Theory And Application Of Dynamic EWMA Control Chart

It is very important to improve product quality and competition for an enterpriseapplying advanced quality technology and quality control methods, which appealresearcher and practicer to design and produce low-cost, short-period, highquality&reliability product. These methods make enterprises win superiority competition.The tendency of current quality engineering is to reduce, restrain and control the variationin the process.Firstly, some shortcomings of traditional control charts are pointed out in this paper.In order to reduce the time to signal when the shifts occurs in the process, this paperproposed the exponentially weighted moving average (EWMA) median control chartswith variable sampling intervals (VSI) and variable sampling size (VSS). Give thedistribution function of the median value assume that the distribution of observationsfrom a process is normally distributed. Then using the Markov chain method andMATLAB to establish a model to calculate the ATS and ANOS of median control chartrespectively.Finally, compare the ATS and the ANOS of the new model separately with that of theconventional fixed sampling interval EWMA control chart and VSI or VSS EWMA meancontrol chart. The data show that the designed new model can effectively reduce the ATSand ANOS when the process is out of control. That is to say, the new model effectivelyimproves the efficiency of the monitoring process, shifts can be discovered in a shorterperiod of time, which make a great significance to the actual production.