A comparative study of CCC and CUSUM charts

Abstract

The cumulative count of conforming (CCC) chart is a new type of control chart used for the monitoring of highquality processes. Instead of counting the number of non-conforming items in samples of fixed size, the cumulative number of conforming items between two non-conforming items is monitored. The CCC chart is convenient to use in a modern manufacturing environment where the product is inspected individually and automatically. The CCC chart has sometimes been confused with the cumulative sum (CUSUM) chart which has been shown to be more sensitive than the traditional Shewhart chart for small process shifts. In this paper the uses of these two types of charts are compared. It shown by numerical illustrations and analytical results that the two charts function in entirely different ways. However, the CUSUM concept can be applied to cumulative counts used in the CCC chart to improve its sensitivity for small process shifts when the process is producing at a very low non-conforming rate. © 1998 John Wiley & Sons, Ltd.