Torque Modelling And Drive Current Optimization Of Permanent-Magnet Spherical Motor With Cylindrical Stepped Magnets

Compared with the traditional multi-dimensional transmission device composed of multiple motors,the spherical motor,as a new type of multi-degree-of-freedom(M-DOF)actuator,has the advantages of simplified structure and high dynamic and steady performance.Electromagnetic analysis is particularly important for the motion control and structural improvement of the spherical motors,and becomes more difficult than traditional motors because of the unique three-dimensional motion characteristics.Based on a permanent magnet spherical motor(PMSp M)with an improved magnetic pole structure,this paper establishes a torque model by deriving the calculation formula of the magnetic flux density and torque calculation formula,and uses finite element analysis and experiments to verify the accuracy of the results.Based on the torque model,the genetic algorithm is used to optimize the calculation of the motor’s drive current.The main research work of this paper is as follows:1)The structure of the PMSp M is introduced.The magnetic field of a single magnetic pole is calculated by the equivalent surface current method,and the magnetic flux density of the rotor is superimposed.The correctness of the calculation results is verified by the FEM and experimental method.2)The electromagnetic torque of a single coil is calculated by the Lorentz force method,and the torque Map in the three-dimensional space of the coil is established.The torque model of the motor is derived by interpolating the torque Map and combining with the superposition theorem.The comparison with the FEM and the traditional Lorentz force method verifies the accuracy and efficiency of this model.3)The experimental platform was built to verify the magnetic field and torque model.The radial magnetic flux density of the rotor was measured by a magnetometer to prove the accuracy of the magnetic field model,and the output torque was measured based on the MEMS sensor,which verified the torque results of the energized single and double coils.The accuracy and validity of the torque model are compared and verified.4)Based on the torque model,the genetic algorithm is used to reversely calculate the drive currents for different optimization goals under a given motion posture,and the calculation results for different optimization goals are analyzed.