Comparison of Volumetric Analysis Methods for Machine Tools with Rotary Axes

Confidence in the ability of a production machine to meet manufacturing tolerances requires a full understanding of the accuracy of the machine. However, the definition of “the accuracy of the machine” is open to interpretation. Historically, this has been in terms of linear positioning accuracy of an axis with no regard for the other errors of the machine. Industry awareness of the three-dimensional positioning accuracy of a machine over its working envelope has slowly developed to an extent that people are aware that “volumetric accuracy” gives a better estimation of machine performance. However, at present there is no common standard for volumetric errors of machine tools, although several researchers have developed models to predict the effect of the combined errors. The error model for machines with three Cartesian axes has been well addressed, for example by the use of homogenous transformation matrices. Intuitively, the number of error sources increases with the number of axes present on the machine. The effect of the individual axis geometric errors can become increasingly significant as the chain of dependent axes is extended. Measurement of the “volumetric error” or its constituents is often restricted to a subset of the errors of the Cartesian axes by solely relying on a laser interferometer for measurement. This leads to a volumetric accuracy figure that neglects the misalignment errors of rotary axes. In more advanced models the accuracy of the rotary axes are considered as a separate geometric problem whose volumetric accuracy is then added to the volumetric accuracy of the Cartesian axes. This paper considers the geometric errors of some typical machine configurations with both Cartesian and non-Cartesian axes and uses case studies to emphasise the importance of measurement of all the error constituents. Furthermore, it shows the misrepresentation when modelling a five-axis machine as a three-plus-two error problem. A method by which the five-axis model can be analysed to better represent the machine performance is introduced. Consideration is also given for thermal and non-rigid influences on the machine volumetric accuracy analysis, both in terms of the uncertainty of the model and the uncertainty during the measurement. The magnitude of these errors can be unexpectedly high and needs to be carefully considered whenever testing volumetric accuracy, with additional tests being recommended

Hermetic-coaxial package design for microwave transistors

Semiconductor package has been developed for high power semiconductor devices that operate in the GHz-frequency range at several watts. Package includes stud, insulating ring, electrically conductive washer, insulating washer, braze ring, and cap. It is mechanically strong and can be used with variety of circuits

Response of primary and secondary systems under dynamic excitation

Master's thesis in Structural engineeringEngineers have gained much knowledge on how a primary system behaves under harmonic excitation and earthquakes, but they do not know as much about how a secondary system affects the behavior. In seismic areas, buildings (primary system) are built to withstand the impact of the earthquake, but the effects on secondary systems are often not taken into consideration when the structure is designed. In the past 40 years a lot of research has been done on developing methods to analyze the nonstructural elements during seismic excitation. However, these methods were mainly focused on the safety of critical equipment in, for example, power plants. In the later years it has been shown that the non-structural elements in conventional buildings also should be taken into consideration in the earthquake design process. A floor response spectrum from the primary structure is often used to estimate the dynamic response of the secondary system, but one problem by doing so is that it does not take into consideration the effect of the interaction between the two systems. The so-called Cardington Building, the primary system used in this thesis, was a seven storey in-situ concrete building erected inside an old Zeppelin hanger which housed the Cardington Laboratory near Bedford, UK, owned and operated by the BRE (Building Research Establishment Ltd). The building was built in 1998, and was a part of the European Concrete Building Project (ECBP). It was constructed like an office block, and its goal was to provide improved design codes, especially for the dynamic properties of the concrete structure. The analyses in this thesis are based on a numerical model of the Cardington Building made in a finite element program called Ruaumoko. The model is calibrated against experimental results from full scale tests performed by Jónas Thór Snæbjörnsson, Ódinn Thórarinsson and Símon Ólafsson in 2000 [2]. The FE model in this thesis is exposed to harmonic excitation in the first tests and excited by earthquakes in the second tests. Also, the seismic coefficients obtained from the earthquake excitations have been compared with the seismic coefficients calculated by equations from the Eurocode 8 standard. From the harmonic excitation tests it is seen that the secondary systems with their natural frequencies inside the resonant frequency range of the primary system get a much higher displacement than the ones outside the resonant frequency range, but in exchange the displacement of the primary system is reduced. For secondary system 6 the displacement of the primary system drops 34 % for the fourth floor and 35 % for the top floor (Figure 5.10 and Figure 5.11). This is true for secondary systems with both 0.8 % damping and 5.0 % damping. When the earthquake tests are performed it is seen that the floor response spectra method gives values that are generally higher than the values computed from the numerical model when the secondary system is attached to the primary system, see Table 5.10. It is seen that the natural frequency and the damping ratio of the secondary system affects the response generated by the two methods of measuring in different ways

Are banks too big to fail or too big to save ? International evidence from equity prices and CDS spreads

Deteriorating public finances around the world raise doubts about countries'abilities to bail out their largest banks. For an international sample of banks, this paper investigates the impact of government indebtedness and deficits on bank stock prices and credit default swap spreads. Overall, bank stock prices reflect a negative capitalization of government debt and they respond negatively to deficits. The authors present evidence that in 2008 systemically large banks saw a reduction in their market valuation in countries running large fiscal deficits. Furthermore, the change in bank credit default swap spreads in 2008 relative to 2007 reflects countries'deterioration of public deficits. The results of the analysis suggest that some systemically important banks can increase their value by downsizing or splitting up, as they have become too big to save, potentially reversing the trend to ever larger banks. The paper also documents that a smaller proportion of banks are systemically important -- relative to gross domestic product -- in 2008 than in the two previous years, which could reflect private incentives to downsize.Banks&Banking Reform,Debt Markets,Access to Finance,Bankruptcy and Resolution of Financial Distress,Economic Theory&Research

Iodinated Aluminum(III) Corroles with Long-Lived Triplet Excited States

The first reported iodination of a corrole leads to selective functionalization of the four C–H bonds on one pole of the macrocycle. An aluminum(III) complex of the tetraiodinated corrole, which exhibits red fluorescence, possesses a long-lived triplet excited state

Are Banks Too Big to Fail or Too Big to Save? International Evidence from Equity Prices and CDS Spreads

Deteriorating public finances around the world raise doubts about countries’ abilities to bail out their largest banks. For an international sample of banks, this paper investigates the impact of government indebtedness and deficits on bank stock prices and CDS spreads. Overall, bank stock prices reflect a negative capitalization of government debt and they respond negatively to deficits. We present evidence that in 2008 systemically large banks saw a reduction in their market valuation in countries running large fiscal deficits. Furthermore, the change in bank CDS spreads in 2008 relative to 2007 reflects countries’ deterioration of public deficits. Our results suggest that some systemically important banks can increase their value by downsizing or splitting up, as they have become too big to save, potentially reversing the trend to ever larger banks. We also document that a smaller proportion of banks are systemically important - relative to GDP - in 2008 than in the two previous years, which could reflect these private incentives to downsize.Banking;Financial crisis;Credit default swap;Too big to fail;Too big to save