An EWMA Standard Deviation Control Chart With Vsi Under Estimated Parameters And Its Application

Statistical Process Control(SPC)has been paid more and more attention with the continuous progress and development of science and technology.It is a process control technology based on the knowledge of mathematical statistical principles.Statistical process control monitors the entire work process to ensure that the process can be carried out steadily and continuously,which can improve product quality and reduce production costs.Control chart is a very practical tool for statistical process control.In 1924,Shewart proposed the first Shewart control chart.In 1954,Page proposed the Cumulative control(CUSUM)control chart based on the sequential probability ratio test,and in 1958 Robert proposed the number moving weighted average(Exponentially Weighted Moving Average,EWMA)control chart.The application of control charts is very extensive.Common applications are in product quality control in industrial production.They are also involved in management,finance,biology and other fields.This article does the following research:In the existing research,the control charts based on parameter estimation are all fixed sampling intervals(Fixed sampling interval,FSI).This paper is based on the design idea of dynamic variable sampling interval control charts,when the sample data with unknown process parameters has unknown interference.We propose a variable sampling interval(VSI)EWMA standard deviation control chart with parameter estimation.Assuming that there are 4 kinds of interference,simulation monitoring through R software shows that: VSI EWMA standard deviation control chart with parameter estimation has better monitoring effect than traditional FSI EWMA standard deviation control chart with parameter estimation,especially when the smooth parameters are relatively small.In the mechanical watch,the gemstone is fixed as a bearing on the clamping plate,which greatly reduces the friction and damage between other components,so it can ensure the quality of the movement and extend its life.It is necessary to monitor the size of gemstone bearings.The traditional FSI EWMA standard deviation control chart with parameter estimation cannot monitor the drift in time,so the VSI EWMA standard deviation control chart with parameter estimation is used for monitoring,and the results are also very good.For the solder paste thickness monitoring on the printed circuit board,according to the requirements of the circuit board production process,the solder paste thickness requires very high accuracy.Monitoring with the traditional Shewart control chart will lead to the inability to monitor the subtle changes in time.The CUSUM control chart,which is very effective for monitoring small drifts,is used to monitor this production process.At the same time,the EWMA control chart is also used to monitor this production process.The small drifts in it are continuously accumulated,and the abnormal conditions in the process can be found as soon as possible.The monitoring effect of the CUSUM control chart is remarkable.