| In the “Outline of the 14 th Five-Year Plan for National Economic and Social Development and Vision 2035 of the People’s Republic of China” issued by China,it is proposed to promote the “high-end CNC machine tool” and other industry innovation development,which will vigorously promote the CNC machine tools toward the direction of high-speed,precision development.As one of the most critical components of CNC machine tools,the performance of electro-spindle directly affects the machining accuracy,stability and application scope of the CNC machine tools.Magnetic bearings do not have the friction and wear problems of the contact bearings,nor do they have the extra fluid supply systems required by other non-contact bearings.Therefore,it is especially suitable for the electro-spindle support system.Based on the theory of the bearingless motor,the magnetic bearings with three-pole can be driven by a three-phase inverter,and the relevant control technology of the three-phase AC motor can be applied to the magnetic bearings.Compared with the common magnetic bearing,it can reduce the volume and cost of the whole system.However,the asymmetry structure increases the nonlinearity and the control difficulty of the system.The magnetic bearing with six-pole increases the symmetry of the structure and improves the unit bearing capacity of the magnetic bearing,which is also conducive to realizing the precise control of the magnetic bearing.Therefore,the use of the inverter-fed six-pole magnetic bearing to support the electro-spindle is conducive to improving the speed of the electro-spindle and prolonging its service life.The research of this dissertation is of great significance to promote the development of the CNC machine tools in the direction towards high-speed and precision.And it contributes to the transformation of China from a manufacturing giant into a manufacturing power and the realization of the high-speed precision electro-spindle.In this dissertation,the magnetic suspended electro-spindle is taken as the research object.The working principle,suspension force mathematical models,parameter optimization design,decoupling control technology and digital control system are studied.The main works and achievements of the dissertation are as follows:1.The overall design scheme of the magnetic suspended electro-spindle is proposed,one end of the electro-spindle is supported by the inverter-fed two-degree-of-freedom(2-DOF)sixpole hybrid magnetic bearing(HMB),and the other end is supported by the inverter-fed threedegree-of-freedom(3-DOF)six-pole HMB.The working principles of the magnetic bearing at two ends are clarified.The radial suspension force mathematical models of the inverter-fed 2-DOF six-pole HMB are deduced by the Maxwell tensor method,and the radial and axial suspension force mathematical models of the 3-DOF six-pole HMB are also deduced by the Maxwell tensor method.And the specific parameter values are also designed2.In view of the problem that single-objective optimization can only make a certain performance index of the magnetic bearings reach the optimal,but it may sacrifice some other unconsidered problems that seriously reduce the performance index of the magnetic bearings,the improved Multi Objective Particle Swarm Optimization(MOPSO)algorithm based on the hybridization concept is proposed to optimize the parameters of the inverter-fed 2-DOF six-pole HMB,so as to achieve the three optimization objectives of larger radial bearing capacity,lower stator eddy current loss and smaller volume.The comprehensive sensitivity analysis is used to divide the optimization variables into significant and non-significant optimization variables.And the improved MOPSO algorithm based on the hybridization concept is adopted to optimize the significant optimization variables,and the 3-D Finite Element Method(FEM)is adopted to optimize the non-significant optimization variables.Finally,the finite element simulation model of the inverter-fed 2-DOF six-pole HMB is constructed,and the comparisons of the simulation results demonstrate the superiority of the optimization results.3.Radial suspension force or axial suspension force expressions usually do not contain variables in the other direction,in order to solve the problem that the significant optimization variables of the inverter-fed 3-DOF six-pole HMB are not included in some optimization objective expressions,the multilevel optimization design is proposed for its parameters,so as to achieve the three optimization objectives of larger radial capacity,larger axial capacity and smaller volume at the same time.Through adopting the comprehensive sensitivity analysis and judging whether the variable is included in the optimization objective expressions,the optimization variables are divided into three levels.The response surface method is adopted to optimize the optimization variables in level 1,the improved MOPSO algorithm is adopted to optimize the optimization variables in level 2,and the 3-D FEM is adopted to optimize the optimization variables in level 3.Finally,the finite element simulation model of the inverter-fed3-DOF six-pole HMB is constructed,and the comparisons of simulation results demonstrate the superiority of the optimization results.4.In view of the problem that during the actual operation process of the HMB,the factors as non-uniform material,installation error,and non-uniform heating will cause the static working point offset when the rotor is stably suspended,which will affect the stiffness coefficient of the HMB system,it is proposed that the influence of the variable stiffness coefficient on the magnetic suspended electro-spindle can be considered in the design process,and combined with the air gap length of the auxiliary bearing to obtain the feasible region of the stable operation of the HMB.By analyzing the influence of the bias magnetic field ratio and the static eccentricity ratio on the variable stiffness coefficient,HMB are divided into stable region and unstable region.The working area of the HMB is obtained by combining the bias field ratio and the air gap length of the auxiliary bearing.Finally,it is verified that the working area of the HMB is in the stable region,indicating that the HMB can work stably.5.In order to solve the coupling problems between the five-degree-of-freedom(5-DOF)of the magnetic suspended electro-spindle system,the Linear Active Disturbance Rejection Control(LADRC)decoupling control method based on the Improved Particle Swarm Optimization(IPSO)algorithm is proposed.The five LADRC decoupling controllers are adopted for the five degrees of freedom of the magnetic suspended electro-spindle,so as to transform the strongcoupling system with multi-input and multi-output into an independent non-coupling system with five inputs and five outputs.In view of the problem that it takes a long time and is difficult to obtain the optimal parameters,when tuning the LADRC decoupling controller relies on the manual experience,the bandwidth tuning method is used to reduce the parameters to be optimized of the LADRC decoupling controller,and the IPSO algorithm based on hybridization concept is proposed to optimize the parameters of the LADRC decoupling controller.The simulation studies of the magnetic suspended electro-spindle system with the PID controller,the PSO-LADRC decoupling controller and the IPSO-LADRC decoupling controller are carried out,the results show that the decoupling and anti-interference performances of the IPSO-LADRC decoupling controller are better than the other two controllers.6.According to the optimized parameters,the experimental prototype of the 5-DOF magnetic suspended electro-spindle is manufactured,and the hardware system design and software system design of the digital control system are carried out.On the basis,the digital control experimental platform of the whole magnetic suspended electro-spindle is constructed.The basic experiment is carried out and the experimental results are analyzed.The comparative experimental studies are carried out for the 5-DOF magnetic suspended electro-spindle system with the PID controller and the proposed decoupling controller,and the results indicates that the proposed IPSO-LADRC control method has better decoupling performance and ability to suppress interference. |
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