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A Study of The reference value of the CUSUM control chart that can detect small average changes in the process

  • Jun, Sang-Pyo (College of General Education, Namseoul Unversity)
  • Received : 2020.11.19
  • Accepted : 2020.11.27
  • Published : 2020.12.31

Abstract

Most process date such as semiconductor and petrochemical processes, autocorrelation often exists between observed data, but when the existing SPC(Statistical process control) is applied to these processes, it is not possible to effectively detect the average change of the process. In this paper, when the average change of a certain size occurs in the process data following a specific time series model, the average of the residuals changes according to the passage of time, and the change pattern of the average is introduced around the ARMA(1,1) process. Based on this result, the reference value required in the design process of the CUSUM (Cumulative sum) control chart is appropriately considered by considering the type of the time series model of the process data of the CUSUM control chart that can detect small mean changes in the process and the width of the process mean change of interest. It was confirmed through simulation that it should be selected and used.

반도체나 석유화학 공정과 같이 프로세스 중심의 장치 산업에서는 흔히 관측된 자료들 사이에 자기상관(Autocorrelation)이 존재하는데, 이러한 공정에 기존의 SPC(Statistical process control)를 적용하는 경우 공정의 평균 변화를 효과적으로 검출하지 못하는 문제가 발생할 수 있다. 본 논문에서는 특정 시계열 모형을 따르는 공정자료에 일정한 크기의 평균 변화가 발생할 때, 잔차는 시간의 흐름에 따라 그 평균이 달라지게 되는데, ARMA(1,1) 과정을 중심으로 평균의 변화 패턴을 소개하고, 이 결과를 바탕으로 공정의 작은 평균 변화를 검출할 수 있는 CUSUM(Cumulative sum) 관리도의 공정 자료가 갖는 시계열 모형의 형태와 관심 있는 공정 평균 변화의 폭을 고려하여 CUSUM 관리도의 설계 과정에서 필요한 참고값이 적절히 선택되어 사용되어야 함을 모의실험을 통해 확인하였다.

Keywords

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