Standards for testing freeform measurement capability of optical and tactile coordinate measuring machines

Abstract

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 digitized. Documented standards, for example ISO 10360, 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. Furthermore, the industry is seeking traceability in 3D measurements of high precision components. A recent requirement is the demand for highly accurate measurements of large gears with diameters up to 1000 mm as used in gear boxes of wind turbines. Up until now it has been impossible to ensure traceability of 3D measurements of big gears, since no traceable standards were available. This paper describes three different types of artefacts that were developed during the project, namely tetrahedron artefacts for testing the basic measurement capability of optical 3D devices, freeform verification artefacts for testing the capability of measuring complex geometry, and a large gear artefact for task related calibration of different types of CMMs. In addition, artefact calibration data and associated measurement uncertainties and international intercomparisons are presented. These developments will be of considerable value to end users, calibration laboratories and producers of optical and tactile CMMs.

The Influence of the Input Parameters Selection on the RANSAC Results

“…The scanned test field is composed of the plane and the semi-sphere which are commonly used geometrical shapes for point cloud registration and segmentation [2,[15][16][17] and calibrating measurement systems [25]. The radius of the semi-sphere (49.70 mm  0.05 mm) was measured with callipers.…”

Metrological characterization of 3D imaging systems: progress report on standards developments

“…It is in this context that other types of artefacts have been tested. Some were created in general workshops others offer measurement traceability in National measurement Institutes (NMI) like the NPL-Freeform 9 [45] or the PTB Micro-cube [33] made of titanium with spherical calottes 10 . The idea of finding a surface with curves that challenge the measurement process in an optical 3D imaging system has been on the mind of researchers for some time.…”

New developments in coordinate measuring machines for manufacturing industries

“…This method involved comparison of measured coordinates with calibrated reference points. Recently, Acko et al [42] have developed methods to guarantee traceability of 3D measurements for gears. Three different artefacts viz.…”