An efficient adaptive exponentially weighted moving average chart for effective fault detection in the process mean
The exponentially weighted moving average (EWMA) control charts with adaptive charting structures have attracted attention from the research community for their dynamically adjusted smoothing parameters, which improve sensitivity to both small and large process shifts. Unlike a traditional EWMA chart, it can maintain stability in normal conditions and detect deviations quickly, thereby improving monitoring efficiency. In this study, we propose a memory-based control chart for the monitoring of the process mean of a normally distributed process. It estimates the mean shifts with an EWMA-based estimator and then finds the smoothing constant for plotting the EWMA statistics using a proposed continuous function. Monte Carlo simulations are conducted to evaluate the performance of the proposed adaptive EWMA (AEWMA) chart under different shifts in the process mean. The run-length profiles metric, along with overall performance measures, was used as a performance evaluation tool, and the proposed AEWMA chart outperformed the competing methods. A real data set from a semiconductor manufacturing process, where the quality characteristic of interest is the wafer flow width, illustrates the applicability in practice.

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