1996 Volume 116 Issue 1 Pages 94-99
Force between an electromagnet and an iron piece is usually calculated with a equation of Maxwell's stress, and for the exact result, the integration of stress is made along a route away from the iron. It, however, is necessary to calculate magnetic flux density components paralell to the integration route as well as perpendicular ones.
The authors propose a new method of calculation using FEM. This method presents that the integration of Maxwell's stress is made on the surface of an iron piece, and magnetic flux is regarded perpendicular to the iron surface. Calculated values of magnetic force, attractive force and restoring force under small parallel displacement to pole face, have been compared with measured ones on an experimental model. The following results are obtained. (1) The magnetic force is calculated using the results of FEM analyses where the number of nodes has been less than 1000. The differences between the calculated and the measured values are smaller than 5%. (2) To obtain the above results, it is necessary that relative permeability of the iron piece is larger than 100 and the side length of each triangle element near the iron corner is less than 2% of the gap length.