A Score-test-based EWMA Control Chart for Detecting Prespecified Quadratic Changes in Linear Profiles

In profile monitoring, some methods have been developed to detect the unspecified changes in the profiles. However, due to the characteristics of a system or process, several prespecified changes may happen in some statistical process control applications, such as the typical form errors in cylindrical surface manufacturing processes. Hence, statistical process control is important and challenging for detecting changes away from the ‘normal’ profile toward one of several prespecified ‘bad’ profiles. A novel score‐test‐based EWMA control chart is proposed to detect the prespecified quadratic changes in linear profiles. Numerical simulation results show that the proposed chart is effective and robust when the vertex varies along one direction, and, in most cases, performs better than alternative methods in detecting small to moderate shifts. Finally, an example is given to illustrate the implementation of the proposed control chart.