This article generalizes the model for the economic design of nx-control charts of Duncan, starting from the more recent papers of Lorenzen and Vance and Banerjee and Rahim. The classical model of Duncan and its several extensions including the unified model of Lorenzen and Vance assumed exponentially distributed in-control periods and provided uniform sampling schemes. Banerjee and Rahim, however, assumed a Weibull-distributed in-control period having an increasing failure rate and used variable sampling intervals. The present article is an extension of the work of Banerjee and Rahim, where a general distribution of in-control periods having an increasing failure rate is assumed and the possibility of age-dependent repair before failure is considered. Several different truncated and nontruncated probability models are chosen. It is proposed that economic benefits can be achieved by adopting a nonuniform inspection scheme and by truncating a production cycle when it attains a certain age. Numerical examples are presented to support this proposition. Finally, the effect of model specification in the choice of failure mechanism is investigated.
