Construction of p-charts using degree of nonconformity

Control charts are among the simplest of on-line statistical process control techniques. When the quality characteristic is a variable, the p-chart takes time to react to shifts in the production process because of its weak response to small variations in the process mean and variance. In this paper, instead of considering an item to be either conforming or nonconforming, the “degree of nonconformity” based on fuzzy concepts is defined and a fuzzy p-chart based on the mean degree of nonconformity is constructed. It is shown that this chart has a better response to variations in both the mean and the variance of the process.