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  • Andrén, Linus, et al. (författare)
  • Active Noise Control Experiments in a Fork-lift Truck Cabin
  • 2004
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  • Andrén, Linus, et al. (författare)
  • Actuator placements and Variations in the Control Path estimates in the Active Control of Boring Bar Vibrations
  • 2004
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  • Andrén, Linus, et al. (författare)
  • Identification of Dynamic Properties of Boring Bar Vibrations in a Continuous Boring Operation
  • 2004
  • Ingår i: Mechanical systems and signal processing. - Academic Press. - 0888-3270. ; 18:4, s. 869-901
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  • Andrén, Linus, et al. (författare)
  • Piezo Ceramic Actuators versus High Magnetostrictive Actuators in the Active control of Tool Vibration
  • 1999
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  • Bartunek, Josef Ström, et al. (författare)
  • Adaptive Fingerprint Binarization by Frequency Domain Analysis
  • 2006
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • 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.
  • Bartunek, Josef Ström, et al. (författare)
  • Improved Adaptive Fingerprint Binarization
  • 2008
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  • Bartunek, Josef Ström, et al. (författare)
  • Neural Network based Minutiae Extraction from Skeletonized Fingerprints
  • 2006
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • 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.
  • Berggren, Magnus, et al. (författare)
  • Audio Processing Solution for Video Conference Based Aerobics
  • 2010
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  • Berggren, Magnus, et al. (författare)
  • Low-complexity network echo cancellation approach for systems equipped with external memory
  • 2011
  • Ingår i: IEEE Transactions on Audio, Speech, and Language Processing. - IEEE. - 1558-7916. ; 19:8, s. 2506-2515
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  • Borgh, Markus, et al. (författare)
  • An improved adaptive gain equalizer for noise reduction with low speech distortion
  • 2011
  • Ingår i: EURASIP Journal on Audio, Speech, and Music Processing. - Springer. - 1687-4714. ; 7
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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