Simple Electro-Mechanical Model of Magnetic Spring Realized from FeNdB Permanent Magnets

Magnetic spring utilizing the repulsive force of two permanent magnets is a new device with application in special textile machines. In order to get reliable rules for its design, the effect of geometrical parameters, magnetic properties, material deviations and mechanical inaccuracies should be known, first of all. The paper presents very simple model of permanent magnets based on surface bounded currents and gives information from detailed measurement of ring shape magnet both of the magnetic field and repulsive force. At present time the magnetic field measurement was performed only in a plane parallel to the spring plane. Nevertheless, the agreement with theory is good and the experimental errors can be estimated and reduced by the method of trials and errors. The value of magnetic flux density agrees with the producer data and its deviation can reach up to 10% along the concentric circle. Also, the direct measurement of repulsive force agrees well with both the simple theory and two-dimensional FEM. Ring magnet with outer diameter of 25 mm exhibits magnetic flux density of 1.15 T on its surface and a repulsive force of about 70 N in close contact between magnets. The dynamic magnet aging was studied, too. The changes in both the magnetic field and repulsive force were negligible after 30 million cycles. After finishing the experiments, the method and all the results can make very efficient and simple design of magnetic spring.