Artefacts with rough surfaces for verification of optical microsensors

Abstract

Optical microsensors are used to carry out a great variety of coordinate metrology tasks on micro-parts. For the testing of such sensors calibrated artefacts are needed. The existing micro-artefacts have smooth surfaces and can therefore only be used for white-light interferometry and tactile probing. For sensors based on triangulation (structured light, autofocus, confocal...), artefacts with optically rough surfaces are needed. Consequently artefact surfaces with a small mechanical roughness but diffuse optical scattering (high optical roughness) are required. For this purpose, different production techniques to roughen smooth surfaces and to form parts having rough surfaces are tested successfully at the Physikalisch-Technische Bundesanstalt (PTB). The roughness Ra is about 0.3 &mgr;m. A suitable artefact set is currently being developed in compliance with the existing standards. A first micro-artefact (micro-contour artefact) is already commercially available. By means of the developed artefacts it also becomes possible to analyze for different optical sensors the dependence between the uncertainty and the measured surface as well as the surface slope.