Modified exponentially weighted moving average control chart for monitoring process dispersion.

AbstractThe exponentially weighted moving average (EWMA) charts are widely used memory-type charts for monitoring small to moderate shifts in process parameters. However, the performance of the EWMA chart has been improved over time due to various modifications and enhancements. This paper proposes two modified EWMA (M‐EWMA) charts to monitor process dispersion. The upper-sided modified EWMA chart is denoted by M‐EWMAU, while a lower-sided modified EWMA chart is symbolized as the M‐EWMAL chart. Monte Carlo simulations determine the proposed schemes’ run length (RL) properties in zero- and steady-state scenarios. The proposed upper- and lower-sided M‐EWMA charts are compared to the upper- and lower-sided CH‐EWMA and SJ-EWMA charts. The comparisons reveal that the proposed M-EWMA charts have better detection ability than the upper- and lower-sided CH-EWMA, and SJ-EWMA charts, respectively. Finally, a real-life application is provided to illustrate the implementation of the upper-sided M-EWMA and CH-EWMA charts practically in both zero-state and steady-state cases. [ABSTRACT FROM AUTHOR]