Abstract
Duncan considered the design parameters of Shewhart control charts in 1956 based on an economic view-point, and ensured that an economic design control chart actually lowers the cost compared with a Shewhart control chart. His research method has been widely used in subsequent studies on the subject and focused on a fixed-sampling interval (FSI). However, it has been discovered that variable-sampling-interval (VSI) control charts are substantially quicker than FSI control charts in detecting shifts in the process. In an earlier study, an economic design of a VSI control chart with a single assignable cause for a continuous flow has been proposed. This research extends a single assignable cause to multiple-assignable causes to construct an economic model of VSI control charts. A numerical example is provided to demonstrate the effectiveness of the proposed model. The result indicates that VSI is more effective than FSI control charts.
Acknowledgements
The authors wish to express appreciation for the support by National Sciences Council of the Republic of China, Grant No. NSC-93-2213-E-212-020. Financial assistance of NSERC of Canada to the second author for this collaborative research is greatly acknowledged as well. The valuable comments and suggestions of the reviewers are greatly appreciated.