Research On Mechanism And Performance Of Inductive Magnetic Levitation Spherical Joint

Magnetically levitated spherical joints have the advantages of high integration,small size and good flexibility,which can accomplish spatial multi-degree-of-freedom motion and avoid the loss caused by mechanical friction,and therefore have received wide attention from industrial applications such as aerospace and intelligent manufacturing.Considering the characteristics of induction magnetic levitation spherical joints with simpler structure and more flexible motion,this paper proposes a new induction levitation and drive structure with a combined arrangement of four circular arc stators,using its low degree of spatial electromagnetic field coupling to ensure that the spherical rotor rotates in space while maintaining stable levitation through a reasonable spatial arrangement,and the specific research is divided into the following aspects.（1）The basic structural components of the induction magnetic levitation spherical joint are introduced,and the structural parameters of the rotor and stator of the spherical joint are designed and selected.The operation principle of the spherical joint is analyzed for the new structure of the spherical joint.The air-gap magnetic field distribution model and the voltage and magnetic chain equations of a single stator spherical joint are constructed with reference to the working mechanism of linear induction motor,and the torque and levitation force equations of a single stator spherical joint are obtained by the principle of virtual displacement.Finally,the force vector model of rotor suspension support and rotation drive is constructed based on the force interaction between the stator and rotor in three-dimensional space.（2）The static magnetic field,dynamic magnetic field and eddy current field of the spherical joint are simulated and analyzed by Maxwell software.The static magnetic field simulation results show that the magnetic induction strength of the stator structure increases with the increase of current,and the static electromagnetic load range of the structure is determined according to the variation law of magnetic induction strength and design requirements.The eddy current field simulation results show that the distribution pattern of induced eddy currents on the rotor is reasonable,which can provide a stable action current for the electromagnetic drive of the rotor.The three-dimensional air-gap magnetic density simulation results show that the induction electromagnetic fields generated by the four stators of the spherical joint in the space air-gap have low coupling degree,and the circumferential distribution pattern of the air-gap magnetic density fits with the theoretical model,thus ensuring the independence of the electromagnetic manipulation of each stator,and controlling the effective suspension support and rotational drive of the rotor through the force coupling between each stator and the rotor.Based on the static analysis results,the operation mechanism of the spherical joint is analyzed in the dynamic magnetic field,and the change process of alternating magnetic poles in the cycle is given,and the torque and normal force of the spherical joint under different parameters are studied.The simulation results show that the spherical joint can obtain large torque and normal force in the current control range of 0-3 A,which indicates the high dynamic tunability and good load-bearing performance of the spherical joint.By changing the structural parameters,the relationships between the air gap size,rotor material,conductive layer thickness and the variation of torque and normal force are determined.Finally,based on the dynamic and static characteristics,the response of the spherical joint under sudden change of load is studied by Maxwell and Simplorer joint simulation,and it is proved that the spherical joint can operate normally and has good sudden change response characteristics.（3）Coupled simulation of electromagnetic vibration of the spherical joint is carried out to analyze the vibration characteristics of the stator-rotor pair by comparing the electromagnetic force wave frequency and the inherent frequency of the structure.Theoretical derivation of the radial electromagnetic force model and harmonic analysis of the electromagnetic force density were carried out to obtain the space-time and space-frequency characteristics of the radial electromagnetic force and to determine the main force wave frequencies that are likely to cause electromagnetic vibration.The inherent frequencies and vibration patterns of each structure were obtained by modal analysis,and the critical rotor speed was also analyzed to avoid resonance near the critical speed.The electromagnetic coupling vibration of the structure was studied by harmonic response analysis,and the coupling vibration amplitude-frequency characteristics were obtained and compared with the electromagnetic force wave and the intrinsic frequency.The results showed that the main force wave frequencies were not near the overall structure intrinsic frequency,and the overall structure vibration amplitude was small.