Decision rule of assignable causes removal under an SPC-EPC integration system

Abstract

In order to obtain the advantages of eliminating both assignable causes and common causes, an effective method to integrate Statistical Process Control (SPC) and Engineering Process Control (EPC) under the continuous process is rousing increasing interest. This study found that an EPC feedback compensation mechanism affects SPC out-of-control detection and degrades the output quality once suddenly assignable causes are removed. Based on this finding, we propose a novel SPC control scheme that can effectively detect and identify the disturbance types. Further, we introduce a cost-oriented decision rule for removing assignable causes in an SPC and EPC integration system. Based on this decision rule, a more accurate selection methodology of SPC charts' control limits is also proposed.