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Research Papers

Dynamic Modeling and Experimental Validation of Eddy Current Dampers and Couplers

[+] Author and Article Information
Andrea Tonoli

Mechanics Department, Mechatronics Laboratory,  Politecnico di Torino, corso Duca degli Abruzzi 24, I-10129 Torino, Italyandrea.tonoli@polito.it

Nicola Amati

Mechanics Department, Mechatronics Laboratory,  Politecnico di Torino, corso Duca degli Abruzzi 24, I-10129 Torino, Italynicola.amati@polito.it

J. Vib. Acoust 130(2), 021011 (Mar 17, 2008) (9 pages) doi:10.1115/1.2827990 History: Received January 02, 2007; Revised August 26, 2007; Published March 17, 2008

The interest in eddy current dampers is increasing especially in aeronautic and automotive industry. Such devices seem to be a valid alternative to conventional fluid film and viscoelastc dampers. Even if several papers have been published on this topic, an electromechanical model taking into account both the resistance and the inductance of the conductor is still lacking. The aim of the present paper is to model the electromagnetic interaction of an eddy current device operating as a damper or as a coupler and to validate it by means of experimental tests performed at steady state and vibrating about a fixed position. The study is based on the computation of the damping torque starting from the basic principles. The analytical models are developed using the bond graph formalism that allows to obtain purely mechanical analogs of the electromechanical system. The main results are the identification of eddy current damper dynamic model and the definition of a set of “conversion rules” allowing to readily obtain the mechanical impedance from the torque to slip speed characteristic and vice versa. The experimental results confirm the band limited effect of the damping, which cannot be neglected for practical applications. The effect can be exploited in eddy current couplers to filter higher order disturbances.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of the induction machine

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Figure 2

Bond graph representation of the electromechanical interaction

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Figure 3

(a) Bond graph model of an induction machine with a single pole pair. (b) Mechanical analogue. The torque T is balanced by the force applied to point P by the spring-damper assemblies.

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Figure 4

Bond graph model of a p pole pairs induction machine

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Figure 5

(a) Static characteristic of an axialsymmetric induction machine. (b) Schematic representation of its mechanical impedance (magnitude in logarithmic scales).

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Figure 6

Test rig used for the identification of the eddy current machine operating at steady state. (a) View of the test rig. (b) Zoom in the induction machine.

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Figure 7

Experimental results of the induction machine characterization at steady state

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Figure 8

Test rig configured for the vibration tests. (a) Front, side view zoomed in the induction machine. The inpulse hammer force in applied at Point A. (b) Lateral view of the induction machine. (c) Top view of the whole test rig.

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Figure 9

Example of numerical and experimental FRF comparison. (a) Identification of the torsional stiffness km and of the structural damping η. (b) Identification of kem using for cem the value obtained by the weight-driven tests (cem=1.24Nms∕rad).

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Figure 10

Identified values of kem in the frequency range of 20–80Hz. Full line, kem mean value obtained as best fit of the experimental points. The experimental points of Zm are plotted with reference to the top-right scale. Full line, Zm plotted using cem=c0 and kem=k¯em.

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