Research On Normal Force Ripple Of Permanent Magnet Linear Servo Motor And Inhibition Method

Linear motor direct drive technology greatly improves the rapid response capability,motion precision and high-speed feed capability of the servo system, which has become one ofthe most representative advanced technology of modern top-grade CNC machine tools. Thesingle-side flat-plate core servo-used permanent magnet linear synchronous motor (PMLSM)with the characteristics of big thrust, high power density, has been the most widely used linearmotor at present. However, due to the impact of slot effect, end effect and magnetic fieldharmonics, there is the large normal force ripple between the mover and stator when the motoris operating, and the friction force perturbation and machine tool vibration caused by thenormal force ripple will influence the accuracy of machine tool greatly. The producingmechanism and weakening methods of the normal force ripple in flat-plate core PMLSM aresystematically studied in this dissertation. Major works are listed as follows:The relation of the PMLSM normal force ripple and magnetic field harmonics and therelativity of the normal force and thrust force are studied. Based on the analysis of thepermanent magnet MMF harmonics, armature MMF harmonics and air gap permeanceharmonics, the normal force ripple analytical expression of the primary end tooth infinitelylong PMLSM can be derived using Maxwell Stress Tensor method and integration method toreveal the law of the normal force ripple. From the perspective of air gap magnetic fieldenergy, the relativity of the normal force and tangential electromagnetic thrust is analyzedusing analytical method, and the influence of the weakening methods of the normal forceripple caused by slot effect, end effect and load disturbance on the tangential electromagneticthrust is comprehensively considered.The effect law of motor parameters on the normal force ripple is study. The normal forceripple is directly related with the tooth tip width and pole arc coefficient. Firstly, the effect lawof the tooth tip width and pole arc coefficient on the amplitude and time of normal force ripplecaused by slot effect (cogging normal force ripple for short) is analytically analyzed. Then thefinite element method (FEM) is adopted to verify the cogging normal force ripple conditionand its influence degree on the thrust performance under different tooth tip widths and pole arccoefficients, which provides theoretical direction for the optimal design of high-performance linear motor.The method of three-section permanent magnets staggered weakening normal force rippleis studied. The law that the method of motor primary tooth tip auxiliary slotting combined withunequal pole arc coefficient to weaken the thrust ripple weakens the normal force ripple isanalyzed, and then the limitation of the two methods is analyzed. On this basis, three-sectionpermanent magnets staggered method is proposed to weaken and even cancel the mainsubharmonic cogging normal force ripple, and to simultaneously avoid the motor producingtransverse pitch motion according to the reversed phase cancellation principle. The FEM isadopted to verify the validity of this method.The method of the phase separation current compensation control strategy weakening thenormal force ripple caused by end effect (end normal force ripple for short) is studied. The endnormal force ripple is the main component of the normal force ripple. Based on the specialthree-phase winding distribution law of fractional slot winding permanent magnet linear servomotor, the phase separation current compensation control strategy is proposed to restrain theend normal force ripple. The principle of thrust performance optimization and normal forceripple minimum is followed when the phase separation current compensation control isadopted. Then the compensation model established method of the end normal force ripple isstudied. Finally, Ansoft series software Simplorer and Maxwell are both adopted to simulateand to verify the validity of this compensation control strategy.The permanent magnet linear servo motor prototype and normal force test system aredesigned to verify the correctness of theory and method. The normal force static measurementof the primary end tooth infinitely long12-slot8-pole whole magnets or three-sectionstaggered magnets PMLSM is carried out to verify the validity of three-section magnetsstaggered method weakening the cogging normal force ripple. The normal force measurementof12-slot11-pole PMLSM adopting the phase separation current compensation control iscarried out to verify the feasibility and validity of the phase separation current compensationcontrol strategy weakening the end normal force ripple.