Research On Brushless Dc Motor With Slotless And Elliptical Magnet Used In Medical Devices

Most existing medical devices use brushless DC motors.In view of the problems of existing brushless DC motors,such as sinusoid of air gap magnetic flux density and large cogging torque,a slotless brushless DC motor adopting a novel elliptical magnetic pole structure is proposed.This kind of motor can make the air gap magnetic close to the trapezoidal wave,further reduce the torque ripple,reduce the vibration and noise,and improve the running performance of the motor.In this paper,the problems of air gap magnetic flux density,magnetic pole ellipticity,vibration and noise are analyzed and studied.Firstly,the structure of the elliptical magnetic slotless brushless DC motor is introduced.The air gap magnetic flux density of the unequal thickness magnetic pole is calculated by the analytical method of air gap magnetic field superposition.The correctness is verified by finite element simulation;To study the effects of parallel and radial magnetization methods on the no-load back-EMF,armature current and electromagnetic torque of the motor;The simulation analysis of the effect of the elliptical magnetic pole on the air gap magnetic flux density,the air gap magnetic density fundamental wave amplitude,the size of the electromagnetic torque and the torque ripple rate under different ellipticity;The stator iron loss of the elliptical pole slotless brushless DC motor under two kinds of materials including amorphous material and soft ferrite was studied,and compared with the conventional silicon steel stator core.Secondly,the influence of the elliptical magnetic pole structure on the vibration and noise of the motor under different ellipticity is studied,including the analytical method and the finite element method to study the natural modal frequency of the stator structure of the motor.In the analytical method,the prototype is simplified to a ring plate,and the natural frequency of the prototype is calculated.The finite element method uses ANSYS software to perform the modal simulation on the stator structure model of the motor,the stator model of the motor after the shell is added,and the stator structure model of the motor after the end cap is added.Based on the analysis of the intrinsic mode,the magnitude and frequency spectrum of the radial electromagnetic force wave of no-load and load of the elliptical magnetic pole slotless brushless DC motor under different ellipticity are analyzed.The radial electromagnetic force waves that cause the electromagnetic noise of the motor are compared and analyzed.The electromagnetic force waves,vibration and noise are coupled and simulated,and the simulation results of vibration acceleration and electromagnetic noise are obtained.At last,a prototype of 104 W elliptical magnetic pole slotless brushless DC motor was prototyped,and the back-EMF experiment was carried out.The voltage,current waveform and electromagnetic torque curve of the motor measured during the load test.A modal test was conducted using the hammer method to measure the natural modal frequency of the motor.In vibration and noise experiments,the vibration acceleration and motor noise of the elliptical magnetic pole slotless brushless DC motor surface of shell were measured;the vibration acceleration and noise of the circular and elliptical magnetic pole slotless brushless DC motors at different speeds were measured and compared.