Monitoring Simple Linear Profiles Using Cumulative Sum Control Charts

In some applications a single variable, either a process variable or product variable, characterizes the state of the process. In the other applications, multiple variables characterize the state of the process. However, in some practical situations, the quality of a process or product is characterized by a relationship between two or more variables instead of by the distribution of a single quality characteristic. This relationship, which can be linear, nonlinear or even a complicated model, is referred to as profile by researchers. Up to now, several methods have been proposed for monitoring simple linear profiles in both Phases I and II. In this paper, for improving phase II monitoring of linear profiles, a method has been proposed which applies Cumulative Sum control charts. Average run length criterion and simulation studies are used in order to evaluate the performance of the proposed method. The results show the suitable performance of the proposed method. Finally, the effect of reference value on the performance of the proposed method is evaluated.