Performance Improvement Study of CV-EWMA Control Chart to Detect Small Shifts of CV

Abstract

In order to control a process that has short production cycle and where the product type and specifications change often with conventional shewhart control charts such as and control charts, a new control chart must be applied every time the parameters change . As this is a very inefficient method in terms of the cost and time, CV control chart using coefficient of variation statistics was developed. As CV control chart reflects only the current sample data on control chart, it can be useful when there is a significant change in process. However, it does not respond sensitively to a process that has subtle change or requires a high control level. CV-EWMA control chart was researched to monitor small shifts in CV. This study proposes a way to improve accuracy and precision of population parameter estimation of conventional CV-EWMA control chart and applied it to a control chart before analyzing its performance. As a result, the accuracy and precision of conventional CV-EWMA control chart has been improved and it was verified that the proposed control chart is a proper control chart to control small shifts of CV.

Efficient Control Charts for Monitoring Process CV Using Auxiliary Information

“…This will highlight the benefit of using auxiliary information for efficient monitoring of process CV. Specifically, the performance of proposed charts is compared with the CV U chart proposed by Kang et al [3], the CV EWMA chart proposed by Hong et al [37], the synthetic CV (CV sync ) control chart proposed by Calzada and Scariano [9], and the improved CV-EWMA (ICV EWMA ) chart proposed by Park et al [38]. Average run length is used as a performance measure for the comparison of these charts.…”