Study on minimizing the detent force of PM linear brushless DC motors

The detent force due to the interaction between the permanent magnets (PMs) and the teeth produces vibrations and noise. Especially, it deteriorates the low speed performances obviously and reduces the positioning precision. Based on the Fourier analysis of the detent force curve as a function of the motor position and initial phase angle of the harmonics of each pole, the detent force can be reduced by optimally choosing the width of the magnets and asymmetric PM arrangement. The detailed rules to arrange and resize the magnets appropriately are presented and investigated. It is shown that such technique can greatly reduce thrust ripple and increase efficiency of a permanent magnet linear brushless DC motor (PMLBDCM). The FEM (finite element method) simulation results are presented to validate the proposed methods.