NPL OPTIMUM – Optical Tracking Instrument for Measurement Using Multilateration

Abstract

Previously we have presented a prototype optical coordinate measurement machine developed at the National Physical Laboratory in the UK. This year we propose to present an update on activity on both a short range demonstrator operating over a desktop volume, and a long range demonstrator operating over the volume of a factory cell. A short range demonstrator has been built to measure targets on a small CMM, providing vibration compensation and outputting real-time coordinate positions and uncertainties. For the long range system we present a complete change to the acquisition system, improving measurement rate by a factor of 30. An essential feature of the long range system is real-time tracking of targets and we will present the methods undertaken to achieve this. Both systems utilise the same operating principle. Frequency scanning interferometry is used to make absolute distance measurements and multilateration calculates target coordinates with uncertainty estimates. The combination of these two techniques results in a coordinate measurement system that is self-calibrating with compensation for systematic errors, calculates inprocess uncertainty estimates, has continuous traceability to the SI metre, and makes rapid coordinate measurements. In our measuring system, multiple sensors each measure the distances to multiple targets, simultaneously.