Design And Analysis Of High Torque Density Permanent Magnet Torque Motor Based On Radial Ring Magnetization

Permanent magnet torque motors need to have high torque density and low torque ripple performance due to the lightweight and high accuracy requirements for cooperative robot joints.However,the existing topology and optimization methods of motors cannot simultaneously achieve the performances mentioned above.Therefore,the multi-pole magnetization method is proposed in this paper to magnetize the multi-pole radial ring magnet,which is applied to the joint torque motor.The designed joint motor possesses high torque density and low torque fluctuation.Firsly,the existing magnetization methods are investigated and compared.The pulse magnetization method is selected according to high coercivity of the neodymium iron boron(Nd Fe B)permanent magnets.In order to study the influence of circuit parameters on the magnetization effect,a pulse circuit is built.The simulation is carried out to investigate the relationship between circuit parameters and peak current and select reasonable circuit parameters.Moreover,a pulse circuit is established for the 20-pole multi-pole magnetic ring rotor.The simulation is conduct based on the coupling model with magnetic field,electric field and temperature field.In the simulation,the B-H magnetization curve of the permanent magnet is used to analyze the magnetic field intensity,pulse current,coil temperature and electromagnetic force during the magnetization process of the multi-pole radial oblique magnetic ring.Then,the core material and coil shape of the magnetization fixture are determined.Compraring the magnetization result of the experiment with that of the simulation,the error is within the allowable range(5%),which verifies the applicability of the finite element method in analyzing the magnetization of Nd Fe B.Finally,the influence of the rotor yoke thickness,pole arc coefficient,pole slot matching and inclined pole angle on the torque density is studied under the overload condition based on the multi-pole magnetic ring structure and the surface-mounted rotor structure.According to the above parameter scheme,the permanent magnet torque motor with high torque density for the robot joint is designed,and the electromagnetic design scheme of the joint torque motor is determined.Through analyzing the electromagnetic characteristics of the motor,a prototype is developed.The working characteristics of the prototype is tested through the hysteresis dynamometer system.The results show that the multi-pole magnetic ring structure rotor can increase the torque density,whihc verifies the feasibility and the effectiveness.of the method.