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Mattsson, Lars
Publications (4 of 4) Show all publications
Ekberg, P. & Mattsson, L. (2018). Traceable X,Y self-calibration at single nm level of an optical microscope used for coherence scanning interferometry. Measurement science and technology, 29(3), Article ID 035005.
Open this publication in new window or tab >>Traceable X,Y self-calibration at single nm level of an optical microscope used for coherence scanning interferometry
2018 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 29, no 3, article id 035005Article in journal (Refereed) Published
Abstract [en]

Coherence scanning interferometry used in optical profilers are typically good for Z-calibration at nm-levels, but the X,Y accuracy is often left without further notice than typical resolution limits of the optics, i.e. of the order of similar to 1 mu m. For the calibration of metrology tools we rely on traceable artefacts, e.g. gauge blocks for traditional coordinate measurement machines, and lithographically mask made artefacts for microscope calibrations. In situations where the repeatability and accuracy of the measurement tool is much better than the uncertainty of the traceable artefact, we are bound to specify the uncertainty based on the calibration artefact rather than on the measurement tool. This is a big drawback as the specified uncertainty of a calibrated measurement may shrink the available manufacturing tolerance. To improve the uncertainty in X, Y we can use self-calibration. Then, we do not need to know anything more than that the artefact contains a pattern with some nominal grid. This also gives the opportunity to manufacture the artefact in-house, rather than buying a calibrated and expensive artefact. The self-calibration approach we present here is based on an iteration algorithm, rather than the traditional mathematical inversion, and it leads to much more relaxed constrains on the input measurements. In this paper we show how the X, Y errors, primarily optical distortions, within the field of view (FOV) of an optical coherence scanning interferometry microscope, can be reduced with a large factor. By self-calibration we achieve an X, Y consistency in the 175 x 175 mu m(2) FOV of similar to 2.3 nm (1 sigma) using the 50x objective. Besides the calibrated coordinate X, Y system of the microscope we also receive, as a bonus, the absolute positions of the pattern in the artefact with a combined uncertainty of 6 nm (1s) by relying on a traceable 1D linear measurement of a twin artefact at NIST.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
optical microscope, 2D accuracy, self-calibration, traceable, high precision
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-223779 (URN)10.1088/1361-6501/aaa39d (DOI)000425138000003 ()2-s2.0-85042553462 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 309672
Note

QC 20180307

Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-03-07Bibliographically approved
Ekberg, P., Daemi, B. & Mattsson, L. (2017). 3D precision measurements of meter sized surfaces using low cost illumination and camera techniques. Measurement science and technology, 28(4), Article ID 045403.
Open this publication in new window or tab >>3D precision measurements of meter sized surfaces using low cost illumination and camera techniques
2017 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 28, no 4, article id 045403Article in journal (Refereed) Published
Abstract [en]

Using dedicated stereo camera systems and structured light is a well-known method for measuring the 3D shape of large surfaces. However the problem is not trivial when high accuracy, in the range of few tens of microns, is needed. Many error sources need to be handled carefully in order to obtain high quality results. In this study, we present a measurement method based on low-cost camera and illumination solutions combined with high-precision image analysis and a new approach in camera calibration and 3D reconstruction. The setup consists of two ordinary digital cameras and a Gobo projector as a structured light source. A matrix of dots is projected onto the target area. The two cameras capture the images of the projected pattern on the object. The images are processed by advanced subpixel resolution algorithms prior to the application of the 3D reconstruction technique. The strength of the method lays in a different approach for calibration, 3D reconstruction, and high-precision image analysis algorithms. Using a 10 mm pitch pattern of the light dots, the method is capable of reconstructing the 3D shape of surfaces. The precision (1 sigma repeatability) in the measurements is < 10 mu m over a volume of 60 x 50 x 10 cm(3) at a hardware cost of similar to 2% of available advanced measurement techniques. The expanded uncertainty (95% confidence level) is estimated to be 83 mu m, with the largest uncertainty contribution coming from the absolute length of the metal ruler used as reference.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017
Keywords
3D reconstruction, large area measurement, camera calibration, structured light, image processing, image metrology
National Category
Computer Vision and Robotics (Autonomous Systems)
Identifiers
urn:nbn:se:kth:diva-205442 (URN)10.1088/1361-6501/aa5ae6 (DOI)000395884500001 ()2-s2.0-85014505994 (Scopus ID)
Note

QC 20170522

Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2018-01-13Bibliographically approved
Daemi, B., Ekberg, P. & Mattsson, L. (2017). Advanced image analysis verifies geometry performance of micro-milling systems. Applied Optics, 56(10), 2912-2921
Open this publication in new window or tab >>Advanced image analysis verifies geometry performance of micro-milling systems
2017 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 56, no 10, p. 2912-2921Article in journal (Refereed) Published
Abstract [en]

Accurate dimensional measurement of micro-milled items is a challenge and machine specifications do not include operational parameters in the workshop. Therefore, a verification test that shows the machine's overall geometrical performance over its working area would help machine users in the assessment and adjustment of their equipment. In this study, we present an optical technique capable of finding micro-milled features at submicron uncertainty over working areas > 10 cm(2). The technique relies on an ultra-precision measurement microscope combined with advanced image analysis to get the center of gravity of milled cross-shaped features at subpixel levels. Special algorithms had to be developed to handle the disturbing influence of burr and milling marks. The results show repeatability, reproducibility, and axis straightness for three micro-milling facilities and also discovered an unknown 2 mu m amplitude undulation in one of them.

Place, publisher, year, edition, pages
OPTICAL SOC AMER, 2017
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-206258 (URN)10.1364/AO.56.002912 (DOI)000398174500047 ()28375261 (PubMedID)2-s2.0-85016553883 (Scopus ID)
Note

QC 20170512

Available from: 2017-05-12 Created: 2017-05-12 Last updated: 2017-06-30Bibliographically approved
Hyll, K., Farahani, F. & Mattsson, L. (2017). Comparison of optical instruments for fines and filler characterisation. Nordic Pulp & Paper Research Journal, 32(1), 97-109
Open this publication in new window or tab >>Comparison of optical instruments for fines and filler characterisation
2017 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 1, p. 97-109Article in journal (Refereed) Published
Abstract [en]

A laser diffractometer and three image-based instruments with spatial resolutions between 0.33 and 10 mu m/pixel were compared through measurements on calibration spheres and fine fractions comprising pulp fines of various types, neat PCC filler, and a mixture of fines and fillers. The laser diffractometer was highly sensitive to the keyed in refractive index of the samples, which was calculated based on volume-based mixing rules. A high-resolution flow cytometer and a high-resolution fibre analyser were found to be complimentary for measurements on neat fines and fines/filler mixtures, and superior to the laser diffractometer. When measuring on fillers, the laser diffractometer performed as well as the high-resolution flow cytometer, which was capable of resolving single filler particles. The sizes of the calibration spheres were overestimated by the image-based instruments, and the measurement uncertainty was high. The uncertainty was mainly attributed to the unrestricted particle motion, and the low accuracy to the dissimilar optical properties of the calibration material, compared to fines. Thus, calibration materials with shape and optical properties more similar to fines should be developed.

Place, publisher, year, edition, pages
AB SVENSK PAPPERSTIDNING, 2017
Keywords
Particle size analysis, Fines, Fillers, Calibration, Laser diffractometry, Flow Cytometry, Flow imaging, Imaging particle analysis, Fibre analyser, PCC
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-206313 (URN)10.3183/NPPRJ-2017-32-01-p097-109 (DOI)000398384400011 ()
Note

QC 20170505

Available from: 2017-05-05 Created: 2017-05-05 Last updated: 2017-05-05Bibliographically approved
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