An ewma-cuscore quality control procedure for process variability

Combined Shewhart-cumulative score (cuscore) quality control schemes are av ailable for controlling the mean of a continuous production process. In man y industrial applications, it is important to control the process variabili ty as well. The proposed exponentially weighted moving average combined She whart-cumulative score ewma-cuscore quality control procedure for detecting shifts in process variability uses the procedures developed by Ncube and W oodall [1] to monitor shifts in the process mean of continuous production p rocesses. It is shown, in the one-sided case, by Average Run Length (ARL) c omparisons, that the proposed scheme performs significantly and uniformly b etter than comparative standard cuscore procedures for shifts in the proces s standard deviation values considered. (C) 1999 Elsevier Science Ltd. All rights reserved.