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  • 1.
    Adolfsson, Stefan
    et al.
    Luleå tekniska universitet.
    Ericsson, Klas
    Luleå tekniska universitet.
    Grennberg, Anders
    Automatic detection of burn-through in GMA welding using a parametric model1996In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 10, no 5, p. 633-651Article in journal (Refereed)
    Abstract [en]

    This paper addresses the problem of automatic detection of burn-through in weld joints. Gas metal arc (GMA) welding with pulsed current is used, and welding voltage and current are recorded. As short-circuitings are common between the welding electrode and the work piece during burn-through, a short-circuit detector is developed to detect these events. To detect another specific characteristic of burn-through - this detector is combined with a square-law detector. This second detector is based on a non-linear modification of an autoregressive model with extra input (ARX-model) of the welding process. The results obtained from this compound detector indicate that it is possible to detect burn-through in the welds automatically. The work also indicates that it is possible to design an on-line monitoring system for robotic GMA welding.

  • 2.
    Almquist, Lars-Olov
    et al.
    Lunds universitet.
    Olsson, Lennart
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems. Luleå tekniska universitet.
    Grennberg, Anders
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Holmner, Nils-Gunnar
    Lunds universitet.
    Registration and analysis of sound from the disintegration of kidney stones with acoustic shock waves1991In: WFUMB Symposium on Safety and Standardisation in Medical Ultrasound: issues and recommendations regarding thermal mechanisms for biological effects of ultrasound ; Hornbaek, Denmark, 30 August-1 September 1991 / [ed] Stan B. Barnett, New York: Pergamon Press, 1991Conference paper (Refereed)
  • 3.
    Andersson, Lennart
    et al.
    Luleå tekniska universitet.
    Grennberg, Anders
    Hedberg, Torbjörn
    Luleå tekniska universitet.
    Näslund, Reinhold
    Persson, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    von Sydow, Björn
    Luleå tekniska universitet.
    Linjär algebra med geometri1990 (ed. 2)Book (Other (popular science, discussion, etc.))
  • 4.
    Andersson, Lennart
    et al.
    Luleå tekniska universitet.
    Grennberg, Anders
    Hedberg, Torbjörn
    Luleå tekniska universitet.
    Näslund, Reinhold
    Persson, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    von Sydow, Björn
    Luleå tekniska universitet.
    Linjär algebra med geometri1986Book (Other (popular science, discussion, etc.))
  • 5.
    Andersson, Lennart
    et al.
    Luleå tekniska universitet.
    Grennberg, Anders
    Hedberg, Torbjörn
    Luleå tekniska universitet.
    Näslund, Reinhold
    Persson, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    von Sydow, Björn
    Luleå tekniska universitet.
    Söderkvist, Inge
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Linjär algebra med geometri1999Book (Other (popular science, discussion, etc.))
  • 6.
    Carlson, Johan E.
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Grennberg, Anders
    A new algorithm for constructing optimal experimental designs1998Report (Other academic)
    Abstract [en]

    In any experimental science we are sometimes confronted with new experimental situations, where underlying physical models are unknown. After a first attempt at identifying physical variables that could effect the experimental result, we need to perform what is called a screening experiment. The objective is to conduct a small number of experiments that span as much of the experimental space as possible, to merit further experiments in smaller, more promising test systems. In this report we present an algorithm that, given a set of possible experiments, selects a subset of these. The selection is designed to cover as much variation as possible in the experimental space, and to assure a minimized expected mean squared error in the model parameter estimation. We verified the algorithm with an example taken from organic synthesis.

  • 7.
    Carlson, Johan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Grennberg, Anders
    Ultrasonic measurements of particle concentration in a multiphase flow1999In: Proceedings: 1999 IEEE Ultrasonics Symposium : October 17 - 20, 1999, Caesars Tahoe, Nevada, USA ; an international symposium / [ed] S. C. Schneider, Piscataway, NJ: IEEE Communications Society, 1999, p. 757-760Conference paper (Refereed)
    Abstract [en]

    Non-invasive measurements of multiphase flows have several important applications in industry. In this paper we present a method that uses pulsed ultrasound and two small receivers to determine the mass concentration of iron ore particles in water. The proposed method is based on the assumption that when ultrasound is transmitted through a scattering medium, the shape of the energy lobe changes. In this paper we use two receivers to monitor how the lobe changes. We show with experiments how the proposed method can be used to determine particle mass fractions from 3 percent and up, with an accuracy of ±1 percent of the mass fraction. In the experiments we used a 3 MHz transmitter and two receivers, one along the acoustical axis and the other 6 mm off-axis, to measure the mass fraction of a polydisperse suspension of iron ore powder in water.

  • 8.
    Carlson, Johan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Grennberg, Anders
    Delsing, Jerker
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Multiphase flow characterized by scattering of ultrasound1998In: Proceedings - The 9th International Conference on Flow Measurement: FLOMEKO / [ed] Jerker Delsing, Kista: ITF , 1998, p. 493-497Conference paper (Refereed)
  • 9.
    Carlson, Rolf
    et al.
    Department of Chemistry, University of Tromsoe.
    Carlson, Johan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Grennberg, Anders
    A novel approach for screening discrete variations in organic synthesis2001In: Journal of Chemometrics, ISSN 0886-9383, E-ISSN 1099-128X, Vol. 15, no 5, p. 455-474Article in journal (Refereed)
    Abstract [en]

    In this paper we present a general strategy for screening discrete variations in organic synthesis. The strategy is based upon principal properties, i.e. principal component characterization of the constituents defining the reaction system. The first step is to select subsets of test items from each class of constituents defining the reaction space, i.e. substrates, reagents, solvents, catalysts, etc., so that the selected items from each class cover the properties considered. The second step is to construct a candidate matrix which contains all possible combinations of the items in the subsets. This matrix is a full multilevel factorial design. The third step is to assign a tentative model for the screening experiment and to construct the corresponding candidate model matrix. The fourth step is to select experiments to yield an experimental design that spans the variable space efficiently and that also gives good estimates of the model parameters. We present an algorithm that uses singular value decomposition to select experiments. The proposed strategy is then illustrated with an example of the Fischer indole synthesis.

  • 10.
    Carlson, Rolf
    et al.
    Tromsø University.
    Carlson, Johan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Grennberg, Anders
    Novel and optimal strategy for screening discrete variations in organic synthesis1999Conference paper (Refereed)
  • 11. Grennberg, Anders
    Measuring subsample time delay differences in narrowband ultrasonic echoes1994In: Norsig 94: Nordic Signal Processing Symposium ; Ålesund, Norway, June 2 - June 4 1994 / [ed] John M. Leirvik; Anders Wahlin, Trondheim: Norsk forening for signalbehandling , 1994, p. 290-293Conference paper (Refereed)
    Abstract [en]

    In many areas the time delay of arrival (TDOA) is desired. In the case of narrowband signals we us a new fast and simple method to estimate small time delays. This method has good accuracy for delays on the order of fractions of the sample interval. It is based on forming the scalar product of the signal and its Hilbert transform. The method can be applied to narrowband signals where the measurements are repeatable, such as ultrasonic imaging. In ultrasonic applications, due to fluctuations in the insonified media, especially in the air, a small random time shift may be present. By placing a wire at a fixed distance from the transducer, so small that it does not disturb the main echo from the surface but still gives a reference echo strong enough to use our method, we make corrections to the arrival time of the main echo.

  • 12. Grennberg, Anders
    et al.
    Almquist, Lars-Olof
    Lunds universitet.
    Holmner, Nils-Gunnar
    Lunds universitet.
    Olsson, Lennart
    Luleå tekniska universitet.
    Secondary sound classification for the assessment of focus positioning in shock-wave lithotripsy1993In: IX Nordic Meeting on Medical and Biological Engineering: abstracts ; regional meeting of the IFMBE., Lund: Medicinsk Teknik , 1993Conference paper (Other academic)
    Abstract [en]

    A problem encountered when using acoustic shock-waves for kidney stone disintegration is that the positioning of the focus relative to a stone, for the best possible fragmenting effect, is crtitical. The standard methods for focus positioning are ultrasound or x-ray imaging. These methods are, however, not always sufficient and a better indication of a well positioned focus would be valuable. The secondary sound emitted as a result of each shock-wave has been found to contain valuable information. A skilled operator is able to hear from the timbre of these sound pulses when the positioning of the focus is adequate. A method for the automatic evaluation of secondary sounds, using a computer, is developed in this work.

  • 13. Grennberg, Anders
    et al.
    Sandell, Magnus
    Luleå tekniska universitet.
    Estimation of subsample time delay differences in narrowband ultrasonic echoes using the Hilbert correlation1994Report (Other academic)
    Abstract [en]

    In many areas the time delay of arrival (TDOA) is desired. Conventional estimators usually have the property of breaking down for low SNR. In the case of narrowbanded signals we propose a fast and simple method to estimate the small time delays. The method is shown to have the same accuracy as conventional methods for small delays and high SNR while it performs better for low SNR. It is based on using the Hilbert transform in correlation between two signals. Apart from using it for better resolution in TDOA, it may also be used in applications with narrowbanded signals where the measurements are repeatable, such as ultrasonic imaging and ECG. In ultrasonic applications, due to fluctuations in the insonified media, a small random time shift may be present causing the signals to be misaligned in time. Averaging signals under these conditions will result in a distortion of the signal shape. We propose an averaging method to avoid this and to accomplish a higher SNR without the distortion. Simulations and experiments from ultrasonic applications are presented.

  • 14. Grennberg, Anders
    et al.
    Sandell, Magnus
    Luleå tekniska universitet.
    Estimation of subsample time delay differences in narrowband ultrasonic echoes using the Hilbert transform correlation1994In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 41, no 5, p. 588-595Article in journal (Refereed)
    Abstract [en]

    In many areas the time delay of arrival (TDOA) is desired. In the case of narrowband signals we propose a fast and simple method to estimate small time delays. This method is shown to have the same or better accuracy as the cross correlation methods for small delays in the order of fractions of the sample interval. It is based on using the Hilbert transform in correlation between two signals and consists of only one scalar product, which makes it fast. It may also be used in applications with narrowband signals where the measurements are repeatable, such as ultrasonic imaging and nondestructive testing. In ultrasonic applications, due to fluctuations in the insonified media, a small random time shift may be present causing the signals to be misaligned in time. Averaging signals under these conditions will result in a distortion of the signal shape. We propose an averaging method to avoid this and to accomplish a higher SNR without the distortion. Simulations and experiments from ultrasonic applications are presented.

  • 15. Grennberg, Anders
    et al.
    Sandell, Magnus
    Luleå tekniska universitet.
    Experimental determination of the single point echo of an ultrasonic transducer using a tomographic approach1992In: Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society: Paris, France, October 29-November 1, 1992, Piscataway, NJ: IEEE Communications Society, 1992, Vol. 5, p. 2151-2152Conference paper (Refereed)
    Abstract [en]

    The impulse response method is often used to study the ultrasonic field radiated by planar or gently curved transducers. This, however, requires one transmitting and one receiving transducer which has to be placed with great accuracy in the ultrasonic field. Here we propose a measuring method with only one transducer which acts both as transmitter and receiver. Echoes from sliding halfplanes are registered and by using tomographic methods, the echo from a single point in the same plane as the halfplanes can then be calculated. Beside the ultrasonic field, these calculations will yield us the transducer's characteristics. These can be used to extract further information from an echo of an arbitrary surface, such as the gradient of the surface

  • 16.
    Olsson, Lennart
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Almquist, Lars-Olov
    Department of Biomedical Engineering, Lund University.
    Grennberg, Anders
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Holmer, Nils-Gunnar
    Department of Biomedical Engineering, Lund University.
    Analysis and classification of secondary sounds from the disintegration of kidney-stones with acoustic shock waves1991In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 17, no 5, p. 491-495Article in journal (Refereed)
    Abstract [en]

    Secondary sound emission, partly in the audible frequency range, from shock wave disintegration of kidney stones has been recorded during the treatment of two patients. A skilled operator can determine by listening if the stone is hit by the shock-wave or not. Spectral analysis of these recordings show differences between sounds which can be used to evaluate the fragmenting effect on the stone. Results are presented of a preliminary discriminating method based on parameters in an autoregressive signal model.

  • 17.
    Sandell, Magnus
    et al.
    Luleå tekniska universitet.
    Grennberg, Anders
    Estimation of the spatial impulse response of an ultrasonic transducer using a tomographic approach1995In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 98, no 4, p. 2094-2103Article in journal (Refereed)
    Abstract [en]

    The impulse response method is often used to study the ultrasonic field radiated by planar or gently curved transducers. These investigations can be extended to include the reflected echoes from point reflectors, which can be used in syntesizing echoes from reflectors of known shapes. The single point echo can be measured directly but there are however certain problems associated with this. This paper proposes an alternative method to estimate the echo from a point-like reflector by measuring the echoes from sliding halfplanes. Using a tomographic approach, the single point echo is estimated from these measurements. To perform the tomographic inversion, a truncated weighted Singular Value Decomposition (SVD) is used in order to catch essential features of the ultrasonic echoes, where the weight functions are chosen specially to suit our application. Numerical solutions are given for the chosen weight functions and an error analysis is carried out.

  • 18.
    Sandell, Magnus
    et al.
    Luleå tekniska universitet.
    Grennberg, Anders
    Estimation of ultrasonic point echoes1993In: Radiovetenskaplig konferens på Lunds tekniska högskola 5-7 april 1993: sammanfattning av posters och föredrag / RVK-93, Lund: Lunds tekniska högskola , 1993, p. 185-188Conference paper (Refereed)
    Abstract [en]

    One important parameter for an ultrasonic transducer is the echo it yields from a pointlike reflector. It can be measured directly but there are however certain problems connected with this. We propose an alternative method to calculate the echo from a pointlike reflector by measuring the echoes from sliding halfplanes. Using a tomographic way of reasoning, we can calculate the point echoes from these measurements. Two methods to numerically perform this inversion are dealt with. The first one is a regularization technique used in conjunction with the analytical inversion formula. The other approach was to find basis functions that are suitable for the inversion of the measurements. These basis functions depend on which norm and weight function you choose. Numerical solutions are given for chosen weight functions and the inversion is shown for both methods.

  • 19.
    Sandell, Magnus
    et al.
    Luleå tekniska universitet.
    Grennberg, Anders
    Spatial decomposition of the ultrasonic echo using a tomographic approach: Part A: The regularization method1994Report (Other academic)
    Abstract [en]

    One of the most common methods for making images with ultrasound is to use the pulse-echo method. Under the assumption of a homogeneous medium, the Time-of-flight (TOF), i.e.\ the time elapsed between transmission and reception of an ultrasonic pulse, is proportional to the distance. Methods for estimating the TOF assumes that the echoes only differ in arrival time. If the shape of the echo is dependent on where on the surface it is reflected, this method can yield an inaccurate image. One parameter of the ultrasonic transducer that could be used to improve this method is the {\em single point echo} (SPE), i.e. the echo from a point reflector. The direct measurement of this echo is however not possible due to practical problems and diffraction effects. In this report, we propose a method to experimentally determine the SPE. We use a tomographic approach where we can determine the SPE from a series of measured echoes from sliding halfplanes.

  • 20.
    Sandell, Magnus
    et al.
    Luleå tekniska universitet.
    Grennberg, Anders
    Spatial decomposition of the ultrasonic echo using a tomographic approach: Part B: The singular system methods1994Report (Other academic)
  • 21.
    Wahlberg, Patrik
    et al.
    Lunds universitet.
    Grennberg, Anders
    Salomonsson, Göran
    Lunds universitet.
    Feature extraction from multichannel EEG transients for clustering purposes1995In: 1995 IEEE Engineering in Medicine and Biology: 17th Annual Conference and 21st Canadian Medical and Biological Engineering Conference, Montréal, Canada, September 20-23, 1995, Piscataway, NJ: IEEE Communications Society, 1995, Vol. 2, p. 915-916Conference paper (Refereed)
    Abstract [en]

    This paper treats the problem of clustering multichannel EEG transients occurring in epilepsy, so called spikes. The authors present a new method for feature extraction which is an expansion along an orthonormal set of matrices, obtained from truncated SVD and Gram-Schmidt orthogonalization. The method is compared to a method used earlier where each channel was Hermite function expanded. The result is that using the same expansion order the new method represents a set of spikes with higher fidelity than the Hermite function method. The output from the feature extraction is a vector for each spike in a set. The vectors from a set is clustered with the standard NM algorithm. Two sets of spikes have been investigated, both being clustered in appearance

1 - 21 of 21
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