Reduction of cogging force in slotless linear permanent magnet motors

There are two potential causes of cogging force in linear permanent magnet motors, resulting from the slotting and the finite length of the iron-cored armature. The paper is concerned with slotless motors, for which a technique is described for minimising the cogging force which is produced when the armature has a mild steel sleeve (yoke). By analysing the cogging-force waveform developed at one end of the sleeve and optimising its axial length so that an opposing coggi ng-force waveform is developed at the other end, it is possible to obtain nearly zero resultant force. The technique has been validated on a prototype motor and found to be effective and simple to implement.