1,721,052 research outputs found
Singularity curves of a parallel pointing system
No full textThis paper studies a parallel pointing system used in aerospace applications for orientating parabolic antennas. In the literature [6,7], the position analysis of this device has been already solved in closed form, whereas simple and efficient tools to address singularities' distribution are still lacking. In this paper, its velocity analysis is addressed, and a singularity locus analytic expression, containing the manipulator geometric parameters and the end-effector orientation parameters, is derived. Moreover, it is shown that the determined singularity locus can be represented by curves (singularity curves) on a Cartesian plane having the generalized coordinates of the mechanism on the coordinate axes. Finally, an example showing the use of the proposed relationships is given and discussed
On the dynamic isotropy of mechanisms with two degrees of freedom
No full textThe comparison of mechanisms with different topology or with different geometry, but with the same topology, is a necessary operation during the design of a machine sized for a given task. Therefore, tools that evaluate the dynamic performances of a mechanism are welcomed. This paper deals with the dynamic isotropy of 2-dof mechanisms starting from the definition introduced in a previous paper. In particular, starting from the condition that identifies the dynamically isotropic configurations, it shows that, provided some special cases are not considered, 2-dof mechanisms have at most a finite number of isotropic configurations. Moreover, it shows that, provided the dynamically isotropic configurations are excluded, the geometric locus of the configuration space that collects the points associated to configurations with the same dynamic isotropy is constituted by closed curves. This results will allow the classification of 2-dof mechanisms from the dynamic-isotropy point of view, and t..
Letter by Benedetto et al regarding article, "importance of refractory pain and hypertension in acute type B aortic dissection: Insights from the international registry of acute aortic dissection (IRAD)"
No full textAnalysis and design of a spherical micromechanism with flexure hinges
No full textThe article describes the design of a robotic wrist able to perform spherical motions: its mechanical architecture is based on parallel kinematics and is suitable to be realized at the mini- or micro-scale by means of flexible joints. In view of the preliminary design, a rigid body model has been studied first and the direct and inverse kinematic analyses have been performed, allowing for the determination of theoretical workspace and passive joints displacements. The rigid body dynamic behavior and the operative ranges of the machine have been assessed through the development of an inverse dynamics model. Then, the micro parts have been designed with the help of FEM and multibody software and the study has been focused on the flexures: since the analyses showed that the centre of the spherical motion moves around several millimeters in the workspace, the original kinematic concept has been modified with the introduction of a ball joint constraining the mobile platform to frame so as to prevent unwanted translations
Surface error correction of a mesh deployable reflector
No full textLarge Deployable Reflector (LDR) systems are commonly used as mesh reflectors for large aperture space antennas in aerospace applications since they provide affordability while guaranteeing at the same time a high gain and a high directivity. To improve the surface accuracy several methods have been studied, most of which measure the distance between the cable-net system that forms the reflector surface and the desired paraboloid. In this paper we want to improve the reflector’s ability to convey a greater concentration of reflected rays in the direction of the feed. To deal with this issue, a numerical optimization algorithm has been proposed
Workspace Analysis and Architecture Optimisation of a 6 d.o.f. Stewart-Platform-based Milling Machine
No full textConvegno tenuto nell'Aprile 200
Radial artery versus saphenous vein graft patency: Meta-analysis of randomized controlled trials
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Impact of the false lumen size on early and late outcomes after surgery ao acute type A aortic dissection
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