Construction of double sampling s ‐control charts for agile manufacturing

Double sampling (DS) $\overline{X}$ ‐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 $\overline{X}$ ‐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 $\overline{X}$ ‐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.