Multiple exponentially weighted moving average control schemes for monitoring and diagnostics of correlated quality variables of different types with individual observations

• Published in: Computers & industrial engineering 2024-08, Vol.194, p.110344, Article 110344
• Main Authors: Huang, Wei-Heng, Yeh, Arthur B.
• Format: Article
• Language: English
• Subjects: Diagnostics; Exponentially weighted moving average; Holm’s step-down multiple testing procedure; Multivariate control chart; Phase-II monitoring
• ISSN: 0360-8352; 1879-0550
• DOI: 10.1016/j.cie.2024.110344

In the era of big data analytics, more data, in terms of quantity and variety, are being collected for quality control purposes, thus leading to new challenges, especially for multivariate statistical process control (MSPC). One such challenge, which has received very little attention, is multivariate control chart (MCC) for monitoring correlated quality variables of different types. A recent study by Huang et al. (2023), which develops a Shewhart type MCC, is the first attempt to tackle such a challenge. The proposed chart of Huang et al. (2023), which utilizes the step-down multiple testing procedure of Holm (1979), not only can monitor correlated variables of different types, but also can provide instantaneous diagnostics of which parameters are out of control when the chart signals. In this study, we adapt and extend the methodology of Huang et al. (2023) to develop an exponentially weighted moving average (EWMA) chart specifically for the case when the sample size is one. The proposed chart is shown to be effective in detecting parameter changes as well as diagnosing which parameters are out of control when the chart signals. •A multiple EWMA chart for monitoring variables of different types is proposed.•It is critical to develop EWMA chart as Shewhart chart is not designed for individual observations.•The proposed chart is shown to be effective in detecting parameter changes.•The proposed chart also provide diagnostics of which parameters are OC when the chart signals.