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- Andrén, Linus, et al.
(författare)
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Piezo Ceramic Actuators versus High Magnetostrictive Actuators in the Active control of Tool Vibration
- 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. 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.
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| 4. |
- Andrén, Thomas, et al.
(författare)
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Correlation of Swedish glacial varves with the Greenland (GRIP) oxygen isotope record
- 1999
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Ingår i: Journal of Quaternary Science. - 0267-8179 .- 1099-1417. ; 14:4, s. 361-371
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Tidskriftsartikel (refereegranskat)abstract
- A mean varve thickness curve has been constructed for a part of the Swedish varve chronology from the northwestern Baltic proper. The mean varve thickness curve has been correlated with the delta(18)O record from the GRIP ice-core using the Younger Dryas-Preboreal climate shift. This climate shift was defined by pollen analyses. The Scandinavian ice-sheet responded to a warming at the end of the Younger Dryas, ca. 10 995 to 10 700 clay-varve yr BP. Warming is recorded as a sequence of increasing mean varve thickness and ice-rafted debris suggesting intense calving of the ice front. The Younger Dryas-Preboreal climatic shift is dated to ca. 10 650 clay-varve yr BP, about 40 yr after the final drainage of the Baltic Ice Lake. Both the pollen spectra and a drastic increase in varve thickness reflect this climatic shift. A climate deterioration, correlated with the Preboreal oscillation, is dated to ca. 10 440 to 10 320 clay-varve yr BP and coincides with the brackish water phase of the Yoldia Sea stage. The ages of the climatic oscillations at the Younger Dryas-Preboreal transition show an 875 yr discrepancy compared with the GRIP record, suggesting a large error in the Swedish varve chronology in the part younger than ca. 10 300 clay-varve yr BP.
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| 5. |
- Andrén, Thomas, et al.
(författare)
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Late Quaternary development of the north-western Baltic Proper : Results from the clay-varve investigation
- 1995
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Ingår i: Quaternary International. - 1040-6182 .- 1873-4553. ; 27, s. 5-10
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Tidskriftsartikel (refereegranskat)abstract
- Within the project "Late Quaternary development of the north-western Baltic Proper" a total of 36 piston core samples have been collected. The results presented in this study are based on analyses of 7 cores with emphasis on the late glacial part of the sequence. The varved glacial clay sequences have been analyzed for calcareous micro-fossils and mineral magnetic properties as well as measurements of clay-varves. The results from these analyses indicate that there is a close correlation between the occurrence of brackish water ostracods and foraminifera and a distinct change in the mineral magnetic parameters. The lithological composition of the clay-varves also differs in this sequence. The duration of this marine phase of the Yoldia Sea stage is 60 to 120 clay-varve years. It is concluded that correlations between the cores can be made using fossil assemblages and mineral magnetic parameters. It has not yet been possible, however, to make any reliable clay-varve connections.
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| 9. |
- Robertsson, A M, et al.
(författare)
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Pleistocene stratigraphy in the Dellen region, central Sweden
- 1997
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 26, s. 237-260
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Tidskriftsartikel (refereegranskat)abstract
- The Pleistocene stratigraphy in the Dellen region, central Sweden was studied using field observations made during mapping of Quaternary deposits and fabric analyses in excavated sections. The lithostratigraphy was also studied by seismic refraction measurements, analyses of grain-size distribution and organic carbon content. Biostratigraphical methods applied were pollen and diatom analyses. A general outline of the Pleistocene stratigraphy in the area is presented. Three different till beds are identified, the lowermost suggested to have been deposited during the Saalian glaciation and the other two during the Weichselian glaciation. According to the interpretation of the stratigraphy, it is questioned whether the first Weichselian ice sheer did in fact reach the Dellen area. A clayey sediment sequence at Norra Sannas accumulated during an interglacial, probably the Eemian. Most of the interglacial vegetation succession is reflected in the identified pollen flora. An initial phase with a light-demanding forest of Betula and Pinus was followed by immigration of Alnus, Picea and scattered occurrences of Corylus. A freshwater diatom flora was identified dominated by plankton taxa, e.g. Aulacoseira italica, A. distans and Cyclotella spp. In the lower part of the sequence a brackish-marine flora was registered, representing accumulation in a bay of the Eemian Sea. Fine-grained sediments at the Sundson and Vastansjo sites are interpreted as rebedded Eemiar. sediments according to the pollen flora. An (Early Weichselian) interstadial age is suggested ibr sediments found at Bjuraker. Dating by the C-14- and OSL methods was carried out on the interglacial and interstadial sediments, respectively. The ages range from approximately 19 000 to 92 000 BP. Correlation of interglacial vegetation history with central Finland and other areas is discussed.
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