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  • 51. Eriksson, Håkan
    et al.
    Börjesson, Per Ola
    Holmer, Nils-Gunnar
    Modelling of Waveform Deformation and Time-of-Flight Estimation, with application to the Ultrasonic Pulse-Echo Method1993Report (Other academic)
  • 52. Eriksson, Håkan
    et al.
    Börjesson, Per Ola
    Holmer, Nils-Gunnar
    Modelling of Waveform Deformation in Time-of-Flight Estimation With Application to the Ultrasonic Pulse-echo Method1992Conference paper (Refereed)
    Abstract [en]

    The authors address the problem of estimating the time-of-flight of ultrasonic pulse-echo signals. The shape of the received waveform is modelled by a linear combination of base signals. A method for obtaining these base signals is presented. The method presumes that the excitation signal is narrow-banded in the frequency domain.

  • 53. Eriksson, Håkan
    et al.
    Börjesson, Per Ola
    Holmer, Nils-Gunnar
    Modelling of Waveform Shape Uncertianties and Time-of-Flight Estimation, with application to the Ultrasonic Pulse-Echo Method1993Conference paper (Refereed)
  • 54. Eriksson, Håkan
    et al.
    Börjesson, Per Ola
    Holmer, Nils-Gunnar
    Ögondjupmätning med ultraljud1990Report (Other academic)
  • 55. Eriksson, Håkan
    et al.
    Ödling, Per
    Börjesson, Per Ola
    Simultaneous Time-of-Flight and Channel Estimation Using a Stochastic Channel Model1993Conference paper (Refereed)
  • 56. Eriksson, Håkan
    et al.
    Ödling, Per
    Börjesson, Per Ola
    Holmer, Nils-Gunnar
    A Robust Correlation Receiver for Distance Estimation1994In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 41, no 5, p. 596-603Article in journal (Refereed)
    Abstract [en]

    Many methods for distance estimation, such as the ultrasonic pulse-echo method, involve the estimation of a Time-of-Flight (TOF). In this paper, a signal model is developed that, apart from the TOF, accounts for an unknown, linear frequency dependent distortion as well as for additive noise. We derive a TOF estimator for this model based on the criteria of Maximum Likelihood. The resulting receiver can be seen as an extension or generalization of the well known cross-correlation, or ''matched filter'', estimator described, e.g., by Nilsson in [12]. The novel receiver is found to be more robust against unknown pulse shape distortion than the cross-correlation estimator, giving less biased TOF estimates. Also, bias versus noise sensitivity can be controlled by proper model order selection.

  • 57.
    Garcia-Zubia, Javier
    et al.
    Univ Deusto, ESP.
    Cuadros, Jordi
    Univ Ramon Llull, ESP.
    Romero, Susana
    Univ Deusto, ESP.
    Hernandez-Jayo, Unai
    Univ Deusto, ESP.
    Orduna, Pablo
    Univ Deusto, ESP.
    Guenaga, Mariluz
    Univ Deusto, ESP.
    Gonzalez-Sabate, Lucinio
    Univ Ramon Llull, ESP.
    Gustavsson, Ingvar
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing. Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering. Blekinge Institute of Technology, Department of Signal Processing.
    Empirical Analysis of the Use of the VISIR Remote Lab in Teaching Analog Electronics2017In: IEEE Transactions on Education, ISSN 0018-9359, E-ISSN 1557-9638, Vol. 60, no 2, p. 149-156Article in journal (Refereed)
    Abstract [en]

    Remote laboratories give students the opportunity of experimenting in STEM by using the Internet to control and measure an experimental setting. Remote laboratories are increasingly used in the classroom to complement, or substitute for, hands-on laboratories, so it is important to know its learning value. While many authors approach this question through qualitative analyses, this paper reports a replicated quantitative study that evaluates the teaching performance of one of these resources, the virtual instrument systems in reality (VISIR) remote laboratory. VISIR, described here, is the most popular remote laboratory for basic analog electronics. This paper hypothesizes that use of a remote laboratory has a positive effect on students' learning process. This report analyzes the effect of the use of VISIR in five different groups of students from two different academic years (2013-2014 and 2014-2015), with three teachers and at two educational levels. The empirical experience focuses on Ohm's Law. The results obtained are reported using a pretest and post-test design. The tests were carefully designed and analyzed, and their reliability and validity were assessed. The analysis of knowledge test question results shows that the post-test scores are higher that the pretest. The difference is significant according to Wilcoxon test (p < 0.001), and produces a Cohen effect size of 1.0. The VISIR remote laboratory's positive effect on students' learning processes indicates that remote laboratories can produce a positive effect in students' learning if an appropriate activity is used.

  • 58.
    Gothberg, Mattias
    et al.
    Atlas Copco, SWE.
    Enblom, Samuel
    Atlas Copco, SWE.
    Rantakokko, Renny
    Atlas Copco, SWE.
    Håkansson, Lars
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing. Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering. Blekinge Institute of Technology, Department of Signal Processing. Blekinge Institute of Technology, School of Engineering, Department of Signal Processing. Blekinge Inst Technol, Dept Appl Signal Proc, Karlskrona, Sweden..
    EFFICIENT MULTI CHANNEL VIBRATION MEASUREMENT-SYSTEMATIC APPROACH2016In: PROCEEDINGS OF THE 23RD INTERNATIONAL CONGRESS ON SOUND AND VIBRATION: FROM ANCIENT TO MODERN ACOUSTICS / [ed] Vogiatzis, K Kouroussis, G Crocker, M Pawelczyk, M, INT INST ACOUSTICS & VIBRATION , 2016Conference paper (Refereed)
    Abstract [en]

    In Atlas Copco a wide range of machines is produced from surface drill rigs, exploration drill rigs, underground drill rigs both for mining and construction to underground loader and haulers for mines. Recently new rock excavation methods have developed in cooperation with large mining companies. The machines are produced in low volume and often customized although having a modular approach. Time for validation is limited due to machines available for test are planned for customer delivery. It is on regular basis needed to validate and investigate vibrational behavior of installations as power packs and drivelines to get loads for simulation, identify resonances, operational deflection shapes, and vibration and stress levels for life length estimations under operational conditions. The time for a 40-180 Channel measurement is now down the range of 13 days. To reduce the time it takes to perform measurement a systematic approach has been taken that includes mainly three areas. First the Bookkeeping of all information and data needed for the analysis and reporting is input before or during the measurement. Systematic Approach of how to setup sensors, handle cable and equipment, planning and measurement. This includes practical examples of how to. Finally it is very important to take steps to assure Quality early in the measurement and also avoiding disturbances in the sensor path. There will be practical examples of important disturbances to look out for and quality check to perform. It should also be noted that the measurements is regular measured in mines or start up halls under rpm sweeps or/and operating conditions of the machines.

  • 59. Granström, Björn
    et al.
    Blomberg, Mats
    Roxström, Anders
    Nordholm, Sven
    Nordebo, Sven
    Claesson, Ingvar
    Eke, Karl
    Waernulf, Bengt
    An Experimental Voice Based Traffic Information Provider for Vehicle Drivers1993Conference paper (Refereed)
  • 60.
    Grbic, Nedelko
    Blekinge Institute of Technology, Department of Signal Processing.
    Development of a General Purpose On-Line Update Multiple Layer Feedforward Backpropagation Neural Network1997Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    This Master thesis deals with the complete understanding and creation of a 3-layer Backpropagation Neural Network with synaptic weight update performed on a per sample basis (called, On-Line update). The aim is to create such a network for general purpose applications and with a great degree of freedom in choosing the inner structure of the network. The algorithms used are all members of supervised learning classes, i.e. they are all supervised by a desired signal. The theory will be treated thoroughly for the steepest descent algorithm and for additional features which can be employed in order to increase the degree of generalization and learning rate for the network. Empirical results will be presented and some comparsions with pure linear algorithms will be made for a signal processing applications, speech enhencement.

  • 61. Grbic, Nedelko
    et al.
    Dahl, Mattias
    Claesson, Ingvar
    Neural Network Based Adaptive Microphone Array System for Speech Enhancement1998Conference paper (Refereed)
    Abstract [en]

    Presents a microphone array system for use in handsfree mobile telephone equipment. The array is based on a fast and efficient “on-site” and “self- calibration” scheme. The performance in suppressing the interior car cabin noise and the far-end speech is approximately 17 dB, respectively, while maintaining the near-end speaker level. The near-end signal is almost undistorted. The performance of two different algorithms, normalized least-mean-square (NLMS) and fully connected backpropagation supervised neural network (MLP-NN) are evaluated. The proposed microphone array calibration scheme can also be used in other situations such as speech recognition devices.

  • 62.
    Grbic, Nedelko
    et al.
    Blekinge Institute of Technology, Department of Signal Processing.
    Haan, Jan Mark de
    Nordholm, Sven
    Blekinge Institute of Technology, Department of Signal Processing.
    Claesson, Ingvar
    Blekinge Institute of Technology, Department of Signal Processing.
    Design of Oversampled Uniform DFT Filter Banks with Reduced Inband Aliasing and Delay Constraints2001Conference paper (Refereed)
    Abstract [en]

    Subband adaptive filters have been proposed to avoid the drawbacks of slow convergence and high computational complexity associated with time domain adaptive filters. Subband processing introduces transmission delays caused by the filter bank and signal degradations due to aliasing effects. One efficient way to reduce the aliasing effects is to allow a higher sample rate than critically needed in the subbands and thus reduce subband signal degradation. We suggest a design method, for a uniform DFT filter bank with any over sampling factor, where the total filter bank group delay may be specified, and where the aliasing and magnitude/phase distortions are minimized.

  • 63. Grbic, Nedelko
    et al.
    Nordholm, Sven
    Cantoni, Antonio
    Limits in FIR subband beamforming for spatially spread near-field speech sources2003Conference paper (Refereed)
    Abstract [en]

    This paper analyses optimal subband beamforming performance mainly aimed at speech enhancement and acoustic echo suppression for personal communication devices, personal computers and wireless cellular telephones. The focus is on theoretical limits of finite impulse response (FIR) beamformers for spatially spread sources in the array near-field. Performance of the Wiener solution is compared to the direct maximization of the array gain for different lengths of the FIR filters and different source interference spreads. The evaluation is performed individually in subbands with constant increasing logarithmic bandwidth. Results show that the difference between the Wiener solution and the direct array gain maximization is less than 2 dB in the measure of Signal-to-Noise plus Interference Ratio (SNIR), for small interference spread. With increasing interference spread the difference in SNIR performance increases, in favor of the array gain maximization.

  • 64. Grbic, Nedelko
    et al.
    Nordholm, Sven
    Cantoni, Antonio
    Optimal FIR Subband Beamforming for Speech Enhancement in Multipath Environments2003In: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 10, no 11, p. 335-338Article in journal (Refereed)
    Abstract [en]

    This paper provides an analysis of optimal finite impulse response subband beamforming for speech enhancement in multipath environments. A modification of the direct path standard Wiener formulation is shown to give near-optimal performance when it comes to signal-to-noise plus interference ratio, by including coherent multipath propagation into the criterion.

  • 65.
    Grbic, Nedelko
    et al.
    Blekinge Institute of Technology, Department of Signal Processing.
    Nordholm, Sven
    Blekinge Institute of Technology, Department of Signal Processing.
    Johansson, Anders
    Blekinge Institute of Technology, Department of Signal Processing.
    Optimal Beamforming for Voice Input to Personal Communication Devices2000Conference paper (Refereed)
  • 66. Gustafsson, Harald
    Acoustic Noise Reduction for Car Environment1998Conference paper (Refereed)
    Abstract [sv]

    Proc of SVIB AU2 Konferens, Riksgränsen.

  • 67. Gustafsson, Harald
    et al.
    Nordholm, Sven
    Claesson, Ingvar
    Spectral Subtraction using Correct Convolution and a Signal Dependent Exponential Averaging Method1999Conference paper (Refereed)
  • 68. Gustafsson, Harald
    et al.
    Nordholm, Sven
    Claesson, Ingvar
    Spectral subtraction using correct convolution and a spectrum dependent exponential averaging method.1998Report (Other academic)
    Abstract [en]

    In handsfree speech communication the signal to noise ratio is poor which makes it difficult for the listener to have a relaxed conversation. By using speech enhancement processing, the quality of conversation will be enhanced. This paper describes a speech enhancement algorithm based on spectral subtraction. The method employs a noise and speech dependent gain function which is used to design a filter. The proper measures have been taken to obtain a causal filter and also to ensure that the circular convolution yields a linear filtering. A novel method that uses spectrum-dependent exponential averaging to decrease the variance of the gain function is also presented. The result obtained is a 13 to 18 dB noise reduction, with minor speech distortion and moderate residual noise distortion.

  • 69.
    Gustavsson, Ingvar
    Blekinge Institute of Technology, Department of Signal Processing.
    Laboratory Experiments in Distance Learning2001Conference paper (Refereed)
    Abstract [en]

    In engineering education, laboratory experiments are indispensable, but they do require instruments and experimental equipment to be performed. Instruments are expensive and mostly located in laboratories. Experiments in circuit theory and other similar courses are easy to control. You use electronic instruments to see what is happening. Instruments are easy to control from a PC and so are switch units used to form test circuits and connect test probes and sources. Anyone can now do experiments over the Internet, from anywhere, using a client PC connected to a lab server at the Blekinge Institute of Technology, BTH, in Sweden. On the client screen you will see virtual front panels of the real instruments located in the lab at BTH. You may use the mouse to set the control knobs. The appearance of the virtual front panel and the real one is almost the same so later it should be easy to use a real instrument. The server supports several clients simultaneously.

  • 70. Gustavsson, Jan-Olof
    Analysis of receivers based on the Generalized Matched Filter in Non-Gaussian Environments1997Report (Other academic)
  • 71. Gustavsson, Jan-Olof
    Detection in Non-Gaussian Noise1993Conference paper (Refereed)
  • 72. Gustavsson, Jan-Olof
    Detection of Signals Corrupted by Non-Gaussian Disturbances.1997Doctoral thesis, comprehensive summary (Other academic)
  • 73. Gustavsson, Jan-Olof
    Estimation in Non-Gaussian Noise and Classification of Welding Signals1991Licentiate thesis, comprehensive summary (Other academic)
  • 74. Gustavsson, Jan-Olof
    Project Work for Course in Median and Morphological Filtering in Signal and Image Processing1990Report (Other academic)
  • 75. Gustavsson, Jan-Olof
    et al.
    Börjesson, Per Ola
    A Generalized Matched Filter1992Conference paper (Refereed)
    Abstract [en]

    Parameter estimation in additive independent identically distributed noise is treated. It is shown that there exists a generalized form of the matched filter which can be used for an arbitrary noise distribution to make e.g. ML-, MAP- or MMSE-estimates of a parameter vector. Simulations are presented to illustrate the performance.

  • 76. Gustavsson, Jan-Olof
    et al.
    Börjesson, Per Ola
    A generalized matched filter1991Report (Other academic)
  • 77. Gustavsson, Jan-Olof
    et al.
    Börjesson, Per Ola
    A Simultaneous Maximum Likelihood Estimator Based on a Generalized Matched Filter1994Conference paper (Refereed)
    Abstract [en]

    This paper discusses parameter estimation and detection in laplace distributed noise. The received signal is modeled as r($DOT@) $EQ As($DOT@,$theta@) $PLU n($DOT@), where A is an unknown amplitude, $theta is the parameter vector to be estimated and n($DOT@) is independent laplace distributed noise. The simultaneous maximum likelihood estimator of (A,$theta@) is derived. The derived estimator is based on a combination of a weighted median filter$LB@1$RB and a generalized form of the ordinary matched filter$LB@2$RB@. Examples of performance for four different detectors are given for a case of binary detection, when the amplitude A or the signal shape s($DOT@,$theta@) are varied. Simulations indicate that the performance of detectors based on the generalized matched filter is not particularly dependent on either the estimate of the amplitude A or the signal shape.

  • 78. Gustavsson, Jan-Olof
    et al.
    Börjesson, Per Ola
    Ankomsttidsskattning av rektangulära pulser i en klass av icke normalfördelat brus1990Conference paper (Refereed)
  • 79. Gustavsson, Jan-Olof
    et al.
    Börjesson, Per Ola
    Ett generaliserat signalanpassat filter1992Conference paper (Refereed)
  • 80. Gustavsson, Jan-Olof
    et al.
    Nordebo, Sven
    Börjesson, Per Ola
    Simultaneous Channel and Symbol Maximum Likelihood Estimation in Laplacian Noise1998Conference paper (Refereed)
    Abstract [en]

    This paper treats channel estimation and signal detection in Laplacian noise. The received signal is assumed to be a transmitted signal which has been corrupted by an unknown channel, modeled as a FIR filter, the output being further disturbed by additive independent Laplacian noise. The transmitted signal is assumed to depend on an unknown parameter belonging to a known finite set. The simultaneous maximum likelihood (ML) estimator of the unknown parameter, as well as of the FIR filter coefficients, is derived. The ML estimate of the channel can be obtained by using a linear programming approach and the decision about the parameter is based on the output from a set of generalized matched filters. Simulation results are included in order to illustrate the performance of the proposed receivers.

  • 81. Gustavsson, Jan-Olof
    et al.
    Nordebo, Sven
    Börjesson, Per Ola
    Simultaneous Channel and Symbol Maximum Likelihood Estimation in Laplacian Noise1997Conference paper (Refereed)
  • 82. Gustavsson, Jan-Olof
    et al.
    Ågren, Björn
    Adolfsson, Stefan
    Quality monitoring and control for robotic welding of Aluminium1991Conference paper (Refereed)
  • 83. Gustavsson, Jan-Olof
    et al.
    Ågren, Björn
    Adolfsson, Stefan
    Dahlberg, Joakim
    Signalbehandling vid GMA svetsning: pulsad svetsning av aluminium1990Report (Other academic)
  • 84.
    Haan, Jan Mark de
    Blekinge Institute of Technology, Department of Signal Processing.
    A Survey on Methods for Time-Frequency Analysis1998Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    Time analysis and frequency analysis are both well-established ways in engineering to gain more knowledge about a physical phenomena. Time and frequncy analysis can be combinen in a joint time and frequency distribution. A simple method to gain a joint distribution is to window segments of the data at different time locations and calculate its Fourier transform. By doing this a set of 'local' spectra are gained and joined to present a time-frequency distribution. This method is well known as the Short-Time Fourier Transform. The Short-Time Fourier Transform has the disatvantage that i does not localize time and frequency phenomena very well. Instead the time-frequency information is scattered which depends on the length of the window. This can be attended to by altering the length of the window bu a certain balance between good time and good frequency localization is unavoidable. To cope with this disadvantage, the Wavelet Transform uses dilated and translated functions, which are local in time, and frequency, which results in good frequency resolutin for low-frequency phenomena and good time resolution for high-frequency phenomena. The advantage of the Wavelet Transform is its efficient fast transform in discrete time. But still, there is no complete solution to the localization problem. Adaptive Time-Frequency Analysis can be advantageous for solving the localization problem. The functionality of methods is hereby adapted to the time-frequency content of the signa. The Adaptive Wavelet Packets Transform is based upon the Wavelet Transform but is a more general way to gain a time-frequency distribution. It is even possible to gain a time-frequency distribution similar to the Short-Time Fourier Transform. The energy levels in the frequency bands determine the frequency resolution. Much energy located in a small frequency band will result in good frequency resolution for the specific band. Other frequency areas will be analyzed with as good time resolution as possible. Sine wave with constant frequency precedes time phenomena. The method is implemented using a fast Quadrature Mirror Filter bank tree which form determines resolution of the analysis. In the Adaptive Window Short-Time Fourier Transform, the time phenomena precede sine waves in the analysis. Good time resolution is gained where the time-frequency concentration is highest for short windows. Other time intervals will be analyzed with a longer window, to gain better frequency resolution. The method is implemented using a set of Fast Fourier Transform calculations.

  • 85.
    Haan, Jan Mark de
    Blekinge Institute of Technology, Department of Signal Processing.
    A Survey on Methods for Time-Frequency Analysis1998Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    Time analysis and frequency analysis are both well-established ways in engineering to gain more knowledge about a physical phenomena. Time and frequncy analysis can be combinen in a joint time and frequency distribution. A simple method to gain a joint distribution is to window segments of the data at different time locations and calculate its Fourier transform. By doing this a set of 'local' spectra are gained and joined to present a time-frequency distribution. This method is well known as the Short-Time Fourier Transform. The Short-Time Fourier Transform has the disatvantage that i does not localize time and frequency phenomena very well. Instead the time-frequency information is scattered which depends on the length of the window. This can be attended to by altering the length of the window bu a certain balance between good time and good frequency localization is unavoidable. To cope with this disadvantage, the Wavelet Transform uses dilated and translated functions, which are local in time, and frequency, which results in good frequency resolutin for low-frequency phenomena and good time resolution for high-frequency phenomena. The advantage of the Wavelet Transform is its efficient fast transform in discrete time. But still, there is no complete solution to the localization problem. Adaptive Time-Frequency Analysis can be advantageous for solving the localization problem. The functionality of methods is hereby adapted to the time-frequency content of the signa. The Adaptive Wavelet Packets Transform is based upon the Wavelet Transform but is a more general way to gain a time-frequency distribution. It is even possible to gain a time-frequency distribution similar to the Short-Time Fourier Transform. The energy levels in the frequency bands determine the frequency resolution. Much energy located in a small frequency band will result in good frequency resolution for the specific band. Other frequency areas will be analyzed with as good time resolution as possible. Sine wave with constant frequency precedes time phenomena. The method is implemented using a fast Quadrature Mirror Filter bank tree which form determines resolution of the analysis. In the Adaptive Window Short-Time Fourier Transform, the time phenomena precede sine waves in the analysis. Good time resolution is gained where the time-frequency concentration is highest for short windows. Other time intervals will be analyzed with a longer window, to gain better frequency resolution. The method is implemented using a set of Fast Fourier Transform calculations.

  • 86. Håkansson, Hans
    et al.
    Lagö, Thomas L
    Olsson, Sven
    A Non-tachometer based Order Analysis Method for Interior Noise Measurements in Cars1994Conference paper (Refereed)
  • 87. Håkansson, Lars
    et al.
    Claesson, Ingvar
    Pettersson, Linus
    Embedded piezoceramic actuators in a tool holder shank for the active control of machine-tool vibration1999Conference paper (Refereed)
    Abstract [en]

    In the turning operation chatter or vibration is a frequent problem, which affects the result of the machining, and, in particular, the surface finish. Tool life is also influenced by vibration. Severe acoustic noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. These problems can be reduced by active control of machine-tool vibration based on high magnetostrictive actuators. However, both the physical features and properties of a active tool holder construction based on high magnetostrictive actuators and the fact that this type of actuators generally have a non-linear behaviour highly reduce its applicability to the general lathe and turning operation. Therefor, a new generation embedded active tool holder shanks based on piezo ceramic actuators have been developed. Based on spectrum estimates, both coherence spectrum and frequency response function estimates has been calculated for both the old tool holder construction and the new generation active tool holder shank. From the results it follows that the phase delay is smaller and the linearity of the new generation active tool holder shank are superior compared to the old technology. It is also obvious that physical features and properties of new generation embedded active tool holder shanks based on piezo ceramic actuators fits the general lathe application.

  • 88. Håkansson, Lars
    et al.
    Claesson, Ingvar
    Sturesson, Per-Olof
    Adaptive Feedback Control of Machine-Tool Vibration based on The Filtered-x LMS Algorithm1998In: Journal of Low Frequency Noise Vibration and Active Control, ISSN 0263-0923, Vol. 17, no 4, p. 199-213Article in journal (Refereed)
    Abstract [en]

    Adaptive feedback control of tool vibrations during metal cutting in a lathe has been investigated. The vibrations were controlled in the primary cutting direction and the control is based on the filtered-x LMS-algorithm. It was found that the adaptive feedback control can achieve a reduction of the tool vibrations with up to 35 dB at 1.7 kHz and simultaneously with approximately 30 dB at 3.1 kHz. A significant improvement of the workpiece surface was experienced together with a substantial reduction of the acoustic noise level with adaptive feedback control. Tool life is also expected to be extended and the material removal rate can probably be increased.

  • 89. Håkansson, Lars
    et al.
    Claesson, Ingvar
    Ståhl, Jan-Eric
    Fix-Number Realization of Adaptive Control of Machine-Tool Vibration1998Conference paper (Refereed)
    Abstract [en]

    In the turning operation the relative dynamic motion between cutting tool and workpiece, or vibration, is a frequent problem, which affects the result of the machining, and, in particular, the surface finish. Tool life is also influenced by vibration. Severe acoustic noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. Dynamic motion between cutting tool and workpiece can be reduced substantially by active control of the machine-tool vibration based on the filtered-x LMS-algorithm. However, in the digital implementation of the filtered-x LMS-algorithm both the inputs and the internal algorithmic quantities are limited to a certain precision. The process of machining a workpiece is also likely to introduce large variations in the level of both input and output signals of the digital controller. The tool shank vibrations can generally be described as a superposition of narrow-band random processes at each modal frequency. Both the variation in signal level and the narrow-band character of the vibration are likely to be unfavorable a fix number realization of the filtered-x LMS-algorithm. The potential large dynamic range in the input signal may introduce coefficient bias and stalling of the convergence of the adaptive FIR filter. Furthermore, both the narrow-band character of the vibration and a large dynamic range in the input signal may result in overflow and thereby seriously degrade the performance of the control system. However, by the use of the leaky filtered-x LMS algorithm problems due to the limited numerical precision such as overflow will be reduced to a large extent.

  • 90. Håkansson, Lars
    et al.
    Claesson, Ingvar
    Ståhl, Jan-Eric
    Andersson, Mats
    Adaptiv reglering av verktygsvibrationer i svarvoperationen1998Conference paper (Refereed)
    Abstract [sv]

    I svarvoperationen är relativ dynamisk rörelse mellan verktyg och arbetsstycke ett vanligt förekommande problem. Rörelsen påverkar bearbetningsresultatet, speciellt arbetsstyckets yta, men även verktygets livslängd påverkas. Arbetsmiljöproblem som buller förekommer också på grund av vibrationer i svarvoperationen. Problemet kan delvis lösas med lämplig konstruktion som ökar styvheten i maskinstrukturen, vilken dock begränsas av den dynamiska styvheten i strukturen hos verktygshållare samt arbetsstycke. Med aktiv reglering av verktygshållarens respons, dvs. aktiv reglering av verktygsvibrationer, kan en ytterligare ökning av den dynamiska styvheten i det skärtekniska systemet erhållas. Regleringen av verktygsvibrationer har utförts med en återkopplad regulator som är baserad på den så kallade "filtered-x LMS"-algoritmen samt aktuatorer baserade på magnetostriktiv teknik. Verktygshållarens respons, verktygsvibrationerna, detekteras med en givare (accelerometer) som är monterad på verktygshållaren. Genom att introducera motvibrationer i verktygshållaren med en sekundär vibrationskälla, aktuator, via regulatorn som matas med de uppmätta vibrationerna, modifieras verktygshållarens respons. Med aktiv reglering av verktygsvibrationer uppmättes en reduktion av vibrationerna med ca 30 dB vid 1.7 kHz. Vidare erhölls en signifikant förbättring av arbetsstyckets yta och en avsevärd reducering av bullernivån erhölls.

  • 91. Håkansson, Lars
    et al.
    Sturesson, Per-Olof
    Claesson, Ingvar
    Active Control of Machine-Tool Vibration1995Conference paper (Refereed)
    Abstract [en]

    A new adaptive technique is presented for the increase of the dynamic stiffness of the cutting tool in a lathe by active control of the tool vibration in the cutting speed direction. Due to the statistic properties of tool vibration that are induced by the stochastic behavior of chip formation process, the controller is based on the filtered-x LMS algorithm which controls an adaptive filter that is based on Wiener filter theory. Hence, the adaptation of the filtered-x LMS algorithm is gradient-based and it is based on a classical optimization technique, the method of steepest descent. In the cutting experiments a tool holder construction with integrated actuators, i.e. secondary sources was used. The cutting experiments shows that the adaptive technique presented in this paper enables an increase in the dynamic stiffness of the cutting tool, i.e. tool vibrations are suppressed.

  • 92. Isaksson, M.
    et al.
    Larsson, R.
    Ödling, Per
    Implementation of a System for Validation of Algorithms used in Digital Radio Communication Schemes1992Conference paper (Refereed)
  • 93. Isaksson, M.
    et al.
    Larsson, R.
    Ödling, Per
    Implementation of a System for Validation of Algorithms used in Digital Radio Communication Schemes1992Conference paper (Refereed)
  • 94. Johansson, Sven
    Active Noise Control in Aircraft: Algorithms and Applications1998Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis consists of five papers which are divided into three main parts. Parts A and B deal with active noise control in a propeller aircraft application, whereas Part C deals with active noise control in a helicopter application. Part A presents a comparison between single- and multiple-reference controllers, while Part B deals with different multiple-reference, multiple-channel algorithms. Finally, Part C presents a hybrid headset. The five papers comprise: Part A1: Comparison between a Single-- versus a Twin--Reference Controller in Narrowband ANC Applications. Part A2: Performance of a Multiple- versus a Single-Reference MIMO ANC Algorithm based on a Dornier 328 Test Data Set. Part B1: A Novel Multiple--Reference, Multiple--Channel, Normalized Filtered--X LMS Algorithm for Active Control of Propeller-Induced Noise in Aircraft Cabins. Part B2: Evaluation of Multiple--Reference Active Noise Control Algorithms on Dornier 328 Aircraft Data. Part C: A New Active Headset for a Helicopter Application. The test data sets used in the computer evaluations are based on real--life data throughout. The data was recorded in a twin-engine propeller aircraft (Dornier 328) and a Super Puma helicopter during flight.

  • 95. Johansson, Sven
    et al.
    Lagö, Thomas L
    Borchers, Ingo
    Renger, Klaus
    Performance of a Multiple versus Single Reference MIMO ANC Algorithm based on a Dornier 328 test data set1997Conference paper (Refereed)
  • 96. Johansson, Sven
    et al.
    Lagö, Thomas L
    Claesson, Ingvar
    ANVC Performance and Robustness for Different Error Sensor Disturbance Signals1997Conference paper (Refereed)
    Abstract [en]

    When designing and using an ANVC system it is of interest how the system will be affected by different disturbances in the error microphones/accelerometers. With the use of a reference signal adaptive feedforward systems can attenuate a primary field substantially given that the noise field is tightly correlated with the reference signal. Questions that often arise in these applications are therefore how disturbances affect the performance: Will random noise in the error microphones affect the algorithm? Will error microphone tonal components affect the algorithm? Will speech in the error microphones affect the algorithm? How is convergence speed reduced by disturbances? In this paper, a filtered-X LMS feedforward controller has been investigated. Different types of noise sources have been injected and convergence speed as well as global reduction have been analyzed, given different contamination levels.

  • 97.
    Johansson, Sven
    et al.
    Blekinge Institute of Technology, Department of Signal Processing.
    Nordebo, Sven
    Blekinge Institute of Technology, Department of Signal Processing.
    Lagö, Thomas L
    Blekinge Institute of Technology, Department of Signal Processing.
    Sjösten, Per
    Blekinge Institute of Technology, Department of Signal Processing.
    Claesson, Ingvar
    Blekinge Institute of Technology, Department of Signal Processing.
    A Novel Multiple-Reference, Multiple-Channel, Normalized Filtered-X LMS Algorithm for Active Control of Propeller-Induced Noise in Aircraft Cabins1998Conference paper (Refereed)
    Abstract [en]

    The dominating cabin noise in propeller aircraft consists essentially of strong tonal components at harmonics of the Blade Passage Frequency (BPF) of the propellers. In order to efficiently reduce such low frequency periodic noise, it is advisable to employ an Active Noise Control (ANC) system based on a feedforward controller. This paper presents a set of normalized complex Filtered-X Least-Mean-Square (FX LMS) algorithms. By using different variants of normalization factors the convergence rate, the tracking performance and the steady-state noise attenuation can be improved. The algorithms presented are based either on a single normalization factor for the whole control system (global normalized FX LMS algorithm), or several individual normalization factors (reference-individual FX LMS algorithm) or the novel actuator-individual FX LMS algorithm. The evaluation is performed on noise recorded during flight in the cabin of a Dornier 328, a twin-engine propeller aircraft.

  • 98. Johansson, Sven
    et al.
    Nordebo, Sven
    Lagö, Thomas L
    Sjösten, Per
    Claesson, Ingvar
    Algoritmer för aktiv bullerundertryckning i propellerflygplan1997Conference paper (Refereed)
    Abstract [en]

    I många praktiska tillämpningar generas buller av roterande maskiner, t.ex. av kompressorer, fläktar, motorer och propellrar. Detta buller består huvudsakligen av periodiska komponenter, grundton med tillhörande övertoner. Vid denna typ av tillämpningar där bullret är lågfrekvent och periodiskt är det lämpligt att använda aktiv bullerreglering. Aktiva system baserade på framkopplad reglerteknik har visat sig ge en bra undertryckning av denna typ av buller. Ett framkopplat reglersystem behöver en synkroniseringssignal från den buller alstrande källan. Denna signal används sedan för att generera referenssignaler innehållande de frekvenser man vill undertrycka. Med hjälp av referenssignalerna generar reglersystemet ett ljudfält som är lika starkt som bullret och i motfas med detta. På detta sätt erhålls en reducering av bullret. För att ställa in den adaptiva regulatorn så att bästa möjliga undertryckning erhålls används reglermikrofoner som mäter det erhållna ljudtrycket. För att erhålla god undertryckning är det viktigt att referenssignalerna är väl korrelerade med bullret. I applikationer där endast en eller flera korrelerade källor bidrar till bullret räcker det att använda ett reglersystem baserat på en synkroniseringssignal, dvs ett enreferenssystem. Är det flera okorrelerade bullerkällor är det emellertid nödvändigt att använda en synkroniseringssignal från varje källa för att erhålla effektiv bullerundertryckning, dvs ett flerreferenssystem. I propellerflygplan härrör bullret huvudsakligen från propellrarna och de dominerande frekvenskomponenterna kan relateras till propellrarnas bladpassagefrekvenser (BPF) samt deras övertoner. Idag är de flesta tvåmotoriga flygplan utrustade med en synkroniseringsenhet, som synkroniserar propellrarnas varvtal. När propellrarna är synkroniserade kan de betraktas som fullständigt korrelerade, vilket medför att ett enreferenssystem kan användas för att åstadkomma en effektiv bullerundertryckning. I situationer där propellrarna är osynkroniserade skiljer sig propellrarnas varvtal åt och propellrarna kan nu betraktas som två okorrelerade källor. I dessa fall bör ett flerreferenssystem användas, eftersom denna regulatortyp kan följa varvtalsförändringar hos båda propellrarna. I denna presentation görs en jämförelse mellan prestanda för ett enreferenssystem och ett flerreferenssystem. Utvärderingen görs för två olika flygsituationer, synkroniserade respektive osynkroniserade propellrar.

  • 99. Johansson, Sven
    et al.
    Nordebo, Sven
    Lagö, Thomas L
    Sjösten, Per
    Claesson, Ingvar
    Borchers, Ingo
    Renger, Klaus
    Evaluation of a Multiple- versus a Single-Reference MIMO ANC Algorithm on Dornier 328 Test Data Set1998Conference paper (Refereed)
    Abstract [en]

    In many applications, such as in propeller aircraft, the dominating noise is periodic. Successful reduction of the periodic noise components can be achieved by using an Active Noise Control (ANC) system based on feedforward techniques. In this paper, a comparison between the performance of single--reference (single-tacho) and multiple--reference (twin-tacho) feedforward control systems is presented. The comparison is made for two different flight conditions, both with and without synchronized propellers. The evaluation results show that a multiple--reference controller provides better performance than a single--reference controller when a slight deviation exists in the propeller synchronization.

  • 100. Johansson, Sven
    et al.
    Winberg, Mathias
    Lagö, Thomas L
    Claesson, Ingvar
    A New Active Headset For a Helicopter Application1997Conference paper (Refereed)
    Abstract [en]

    In helicopters, the low frequency noise generated by the rotors and engines often masks and jeopardizes safe communication. Additionally, pilots are likely to suffer from hearing damages due to the higher sound levels in the headset produced when compensating for the noise by increased speakerlevels. A feasible approach is to reduce the low frequency noise using active techniques, thereby enabling lower speakerlevels. In many Active Noise Control (ANC) applications the primary noise field is either periodic or broadband which simplifiesthe choice of algorithm. In our application, noise up to 100Hz is dominated by tones and in the range from 100 Hz to 400 Hz the noise characteristicsis more broadband. In order to achievean efficient attenuation of the primary noise, a combination of a digital feedforward controller and an analog feedback controller is employed. The feedforward controller is tachometer based and reduces the tonal components, while the feedback controller attenuates the more broadband noise. In this paper, a combination of these two techniques is evaluatedon real data.

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