Exponentially weighted moving average distance square scheme for joint monitoring of process mean and variance

Abstract

In quality control, joint monitoring of process mean and variance has become more popular due to the disadvantages of monitoring mean and variance alone. This paper introduce a new joint monitoring scheme for process mean and variance. In this new scheme, exponential moving average technique is applied to the statistics D2t developed in the Shewhart distance scheme by Razmy (2010). The optimal design parameter were found through simulations for designing this new scheme. The design techniques of this scheme are illustrated with an example. A big advantage of this new scheme is, unlike most existing joint monitoring schemes, the design parameters of this scheme are independent on the sample size thus the quality engineers have fewer constraints in implementing this scheme.