Ändra sökning
Avgränsa sökresultatet
1234567 1 - 50 av 361
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1. Adolfsson, Stefan
    et al.
    Bahrami, Ali
    Bolmsjö, Gunnar
    Claesson, Ingvar
    Automatic quality monitoring in robotised GMA welding using a repeated sequential probability ratio test method1997Ingår i: International Journal for the Joining of Materials, ISSN 0905-6866, Vol. 9, nr 1, s. 2-8Artikel i tidskrift (Refereegranskat)
  • 2. Adolfsson, Stefan
    et al.
    Bahrami, Ali
    Claesson, Ingvar
    A Sequential Probability Ratio Test Method for Quality Monitoring in Robotised GMA Welding1997Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper deals with the problem of automatic monitoring the weld quality when welding with Gas Metal Arc (GMA) in short circuiting mode. Experiments with two different types of T-joints are performed in order to provoke optimal and non-optimal welding conditions. During the experiments, voltage and current are measured from the welding process. A simple statistical change detection algorithm for the weld quality, the repeated Sequential Probability Ratio Test (SPRT), is used. The algorithm can equivalently be viewed as a cumulative sum (CUSUM) - type test. The test statistics is based upon the fluctuations of amplitude in the weld voltage. It is shown that the fluctuations of the weld voltage amplitude decreases when the welding process is not operating under optimal condition. The results obtained from the experiments indicate that it is possible to detect changes in the weld quality automatically and on-line.

  • 3. Adolfsson, Stefan
    et al.
    Bahrami, Ali
    Claesson, Ingvar
    Quality Monitoring in Robotised Welding using Sequential Probability Ratio test1996Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper addresses the problem of automatic monitoring the weld quality produced by robotised short arc welding. A simple statistical change detection algorithm for the weld quality, recursive sequential probability ratio test (SPRT), is used. The algorithm may equivalently be viewed as a cumulative sum (CUSUM) type test. The test statistics is based upon the variance of the amplitude of the weld voltage. It is shown that the variance of the weld voltage amplitude decreases when the welding process is not operating under optimal condition. The performance of the algorithm is evaluated using experimental data. The results obtained from the algorithm indicate that it is possible to detect changes in the weld quality automatically and on-line

  • 4. Adolfsson, Stefan
    et al.
    Bahrami, Ali
    Claesson, Ingvar
    Bolmsjö, Gunnar
    On-line quality monitoring in short: circuit gas metal arc welding1999Ingår i: Welding Journal, ISSN 0043-2296, Vol. 78, nr 2, s. 59S-73SArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper addresses the problems involved in the automatic monitoring of the weld quality produced by robotized short-arc welding. A simple statistical change detection algorithm for the weld quality, the repeated Sequential Probability Ratio Test (SPRT), was used. The algorithm may similarly be viewed as a cumulative sum (CUSUM) type test, and is well-suited to detecting sudden minor changes in the monitored test statistic. The test statistic is based on the variance of the weld voltage, wherein it will be shown that the variance decreases when the welding process is not operating under optimal conditions. The performance of the algorithm is assessed through the use of experimental data. The results obtained from the algorithm show that it is possible to detect changes in weld quality automatically and on-line.

  • 5. Andrén, Linus
    et al.
    Håkansson, Lars
    Brandt, Anders
    Claesson, Ingvar
    Identification of Dynamic Properties of Boring Bar Vibrations in a Continuous Boring Operation2004Ingår i: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 18, nr 4, s. 869-901Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vibrations in internal turning operations are usually a cumbersome part of the manufacturing process. This article focuses on the boring bar vibrations. Boring bar vibrations in alloyed steel, stainless steel and cast iron have been measured in both the cutting speed direction and the cutting depth direction with the aid of accelerometers. The dynamic response of a boring bar seem to be a time varying process that exhibits non-linear behaviour. The process is influenced by non-stationary parameters that are not under the control of the operator or experimenter. The vibrations are clearly dominated by the first resonance frequency in one of the two directions of the boring bar. The problem with force modulation in rotary machinery, which appears as side band terms in the spectrum, is also addressed. Furthermore, the resonance frequencies of the boring bar are correlated to an Euler-Bernoulli beam model.

  • 6. Andrén, Linus
    et al.
    Håkansson, Lars
    Brandt, Anders
    Claesson, Ingvar
    Identification of Motion of Cutting Tool Vibration in a Continuous Boring Operation: Correlation to structural Properties2004Ingår i: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 18, nr 4, s. 903-27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The internal turning operation has a history of being a cumbersome metal working process as vibration in boring operations is usually inevitable. In this article, the deflection shapes and/or mode shapes as well as the resonance frequencies of a boring bar have been put under scrutiny. Three methods have been used in order to investigate dynamic properties of a clamped boring bar: a theoretical Euler-Bernoulli beam model, an experimental modal analysis and an operating deflection shape analysis. \\ The results indicate a correlation between the shapes of the deflection shapes and/or mode shapes produced by the three different analysis methods. On the other hand, the orientation of the forced deflection shapes and/or mode shapes and the resonance frequencies demonstrates differences between the three methods. During continuous cutting, it is demonstrated that the bending motion of the first two resonance frequencies is to a large extent in the cutting speed direction.

  • 7. Andrén, Linus
    et al.
    Håkansson, Lars
    Claesson, Ingvar
    Active Control of Boring Bar Vibrations Using the Leaky Feedback Filtered X-LMS2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    The boring operation is a cumbersome manufacturing process marred by noise and vibration related problems. The manufacturing industry is having trouble with these kinds of metal cutting operations. There exist several approaches to reduce the vibrations in cutting operations in general. Passive tuned dampers in boring bars have been commercially available for some time. An active solution is likely to be more robust to changes in the spectral content, where the passive counterpart have a small operable area, the active solution is able to adapt to these kinds of changes. Active vibration control in boring operations has been proven to be feasible. The algorithm used in the successful experiments was the feedback filtered X-LMS algorithm. This algorithm does however not guarantee a stable behavior, but incorporating a leakage factor will make the algorithm more robust. Power spectral density of boring bar vibration of real cutting experiments show that the leaky filtered X-LMS algorithm is a possible candidate to be a suitable control algorithm. Nyquist diagrams of the controller during operation show that the stability is increased significantly.

  • 8. Andrén, Linus
    et al.
    Håkansson, Lars
    Claesson, Ingvar
    Active Control of Machine Tool Vibrations in External Turning Operations2003Ingår i: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture, ISSN 0954-4054, E-ISSN 2041-2975, Vol. 217, nr 6, s. 869-872Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vibration and noise in metal cutting are ubiquitous problems in the workshop. The external turning operation is one kind of metal cutting that exhibits vibration related problems. Severe noise is also a problem growing in proportion due to regulations in preventing hearing loss. Active vibration control is a potential solution to such problems. With the piezo ceramic actuator technology of today, the size of the actuator can be kept small and still be able to produce a sufficient amount of force for the anti vibrations. Results from several continuous cutting experiments show a 40 dB reduction of the cutting tool vibration level. The design of the active technique enables this technology to be applicable to a general lathe provided the mounting arrangement is fairly similar.

  • 9. Andrén, Linus
    et al.
    Håkansson, Lars
    Claesson, Ingvar
    Actuator placements and Variations in the Control Path estimates in the Active Control of Boring Bar Vibrations2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    A classical example of chatter prone machining is the boring operation. Turning under conditions with high vibrations in the cutting tool deteriorates the surface finish and may cause tool breakage. Severe noise is also a consequence of the high vibration levels in the boring bar. Active control is one possible solution to the noise and vibration problem in boring operations. In boring operations the boring bar usually have vibration components in both the cutting speed and the cutting depth direction. The introduction of the control force in different angles in between the cutting speed and the cutting depth directions have been investigated. Furthermore, control path estimates produced when the active boring bar was not in contact with the workpiece and during continuous cutting operation are compared. Experimental results indicate that the control force should be introduced in the cutting speed direction. Although the vibrations are controlled in just the cutting speed direction the vibrations in the cutting depth direction are also reduced significantly.

  • 10. Andrén, Linus
    et al.
    Håkansson, Lars
    Claesson, Ingvar
    Performance Evaluation of Active Vibration Control of Boring Operations Using Different Active Boring Bars2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    Vibration and noise in boring operations are ubiquitous problems in the workshop. In boring operations, the boring bar is subjected to forces from both the cutting speed and the cutting depth direction. To solve the vibration problem using active techniques would normally require two actuators in order to enable the control of both directions. By mounting one actuator in between the cutting speed and the cutting depth direction it is possible to achieve an active control solution with one actuator. Using only one actuator not only simplifies the control algorithm and saves extra equipment but is also favourable in terms of modifications of the boring bar. The harsh environment in a lathe more or less requires that both sensors and actuators are embedded and sealed into the boring bar. Since the forces that are to be controlled are large, the space needed for the actuator is substantial. Thus using only one actuator will keep the modified boring bar stiffer than a two actuator design. Three boring bars with the actuator mounted at different angles between the cutting speed and the cutting depth directions have been tested. Results from cutting experiments show that the one actuator solution has good potentials to the vibration problem in boring operations.

  • 11. Andrén, Linus
    et al.
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Piezo Ceramic Actuators versus High Magnetostrictive Actuators in the Active control of Tool Vibration1999Konferensbidrag (Refereegranskat)
    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. In the active control system for the control of tool vibration a tool holder construction with integrated high magnetostrictive actuators was used. However, high magnetostrictive actuators generally have a non-linear behavior and it is a well known fact that non-linear properties in the forward path in an active control system is likely to degrade the robustness of the control system. A new generation embedded active tool holder shanks based on piezo ceramic actuators has 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. The physical features and properties of the new generation active tool holders are superior to the old tool holder.

  • 12. Andrén, Linus
    et al.
    Johansson, Sven
    Winberg, Mathias
    Claesson, Ingvar
    Active Noise Control Experiments in a Fork-lift Truck Cabin2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    High comfort for the driver in working vehicles is an important feature as well as a demand from the drivers. Low noise level is an essential factor for the manufacturer to maintain a high standard and comfort of vehicles. In many cases the noise inside the cabin can be related to the engine orders. Hydraulic pumps and fans are also related to the engine but not necessarily integers of the engine order. Passive absorbers are not suitable for the lowest frequencies and one approach is to use an active noise control system to solve the noise problem at low frequencies. In the present experiment loudspeakers were mounted inside the cabin of a fork lift-truck to produce the secondary noise field. To sense the residual noise, microphones were installed close to the driver's head. The aim is to create a zone of reduced noise around the head. Since a large portion of the noise inside the cabin can be related to the engine, an active control system based on a feedforward solution is possible. Experimental results from a feedforward solution of active noise control in a fork-lift truck cabin show that the noise level in the low frequency region can be reduced significantly.

  • 13.
    Bartunek, Josef Strom
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Nilsson, Mikael
    Sällberg, Benny
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Claesson, Ingvar
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Adaptive Fingerprint Image Enhancement With Emphasis on Preprocessing of Data2013Ingår i: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 22, nr 2, s. 644-656Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article proposes several improvements to an adaptive fingerprint enhancement method that is based on contextual filtering. The term adaptive implies that parameters of the method are automatically adjusted based on the input fingerprint image. Five processing blocks comprise the adaptive fingerprint enhancement method, where four of these blocks are updated in our proposed system. Hence, the proposed overall system is novel. The four updated processing blocks are: 1) preprocessing; 2) global analysis; 3) local analysis; and 4) matched filtering. In the preprocessing and local analysis blocks, a nonlinear dynamic range adjustment method is used. In the global analysis and matched filtering blocks, different forms of order statistical filters are applied. These processing blocks yield an improved and new adaptive fingerprint image processing method. The performance of the updated processing blocks is presented in the evaluation part of this paper. The algorithm is evaluated toward the NIST developed NBIS software for fingerprint recognition on FVC databases.

  • 14. Bartunek, Josef Ström
    et al.
    Nilsson, Mikael
    Nordberg, Jörgen
    Claesson, Ingvar
    Adaptive Fingerprint Binarization by Frequency Domain Analysis2006Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a new approach for fingerprint enhancement by using directional filters and binarization. A straightforward method for automatically tuning the size of local area is obtained by analyzing entire fingerprint image in the frequency domain. Hence, the algorithm will adjust adaptively to the local area of the fingerprint image, independent on the characteristics of the fingerprint sensor or the physical appearance of the fingerprints. Frequency analysis is carried out in the local areas to design directional filters. Experimental results are presented.

  • 15. Bartunek, Josef Ström
    et al.
    Nilsson, Mikael
    Nordberg, Jörgen
    Claesson, Ingvar
    Improved Adaptive Fingerprint Binarization2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper improvements to a previous work are presented. Removing the redundant artifacts in the fingerprint mask is introduced enhancing the final result. The proposed method is entirely adaptive process adjusting to each fingerprint without any further supervision of the user. Hence, the algorithm is insensitive to the characteristics of the fingerprint sensor and the various physical appearances of the fingerprints. Further, a detailed description of fingerprint mask generation not fully described in the previous work is presented. The improved experimental results are presented.

  • 16. Bartunek, Josef Ström
    et al.
    Nilsson, Mikael
    Nordberg, Jörgen
    Claesson, Ingvar
    Neural Network based Minutiae Extraction from Skeletonized Fingerprints2006Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Human fingerprints are rich in details denoted minutiae. In this paper a method of minutiae extraction from fingerprint skeletons is described. To identify the different shapes and types of minutiae a neural network is trained to work as a classifier. The proposed neural network is applied throughout the fingerprint skeleton to locate various minutiae. A scheme to speed up the process is also presented. Extracted minutiae can then be used as identification marks for automatic fingerprint matching.

  • 17. Berg, Magnus
    et al.
    Bondesson, Erik
    Low, Siow Yong
    Nordholm, Sven
    Claesson, Ingvar
    A combined on-line PCA-ICA algorithm for blind source separation 2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we introduce and investigate a method combining principle component analysis (PCA) and independent component analysis (ICA) for blind source separation (BSS). A recursive method for the PCA is applied to meet the demands of a real-time application, and likewise a modified on-line version of the information maximization principle is used. The combined PCA-ICA algorithm, first reduces the dimension of the problem and then separates the signals. Evaluation of the proposed algorithm in a real room shows superior noise suppression capabilities compared to the use of PCA or ICA individually. The proposed algorithm achieves an impressive noise suppression/separation of up to 14 dB with only two microphones. Most importantly this is achieved with negligible distortion of the recovered signal. © 2005 IEEE.

  • 18. Berggren, Magnus
    et al.
    Borgh, Markus
    Schuldt, Christian
    Lindström, Fredric
    Claesson, Ingvar
    Low-complexity network echo cancellation approach for systems equipped with external memory2011Ingår i: IEEE Transactions on Audio, Speech, and Language Processing, ISSN 1558-7916, E-ISSN 1558-7924, Vol. 19, nr 8, s. 2506-2515Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Long delays and sparseness characterize impulse responses in telecommunication networks and a vast number of solutions for network echo cancellation have been proposed over the years. In this paper, an approach for detecting dispersive regions of a sparse impulse response and a proportionate normalized least mean square (PNLMS)-based selective updating approach are combined with an adaptive double-talk detector to form a complete solution for echo cancellation. The proposed solution has low computational complexity and is targeted for systems equipped with external memory.

  • 19. Berggren, Magnus
    et al.
    Lindström, Fredric
    Waye, Kerstin Persson
    Claesson, Ingvar
    Analysis of How the Noise Level Depends on Different Activities in a Child Day-Care Center2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In child day-care centers the noise level can rise to high levels and in some cases become so high that the people present risk hearing damage. The purpose of this investigation was to study how the noise level depends on the different activities during the day. The study was performed at a child day-care center and 6 children and 5 adult female teachers participated. The participants had a microphone attached next to the ear connected to a wearable digital recorder. A total of 32.5 hours of data was recorded. By listening tests the recorded data could be sorted by activity and by number of people present in the same room as the test subject. Activities were classified as belonging to one of the following: outdoor activity, indoor play, singing, storytelling and gathering. Further, by listening, the data was classified in small group/large group (3 or less/more than 3). The results show that the average noise level (LAeq) for outdoor activity was the highest and was measured to 88.1 dBA (average over 7h52min). Singing was 81.5 dBA (1h26min), indoor play 81.3 dBA (19h21min), storytelling 76.6 dBA (1h09min) and gathering 75.0 dBA (2h44min). The noise level difference between all activities except between singing and indoor play and gathering and storytelling could be verified using t-test (p<0.001). Further, the results showed that the average noise level was 86.6 dBA (14h11min) for the large group and 79.6 dBA (18h21min) for the small group. This difference, of 7.0 dB was statistically validated (p<0.001) using t-test.

  • 20. Berggren, Magnus
    et al.
    Stjernberg, Louise
    Lindström, Fredric
    Claesson, Ingvar
    Audio Processing Solution for Video Conference Based Aerobics2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper an audio processing solution for video conference based aerobics is presented. The proposed solution leaves the workout music unaltered by separating it from the speech and processing each signal separately. The speech signal processing is also performed at a lower sample rate, which saves computational power. Real time evaluation of the system shows that high quality music as well as a good two-way communication is maintained during the aerobic session.

  • 21. Borgh, Markus
    et al.
    Berggren, Magnus
    Schüldt, Christian
    Lindström, Fredric
    Claesson, Ingvar
    An improved adaptive gain equalizer for noise reduction with low speech distortion2011Ingår i: EURASIP Journal on Audio, Speech, and Music Processing, ISSN 1687-4714, E-ISSN 1687-4722, Vol. 7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In high-quality conferencing systems, it is desired to perform noise reduction with as limited speech distortion as possible. Previous work, based on time varying amplification controlled by signal-to-noise ratio estimation in different frequency subbands, has shown promising results in this regard but can suffer from problems in situations with intense continuous speech. Further, the amount of noise reduction cannot exceed a certain level in order to avoid artifacts. This paper establishes the problems and proposes several improvements. The improved algorithm is evaluated with several different noise characteristics, and the results show that the algorithm provides even less speech distortion, better performance in a multi-speaker environment and improved noise suppression when speech is absent compared with previous work.

  • 22. Borgh, Markus
    et al.
    Lindström, Fredric
    Waye, Kerstin Persson
    Claesson, Ingvar
    Blekinge Tekniska Högskola, Sektionen för teknik, Avdelningen för signalbehandling.
    The Effect of Own Voice on Noise Dosimeter Measurements: A Field Study in a Day-Care Environment, Including Adults and Children2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Noise dosimeters are valuable tools in assessing the individual noise dose in the workplace. At non-industrial work places with a high degree of communication, such measurements would include the wearer’s own voice which would be registered as noise. This may not always be desirable. The purpose of this investigation was to study the effect of the wearers own voice in noise dosimeter measurements, and especially the difference between children and adults as test subjects. The study took place at a day-care center and sixteen children and thirteen adult female preschool teachers participated. The participants wore a digital recorder during the day, which recorded the sound signal and vibrations originating from an accelerometer attached to the neck of the test subjects, for distinguishing of whether the subject was speaking or not. Thus, average A-weighted noise levels with and without the influence of the subjects own voice could be obtained. The Leq for the measurements with and without the own voice was 84.6 dBA and 72.2 dBA for the children, respectively, and 79.3 dBA and 70.0 dBA for adults. Student’s t-test showed a significant (p<0.01) difference of 12.4 dBA for children and 9.3 dBA for adults when comparing measurements including and excluding the own voice and also that the difference was significantly larger for children. Thus, the study conclude that the influence from the own voice implied an augmentation of the Leq value and that there is a significant difference between children and adults in how large this augmentation is.

  • 23. Borgh, Markus
    et al.
    Schüldt, Christian
    Blekinge Tekniska Högskola, Sektionen för teknik, Avdelningen för signalbehandling.
    Claesson, Ingvar
    Blekinge Tekniska Högskola, Sektionen för teknik, Avdelningen för signalbehandling.
    Efficient asynchronous re-sampling implementation on a low-power fixed-point DSP2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents an asynchronous resampling implementation on a low-power fixed-point DSP, which uses around 47% less computational resources compared to the solution provided by the DSP manufacturer, without compromising audio quality.

  • 24. Claesson, Ingvar
    Dual Microphone input for Mobile Telephony2000Konferensbidrag (Refereegranskat)
  • 25. Claesson, Ingvar
    FFT i ett historiskt perspektiv1997Konferensbidrag (Refereegranskat)
    Abstract [en]

    Några nedslag i Fouriertransformens historia och FFT:ns ursprung från 1805 och framåt behandlas i denna populära betraktelse. Vi stannar upp ett slag hos Gauss, funderar över vad han gjort för oss ingenjörer och vi avslutar med en del praktiska konsekvenser och tips som är aktuella idag.

  • 26. Claesson, Ingvar
    FFT i ett historiskt perspektiv1997Konferensbidrag (Refereegranskat)
  • 27. Claesson, Ingvar
    FFT i ett historiskt perspektiv1997Ingår i: SVIB vibrationsnytt , ISSN 0281-6830, Vol. 14/15, nr 1, s. 11-15Artikel i tidskrift (Refereegranskat)
  • 28. Claesson, Ingvar
    et al.
    Dahl, Mattias
    Nordebo, Sven
    Applied Complex Chebyshev Optimization Using Dual Nested Complex Approximation2001Konferensbidrag (Refereegranskat)
  • 29. Claesson, Ingvar
    et al.
    Dahl, Mattias
    Nordebo, Sven
    Nordholm, Sven
    Acoustic Echo Cancelling with microphone arrays1995Konferensbidrag (Refereegranskat)
  • 30. Claesson, Ingvar
    et al.
    Dahl, Mattias
    Nordebo, Sven
    Nordholm, Sven
    Chebyshev Optimization of Circular Arrays Inequalities1998Konferensbidrag (Refereegranskat)
  • 31. Claesson, Ingvar
    et al.
    Håkansson, Lars
    Active Control of Machine-Tool Vibration in a Lathe1997Konferensbidrag (Refereegranskat)
    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, in particular the surface finish. The tool life is also influenced by the vibrations. When the working environment is considered, noise is frequently introduced by dynamic motion between the cutting tool and the workpiece. By proper machine design, e.g. improved stiffness of the machine structure, the problem of relative dynamic motion between cutting tool and workpiece may be partially solved. However, by active control of machine-tool vibration, a further reduction of the dynamic motion between cutting tool and workpiece can be achieved. It was found that adaptive feedback control based on the filtered-x LMS-algorithm enables a reduction of the vibration with up to 40 dB at 1.5 kHz and simultaneously with approximately 40 dB at 3 kHz. A significant improvement of the workpiece surface was observed and a substantial improvement of the acoustic noise level was obtained with adaptive control.

  • 32. Claesson, Ingvar
    et al.
    Håkansson, Lars
    Adaptive Active Control of Machine-Tool Vibration In a Lathe1998Ingår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 3, nr 4, s. 155-162Artikel i tidskrift (Refereegranskat)
    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. Noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. With proper machine design, i.e. improved stiffness of the machine structure, the problem of relative dynamic motion between cutting tool and workpiece may be partially solved. However, by active control of machine-tool vibration, a further reduction of the dynamic motion between cutting tool and workpiece can be achieved. It was found that adaptive feedback control of tool vibration in the cutting speed direction, based on the filtered-x LMS-algorithm, enables a reduction in vibration, by up to 40 dB at 1.5 kHz, and by approximately 40 dB at 3 kHz. It was also observed that the introduction of leakage in the filtered-x LMS-algorithm improved the stability properties of the feedback control system. A significant improvement in the workpiece surface was observed and a substantial improvement in the acoustic noise level was obtained with adaptive control.

  • 33.
    Claesson, Ingvar
    et al.
    Blekinge Tekniska Högskola, Institutionen för signalbehandling.
    Håkansson, Lars
    Blekinge Tekniska Högskola, Institutionen för signalbehandling.
    Lagö, Thomas L
    Robust Control of Machine-Tool Vibration in a Lathe1999Konferensbidrag (Refereegranskat)
    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. These problems can be reduced substantially by active control of the machine-tool vibration. Adaptive feedback control based on the filtered-x LMS-algorithm, enables a reduction of the vibration by up to 40 dB at 1.5 kHz and by approximately 40 dB at 3 kHz. The active control performeds a broadband attenuation of the sound pressure level by up to 35 dB. However, the process of machining a workpiece usually involves a variety of cutting data which in turn are likely to cause substantial variations in the spectral properties of the tool vibrations. Hence, variations in the spectral properties originates from changes in the excitation of the tool holder and changes in the structural response of the tool holder. To handle the potential large variations in the spectral properties of tool vibration in the turning operation the robustness of the control system has to be improved. By applying the leaky version of the filtered-x LMS algorithm in the active control of machine tool vibration it was found that the robustness of the adaptive control system was improved substantially to large variations in the spectral properties of tool vibration.

  • 34. Claesson, Ingvar
    et al.
    Nilsson, Andreas
    Cancellation of Humming GSM Mobile Telephone Noise2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    A sometimes annoying problem in the most internationally widespread cellular telephone system, the GSM system, is an interfering signal generated by the switching nature of TDMA cellular telephone system. A humming noise originating from the speech frames, equivalent to 160 samples of data corresponding to 20 ms at 8 kHz sampling rate is sometimes clearly audible. This paper describes a study of two different software solutions designed to suppress such interference internally in the mobile handset. The methods are Notch Filtering, which is performed on a sample-per-sample basis, and Speech Frame Noise Cancellation, which is an alternative method employing correlators and subtraction, similar to Active Noise Control.

  • 35. Claesson, Ingvar
    et al.
    Nilsson, Andreas
    GSM TDMA Frame Rate Internal Active Noise Cancellation2003Ingår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 8, nr 3, s. 159-166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A common problem in the world's most widely-used cellular telephone system, the GSM system, is the interfering signal generated by the switching nature of TDMA cellular telephony in handheld and other terminals. Signals are sent as chunks of data, speech frames, equivalent to 160 samples of data corresponding to 20 ms at sampling rate of 8 kHz. This paper describes a study of two different software solutions designed to suppress such interference internally in the mobile handset. The methods are 1) notch filtering, which is multiplicative in frequency, and 2) subtractive noise cancellation, which is an alternative method employing correlators. The latter solution is a straigtforward, although somewhat unorthodox, application of "in-wire" active noise control. Since subtraction is performed directly in the time domain, and we have access to the state of the mobile, it is also possible to consider a recurring pause in the interference caused by the idle frame in the transmission, when the mobile listens to other base stations communicating. More complex control algorithms, based on the state of the communication between the handset and the base station, can be utilised.

  • 36. Claesson, Ingvar
    et al.
    Nordholm, Sven
    A Spatial Filtering Approach to Robust Adaptive Beamforming1992Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X , Vol. 40, nr 9, s. 1093-1096Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This communication treats the problem of controlling the superresolution in adaptive beamformers. A straightforward method is presented that works for both narrow-band and broad-band arrays. The method is based on forming the blocking matrix in a general sidelobe canceller (GSC) structure using a spatial FIR filter. The suppression of this spatial filter and the implicit noise of the leaky (LMS) algorithm together determine the beamformer.

  • 37. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Robust Adaptive Beamforming using Spatial Filter Design1990Rapport (Övrigt vetenskapligt)
  • 38. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Bengtsson, Bengt
    Car Perfomance of an Adaptive Microphone Array1992Konferensbidrag (Refereegranskat)
  • 39. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Bengtsson, Bengt
    Car Performance of an Adaptive Microphone Array1992Konferensbidrag (Refereegranskat)
    Abstract [en]

    Hands free input of mobile telephones is often almost impossible due to the noise situation in the car and the channel quality. The authors present a method to enhance the quality using an adaptive microphone array. Measurements show an improvement of the input with approximately 10 dB. Tape results are available for subjective evaluation

  • 40. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Bengtsson, Bengt
    Car Performance of an Adaptive Microphone Array1992Konferensbidrag (Refereegranskat)
    Abstract [en]

    Hands free input of mobile telephones is often almost impossible due to the noise situation in the car and the channel quality. The authors present a method to enhance the quality using an adaptive microphone array. Measurements show an improvement of the input with approximately 10 dB. Tape results are available for subjective evaluation.

  • 41. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Bengtsson, Bengt
    Car Performance of an Adaptive Microphone Array1992Konferensbidrag (Refereegranskat)
  • 42. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Bengtsson, Bengt
    Eriksson, Per
    A Multi-DSP implementation of a Broadband Adaptive Beamformer for use in a Hands-free Mobile Radio Telephone1991Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545 , Vol. 40, nr 1, s. 194-202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An implementation of a broadband adaptive array on a multiprocessor digital signal processing (DSP) system for use in a hands-free mobile radio telephone is described. This implementation of a five-microphone adaptive Griffiths-Jim array can handle FIR filters with up to 128 taps behind each microphone at a sampling rate of 8 kHz. The filter structure makes it possible to combine an adaptive array with a noise canceler. The near-field problem has been solved by using focusing, a speech-controlled adaptive algorithm, and a short hourglass. Preliminary measurements indicate a considerable potential for this technique in hands-free mobile telephony. The array gives a 20-30-dB suppression of a broadband jammer covering 300-1100 Hz, even with three reflecting walls surrounding the microphone.

  • 43. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Eriksson, Per
    Noise Canceling Convergence Rates for the LMS Algorithm1991Ingår i: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 5, nr 5, s. 375-388Artikel i tidskrift (Refereegranskat)
  • 44. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Eriksson, Per
    Noise Cancelling Convergence Rates for the LMS Algorithm1991Ingår i: Mechanical Systems & Signal Processing, ISSN 0888-3270 , Vol. 5, nr 5, s. 375-388Artikel i tidskrift (Refereegranskat)
  • 45. Claesson, Ingvar
    et al.
    Nordholm, Sven
    Eriksson, Per
    Wiener Solution for the Broadband Griffiths-Jim Beamformers1990Konferensbidrag (Refereegranskat)
    Abstract [en]

    The problem of finding the Wiener filters for a wideband adaptive beamformer is treated. Explicit expressions are given for the filters and the error power spectrum in the frequency domain. The expressions are simple to program and make it possible to investigate superresolution for wideband signals and to determine sufficient lengths of finite-impulse-response filters in adaptive arrays.

  • 46. Cornelius, Per
    et al.
    Grbic, Nedelko
    Claesson, Ingvar
    Microphone array system for speech enhancement in a motorcycle helmet2005Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In this report a real case study of the sound environment within a helmet while driving motorcycle is investigated. A solution to perform speech enhancement is proposed for the purpose of mobile speech communication. A microphone array, mounted onto the face shield in front of the user's mouth, is used to capture the spatio-temporal properties of the acoustic wave ¯eld inside the helmet. The power of the spatially spread noise within the helmet is small when standing still while it may heavily exceed the power of the speech when driving at high speeds. This will result in dramatically reduced speech intelligibility in the communication channel. The highly dynamic noise level imposes a challenge for existing speech enhancement solutions. We propose a subband adaptive system for speech enhancement which consists of a soft constrained beamformer in cascade with a signal-to-noise ratio dependent single microphone solution. The beamformer make use of a calibration signal gathered in the actual environment from the speaker's position. This calibration procedure e±ciently captures the acoustical properties in the environment. Evaluation of the beamformer and the single microphone algorithm, both as either parts by them selves and as a cascaded structure, together with the optimal subband Wiener solution is presented. It is shown that a cascaded combination of the calibrated subband beamforming technique together with the single channel solution outperforms either one by it self, and provides near optimal results at all noise levels.

  • 47. Cornelius, Per
    et al.
    Yermeche, Zohra
    Grbic, Nedelko
    Claesson, Ingvar
    A Spatially Constrained Subband Beamforming Algorithm for speech enhancement2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper discusses speech enhancement in an enclosed environment such as communication in a motorcycle helmet. A new constrained subband adaptive beamformer is proposed, which uses the concept of an earlier proposed calibrated beamformer mainly developed for a hands-free in-car environment. The highly non-stationary nature of the disturbing sound field encountered in an motorcycle helmet and the fact that the source is situated in the extreme nearfield of the array, causes the beamformer to produce an unwanted fluctuation in the output level. The spatially constrained beamformer proposed in this paper makes sure that the output maintains a constant gain, as long as the corresponding source originates from the desired location.

  • 48. Dahl, Mattias
    et al.
    Claesson, Ingvar
    A Neural Network Trained Microphone Array System for Noise Reduction1996Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a neural network based microphone array system, which is capable to continuously perform speech enhancement and adaptation to nonuniform quantization, such as A-law and $mu@-law. Such a quantizer is designed to increase the Signal to Quantization Noise Ratio (SQNR) for small amplitudes in telecommunications systems. The proposed method primarily developed for hands-free mobile telephones, suppresses the ambient car noise with approximately 10 dB. The system is based upon a multi-layered nonlinear back-propagation trained network by using a built-in calibration technique.

  • 49. Dahl, Mattias
    et al.
    Claesson, Ingvar
    Acoustic Echo Cancelling with Michrophone Arrays1995Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This report describes a novel method to perform acoustic echo cancelling with microphone arrays. The method employs a digital self-calibrating microphone system. The on-site calibration process is a simple indirect calibration which adapts in each special case to the environment and electronic equipment. The method also continuously takes into account environmental disturbances such as car engine noise and fan noise. The method is primarily aimed at handsfree mobile telephones, by suppressing the handsfree loudspeaker and car noise simultaneously. The report also contains an extensive evaluation in a car.

  • 50. Dahl, Mattias
    et al.
    Claesson, Ingvar
    Acoustic Noise and Echo Canceling with Microphone Array1999Ingår i: IEEE Transactions on Vehicular Technology , ISSN 0018-9545 , Vol. 48, nr 5, s. 1518-1526Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel method of performing acoustic echo canceling using microphone arrays is presented. The method employs a digital self-calibrating microphone system. The calibration process is a simple indirect on-site calibration that adapts to the particulars of the acoustic environment and the electronic equipment in use. Primarily intended for handsfree telephones in automobiles, the method simultaneously suppresses the handsfree loudspeaker and car noise. The system also continuously takes into account disturbances such as fan noise. Examples from an extensive evaluation in a car are also included. Typical performance results demonstrate 20-dB echo cancellation and 10-dB noise reduction simultaneously.

1234567 1 - 50 av 361
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf