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E. Schmidt, W. Paradeiser, F. Dohnal, H. Ecker:
"Design of an electromagnetic actuator for parametric stiffness excitation";
COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 26 (2007), 3; 800 - 813.

Purpose
To give an overview of the design features, the modelling and the testing of a novel electro¬magnetic actuator to achieve a controllable stiffness to be used as a device for parametric stiffness excitation.
Design/methodology/approach
In principle the actuator consists of a current driven coil placed between two permanent magnets. Repellent forces are generated between the coil and the magnets, centering the coil between the magnets. A 2D finite element analysis is carried out to predict the forces generated by this arrangement depending on the coil current and position. Force measurements are also made using the actual actuator.
Findings
Actuator forces as predicted by the FE-analysis are in excellent agreement with the measured data, confirming the validity of the numerical model. Stiffness of the actuator is defined as the increase of force per unit of coil displacement. Actuator stiffness depends linearly on the coil current, but in a non-linear manner on the coil displacement. The performance of the actuator is sufficient to demonstrate the effect of a so-called parametric anti-resonance on a test stand.
Research limitations/implications
Although the performance of the actuator is satisfactory, there is potential for further improvement of the actuator design. In the future the design will be optimised with respect to the maximum stiffness developed as well as to minimize the non-linear characteristic of the actuator.
Originality/value
This paper reports for the first time on an electromechanical device to create a time-periodic stiffness variation to be used for research in the field of parametrically excited mechanical systems. The device is used to prove experimentally an effect to suppress mechanical vibrations, which has been studied so far only in theoretical studies.

Project Head Horst Ecker:
Schwingungsunterdrückung durch Parametererregung