NPL freeform artefact for verification of non-contact measuring systems.

摘要

For decades three-dimensional (3D) measurements of engineering components have been made using fixed metrology-room based coordinate measuring machines (CMMs) fitted most commonly with single point or to a much lesser extent, scanning tactile probes. Over the past decade there has been a rapid uptake in development and subsequent use of portable optical-based 3D coordinate measuring systems. These optical based systems capture vast quantities of point data in a very short time, often permitting freeform surfaces to be digitised. Documented standards for the verification of fixed CMMs fitted with tactile probes are now widely available, whereas verification procedures and more specifically verification artefacts for optical-based systems are still in their infancy. To assist industry in the verification of optical based coordinates systems, this paper describes a freeform verification artefact that has been developed, calibrated and used to support a measurement intercomparison between a fixed CMM and a number of optical based systems. These systems employ technologies involving laser triangulation scanning, photogrammetry and fringe projection. The NPL freeform verification artefact is presented and a measurement intercomparison is reported which identifies that the accuracy of the optical-based systems tested is not as good as tactile probing systems.