Modelling And Analysis Of Friction Torque In Permanent-magnet Spherical Motor

Both the stator and the rotor of the permanent-magnet spherical motor have a spherical structure and can complete multi-degree-of-freedom(multi-DOF)movement.However,there is contact between the support structure on the stator and the rotor.The friction torque generated by the contact causes the motor to climb or jitter during the trajectory tracking process,which seriously affects the tracking control accuracy.In order to improve the precision of trajectory tracking and realize the industrial application of spherical motor,the modeling and compensation of its friction torque are the key points.This paper reviews the development process of supporting structure the spherical motor,and analyzes the generation mechanism of friction torque under different support structures.At present,the friction torque theory modeling is mainly aimed at the single-degree-of-freedom system,and the friction torque theory modeling for the multi-DOF system such as spherical motor has yet to be developed.Therefore,this article focuses on a permanent-magnet spherical motor,from three aspects: friction model,dynamic model,and friction parameter identification.The main works of this paper are as follows:1)Analyzed the Coulomb friction model and the Stribeck friction model,extended the two friction models to the multi-DOF scene and applied them to the PMSp M.Based on the two models,a rotor dynamics model considering friction torque is established based on the Lagrangian energy method and the the theorem of moment of momentum.2)Based on the analysis of the dynamics model,design and establish a friction torque experiment platform for the PMSp M.Control the experiment platform to drag the PMSp M to complete the constant speed friction torque detection experiment three degrees of freedom.The experimental data of Coulomb friction model and Stribeck friction model are obtained through experiments.3)For the Coulomb friction model,the parameter identification is completed by fitting multi-physics coupling simulation data and experimental data.Aiming at the Stribeck friction model,particle swarm optimization is used to complete parameter identification on the experimental data.Thus,two friction models for the PMSp M are established.4)For the Coulomb and Stribeck friction model,the validity of parameter identification results was verified by tilting motion experiment and the second constant velocity friction torque experiment,respectively.Finally,two kinds of friction models were used to realize friction compensation in closed-loop trajectory tracking,and the compensation effects of the friction models were verified and compared.