Metrological performance of optical coordinate measuring machines under industrial conditions

An increasing number of manufactured parts are measured in industry using non-contact measuring systems. The paper describes an industrial comparison of coordinate measuring machines (CMMs) equipped with optical sensors, performed in Europe from August 2007 to January 2009 involving 21 optical CMMs. Participants, mainly small-medium size industrial companies, were asked to measure a set of calibrated artefacts with measurement tasks of different complexity. They include both 1D/2D standards (glass scale and optomechanical hole plate) and 3D injection moulded workpieces of different colours (four plastic Lego bricks). In addition to the evaluation of actual metrological performances of optical CMMs in industry, an important aim of the comparison was to investigate the validity of measurement uncertainty statements provided by participants. The focus of this investigation was on the additional error sources that emerge when using optical CMMs. Results demonstrate that: (i) the interactions of optical sensors with material and surface of parts are among the most important error sources; (ii) the users of optical CMMs in most cases are not aware of the magnitude of these effects; (iii) specific uncertainty evaluation procedures, suitable for industrial users of optical coordinate measurements, are needed.