Research On Small Axial-flux Permanent Magnet Vernier Motor Based On Magnetic Flux Modulation

The focusing system with telephoto lens characterized the heavy load has a rapid development in recent years and is widely used in various fields,such as photography,medical and precision drives.The power of the focusing system comes from driving motor,so the driving motor with high power density is extremely meaningful.Traditional focusing motor used in low speed field implement the high torque driving through precise speed reducer.But they also have the disadvantages of large size,low efficiency,complex structure and are not easy to install.Therefore,the low speed,direct driving motor,with high torque density and no requirement of transmission,has broad prospects in this field.For the above situation,this dissertation adopts the Permanent Magnet Vernier Motor,which has the characteristic of low speed high torque,to the focusing system.Furthermore,based on the permanent magnet vernier motor in focusing system,the following aspects are studied:A small direct-drive axial-flux Permanent Magnet Vernier Motor is designed,based on the structure and performance requirements of a Samsung digital camera.Considering the design requirements and the topology of Permanent Magnet Vernier Motor,the designed motor uses axial ringed structure to direct driving due to the restrictions of power density,structure and driving system mode.At the same time,the radial length of stator tooth is strictly designed to satisfy the strict condition of inner and outer diameter.Analyzed by the 3D finite element method,the basic characters of target motor is feasible for focusing system.Considering the structure characters of target motor,the improved analysis method and the finite element methods are proposed based on the traditional analysis method of Permanent Magnet Vernier Motor.This paper gives a more accurate analyzed method,considering the radial and circumferential distribution of the magnetic field.Furthermore,a quasi-3D finite element method is used to consider the radial magnetic field and end effect.Various sensitive parameters are considered to analyze the torque characteristics further and an optimization scheme using effective flux density is given.A specific analytical analysis method for cogging torque and magnetic field harmonic torque is given for the axial characteristic of the target motor.Using cogging torque obtained by quasi-3D finite element method and defined effective flux density as targets,genetic algorithm is used to optimize the motor parameters.The results of 3D finite element method indicate the excellence of the optimized motor.A non-uniformly distributed tooth structure is proposed for open-slot vernier motor to improve the torque density further.Based on the principle of m agnetic flux modulation,the non-uniformly distributed tooth enriches the harmonic component of magnetic density,which increases the effective flux den sity and torque,caused by changing the distribution of stator tooth.The basic principle,design method of tooth and the decreasing of cogging torque are introduced in detail and used for focusing driving motor.The c omparing results of uniformly distributed tooth and proposed tooth structure analyzed by 3D finite element method verify the superiority of proposed structure.Finally,the testing platform is built to test the basic characters of initial prototype.Basic results of experiment are given and analyzed.