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  • 1.
    Broberg, Patrik
    University West, Department of Engineering Science, Division of Process and Product Development.
    Towards Automation of Non-Destructive Testing of Welds2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    All welding processes can give rise to defects that will weaken the joint and can lead to failure of the welded structure. Because of this, non-destructive testing (NDT) of welds have become increasingly important to ensure the structural integrity when the material becomes thinner and stronger and welds become smaller; all to reduce weight in order to save material and reduce emissions due to lighter constructions.

    Several NDT methods exists for testing welds and they all have their advantages and disadvantages when it comes to the types and sizes of defects that are detectable, but also in the ability to automate the method. Several methods were compared using common weld defects to determine which method or methods were best suited for automated NDT of welds. The methods compared were radiography, phased array ultrasound, eddy current, thermography and shearography. Phased array ultrasound was deemed most suitable for detecting the weld defects used in the comparison and for automation and was therefore chosen to be used in the continuation of this work. Thermography was shown to be useful for detecting surface defects; something not easily detected using ultrasound. A combination of these techniques will be able to find most weld defects of interest.

    Automation of NDT can be split into two separate areas; mechanisation of the testing and automation of the analysis, both presenting their own difficulties. The problem of mechanising the testing has been solved for simple geometries but for more general welds it will require a more advance system using an industrial robot or similar. Automation of the analysis of phased array ultrasound data consists of detection, sizing, positioning and classification of defects. There are several problems to solve before a completely automatic analysis can be made, including positioning of the data, improving signal quality, segmenting the images and classifying the defects. As a step on the way towards positioning of the data, and thereby easing the analysis, the phase of the signal was studied. It was shown that the phase can be used for finding corners in the image and will also improve the ability to position the corner as compared to using the amplitude of the signal. Further work will have to be done to improve the signal in order to reliably analyse the data automatically.

  • 2.
    Guevara-Garca, Alfredo
    et al.
    McMaster University, Department of Chemistry and Chemical Biology.
    Echegaray, Eleonora
    Pontificia Universidad Catlica de Chile, Facultad de Qumica, Laboratorio de Qumica Terica Computacional (QTC).
    Toro-Labbe, Alejandro
    Pontificia Universidad Catlica de Chile, Facultad de Qumica, Laboratorio de Qumica Terica Computacional (QTC).
    Jenkins, Samantha
    University West, School of Business, Economics and IT, Division of Computer Science and Informatics.
    Kirk, Steven R.
    University West, School of Business, Economics and IT, Division of Computer Science and Informatics.
    Ayers, Paul W.
    McMaster University, Department of Chemistry and Chemical Biology.
    Pointing the way to the products Comparison of the stress tensor and the second-derivative tensor of the electron density2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 23, p. 234106-Article in journal (Refereed)
    Abstract [en]

    The eigenvectors of the electronic stress tensor can be used to identify where new bond paths form in a chemical reaction. In cases where the eigenvectors of the stress tensor are not available, the gradient-expansion- approximation suggests using the eigenvalues of the second derivative tensor of the electron density instead; this approximation can be made quantitatively accurate by scaling and shifting the second-derivative tensor, but it has a weaker physical basis and less predictive power for chemical reactivity than the stress tensor. These tools provide an extension of the quantum theory of atoms and molecules from the characterization of molecular electronic structure to the prediction of chemical reactivity. © 2011 American Institute of Physics.

  • 3.
    Gustavsson Christiernin, Linn
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Computer Science.
    Bäckman, Rickard
    University West, Department of Technology, Mathematics and Computer Science, Division for Computer Science.
    Gidmark, Mikael
    University West, Department of Technology, Mathematics and Computer Science, Division for Computer Science.
    Persson, Ann
    University West, Department of Technology, Mathematics and Computer Science, Division for Computer Science.
    iLayer: MLD in an operating system interface2006In: AVI: Proceedings of the working conference on advanced visual interfaces  (AVI '06 ) Venezia, Italy   May 23 - 26, 2006, ACM , 2006, p. 87-90Conference paper (Refereed)
  • 4.
    Ryberg, Anders
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Christiansson, Anna-Karin
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Eriksson, Kenneth
    University West, Department of Technology, Mathematics and Computer Science, Division for Mathematics and Sciences.
    Lennartson, Bengt
    Chalmers University of Technology.
    A new Camera Model and Algorithms for higher Accuracy and better Convergence in Vision-based Pose Calculations2006In: Mechatronics and Automation, Proceedings of the 2006 IEEE International Conference on, 2006, p. 194-199Conference paper (Refereed)
    Abstract [en]

    This paper presents novel strategies for better calibration and pose calculations of a system for determining the pose, i.e. position and orientation, of a camera. The system in question has a camera aimed to be placed on the hand of an industrial robot for welding, but is useful for any application with a need for measuring position and/or orientation. To calculate the pose of the camera circular reference points that can be recognized in the images are distributed in the working area. From their 2D image coordinates the 6D pose of the camera can be calculated. First the system is calibrated, i.e. the positions of the reference points and the camera parameters are determined. This is done by first taking images of the reference points from different locations, and then do a "total calibration" procedure to calculate the unknown parameters. For a specific system, called PosEye, it was concluded that the accuracy needs to be improved for welding applications. Also a method for making the calculations converge more easily, was needed. To meet these demands a new camera model is proposed, and three preprocessing calculation steps are presented. The new camera model increases accuracy by considering more distortion effects. The preprocessing steps give better initial values for more robust convergence of the algorithms and increased accuracy

  • 5.
    Ryberg, Anders
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Christiansson, Anna-Karin
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Eriksson, Kenneth
    University West, Department of Technology, Mathematics and Computer Science, Division for Mathematics and Sciences.
    Lennartson, Bengt
    Chalmers University of Technology.
    A new Camera Model for Higher Accuracy Pose Calculations2006In: Industrial Electronics, 2006 IEEE International Symposium on Industrial Electronics, 2006, p. 2798-2802Conference paper (Refereed)
    Abstract [en]

    A position and orientation (pose) measurement system is being developed. The system, called PosEye, is based on a camera and by using the information in the image, the pose of the camera taking the image can be calculated. The system is aimed to be placed on an industrial robot for welding, but it is flexible and can also be used in many other applications. The accuracy has been measured, and it is concluded that the accuracy needs to be improved for welding applications. To make the pose measurement, reference points, that can be recognized in the image, are distributed in the working area. The positions of the reference points and the parameters in a camera model are initially computed automatically from sample images from a number of directions to the reference points. After this calibration, the pose can be calculated at each sample image. For high accuracy there is a need to have a camera model that takes into account a number of distortion effects, which are further developed in this paper. The new model is used to express an optimization cost function that can be used for both the pose calculation, and the extensive calibration, that determines camera parameters in the camera model and the positions of the reference points

  • 6.
    Ryberg, Anders
    et al.
    University West, Department of Engineering Science.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Production Systems.
    Eriksson, Kenneth
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Camera Modelling and Calibration - with Applications2008In: Computer Vision / [ed] Zhihui, X., Vienna: I-Tech Education and Publishing , 2008, p. 303-332Chapter in book (Other academic)
  • 7.
    Ryberg, Anders
    et al.
    University West, Department of Engineering Science.
    Lennartson, Bengt
    University West, Department of Engineering Science.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science.
    Asplund, Lars
    Mälardalen University.
    Ericsson, Mikael
    University West, Department of Engineering Science.
    Analysis and evaluation of a general camera model2011In: Computer Vision and Image Understanding, ISSN 1077-3142, E-ISSN 1090-235X, Vol. 115, no 11, p. 1503-1515Article in journal (Refereed)
    Abstract [en]

    A versatile General Camera Model, GCM, has been developed, and is described in detail. The model is general in the sense that it can capture both fisheye and conventional as well as catadioptric cameras in a unified framework. The camera model includes efficient handling of non-central cameras as well as compensations for decentring distortion. A novel way of analysing radial distortion functions of camera models leads to a straightforward improvement of conventional models with respect to generality, accuracy and simplicity. Different camera models are experimentally compared for two cameras with conventional and fisheye lenses, and the results show that the overall performance is favourable for the GCM.

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