Ändra sökning
Avgränsa sökresultatet
27282930 1451 - 1467 av 1467
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.
  • 1451. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Developments Steps of an Active Boring Bar for Industrial Application2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the manufacturing industry, boring bar vibration in internal turning is a frequent problem. Boring bars are often used to machine deep and precise holes in workpieces and are thus usually long and slender. The consequences of boring bar vibration are generally; reduced tool life, poor surface finish and high sound levels in the working environment. Boring bar vibration may however be attenuated using a suitable active vibration control system. Such system may for instance rely on feedback control and an active boring bar with embedded actuators. There are some steps between research results, having a controlled laboratory setup working, and applying the technology in industry, that are essential. Several prototypes of an active boring bar for industrial applications have been produced as part of this research. Different development phases and some challenges along the road to a successful product are discussed. Also, an active boring bar vibration control system in industry is presented and what challenges such a development may include.

  • 1452. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Dynamic Properties of Tooling Structure: Hydraulic Clamping versus Standard Screw Clamping in a Lathe Application2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    During turning, the metal deformation process excites the tooling structure and may result in high and degrading tool vibration levels. In internal turning the boring bar is generally the weakest link of the tooling structure. The boundary conditions imposed on the boring bar by the clamping housing influence the dynamic properties of a clamped boring bar. The dynamic properties of a clamped boring bar have been investigated for two different clamping housings; one that clamps the boring bar by means of hydraulic pressure and one that clamps the boring bar by means of clamping screws. Both experimental and analytical methods have been utilized in the investigation.

  • 1453. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Estimation and Simulation of the Nonlinear Dynamic Properties of a Boring Bar2011Ingår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 16, nr 1, s. 35-43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, an initial investigation of the nonlinear dynamic properties of clamped boring bars is carried out. Two nonlinear, single-degree-of-freedom models with different softening spring nonlinearities are introduced for modeling the nonlinear dynamic behavior of the fundamental bending mode in the cutting speed direction of a boring bar. Also, two different methods for the simulation of nonlinear models are used. The dynamic behavior in terms of frequency response function estimates for the nonlinear models and the experimental modal analysis of the clamped boring bar is compared. Similar resonance frequency shift behavior for varying excitation force levels is observed for both the nonlinear models and the actual boring bar.

  • 1454. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    INVESTIGATION OF THE DYNAMIC PROPERTIES OF A BORING BAR CONCERNING DIFFERENT BOUNDARY CONDITIONS2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    The boring bar is one of the most widely used types of tool holder in metal cutting operations. The turning process subjects the tool to vibration, and cutting in deep workpiece cavities is likely to result in high vibration levels. The consequences of such vibration levels are generally; reduced tool life, poor surface finishing and disturbing sound. Internal turning frequently requires a long and slender boring bar in order to machine inside a cavity, and the vibrations generally become highly correlated with the fundamental bending mode of the boring bar. Different methods can be applied to reduce the vibrations, the implementation of the most efficient and stable methods require in depth knowledge concerning the dynamic properties of the tooling system. Furthermore, the interface between the boring bar and the clamping house has a significant influence on the dynamic properties of the clamped boring bar. In this paper different cases of boundary condition of the boring bar are presented partly analytically but also experimentally. This paper focuses on dynamic properties of a boring bar that arise due to different clamping conditions of the boring bar introduced by a clamping house commonly used in the manufacturing industry.

  • 1455. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Investigation of the Dynamic Properties of a Passive Damped Boring Bar2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Vibration problem during metal cutting is a degrading reality in the manufacturing industry and have a negative impact on the productivity which increases the over all production costs. Sometimes it’s also impossible to achieve the required tolerances. Different methods can be applied to reduce the vibrations, for example by using passively tuned damper or active control. This paper examines the dynamic properties of a boring bar with passive tuned damper, aiming on enhanced vibration con-trol combining passive control and active control. By combining these two methods it is likely that the performance of the passive tuned damper will be enhanced in the sense of wider working range with respect to cutting parameters and materials of workpieces. However, implementation of effi-cient and stable methods requires in-depth knowledge concerning the dynamic properties of the tooling system. The examination of the passive boring bar covers a wide range of cutting parame-ters and the main classes of workpiece materials. This is the first step in the development of a bor-ing bar involving two technologies complementing each other, that is, passive tuned damper and active control which is an already patented technology.

  • 1456. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Vibration in Turning and the Active Control of Tool Vibration2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    A frequent problem in the manufacturing industry today is the vibrations or chatter induced in machine tools during machining. Chatter in machine tools affect the result of machining, particularly the surface finish. Furthermore, tool life is correlated with the degree of vibration and acoustic noise introduced. The material deformation process during turning induces a broadband excitation of the machine tool and chatter or tool vibration is usually related to a low-order bending mode of, for example, the tool holder shank in external turning, the boring bar in internal turning. Frequently, the tool holder responses during continuous unstable machining have non-linear properties and exhibit advanced stochastic behaviour. Generally, the tooling structure - the interface between the cutting tool or insert and the machine tool - is the weakest link in a machining system. Active control of tool vibration, however, enables a flexible solution to selectively increase the dynamic stiffness of the tooling structure at the actual frequency of the dominating bending modes. Based on adequate controllers, tool holder shanks and boring bars with embedded actuators and vibration sensors tool vibration in turning may be reduced significantly.

  • 1457. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Sigfridsson, Andreas
    Svensson, Tobias
    Lagö, Thomas L
    A First Prototype of an Active Boring Bar Tested in Industry2006Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Metal cutting is a common process in the manufacturing industry. Vibration problem during metal cutting is a reality for these manufactures. The vibration level depends on many different parameters such as material type, dimensions of the workpiece and boring bar, cutting data and operation mode. Internal cutting is one of the most troublesome operation modes, without any continuous monitoring and control from an operator grave vibration levels quickly arises. From the industry point of view this is an expense in the production line. The reduced tool life and the coarse surface finishing caused by the large vibration will force the operator to stop the cutting process, either to change tool when it is broken or change cutting data like decreasing the cutting depth. Any interference like this increases the working time for each component tremendous. These problems have been located and examined in an industry producing and renovating components using a lathe. One lathe was chosen for further investigation by experimental modal analysis and analysis during operational mode. The examination was done in an environment with machining processes in full operation mode and also during non-working ours. After analyzing the problem different solution where scrutinized and a first prototype where constructed. The solution to the problem is an active boring bar. This paper will present the procedure from analyzing a problem in industry to the test of the first prototype of the solution.

  • 1458. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Sigfridsson, Andreas
    Svensson, Tobias
    Lagö, Thomas L
    Active Boring Bar Prototype Tested in Industry2006Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Metal cutting processes are common in the manufacturing industry. Vibration problems during metal cutting are a degrading reality in the manufacturing industry and have a negative impact on the productivity and increase’s the production costs. The vibration level depends on many different parameters such as material type, dimensions of the workpiece, tool, tooling structure, machine structure, the cutting data and operation mode. Internal turning is one of the most troublesome operation modes concerning vibration. It generally requires that extra care must be taken with pro-duction planning and in the preparations for the machining of a workpiece. Frequently, continuous monitoring and control by a skilled operator is required to avoid grave degrading vibration levels. The reduced tool life and the coarse surface finishing generally caused by large vibration levels will e.g. force the operator to stop the cutting process, either to change tool when it is broken or change cutting data like decreasing the cutting depth. Any interference like this increases the production time and cost for each component tremendously. In an industry producing and renovating compo-nents using different machine tools, a particular lathe used for internal turning of certain details with extensive vibration problem was chosen for further investigation by experimental modal analysis and vibration analysis during operation. The examination was done in an environment with ma-chine tools in full operation and also during non-working ours. After analyzing the problem different solutions for the reduction of the vibration problem was investigated and subsequently a first proto-type was constructed. The solution to the problem is active control of the tool vibration using an active boring bar. This paper will present the procedure from analyzing a problem in industry to the test of the first prototype of the solution.

  • 1459. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Lagö, Thomas L
    Claesson, Ingvar
    Investigation of the Dynamic Properties of a Milling Tool Holder2009Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Vibration problems during metal cutting occur frequently in the manufacturing industry. The vibration level depends on many different parameters such as the material type, the dimensions of the workpiece, the rigidity of tooling structure, the cutting data, and the operation mode. In milling, the cutting process subjects the tool to vibrations, and having a milling tool holder with a long overhang will most likely result in high vibration levels. As a consequence of these vibrations, the tool life is reduced, the surface finishing becomes poor, and disturbing sound appears. In this report, an investigation of the dynamic properties of a milling tool holder with moderate overhang has been carried out by means of experimental modal analysis and vibration analysis during the operating mode. Both the angular vibrations of the rotating tool and the vibrations of the machine tool structure were examined during milling. Also, vibration of the workpiece and the milling machine was examined during cutting. This re- port focuses on identifying the source/sources of the dominant milling vibration components and on determining which of these vibrations that are related to the structural dynamic properties of the milling tool holder.

  • 1460. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Lagö, Thomas L
    Håkansson, Lars
    Analysis of Dynamic Properties of Boring Bars Concerning Different Clamping Conditions2007Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The boring bar is one of the most widely used type of tool holders in metal cutting operations. The turning process subjects the tool to vibrations, and cutting in deep workpiece cavities is likely to result in high vibration levels. The consequences of such vibration levels generally results in: reduced tool life, poor surface finishing and disturbing sound. Internal turning frequently requires a long and slender boring bar in order to machine inside a cavity, and the vibrations generally become highly correlated with one of the fundamental bending modes of the boring bar. Different methods can be applied to reduce the vibrations, the implementation of the most efficient and stable methods require in depth knowledge concerning the dynamic properties of the tooling system. Furthermore, the interface between the boring bar and the clamping house has a significant influence on the dynamic properties of the clamped boring bar. This report focuses on the dynamic properties of a boring bar that arise under different clamping conditions of the boring bar and are introduced by a clamping house (commonly used in the manufacturing industry). The dynamic properties of a boring bar (for different cases of boundary condition of the boring bar) are presented partly analytically but also experimentally.

  • 1461.
    Åkesson, Henrik
    et al.
    Blekinge Tekniska Högskola, Institutionen för telekommunikation och signalbehandling.
    Sällberg, Benny
    Blekinge Tekniska Högskola, Institutionen för telekommunikation och signalbehandling.
    Identification and Analysis of Nonlinear Systems2003Självständigt arbete på avancerad nivå (magisterexamen)Studentuppsats (Examensarbete)
    Abstract [en]

    In classical mechanical engineering the predominant group of system analysis and identification tools relies on Linear Systems, where research have been carried out for over half a century. Usage of Linear Systems is most widely spread, often due to its simple mathematics and formulation for many engineering problems. Although linearizing is a means for simplifying a problem, it will introduce more or less severe modelling errors. In some cases the errors due to linearizing are too large to be practically acceptable, and therefore nonlinear structures and models are sometimes introduced. This thesis aims in implementing and evaluating some popular methods and algorithms for nonlinear structure analysis and identification, with emphasis on systems having nonlinear terms. Preferably the algorithms should be optimized in their computational load. The result are several algorithms for nonlinear analysis and identification. The ones giving best results were the frequency based methods Reverse Path and a Frequency Domain Structure Selection Method (FDSSA). The time domain based method, Nonlinear Autoregressive Moving Average with Exogenous Input (NARMAX), in which a lot of hope had been put, did perform very well in giving good system descriptions, but due to its nonphysical representation it was not suitable for usage in this thesis. The algorithms and methods were finally applied for two cases, a four system black-box case and an experimental test-rig case. The methods did perform well in three out of four systems in the first case, but the methods did not perform well for the second case, due to problems in applying correct levels of excitation force at the test-rig’s resonance frequencies.

  • 1462. Ödling, Per
    Design and Analysis of Digital Receivers1995Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 1463. Ödling, Per
    Low Complexity Digital Receivers1993Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 1464. Ödling, Per
    et al.
    Börjesson, Per Ola
    Koski, Timo
    A Reduced Complexity Viterbi Equalizer used in Conjunction with a Pulse Shaping Method1992Konferensbidrag (Refereegranskat)
  • 1465. Ödling, Per
    et al.
    Koski, Timo
    Börjesson, Per Ola
    A Reduced Complexity Viterbi Equalizer used in Conjunction with a Pulse Shaping Method1992Konferensbidrag (Refereegranskat)
  • 1466. Ödling, Per
    et al.
    Koski, Timo
    Börjesson, Per Ola
    A Reduced Complexity Viterbi Equalizer used in Conjunction with a Pulse Shaping Method1992Konferensbidrag (Refereegranskat)
    Abstract [en]

    The complexity of the Viterbi algorithm can be reduced by linear pre-equalization. The authors introduce a linear preprocessor using the weighted least squares filtering (WLS). The geometric technique of L. Barbosa (see IEEE Trans. Inf. Theory, vol.35, no.2, p.419-27, 1989) is evoked for analytical representation of the complexity reduction by pre-equalization, and for evaluation of error performance. They evaluate the bit error rate of the WLS preprocessor and of the linear preprocessor of Falconer and Magee (see Bell System Tech. Journal, vol.52, no.9, p.1541-62, 1973)

  • 1467. Östlin, Erik
    On Radio Wave Propagation Measurements and Modelling for Cellular Mobile Radio Networks2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    To support the continuously increasing number of mobile telephone users around the world, mobile communication systems have become more advanced and sophisticated in their designs. As a result of the great success with the second generation mobile radio networks, deployment of the third and development of fourth generations, the demand for higher data rates to support available services, such as internet connection, video telephony and personal navigation systems, is ever growing. To be able to meet the requirements regarding bandwidth and number of users, enhancements of existing systems and introductions of conceptually new technologies and techniques have been researched and developed. Although new proposed technologies in theory provide increased network capacity, the backbone of a successful roll-out of a mobile telephone system is inevitably the planning of the network’s cellular structure. Hence, the fundamental aspect to a reliable cellular planning is the knowledge about the physical radio channel for wide sets of different propagation scenarios. Therefore, to study radio wave propagation in typical Australian environments, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Australian Telecommunications Cooperative Research Centre (ATcrc) in collaboration developed a cellular code division multiple access (CDMA) pilot scanner. The pilot scanner measurement equipment enables for radio wave propagation measurements in available commercial CDMA mobile radio networks, which in Australia are usually deployed for extensive rural areas. Over time, the collected measurement data has been used to characterise many different types of mobile radio environments and some of the results are presented in this thesis. The thesis is divided into an introduction section and four parts based on peer-reviewed international research publications. The introduction section presents the reader with some relevant background on channel and propagation modelling. Also, the CDMA scanner measurement system that was developed in parallel with the research results founding this thesis is presented. The first part presents work on the evaluation and development of the different revisions of the Recommendation ITU-R P.1546 point-to-area radio wave propagation prediction model. In particular, the modified application of the terrain clearance angle (TCA) and the calculation method of the effective antenna height are scrutinized. In the second part, the correlation between the smallscale fading characteristics, described by the Ricean K-factor, and the vegetation density in the vicinity of the mobile receiving antenna is investigated. The third part presents an artificial neural network (ANN) based technique incorporated to predict path loss in rural macrocell environments. Obtained results, such as prediction accuracy and training time, are presented for different sized ANNs and different training approaches. Finally, the fourth part proposes an extension of the path loss ANN enabling the model to also predict small-scale fading characteristics.

27282930 1451 - 1467 av 1467
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