Note on 'Construction of Double Sampling s-Control Charts for Agile Manufacturing'

Double sampling (DS) X-control charts are designed to allow quick detection of a small shift of process mean and provides a quick response in an agile manufacturing environment. However, the DS X-control charts assume that the process standard deviation remains unchanged throughout the entire course of the statistical process control. Therefore, a complementary DS chart that can be used to monitor the process variation caused by changes in process standard deviation should be developed. In this paper, the development of the DS s-charts for quickly detecting small shift in process standard deviation for agile manufacturing is presented. The construction of the DS s-charts is based on the same concepts in constructing the DS X-charts and is formulated as an optimization problem and solved with a genetic algorithm. The efficiency of the DS s-control chart is compared with that of the traditional s-control chart. The results show that the DS s-control charts can be a more economically preferable alternative in detecting small shifts than traditional s-control charts. Copyright  2002 John Wiley & Sons, Ltd.