| Magnetically suspended gyroscope flywheel can not only measure the attitude of spacecraft by using the fixed axis of the rotor,but also control the attitude of spacecraft by deflecting the rotating axis of the rotor and outputting the gyroscopic moment.In this paper,a new magnetically suspended gyroscope flywheel with kinds of magnetic bearings was introduced.Spherical magnetic resistance magnetic bearings are applied to control 3-DOF translation of the rotor and Lorentz force-type magnetic bearings are used to control 2-DOF deflection of the rotor.The interference of translational suspension on deflection suspension is eliminated and the precision of output gyro moment depends on Lorentz force-type magnetic bearings in this magnetically suspended gyroscope flywheel.However,the poor uniformity of air gap magnetic density of the conventional Lorentz force-type magnetic bearing makes it difficult to achieve high precision torque output,which restricts the improvement of the performance of magnetic suspension gyroscope flywheel.In this paper,the magnetic circuit and air gap magnetic field distribution of Lorentz force magnetic bearings are studied and Lorentz force-type magnetic bearings with high magnetic field intensity and uniformity of magnetic density are designed,so as to achieve high precision and high torque output.Ignoring the peripheral magnetic leakage of the conventional Lorentz force-type magnetic bearing,the electromagnetic force mathematical model is established by using the equivalent magnetic circuit method.The distribution of magnetic field in the radial section is analyzed by finite element method.It is found that the longitudinal diffusion of magnetic field is the main factor leading to the poor uniformity of air gap magnetic density.The trapezoidal section permanent magnet scheme and the spherical trapezoidal section permanent magnet scheme are proposed,and the air gap magnetic density characteristics of the three schemes are compared and analyzed.By optimizing the three key structures of the air gap side angle,the length of the magnetic isolation ring and the magnetizing length of the magnet steel,the air gap magnetic field strength and the magnetic density uniformity of Lorentz force-type magnetic bearing with spherical trapezoidal section permanent magnets are further improved.Due to the limitation of processing technology,the large size annular magnets in Lorentz force-type magnetic bearings are often joined together by arc-shaped magnets.By analyzing the circumferential magnetic density distribution of the air gap,it is found that the gap at the joint of the magnet steel is the main reason for the poor circumferential uniformity of the magnetic density.An internal Lorentz force-type magnetic bearing is presented.The simulation results show that the circumferential fluctuation of magnetic density can be effectively suppressed and the uniformity of magnetic density can be improved by the paramagnetic effect of soft magnetic materials,but the magnetic intensity of air gap is low.Considering the peripheral magnetic leakage,the air gap magnetic density is calculated by reluctance splitting and equivalent magnetic circuit method.Considering the position of each coil,the mathematical model of electromagnetic force is established.The magnetization length of the magnet,the edge angle of the magnetic conduction ring and the side top angle of the air gap of the magnet are optimized respectively to improve the magnetic density characteristics of the implicit scheme In order to further expand its structure,a double magnetic circuit implicit Lorentz force magnetic bearing is proposed,its double magnetic circuit is analyzed,and its magnetic density distribution characteristics in the radial section and circumference are studied.A design method of magnetic circuit superposition is proposed and a Lorentz force-type magnetic bearing with magnetic concentrating is designed.The longitudinal diffusion and circumferential flux fluctuation of magnetic density are effectively suppressed by using multi-branch flux superposition and paramagnetic ring.Compared with the explicit scheme,the magnetic concentration scheme can effectively improve the uniformity of magnetic density without reducing the intensity of air gap magnetic field.Due to its difficulty of dividing into the magnetic circuit for complicated assembled magnetic field,a dividing magnetic reluctance region with the media boundary method is proposed.Considering the position and size of each coil in deflection state,the electromagnetic force mathematical model of magnetic concentrating scheme is established.The variation of electromagnetic force and deflection moment of explicit scheme and magnetic concentrating scheme with control current and rotor deflection angle is analyzed by finite element method.The results show that the electromagnetic force of the magnetic concentrating scheme has good linearity under the deflection state,and it is very suitable for the output of high precision and high torque of the magnetic suspension gyroscope flywheel.Finally,the idea and method of designing and improving Lorentz force-type magnetic bearings are briefly summarized by transforming the magnetic flux congregating Lorentz force-type magnetic bearings into V-type structure.Finally,the advantages and disadvantages of explicit scheme,implicit scheme and magnetic concentrating scheme are summarized and analyzed.The direction and content of improving the magnetic force performance of Lorentz force magnetic bearings are further pointed out. |
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