The Uncertainty of Coordinate Metrology as a Function of Sampling Strategy

Abstract

The main objective in all metrology processes is to limit uncertainty. The objective of coordinate metrology processes is not any different. A coordinate metrology process is successful only if it reduces the level of uncertainty in geometric and dimensional information of the available physical object so that downstream processes can rely on the information and can be planned according to it. As an example, a machined surface can be inspected by a coordinate measuring machine (CMM) to develop information about detailed deviations on its geometric profile. Using this information, the downstream process (which can be, for example, assembly to other parts, or another phase of machining) can be planned. If the coordinate metrology process is capable of reducing uncertainty to the level that meets the required precision for the downstream process, then it is selected and conducted properly. Otherwise it will be a waste of time and money that will mislead the downstream processes. The sophistication of today’s coordinate metrology equipment, the required time to perform the coordinate metrology processes, and the need to employ very well-trained experts all combine to make inspection a relatively expensive task. However, without having a good understanding of the inspection uncertainty, the results may become unacceptable. Many parameters affect the uncertainty of coordinate metrology inspection. However, they all can be categorized by the groups of uncertainty in sampling strategy