Generalised cumulative count of conforming (GCCC) charts have been proposed formonitoring a high-yield process that allows the items to be inspected sample by sample andnot according to the production order. Recent study has shown that the GCCC chart with avariable sampling interval (VSI) is superior to the traditional one with a fixed samplinginterval (FSI) because of the additional flexibility of sampling interval it offers. However,the VSI chart is still costly when used for the prevention of defective products. This paperpresents an economic model for the design problem of the VSI GCCC chart, taking intoaccount the correlation of the production outputs within the same sample. In the economicdesign, a cost function is developed that includes the cost of sampling and inspection, thecost of false alarms, the cost of detecting and removing the assignable cause, and the costwhen the process is out-of-control. An evolutionary search method using the cost function ispresented for finding the optimal design parameters of the VSI GCCC chart. Comparisonsbetween VSI and FSI charts for expected cost per unit time are also made for variousprocess and cost parameters.
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