139,861 research outputs found
Development of a Novel MultiBody Mechatronic Model for Five-Axis CNC Machine Tool
No full textThe paper presents the development of a mechatronic hybrid model for Geiss five-axis CNC machine tool using MultiBody-System (MBS) approach. The motion control systems comprising electrical and mechanical elements are analyzed and modeled. The 3D assembly of the machine tool is built in SolidWorks and exported into SimMechanics which interfaces seamlessly with SimPowerSystems, SimDriveline, and Simulink packages. CNC machine tools are mechatronic systems incorporating non-linearities so the proposed multibody mechatronic model (which considers the coupling of elastic mechanical structures with the control systems) represents accurately the dynamic behaviour of the actual machine by using only one simulation environment
MACHINING CENTERS FOR HIGH SPEED MACHINING: A NEW DESIGN APPROACH
No full textA machining center is nowadays a complex mechanical, electronic, electrical system that needs integrated design capabilities which very often require a high time-consuming effort. Numerical techniques for designing and dimensioning the machine structure and components usually requires different knowledge according to the system that have to be designed. The paper refers about the efforts of the authors to develop an innovative designing platform that allows to perform the complete project of a new machine optimized in its dynamic behaviour. An integration of the different systems developed, each of which respond to specific necessities of designer, is here presented. In particular a dynamic analysis system (pre-project simulation system), based on a lumped mass approach, that rapidly allows to setup the drives of the machine and an integrated dynamic simulation system, based on a fem approach, that permit a dynamic optimization, are shown. Inside the two systems specific cnc models have been developed. A multilevel data base, and an operator interface module provide to complete the designing platform. The proposed approach represents a significant step toward the virtual machining for the prediction of the quality of the worked surface
Improving the Dynamic Performance of Five-Axis CNC Machine Tool by using the Software-in-the-Loop (SIL) Platform
No full textThe paper presents the development and implementation of a Software-in-the-loop (SIL) platform allowing the real-time simulation of the hybrid model of five-axis CNC machine tool which is implemented in SIMULINK. The interfacing between dSPACE software and the feed drives models in SIMULINK is explined. The values for the simulated positioning errors between the position demand and simulated position of orthogonal trimming head for the gantry axis are in the order of microns so proposed SIL model is validated. The accurate SIL platform could be used to build and optimise the machining process models including CNC machine tools under cutting conditions and improve machines’ dynamic performance
Open Controller Architecture – Past, Present and Future
No full textArticolo pubblicato sulla rivista ISI CIRP Annal
Investigation of Cr addition effect on structural, morphological, electrical and magnetic properties of Bi(Pb)-2212 superconductors
No full textThe main purpose of this research work will assess the effect of Cr addition on the properties of Bi1.8Pb0.4Sr2CaCu2O8+d superconducting ceramics. The samples are produced from industrial powders with different amounts of Cr (0, 1, 2, 3, 4, 5, 6 and 7 wt %) by sol–gel synthesis route. The influence of doping element has been determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical resistivity and magnetic characterizations. In particular, the eventual presence of secondary phases as a result of Cr doping on the undoped sample was investigated by using XRD. By means of SEM analysis, the Cr doping influence on the grain morphology of the samples was explored. Contrarily, the Tc,on and the Tc,off of the samples have been obtained by using electrical resistivity measurements and their behavior as a function of the Cr doping has been discussed. Finally, by performing magnetization analysis versus temperature and magnetic field, the behavior of the critical temperature Tc and of the critical current density Jc as a proportion of the Cr concentration has been discussed
Spatially-localized time dependent solutions including turbulence and their interactions in 2D Kolmogorov flow
No full textIn 2D Kolmogorov flow in small aspect ratio domains, spatially-localized solutions such as kink, traveling or time-dependent kink-antikink pars coexist. However, the conservation of the flow rate in the y direction strongly restrict combination of localized solutions and their positioning. We find that by adding a homogeneous flow U y their positioning is controlled and each of localized solutions including a spatially-localized chaos is isolated. Numerical results suggest that these isolated solutions can be elements constructing a whole flow
A Review on Real-Time Simulation of CNC Machine Tool Dynamics
No full textThis paper is an endeavour to critically appraise the existing methods used for real-time simulation of machine tool dynamics with the emphasis on modelling and simulation of the dynamic behaviour of CNC machine tool feed drives and mechatronic systems for machine tools. The actual approaches for linking the feed drive models with structural models for CNC machine tools are examined. Also the feasibility of using the multidisciplinary approach employing the concepts of virtual machine tools and virtual machining into the design and control processes related to manufacturing process is analysed
Characteristics of overlap region in high-Reynolds number turbulent channel flow
No full textDirect numerical simulation of the fully developed turbulent channel flows have been carried out at the Reynolds number based on the friction velocity and the channel half width, 2000, 4000 and 8000. A hybrid 10th order accurate finite difference scheme in the stream and spanwise directions, and a second-order scheme in the wall-normal direction is adapted as the spatial discretization method. We observed the plateau profiles in the indicator function corresponded to the von Karman constant. Furthermore, second peak of streamwise pre-multiplied spectra were appeared in the same wall normal height, 300 < y+ < 600, in case of Re = 4000. Nevertheless, the effects of the lager than the channel half height scale on the streamwise turbulent intensity are fixed contributions without dependence on Reynolds number. These results suggested that the new streamwise vortexes are formed between buffer layer and outer layer with increasing of Reynolds number
La 'circunstancia' de 'Herederos y Pretendientes
No full textIn June 2010, the Ortega y Gasset Foundation hosted a Conference about the “Spanish Philosophical Transition” in order to debate the book of Francisco Vázquez, La filosofía española. Herederos y Pretendientes. Una lectura sociológica (1963-1990), recently published. This paper is the author’s response to criticism raised in the Conference and to published reviews received by this book. First, the author summarized the argument of Herederos y pretendientes. Secondly he responds and takes into account the most important objections against the book’s hypothesis and methodology. Finally the author evaluates the favorable judgments received by the book and suggests the limits of the historian’s task.Fundación Ortega y Gasset-Marañó
Author self-citation in orthodontics is associated with author origin and gender.
No full textBACKGROUND
The aims of this bibliometric study were to determine author self-citation trends in high-impact orthodontic literature and to investigate possible association between self-citation and publication characteristics.
METHODS
Six orthodontic journals with the highest impact factor as ranked by 2017 Journal Citation Reports were screened for a full publication year (2018) for original research articles, reviews, and case reports. Eligible articles were scrutinized for article and author characteristics and citation metrics. Univariable and multivariable negative binomial regression was used to examine associations between self-citation incidence and publication characteristics.
RESULTS
Medians for author self-citation rate of the most self-citing authors and self-citations were 3.03% (range 0-50) and 1 (range 0-19), respectively. In the univariable analysis, there was no association between self-citation counts and study type (P = 0.41), article topic (P = 0.61), number of authors (P = 0.62), and rank of authors (P = 0.56). Author origin (P = 0.001), gender (P = 0.001) and journal (P = 0.05) were associated with self-citation counts and in the multivariable analysis only origin and gender remained strong self-citation predictors. Asian authors and females self-cited significantly less often than all other regions and male authors.
CONCLUSIONS
Authors in orthodontics do not self-cite at a frequency that suggests potential citation manipulation. Author origin and gender were the only variables associated with citations counts. More bibliometric research is necessary to draw solid conclusions about author self-citation trends in orthodontic literature
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