Design of an electromagnetic actuator for parametric stiffness excitation

Purpose - An overview is given on design features, numerical modelling and testing of a novel electromagnetic 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 two magnets. The 2D finite element analyses are carried out to predict the forces generated by this arrangement depending on coil current and coil position. Force measurements are also made using the actual device. Findings - Actuator forces as predicted by the finite element analyses 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 nonlinear 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. 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.