| 201. |
- Hedberg, Claes
(författare)
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The multi-frequency solution for periodic nonlinear and dissipative waves
- 1999
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Konferensbidrag (refereegranskat)abstract
- The solution for multi-frequency plane waves propagating through a dissipative and nonlinear medium is shown for some examples of periodic conditions. The expression may for any given condition be expressed analytically as a ratio of Fourier series with Bessel function coefficients. In the examples are shown how the final appearance of any initial wave always is a pure periodic wave in the lowest frequency existing in the problem - the period of the condition.
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| 202. |
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| 203. |
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| 204. |
- Håkansson, Lars, et al.
(författare)
-
Active Control Machine Tool Chatter Embedded Piezo Ceramic Actuators in Tool Holder Shank
- 1999
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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. 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 performed a broadband attenuation of the sound pressure level by up to 35 dB . A significant improvement of the workpiece surface was also observed. In the active control of tool vibration a tool holder construction based on integrated high magnetostrictive actuators was used. However, both the physical features and properties of an 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.
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| 205. |
- Håkansson, Lars, et al.
(författare)
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Active Control of Chatter in Turning : The Origine of Chatter
- 1999
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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. 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. To achieve a further reduction of the dynamic motion between cutting tool and workpiece one solution is the active control of machine-tool vibration. However, to successfully apply active control of tool vibration in the external turning operation the response of the tool holder shank has to be investigated in order to enable the proper introduction of secondary vibration in the tool holder shank and to select a suitable controller. The investigation of the dynamic response of the tool holder shank relies on a stochastic approach while the structural dynamic properties have been evaluated by a normal mode analysis. This resulted in active control of tool vibration in a lathe that enables a reduction of the vibration by up to 40 dB at 1.5 kHz and by approximately 40 dB at 3 kHz.
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| 206. |
- Håkansson, Lars, et al.
(författare)
-
Active Control of Machine Tool Chatter
- 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. 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 by up to 40 dB at 1.5 kHz and by approximately 40 dB at 3 kHz. The active control performed a broadband attenuation of the sound pressure level by up to 35 dB. A significant improvement of the workpiece surface was also observed.
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| 207. |
- Håkansson, Lars, et al.
(författare)
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Active Control of Machine-Tool Vibration
- 1995
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 208. |
- Håkansson, Lars, et al.
(författare)
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Adaptiv reglering av verktygsvibrationer i svarvoperationen
- 1998
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 209. |
- Håkansson, Lars, et al.
(författare)
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Adaptive Feedback Control of Machine-Tool Vibration based on The Filtered-x LMS Algorithm
- 1998
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Ingår i: Journal of Low Frequency Noise Vibration and Active Control. - 0263-0923. ; 17:4, s. 199-213
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 210. |
- Håkansson, Lars, et al.
(författare)
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Embedded Piezoceramic Actutaors in a Tool Holder Shank for the Active Control of Machine-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 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.
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