20th International Forgemasters Meeting - IFM 2017

Dimensional inspection is essentially important to prove conformance to specifications of customers’ drawings in terms of quality assurance. Requirements concerning geometry of products are getting detailed and strict as represented by GPS (Geometrical Product Specifications) standards currently being developed by ISO/TC 213. Dimensional inspection by conventional measuring equipment such as steel tape measure, micrometer, templates etc. highly relies on the skill and ability of inspectors. In order to satisfy strict geometrical requirements with confidence, we have introduced a portable CMM (coordinate measuring machine), Leica Laser Tracker AT960-LR, which enables to perform dimensional inspection everywhere in machine shops with high accuracy. There are some cases where the evaluation of measuring uncertainty is needed, however, it is challenging for laser tracker especially because the uncertainty depends on the measuring strategy, namely the number of data points to obtain, the location of data points, evaluation method of obtained data points, etc. Here we discuss uncertainty of the distance between two points as well as uncertainty of center point and radius of best-fit (least squares method) circle and sphere by the analysis of uncertainty propagation of least squares method. It is concluded that introduction of laser tracker can reduce the measuring uncertainty and contribute to reliable dimensional measurements. Keywords: Dimensional inspection: Laser tracker; CMM; Uncertainty