearance were suggested for brassiere size chart. The suggested brassierc sizes covened 87.6% of all subjects. Considering that KS brassiere size thart consisting of 32 sizes covers 88.5%, the suggested brassiere size chart would be considered quite feasible. Also is suggested supply reference measurement chart relevant to brassiere manufacturing for 10 most frequent sizes.

• 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.

• Journal of the Korean Data and Information Science Society
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• 제14권4호
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• pp.1045-1053
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• 2003

Markovian EWMA control chart for simultaneously monitoring mean vector of the several correlated quality characteristics is investigated. Properties of multivariate Shewhart chart and EWMA chart are evaluated for matched FSI (fixed sampling interval) and VSI(variable sampling interval) scheme. We obtained VSI EWMA chart is more efficient than Shewhart chart for small or moderate shifts. And, we obtained stablized numerical results with Markov chain method when the number of transient state is greater than 100.

• 대한안전경영과학회지
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• 제14권3호
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• pp.167-174
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• 2012

In the manufacturing process the most widely used $\bar{X}$ chart has been applied to control the process mean. Also, Accelerated Life Test(ALT) is commonly used for efficient assurance of product life in development phases, which can be applied in production reliability acceptance test. When life data has lognormal distribution, through censored ALT design so that censored ALT data has asymptotic normal distribution, $ALT\bar{X}$ control chart integrating $\bar{X}$ chart and ALT procedure could be applied to control the mean of process in the manufacturing process. In the situation that process variation is controlled, $Z_p$ control chart is an effective method for the very small fraction nonconforming of quality characteristic. A simultaneous control scheme with $ALT\bar{X}$ control chart and $Z_p$ control chart is designed for the very small fraction nonconforming of product lifetime.

• 산업경영시스템학회지
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• 제24권67호
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• pp.27-36
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• 2001

A standard assumption when using a control chart to monitor a process is that the observations from the process output are statistically independent. However, for many processes the observations are autocorrelated and this autocorrelation can have a significant effect on the performance of the control chart. In this paper, we consider combined control chart of monitoring the mean of a process in which the observations can be modeled as a first-order autoregressive process. The Shewhart control chart of residuals-EWMA control chart of the observations is considered and the method of combination is recommended. The performance of the proposed control chart is compared with the performance of other control charts using a simulation.

• 산업경영시스템학회지
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• 제23권56호
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• pp.83-92
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• 2000

This paper presents a study on control schemes for gradual increases (drifts) in a process variance. A new control chart, the Drifting Variance Control Chart (DVCC) is designed using Likelihood Ratio Test (LRT), and the ARL performance of the chart is evaluated for different subgroup sizes. The performance of this chart is then compared to some of the popular control schemes for the process dispersion, like the Shewhart S$^2$chart, the CUSUM chart and the EWMA chart. Results are presented and discussed. Also included is a sensitivity analysis that investigates how the DVCC performs when applied to a stepped change in process variance.