Range extension of a scanning confocal chromatic sensor for precise robotic inline 3D measurements

Abstract

This paper introduces the intermediate range extension concept of a precision 3D measurement module for robotic inline measurements. A scanning confocal chromatic sensor (SCCS) is integrated with a magnetically levitated and actuated measurement platform (MP) for enabling the acquisition of 3D images with sub-micrometer resolution. The MP is capable of tracking a sample surface in the out-of-plane degrees of freedom to actively compensate for relative motion between the SCCS and the sample. Using the MP to position the SCCS at multiple measurement locations, 3D measurements of the surface structure under test are acquired with overlapping regions between neighbouring frames. A 3D image processing and parallel registration algorithm is implemented in order to ensure a robust and precise merging of the individual 3D images. Experimental results demonstrate an extension of the SCCS' lateral measurement range by a factor 3 to about 500×500μm2 while achieving sub-micrometer resolution in the entire range-extended 3D measurement. Compared to state-of-the-art repositioning with the robot, the measurement accuracy is increased by a factor of 9.