Research On Magnetic Modeling And Motion Control Of Magnetic Levitation Rotary Table

With the development of modern manufacturing industry towards high precision,in precision manufacturing fields such as micro-machining,IC manufacturing,optical component processing and other industries,the positioning accuracy of the positioning platform in manufacturing equipment directly determines the precision level of processed products.Magnetic levitation positioning platform has a very good application prospect in precision manufacturing and other industrial fields due to its advantages of no mechanical friction,multi-degree-of-freedom movement and operation in vacuum.In this paper,a magnetic-moving magnetic levitation rotary table system is studied.The magnetic field model,electromagnetic force model and motion control strategy of the magnetic levitation rotary table are studied.A magnetic levitation prototype is made and the hardware system is built to realize the static test and motion control experiment verification of the magnetic levitation rotary table.Specific research contents include:Firstly,a magnetic field model of circumferential HALBACH magnetic array based on two-dimensional harmonic method is proposed.The magnetization vector is derived from the physical model of the actual distribution of circumferential magnetic array and the analytical expression of magnetic flux density distribution is derived from Maxwell’s theory.Secondly,according to the magnetic flux density expression derived,the magnetic force and torque of the magnetic levitation actuator are solved by Lorentz integral,and the electromagnetic force is numerically calculated by Gaussian quadrature method.The proposed magnetic modeling method provides a more accurate electromagnetic force model for dynamic analysis of magnetic levitation rotary table controller design and structural optimization design of magnetic levitation rotary table.Thirdly,a fractional order sliding mode motion control strategy based on nonlinear disturbance observer is proposed to control magnetic levitation rotary table.According to the electromagnetic force model of the magnetic levitation rotary table,the dynamic analysis is completed,and the state equations of continuous domain and discrete domain are constructed.Aiming at the characteristics of magnetic levitation system with strong coupling,multi-input,multi-output and nonlinear characteristics,a fractional order proportional differential integral sliding mode surface was designed,and a nonlinear sliding mode control law with finite time convergence was designed in discrete domain,and a nonlinear disturbance observer was used to compensate the system lumped uncertainty.The proposed fractional order sliding mode motion control strategy improves the multi-dof trajectory tracking capability of the magnetic levitation rotary table and achieves better motion control effect.Finally,a prototype is made based on the software and hardware design process of magnetic levitation rotary table for system verification,and the human-computer interaction control interface of the system is designed.The boundary element software Radia TM was used for electromagnetic simulation and static test of the platform was carried out.The magnetic field modeling method reduced the maximum error of the magnetic field at the radial edge of the magnetic array from 104.19% to 3.29%,and the magnetic force modeling method improved the calculation accuracy of magnetic force and torque by 60.74% and 84.39%,respectively.According to the realized closed-loop motion control scheme of the magnetic levitation rotary table,the system motion control experiment is carried out.The fractional order sliding mode control strategy achieves good results in the 6-dof trajectory tracking motion control and the decoupled motion control of magnetic levitation rotary table,and ensures the performance of the system in fast working environment.Experiments were carried out to simulate the possible uncertain disturbances of the positioning platform in practical application scenarios,and the results verified that the proposed control strategy also had good disturbance rejection characteristics,which provided feasible support for the application control of magnetic levitation rotary table.The software and hardware design process of magnetic levitation rotary table studied in this paper provides a theoretical and experimental solution for industrial application of magnetic levitation positioning platform.