Study On Dynamic System Of High Temperature Superconducting Magnetic Bearing Twisting Device

As the largest spinning mode in spinning production,ring spinning is an important way for producing high-quality yarn.Compared with some new and efficient spinning methods,the yarn produced by ring spinning is of good quality,but the production efficiency is low.The main reason restricting the production capacity of spinning frame is that there is inevitable friction between the travelers and the rail ring in the existing twisting mechanism.When the spindle speed is too high,the friction in the twisting mechanism will cause serious wear of the travelers and even burn the yarn.In recent years,the innovation of using superconducting magnetic bearings(SMB)as the twisting element of ring spinning has pointed out a new direction for the development of ring spinning frame.The device uses a permanent magnet(PM)rotor instead of the travelers in the existing twisting mechanism,and converts the rotation movement of the travelers on the rail ring into the frictionless rotation of the suspended permanent magnet rotor in the air,thereby greatly improving the production capacity of the spinning frame.To achieve this goal,two major problems need to be overcome: on the one hand,how to ensure that the yarn quality is not affected by the low temperature of liquid nitrogen while the superconductor cools into the superconducting state;on the other hand,how to ensure the smooth operation of the high-speed rotating permanent magnet twisted rotor.Aiming at the first problem,a design scheme of placing the stator of high temperature superconducting(HTS)stator in an annular continuous flow lowtemperature thermostat is proposed,and designs the mechanical structure of the HTS module and the cryogenic thermostat.It not only ensures that the yarn quality is not affected by the low temperature of liquid nitrogen,but also prevents the external temperature from affecting the working stability of HTS stator.For the second problem,this paper mainly studies the dynamic stability of permanent magnet rotor from two directions.Based on the molecular current hypothesis of permanent magnet,the calculation equation of magnetic field distribution of single hollow permanent magnet ring expressed in the form of complete elliptic integral is established by using Biot-Savart law and vector superposition principle.The electromagnetic constitutive relation of superconductor adopts power exponent model,and the three-dimensional electromagnetic field numerical calculation model of SMB twisting system is established by using H method.On this basis,the relationship between suspension stiffness and permanent magnet rotor outer diameter,permanent magnet rotor thickness and field cooling height is given,and the relevant suspension parameters are preliminarily determined.The second is the tension of balloon and the interference of balloon resonance on permanent magnet rotor.In this paper,the balloon shape and yarn tension are solved by variational method and differential method.In addition to the commonly used differential method,the variational equation of balloon is established by using Hamilton principle,the Bezier function is used as the approximation curve of balloon,and the semi-analytical solution of steady-state balloon is obtained by using the successive linearization equation of Galerkin method,which is compared with the results obtained in relevant literature.The binocular stereo vision system is built,and the spatial coordinates of balloon are extracted through Open CV-Python,which provides an experimental basis for balloon theory model.The radial tension exerted by balloon yarn curve on PM ring is emphatically studied,and the factors affecting radial yarn tension are analyzed.The linearized equations of motion are completed by elimination of the nonlinear displacement terms and cancellation of the steady-state terms.The vibration modes and natural frequencies of balloon yarn under different working conditions are calculated and compared with the experimental results.The experimental device to verify the natural frequency of the balloon is designed.The modal responses of the first two natural frequencies of the spinning balloon are obtained by stroboscopic instrument and digital camera,and compared with the natural frequency predicted by theory.