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Publications (10 of 23) Show all publications
Wahl, J., Gren, P., Bergström, P., Lindbäck, T., Magnusson, M., Domeij, K. & Sjödahl, M. (2018). Comparison between process simulation and deformation measured by defocused speckle photography. In: M. Kujawińska ; L. R. Jaroszewicz (Ed.), Speckle 2018: VII International Conference On Speckle Metrology. Paper presented at SPECKLE 2018: VII International Conference on Speckle Metrology, 9-12 September 2018, Janów Podlaski, Poland.. SPIE - International Society for Optical Engineering, 10834, Article ID 108341K.
Open this publication in new window or tab >>Comparison between process simulation and deformation measured by defocused speckle photography
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2018 (English)In: Speckle 2018: VII International Conference On Speckle Metrology / [ed] M. Kujawińska ; L. R. Jaroszewicz, SPIE - International Society for Optical Engineering, 2018, Vol. 10834, article id 108341KConference paper, Published paper (Refereed)
Abstract [en]

Defocused laser speckle photography is used as a tool to measure the heat responses in a titanium component during laser heating. The evolution of the response is compared with a set of preprocessed Finite Element Simulations of the corresponding process with the aim to verify the simulation model and to find the simulation settings that best resemble the experimental results. The titanium component consists of a 300 x 100 mm2 substrate of thickness 3.2 mm on which a 200 x 30 x 11 mm3 ridge is built up using the laser metal deposition by wire process. The component is heated on the top of the ridge by a 300 W laser for 10 s and the deformation of the subtrate is followed throughout the heating-cooling cycle. The simulated deformation gradient is shown to resemble the measured response, and the magnitude of the response indicates that about 70 % of the laser power transferres into heat in the metal.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2018
Series
Proceedings of SPIE - the International Society for Optical Engineering, ISSN 0277-786X ; 10834
Keywords
Laser speckle, deformation, in-process measurement
National Category
Applied Mechanics Other Mechanical Engineering
Research subject
Experimental Mechanics; Computer Aided Design
Identifiers
urn:nbn:se:ltu:diva-71895 (URN)10.1117/12.2319384 (DOI)000455052600052 ()2-s2.0-85058383509 (Scopus ID)9781510622975 (ISBN)
Conference
SPECKLE 2018: VII International Conference on Speckle Metrology, 9-12 September 2018, Janów Podlaski, Poland.
Funder
VINNOVA
Available from: 2018-12-05 Created: 2018-12-05 Last updated: 2019-01-28Bibliographically approved
Bergström, P., Michael, F. & Sjödahl, M. (2018). Virtual projective shape matching in targetless CAD-based close-range photogrammetry for efficient estimation of specific deviations. Optical Engineering: The Journal of SPIE, 57(5), Article ID 053110.
Open this publication in new window or tab >>Virtual projective shape matching in targetless CAD-based close-range photogrammetry for efficient estimation of specific deviations
2018 (English)In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 57, no 5, article id 053110Article in journal (Refereed) Published
Abstract [en]

A concept for targetless, computer-aided design (CAD)-based, close-range photogrammetry for online shape inspection is introduced. The shape of an object, which is arbitrarily located on a conveyor belt, is to be measured and compared with its nominal shape as defined by a CAD model. For most manufactured objects, deviations are only measured at a few given comparison points. These deviations can be estimated using local photogrammetry based on a priori geometrical information given by the CAD model and the comparison points. Our method results in faster output with higher precision, because we do not generate a shape representation of the entire measured object using typical photogrammetric methods. Images depicting the object from convergent angles are captured by an array of cameras in a precalibrated network, and the CAD model is matched and aligned, within the projective geometry of the camera network, to the depicted object in the images without the use of targets. An algorithm for solving this virtual projective targetless shape matching problem is presented.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2018
Keywords
computer-aided design, close-range, matching, online, photogrammetry, shape
National Category
Reliability and Maintenance Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-68856 (URN)10.1117/1.OE.57.5.053110 (DOI)000435435300019 ()2-s2.0-85047752202 (Scopus ID)
Projects
SIVPRO
Note

Validerad;2018;Nivå 2;2018-05-28 (andbra)

Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2018-12-14Bibliographically approved
Bergström, P. & Edlund, O. (2017). Robust registration of surfaces using a refined iterative closest point algorithm with a trust region approach. Numerical Algorithms, 74(3), 755-779
Open this publication in new window or tab >>Robust registration of surfaces using a refined iterative closest point algorithm with a trust region approach
2017 (English)In: Numerical Algorithms, ISSN 1017-1398, E-ISSN 1572-9265, Vol. 74, no 3, p. 755-779Article in journal (Refereed) Published
Abstract [en]

The problem of finding a rigid body transformation, which aligns a set of data points with a given surface, using a robust M-estimation technique is considered. A refined iterative closest point (ICP) algorithm is described where a minimization problem of point-to-plane distances with a proposed constraint is solved in each iteration to find an updating transformation. The constraint is derived from a sum of weighted squared point-to-point distances and forms a natural trust region, which ensures convergence. Only a minor number of additional computations are required to use it. Two alternative trust regions are introduced and analyzed. Finally, numerical results for some test problems are presented. It is obvious from these results that there is a significant advantage, with respect to convergence rate of accuracy, to use the proposed trust region approach in comparison with using point-to-point distance minimization as well as using point-to-plane distance minimization and a Newton- type update without any step size control.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Mathematical Analysis
Research subject
Mathematics; Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-59969 (URN)10.1007/s11075-016-0170-3 (DOI)000395033800006 ()2-s2.0-84978159472 (Scopus ID)
Funder
VINNOVA
Note

Validerad; 2017; Nivå 2; 2017-02-24 (andbra)

Available from: 2016-10-26 Created: 2016-10-26 Last updated: 2018-11-15Bibliographically approved
Bergström, P., Fergusson, M., Folkesson, P., Runnemalm, A., Ottosson, M., Andersson, A. & Sjödahl, M. (2016). Automatic in-line inspection of shape based on photogrammetry. In: SPS16: . Paper presented at 7th Swedish Production Symposium, Lund, 25-27 October 2016. Lund: SPS16
Open this publication in new window or tab >>Automatic in-line inspection of shape based on photogrammetry
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2016 (English)In: SPS16, Lund: SPS16 , 2016, , p. 9Conference paper, Published paper (Refereed)
Abstract [en]

We are describing a fully automatic in-line shape inspection system for controlling the shape of moving objects on a conveyor belt. The shapes of the objects are measured using a full-field optical shape measurement method based on photogrammetry. The photogrammetry system consists of four cameras, a flash, and a triggering device. When an object to be measured arrives at a given position relative to the system, the flash and cameras are synchronously triggered to capture images of the moving object. From the captured images a point-cloud representing the measured shape is created. The point-cloud is then aligned to a CAD-model, which defines the nominal shape of the measured object, using a best-fit method and a feature-based alignment method. Deviations between the point-cloud and the CAD-model are computed giving the output of the inspection process. The computational time to create a point-cloud from the captured images is about 30 seconds and the computational time for the comparison with the CAD-model is about ten milliseconds. We report on recent progress with the shape inspection system.

Place, publisher, year, edition, pages
Lund: SPS16, 2016. p. 9
Series
Swedish Production Symposium ; 7
National Category
Mathematical Analysis Applied Mechanics Production Engineering, Human Work Science and Ergonomics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-60006 (URN)
Conference
7th Swedish Production Symposium, Lund, 25-27 October 2016
Projects
SIVPRO
Funder
VINNOVA
Available from: 2016-10-27 Created: 2016-10-27 Last updated: 2018-02-05Bibliographically approved
Bergström, P. (2016). Reliable updates of the transformation in the iterative closest point algorithm (ed.). Paper presented at . Computational optimization and applications, 63(2), 543-557
Open this publication in new window or tab >>Reliable updates of the transformation in the iterative closest point algorithm
2016 (English)In: Computational optimization and applications, ISSN 0926-6003, E-ISSN 1573-2894, Vol. 63, no 2, p. 543-557Article in journal (Refereed) Published
Abstract [en]

The update of the rigid body transformation in the iterative closest point (ICP) algorithm is considered. The ICP algorithm is used to solve surface registration problems where a rigid body transformation is to be found for fitting a set of data points to a given surface. Two regions for constraining the update of the rigid body transformation in its parameter space to make it reliable are introduced. One of these regions gives a monotone convergence with respect to the value of the mean square error and the other region gives an upper bound for this value. Point-to-plane distance minimization is then used to obtain the update of the transformation such that it satisfies the used constraint.

National Category
Computational Mathematics
Research subject
Scientific Computing
Identifiers
urn:nbn:se:ltu:diva-13681 (URN)10.1007/s10589-015-9771-3 (DOI)000370561000009 ()2-s2.0-84957847071 (Scopus ID)cf2fbf5f-f67c-4169-9679-18cbe15e027c (Local ID)cf2fbf5f-f67c-4169-9679-18cbe15e027c (Archive number)cf2fbf5f-f67c-4169-9679-18cbe15e027c (OAI)
Note
Validerad; 2016; Nivå 2; 20150616 (berper)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Bergström, P. (2015). Evaluation of NURBS Surfaces for Regular Structured Parameter Values (ed.). Paper presented at . Journal of Computing and Information Science in Engineering, 15(1), Article ID 11005.
Open this publication in new window or tab >>Evaluation of NURBS Surfaces for Regular Structured Parameter Values
2015 (English)In: Journal of Computing and Information Science in Engineering, ISSN 1530-9827, E-ISSN 1944-7078, Vol. 15, no 1, article id 11005Article in journal (Refereed) Published
Abstract [en]

The evaluation of surface points and derivatives of NURBS surfaces for parameter values that are regularly distributed in a rectangular structure is considered. Because of the regularity, parts of the computations can be done on just a small portion of all parameter values and computed data is stored and reused for many other parameter values. Hence, the evaluation of NURBS surfaces can be performed faster when the regularity is used. We are making a complexity analysis of the number of floating point operations, which is required for the evaluations. To get knowledge about how the evaluations perform in practice, we are doing a numerical experiment where we are measuring the runtime to obtain the output both by using ordinary evaluation of the NURBS surface and by making use of the regular structure. Making use of the regularity gives significantly faster output.

National Category
Computational Mathematics
Research subject
Scientific Computing
Identifiers
urn:nbn:se:ltu:diva-14072 (URN)10.1115/1.4028956 (DOI)000349754800005 ()2-s2.0-84940558817 (Scopus ID)d62fdb73-419d-4de8-8829-caa668b045dd (Local ID)d62fdb73-419d-4de8-8829-caa668b045dd (Archive number)d62fdb73-419d-4de8-8829-caa668b045dd (OAI)
Note
Validerad; 2015; Nivå 2; 20141109 (berper)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Khodadad, D., Bergström, P., Hällstig, E. & Sjödahl, M. (2015). Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements (ed.). Paper presented at . Applied Optics, 54(16), 5003-5010
Open this publication in new window or tab >>Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements
2015 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 54, no 16, p. 5003-5010Article in journal (Refereed) Published
Abstract [en]

The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18  mm×18  mm.

Keywords
digital holography, Speckle imaging, Interferometry, metrology, calibration, surface measurement, multiplexing, single shot, Technology - Engineering physics, Teknikvetenskap - Teknisk fysik
National Category
Applied Mechanics Computational Mathematics
Research subject
Experimental Mechanics; Scientific Computing
Identifiers
urn:nbn:se:ltu:diva-10347 (URN)10.1364/AO.54.005003 (DOI)000355555700009 ()2-s2.0-84942372341 (Scopus ID)924b8540-da35-4fa3-90a0-89f1ac2a9d3d (Local ID)924b8540-da35-4fa3-90a0-89f1ac2a9d3d (Archive number)924b8540-da35-4fa3-90a0-89f1ac2a9d3d (OAI)
Note
Validerad; 2015; Nivå 2; 20150522 (davkho)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Khodadad, D., Bergström, P., Hällstig, E. & Sjödahl, M. (2014). Dual-wavelength digital holography: single shot calibration (ed.). In: (Ed.), (Ed.), Interferometry XVII: Techniques and Analysis. Paper presented at Interferometry XVII : Techniques and Analysis 17/08/2014 - 21/08/2014. Bellingham, Wash: SPIE - International Society for Optical Engineering, Article ID 920305.
Open this publication in new window or tab >>Dual-wavelength digital holography: single shot calibration
2014 (English)In: Interferometry XVII: Techniques and Analysis, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2014, article id 920305Conference paper, Published paper (Refereed)
Abstract [en]

In an on line shape measurement in disturbed environment, use of many wavelengths in order to avoid phase ambiguity may become a problem as it is necessary to acquire all holograms simultaneously due to environmental disturbances. Therefore to make the shape data available the different holograms have to be extracted from a single recorded image in spectral domain. Appropriate cut areas in the Fourier method are therefore of great importance for decoding information carried by different wavelengths. Furthermore using different laser sources, induces aberration and pseudo phase changes which must be compensated. To insure any phase change is only because of the object shape, calibration is therefore indispensable. For this purpose, effects of uncontrolled carrier frequency filtering are discussed. A registration procedure is applied using minimum speckle displacements to find the best cut area to extract and match the interference terms. Both holograms are numerically propagated to a focus plane to avoid any unknown errors. Deviations between a reference known plate and its measurement are found and used for calibration. We demonstrate that phase maps and speckle displacements can be recovered free of chromatic aberrations. To our knowledge, this is the first time that a single shot dual wavelength calibration is reported by defining a criteria to make the spatial filtering automatic avoiding the problems of manual methods. The procedure is shown to give shape accuracy of 35μm with negligible systematic errors using a synthetic wavelength of 1.1 mm.

Place, publisher, year, edition, pages
Bellingham, Wash: SPIE - International Society for Optical Engineering, 2014
Series
Proceedings of S P I E - International Society for Optical Engineering, ISSN 0277-786X ; 9203
Keywords
digital holography, dual-wavelength, single shot, calibration, speckle displacements, on line shape measurement, image correlation, Technology - Engineering physics, Teknikvetenskap - Teknisk fysik
National Category
Applied Mechanics Computational Mathematics
Research subject
Experimental Mechanics; Scientific Computing
Identifiers
urn:nbn:se:ltu:diva-39188 (URN)10.1117/12.2062101 (DOI)000354364200005 ()2-s2.0-84922880623 (Scopus ID)dd50de19-cde8-41f8-bbb9-c54962ee2580 (Local ID)9781628412314 (ISBN)dd50de19-cde8-41f8-bbb9-c54962ee2580 (Archive number)dd50de19-cde8-41f8-bbb9-c54962ee2580 (OAI)
Conference
Interferometry XVII : Techniques and Analysis 17/08/2014 - 21/08/2014
Note
Godkänd; 2014; 20140827 (davkho)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-07-10Bibliographically approved
Bergström, P., Khodadad, D., Hällstig, E. & Sjödahl, M. (2014). Dual-wavelength digital holography: single-shot shape evaluation using speckle displacements and regularization (ed.). Paper presented at . Applied Optics, 53(1), 123-131
Open this publication in new window or tab >>Dual-wavelength digital holography: single-shot shape evaluation using speckle displacements and regularization
2014 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 53, no 1, p. 123-131Article in journal (Refereed) Published
National Category
Computational Mathematics Applied Mechanics
Research subject
Scientific Computing; Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-13247 (URN)10.1364/AO.53.000123 (DOI)000329034300018 ()2-s2.0-84891611011 (Scopus ID)c7007a95-2668-4842-9dbb-89edbe94a0fa (Local ID)c7007a95-2668-4842-9dbb-89edbe94a0fa (Archive number)c7007a95-2668-4842-9dbb-89edbe94a0fa (OAI)
Note
Validerad; 2014; 20131210 (berper)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Bergström, P. & Edlund, O. (2014). Robust registration of point sets using iteratively reweighted least squares (ed.). Computational optimization and applications, 58(3), 543-561
Open this publication in new window or tab >>Robust registration of point sets using iteratively reweighted least squares
2014 (English)In: Computational optimization and applications, ISSN 0926-6003, E-ISSN 1573-2894, Vol. 58, no 3, p. 543-561Article in journal (Refereed) Published
Abstract [en]

Registration of point sets is done by finding a rotation and translation that produces a best fit between a set of data points and a set of model points. We use robust M-estimation techniques to limit the influence of outliers, more specifically a modified version of the iterative closest point algorithm where we use iteratively re-weighed least squares to incorporate the robustness. We prove convergence with respect to the value of the objective function for this algorithm. A comparison is also done of different criterion functions to figure out their abilities to do appropriate point set fits, when the sets of data points contains outliers. The robust methods prove to be superior to least squares minimization in this setting.

National Category
Computational Mathematics
Research subject
Scientific Computing
Identifiers
urn:nbn:se:ltu:diva-3921 (URN)10.1007/s10589-014-9643-2 (DOI)000337084900002 ()2-s2.0-84904999267 (Scopus ID)1c497761-d55b-4956-85e6-e160c9668a13 (Local ID)1c497761-d55b-4956-85e6-e160c9668a13 (Archive number)1c497761-d55b-4956-85e6-e160c9668a13 (OAI)
Note

Validerad; 2014; 20140206 (berper)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-12-14Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7566-3656

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