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 cogging-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.
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Zhu et al. (1997) studied this question.