Economic design of cumulative count of conforming control charts based on average number of inspected items


Department of Industrial Engineering, Yazd University, Yazd, P.O. Box 89195-741, Iran.


Nowadays, continuous improvement can be regarded as the essence of survival and growth in order to not only increase the competition in global market, but also requirement for ever-decreasing defect levels in processes. Therefore, new statistical analysis techniques and decision-making procedures have been continuously evolved, both to handle high quality processes and to look for process improvement opportunities. CCC-r chart, or extended approach of CCC charts, is generally a technique for high quality processes, when nonconforming items are rarely observed. This study develops a mathematical model based on the average number of inspected items for the economic design of CCC-r chart, so that the average cost per item is minimized. The optimal designed parameters for di erent nonconforming fractions and di erent parameters in each iteration are calculated. In addition, with respect to Type I error ( ) and Type II error ( ) in the process, sensitivity analysis of the model is carried out.