Traceability of 3D optical measuring instruments in industrial environments using customized material standards

Mínguez Martínez, Alberto (2021). Traceability of 3D optical measuring instruments in industrial environments using customized material standards. Thesis (Doctoral), E.T.S.I. Industriales (UPM).


Title: Traceability of 3D optical measuring instruments in industrial environments using customized material standards
  • Mínguez Martínez, Alberto
  • Vicente y Oliva, Jesús de
Item Type: Thesis (Doctoral)
Date: 2021
Faculty: E.T.S.I. Industriales (UPM)
Department: Física Aplicada e Ingeniería de Materiales
Creative Commons Licenses: Recognition - No derivative works - Non commercial

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Nowadays, material characterization is the foundation of science and industrial development. The different fields of metrology, the science of measurement, play an important role in helping researchers and engineers’ study and work on material science. In addition, the current tendency in industry is towards the miniaturization of systems and materials and the fabrication of parts at the micro- and nanoscale. For this reason, one of the most important fields of study in material science is surface characterization. For this kind of applications, involving measurements in the submillimeter range, the use of optical, non-contact instruments with suitable traceability is usually advisable. This topic is currently a field of growing interest, as many functional properties depend on the surface texture. Besides, coordinate metrology techniques are widely used in industry to carry out dimensional measurements. These techniques are capable of measuring many types of three-dimensional geometries with great flexibility and sufficient accuracy. However, as the samples could be affected and modified if they are measured using contact methods, coordinate metrology techniques should be adapted for measurements in ranges lower than millimeter. For these applications, non-contact measuring instruments are used, and optical measuring instruments are, probably, the most extended across the industry. Among all the existing optical measuring instruments, confocal microscopy is a powerful tool as it permits dimensional and 2D/3D roughness measurements without mechanical contact. Confocal microscopy has applications in many fields, both in research and industrial applications. This type of microscope is widely used in biomedical science, material science, and surface quality metrology at micro and macro scales. This measuring instrument allows images of optical sections of samples to be obtained, filtering out of focus reflected light, and from which the full 3D object geometry can be reconstructed using specialized software. Confocal microscopy could become very important in the near future as it enables to obtain Z-axis measurements at these scales. In all the fields where the confocal microscopes are used, it is very important to have good traceability of the scales. Controlling them, it is possible to increase the knowledge about materials science and industrial processes and to carry out continuous improvements. In this document, it is proposed a calibration procedure for the confocal microscope that is frequently used in the research center “Centro Láser” of UPM (CL-UPM). In the first part, it is proposed a calibration procedure that includes: - Calibration of the X and Y scales, using a stage micrometer as a reference measurement standard. - Estimation of perpendicularity error between X and Y axes. - Estimation of the flatness deviation of the focal plane using an optical flat. - Calibration of Z scale using a calibrated steel sphere instead of step height standards. - Calibration of the confocal microscope for the measurement of 2D roughness using periodic and aperiodic 2D roughness measurement standards. - All uncertainties are estimated following the mainstream GUM method (Guide to the Expression of Uncertainty in Measurement) or EA-04/02 M:2013 document, as they are standard procedures in calibration laboratories accredited under ISO 17025. It has been tried that the reference material standards were: - Easy to find in industrial environments and research centers. - Easy to calibrate with low enough uncertainties in National Measurement Institutes or in accredited calibration laboratories. - Stable mechanical artifacts that could guarantee long recalibration intervals. - Common in the field of dimensional metrology in order to facilitate their acquisition, calibration, and correct use. Finally, equations to calculate the uncertainties of use are given. This procedure is applicable only for measurements carried out in the central position of the confocal microscope. This means that the measuring range, limited by objective field, is very narrow. Therefore, when measuring samples with higher dimensions it becomes necessary to adapt the calibration procedure and material standards covering higher ranges should be used. However, the commercial material standards introduce much uncertainty to the measure because it depends too much on the person who is carrying out the measurement. One potential solution is to create brand new, customized material standard, covering the desired measurement range, and that could be easily traced using traditional methods. For this purpose, it is proposed a method to manufacture material standard with the desired motif scribed over it using the CL-UPM resources, that is, using laser technology. In addition, a review of the existing commercial material standard for surface texture traceability is given and different motifs to be scribed using lasers are proposed. In this way, the needs to provide traceability to a larger volume should be covered and it would be able to give traceability to the scales of the confocal microscope in larger ranges. Using the new, laser manufactured material standard and adapting slightly the calibration procedure, it is proposed a method for the calibration of the scales for the whole measuring volume of the confocal microscope, avoiding measurements near the end of the stroke. It is expected that this work will serve as a starting point so that other industries, research centers and laboratories can give traceability in a fast, simple, and economic way to their optical measuring instruments.

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Item ID: 69160
DC Identifier:
OAI Identifier:
DOI: 10.20868/UPM.thesis.69160
Deposited by: Archivo Digital UPM 2
Deposited on: 11 Jan 2022 08:40
Last Modified: 11 Jan 2022 08:40
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