CST – Computer Simulation Technology

Magnetostatic Simulation of a Magnetic Brake

Figure 1 shows the geometry of the magnetic brake which consists of magnetic steel plate, a permanent magnet and a current coil. The coil generates a magnetic field which acts against the field of the permanent magnet. The brake is applied when the coil current is zero. Increasing the coil current will release the brake. The braking force can be calculated as a function of the coil current. Two models were simulated for this device, one simplified by removing the mechanical bolt holes and the other with all features retained. These two models can be cross-checked to establish whether the problem can be simulated as a 2D axi-symmetric problem.

Figure 1: Full geometry of the brake model

A view of the simplified model is shown in figure 2 where the cross-section was swept over an angle of 360 degrees. The material applied to all magnetic components was a non-linear magnetic steel. This can be simulated with the non-linear magnetostatic solver in CST EMS. Figure 2 shows the field generated by the permanent magnet without the coil field i.e. brake-locked condition. Despite the lack of coil excitation, some flux nevertheless returns along a magnetic path around the coil....

Figure 2: Magnetic flux density on a cross section through the magnetic brake

Figure 3: Force versus current characteristic for the simplified and full models

Figure 4 shows the results obtained from the simplified model, which would be equivalent to an axi-symmetric RZ model, and from the full model which includes the discontinuities in the rotational direction i.e. bolt holes etc. It can be clearly seen that there is a deviation in the force-current characteristic between the models. A full 3D model is certainly advantageous for the correct modelling of this device.

With the full parametric modelling facilities in CST EMS, simulation of such devices can easily be achieved. In addition to the built-in modelling tools, CST EMS also offers comprehensive CAD Import facilities for importing more complex models. Parameterisation and optimisation tools are, by default, available in CST EMS.

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