Research On Electromagnetic Performance Of End-iron-free Voice Coil Motor

Voice coil motor(VCM)is a kind of DC linear motor based on the principle of Ampere force,which offers many advantages,such as simple structure,small volume,quick response,and no cogging effect.However,VCM has obvious end effect,which leads to the decrease of thrust density and the increase of thrust ripple.In this thesis,a new VCM structure was proposed to suppress the end effect of VCM used in linear impact system.And the measures of structure improvement were presented accordingly for higher thrust density and better dynamic impact performance.The main work of this thesis are as follows:According to the actual demand of linear impact system,the classification of VCM was determined.The end-iron-free structure was proposed by analyzing the magnetic field distribution of VCM in this thesis.Then the magnetic equivalent circuit model of end-iron-free VCM was established,so that the relationship between the average thrust and permanent magnet(PM)length ratio was studied by analytical method.It was found that there is a maximum point in the curve of average thrust with PM length ratio,which indicates the optimization direction of VCM thrust characteristic.Aiming at relatively better motor structure,the magnetic field distribution and thrust characteristics under different PM length ratio were compared by finite element calculation.For Halbach VCM,the arrangement of PMs and radial-magnetized PM length ratio were adjusted after removing the end iron.Subsequently,the static thrust experiment was carried out to verify the analysis.Besides,the application of VCM studied in this thesis is linear impact system,the attention was paid to analyzing the influence of the end-iron-free structure on the dynamic impact performance of VCM.The dynamic impact mathematical model of VCM was established.By comparing the dynamic impact performance of VCMs before and after improvement,the thrust curve was forwarded to further improve the dynamic impact performance of end-iron-free VCM by means of the optimization of magnet separator ring length ratio.Subsequently,the dynamic impact experiment was carried out to verify the analysis.The analysis and experimental results show that the end-iron-free structure can effectively suppress the reverse magnetic flux near the end of VCM and Halbach VCM on the premise that the mass and volume of the motor are significantly reduced.The original "three magnetic circuit" structure is converted to "two magnetic circuit" structure.By adjusting the PM length ratio,higher thrust density and lower thrust ripple are obtained.In addition,the end-iron-free VCM has good dynamic impact performance.And it has better starting performance and higher impact efficiency after forwarding the thrust curve.