Construction of control charts using fuzzy multinomial quality

Abstract

Control charts are the simplest type of on-line statistical process control techniques. One of the basic control charts is p-chart. In classical p-charts, each item classifies as either "nonconforming" or "conforming" to the specification with respect to the qualky characteristic. In practice, one may classify each item in more than two categories such as "bad", "medium", "good", and "excellent". Based on this, we introduce a fuzzy multinomial chart (FM-chart) for monitoring a multinomial process. Control limits of FM-chart are obtained by using the multinomial distribution and the degrees of membership which one assigned to the distinct categories. The comparison of the FM-chart and the p-chart based on a food production process illustrates that the FM-chart leads to better results. © 2008 Science Publications.