Two-phase inspection policies on an imperfect metrology tool

When considering quality control of the output of production machines, the classical literature assumes a single inspection phase that can be perfect or imperfect. This paper formalizes and studies new two-phase in-line quality control policies on a single metrology (also called measurement or inspection) tool with limited capacity that can perform two types of measurements. The first type is reasonably fast but imperfect, and the second type yields perfect results but is significantly slower. After motivating and describing the problem, the risk, expressed as the expected product loss, and the capacity consumption of the control phase, performed with the two types of measurements, and of the probing phase, only performed with the perfect type of measurements, are modeled mathematically. Two types of probing phases are investigated. The models are used in an integer linear program to determine an optimal sampling plan. Computational experiments show the dominance of one type of probing phase, and several recommendations to practitioners are given.