METROMEET - 5th International Conference on Industrial Dimensional Metrology

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Programme

Optical and Tactile- Comparisons in Contour and Surface Metrology

Dr. -Ing. Dietrich Imkamp
Carl Zeiss Indutrial Metrology - Germany

Presentation abstract

There is an ongoing discussion in the scientific metrology community concerning the comparability of tactile and optical measurements. There is no doubt that optical results can differ from tactile results. The size of the difference depends on the measuring task and the influences during measurement. Due to improvements in the evaluation of optical measurements and a better understanding of the influences the difference for many measuring task is reduced to a level that can be neglected. In this case the optical metrology has advantages especially concerning measuring time. The results of two investigations concerning the comparison of optical and tactile measurements are presented here.
The importance of optical technique for surface metrology increases because optics can reduce measuring time significantly. But the recorded raw data look different.These differences lead also to different surface parameters if the same evaluation strategy is used. Therefore it is necessary to choose an appropriated evaluation to receive comparable results. In most cases the tactile results determine the general accepted results.
A comparison between optical results and tactile results from reference measurements delivers the necessary information for an adjusted filtering of the optical data to receive comparable results. This adjusted filtering can be used for further measurements within predefined constrains (e.g.: optical and mechanical surface properties, ambient light and optical measuring principle). The procedure is presented for several test pieces from and an industrial application.
Coordinate measuring machines (CMM) with camera sensors and contour measuring machines are used to measure two dimensional contours. Optical CMMs perform these measurements very fast. But due to the above mentioned reasons the results can be different to the tactile ones.
A German guideline describes a contour gage with calibrated features like distances, radii and angles that was originally designed for the acceptance test of contour measuring machines. This gage can be measured on optical CMMs with camera sensors too. Therefore it was used to compare results from optical CMMs and contour measuring machines. The investigations show strong influences from the form of the edges of the gage and the alignment. Taking into account these influences comparable results in the micrometer range are possible.

Information about the speaker

Dr. Dietrich Imkamp, born 1968, studied production engineering at the RWTH Aachen University, Germany. He was from 1994 to 1999 research assistant at the Chair of Metrology and Quality Management of the Laboratory for Machine Tools and Production Engineering (WZL) of the RWTH Aachen University (www.wzl.rwth-aachen.de). From 2000 to 2007 he worked as senior product manager for bridge type coordinate measuring machines at Carl Zeiss Industrial Metrology GmbH in Oberkochen, Germany. Since 2008 he is business unit manager for form and surface metrology in the same company.
Dr. Imkamp worked in several research projects from the Deutschen Forschungsgemeinschaft (DFG, German Research Foundation) also in collaboration with the Physikalischen Technischen Bundesanstalt (PTB, National institute of Germany). From 1994 to 2000 he was member of the technical committee 3.31 "Coordinate Measuring Machines" of VDI/VDE (The Association of German Engineers, www.vdi.de). Since 2007 he is member of the advisory board of the VDI/VDE Society for Measurement and Automatic Control and chairman of the Manufacturing Metrology department. He is contract lecturer at the University of Applied Science in Stuttgart. He published more than 30 papers and presentations about different topics in metrology and quality management.