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Point Cloud Uncertainty in Optical Coordinate Metrology Event

Optical metrology is increasingly used on the production floor for surface and coordinate measurement, but the traceability and uncertainty infrastructure, something we almost take for granted with contact measurement methods, is missing. Why? Whilst it is relatively simple to understand and model the physical interaction of a contact probe tip with a surface, it not so simple to model the equivalent optical interaction – it is a more complex physics problem.

This problem is exacerbated by the increasingly complex nature of the shapes and surfaces used in advanced manufacturing. For these reasons, it is still rare to see optical coordinate metrology data or parameters quoted with uncertainty. To partly address this issue in the surface texture measurement community, a framework is being developed that introduces a number of common or instrument-independent metrological characteristics – these can be determined with suitable artefacts and procedures, and the resulting characteristic values can then be propagated through a measurement model to give an evaluation of measurement uncertainty. However, this framework can only be applied to surfaces with relatively simple geometries, where optical effects, such as multiple scattering, can be ignored.

In an online event taking place May 20th (World Metrology Day) Richard Leach will present research aimed at extending the framework to any surface geometry with any optical surface measuring instrument and allow direct comparison of the performances of different optical instruments. This will represent a major breakthrough both from academic and industrial impact points of view. I will present early research to develop a suite of “virtual” optical instruments by systematically combining surface scattering models with three-dimensional optical imaging theory and surface reconstruction models. The virtual systems will be integrated into the physical instruments to predict optical responses to any surface geometry and evaluate the task-specific measurement uncertainty.

Richard is Professor in Metrology at the UK’s University of Nottingham, Director of the Midlands Centre for Data-Driven Metrology, Head of the Manufacturing Metrology Team and previously had spent 25 years at the National Physical Laboratory. He has been researching and lecturing on surface metrology for over 30 years. He is on the Council of the European Society of Precision Engineering and Nanotechnology (president elect), the Board of the American Society of Precision Engineering and several international standards committees.

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