Development of a cylindricity measurement with nanometre uncertainty

Cylindricity is a geometric specification that describes the three-dimensional shape of a cylindrical element. Its control using commercial machines raises a number of practical issues that limit current measurement capabilities. Indeed, there is currently no measuring instrument capable of generating a three-dimensional mapping of the cylindricity deviation with a nanometric uncertainty. The Laboratoire Commun de Métrologie LNE-CNAM has recently developed a ultra-high accuracy cylindricity measuring machine named NanoCyl. As a primary standard, the NanoCyl aims to improve the current calibration and cylindricity measurement capabilities. In this thesis, a general description of the NanoCyl is provided. Its design is then completed by the development of a new sensor carriage structure including a linear positioning axis with nanometer resolution for docking the target surface. A mathematical and geometrical analysis of the sources of uncertainty leads to the proposal of adjustment strategies to minimize measurement errors. An error separation method based on the Fourier transform is developed in the specific case of commercial machines. The method is then adapted to the NanoCyl architecture and validated experimentally. An optimal cylindricity measurement protocol for measurements with nanometre uncertainty is then described. It allows the identification of all the components of the cylindricity deviation. Experimental studies are conducted on a cylindrical artefact in order to validate the introduced protocol. The results obtained show an achievable measurement uncertainty of the order of 30 nm.

Precision engineering, Dimensional metrology, Error separation methods, Cylindricity