Premium
Monitoring capability indices using an EWMA approach
Author(s) -
Castagliola Philippe,
Vännman Kerstin
Publication year - 2007
Publication title -
quality and reliability engineering international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 62
eISSN - 1099-1638
pISSN - 0748-8017
DOI - 10.1002/qre.838
Subject(s) - ewma chart , process capability index , control chart , process capability , process (computing) , statistical process control , range (aeronautics) , logarithm , standard deviation , transformation (genetics) , property (philosophy) , computer science , reliability engineering , mathematics , data mining , statistics , engineering , work in process , operations management , mathematical analysis , biochemistry , chemistry , philosophy , epistemology , gene , operating system , aerospace engineering
When performing a capability analysis it is recommended to first check that the process is stable, for example, by using control charts. However, there are occasions when a process cannot be stabilized, but it is nevertheless capable. Then the classical control charts fail to efficiently monitor the process position and variability. In this paper we propose a new strategy to solve this problem, where capability indices are monitored in place of the classical sample statistics such as the mean, median, standard deviation, or range. The proposed procedure uses the $C_p(u,v)$ family of capability indices proposed by Vännman combined with a logarithmic transformation and an EWMA approach. One important property of the procedure presented here is that the control limits used for the monitoring of capability indices only depend on the capability level assumed for the process. The experimental results presented in this paper demonstrates how this new approach efficiently monitors capable processes by detecting changes in the capability level. Copyright © 2006 John Wiley & Sons, Ltd.