Economic Design of MEWMA VSSI Control Charts for Multiattribute Processes

Since little attention has been devoted to multiattribute control charts in the literature, in this research a new methodology is developed to employ the multivariate exponentially weighted moving average (MEWMA) chart for multiattribute processes. Moreover, since the variable sample size and sampling interval (VSSI) MEWMA charts detect small process mean-shifts faster than the traditional MEWMA, an economic design of VSSI MEWMA chart is proposed to obtain the optimum design parameters of the chart. The sample size, the sampling interval, and the warning/action limit coefficients are obtained using a genetic algorithm such that the expected total cost per hour is minimized. At the end, a sensitivity analysis has been carried out to investigate the effects of the cost and model parameters on the solutions obtained.