Study On Normal Force Ripple And Its Weakening Method Of PMLSM In Slot Effect

The linear motor gradually replaced the traditional ball screw system because of“Direct driving” with the application of PMLSM more and more used in CNCmachine tool. The breaking magnetic, alveolar structure and MMF harmonics andother factor, directly affect the normal force ripple. The normal force ripple can causethe CNC machine tool vibration, also can cause friction perturbation, influence thethrust force ripple indirectly, affect the accuracy of CNC machine tool. So the normalforce ripple more and more is concerned by scholars home and abroad. There is nodelay to research the normal force ripple that it has restricted the development of highprecision machine tools in China. The cogging effect is one of the main reasonscaused by the normal force ripple, so the thesis study the cogging effect normal forceripple as follows:Firstly, study on the causes of cogging effect normal force ripple. From the angleof field magnetomotive force, the thesis use the method of Maxwell Stress Tensor toderive the analytic expression of normal force in the case of armature open circuit andthe Fourier decomposition to find harmonic rule, which is validated by finite elementmethod, verify the validity of the method.Secondly, on the basis of the analytic expression, we analyze linear motor’s airgap permeance and proposed the tooth width coefficient of linear motor to weaken thecogging normal force ripple. Study the normal force ripple variety with tooth widthcoefficient, which is validated by finite element method，verify the validity of themethod.Thirdly, based on the analysis of the analytic expression, analyze the linear motorand the main harmonic number of slot effect, we proposed suitable selection of polearc coefficient to weaken normal force ripple. Study normal force ripple and thrust ripple with the pole arc coefficient in the same and different tooth width.By using the finite element softwareANSOFT verify the validity of this method.Finally，optimize the motor, verify tooth width coefficient and pole arc coefficientof the normal force ripple minimum respectively, and the normal force ripple is thesmallest. Then consider the thrust force to ensure it smallest, and have comprehensiveoptimization.The thesis has theoretical significance and practical value to study linear motor’sthe analytic expression, and Weakening method and proposed has the guiding sense tothe motor designer.