Automatic 3D surface reconstruction and sphericity measurement of micro spherical balls of miniaturized coordinate measuring probes

This paper proposes an automatic three-dimensional (3D) surface contouring approach for accurate sphericity evaluation of micro tip balls of coordinate measuring probes using optical measurement and surface reconstruction. In the proposed approach, 3D volumetric data of the tip were constructed from cross-section contours using a 3D mapping algorithm. In addition, a volumetric intersection algorithm was derived from the optical perspective projection principle to remove artefact surface profiles from the volumetric data. A sphericity evaluation method involving minimum zone optimization was also developed to determine the sphericity of the inspected micro tip ball. The developed method is capable of measuring micro spherical balls having a diameter ranging from a few tenths of a micrometre up to several millimetres. An industrial case study was employed to verify the feasibility of the approach. The measurement results demonstrated that the proposed approach could achieve 3D surface reconstruction and evaluate sphericity of micro balls with maximum measurement errors of +/- 0.5 mu m.