Electromagnetic Structure Design And Control Research Of Zero Stiffness Magnetic Levitation Fine Stage

In the field of ultra-precision manufacturing,the positioning accuracy and dynamic characteristics of the multi-degree-of-freedom fine stage directly determine the performance of the processing equipment.With the continuous improvement of the performance of processing equipment,the magnetic levitation fine stage has become an important development direction of ultra-precision processing equipment due to its outstanding advantages such as vacuum compatibility,non-contact friction and no need for lubrication.Aiming at the vibration isolation and lightweight requirements of the micro-motion stage,this thesis proposes a new type of zero-stiffness magnetic levitation fine stage.The electromagnetic topology of the passive support unit can effectively compensate the load weight,and it can cooperate with the combination of coils to achieve six-degree-of-freedom active control.Compared with the traditional structures,the zero-stiffness magnetic levitation fine stage not only has a light structure and a good vibration isolation effect,but also effectively improves the positioning accuracy and dynamic characteristics.The main research contents of this thesis are as follows:The structure design of a new zero-stiffness magnetic levitation fine stage is carried out and the magnetic field modeling is completed.First,the configuration of this driven unit which could realize a single-degree-of-freedom passive support and two-degree-of-freedom active control is proposed.Then,a six-degree-of-freedom magnetic levitation fine stage is designed using three driven units.The electromagnetic analysis and numerical modeling are carried out using the equivalent magnetic charge method and the finite element method respectively,and the methods of generating zero stiffness and suppressing force fluctuation are analyzed.The vertical stiffness variation characteristics of the zero stiffness magnetic levitation fine stage are explored and the design optimization is completed.The influences of the main structural parameters of the driven unit on the vertical force and vertical stiffness are calculated and analyzed by analytical method and numerical method.In order to ensure the calculation accuracy and speed up the calculation time,a hybrid method for optimizing the structure of the magnetic levitation fine stage is proposed by combining the characteristics of these two methods.Based on the analytical model,the optimal solution in the parameter domain is initially found,and the finite element method is used to calculate the magnitude of the vertical force and the drift distance of the zero stiffness point in the working interval.The drift distance is eliminated by tuning the size of this structure finely.The optimized design of the driven unit can provide a vertical support force of 20 N,and the vertical stiffness is within±5 N/m.The six-degree-of-freedom motion control system modeling and fractional-order controller design of a zero-stiffness magnetic levitation micro-motion stage are carried out.The six-degree-of-freedom decoupling calculation is carried out on the magnetic levitation fine stage,and the mathematical model of the single-degree-of-freedom control system is established.Taking the shortest step response adjustment time as the optimization goal,the controller optimization design is carried out.Compared with the integer-order PID controller,the adjustment time of the fractional-order PI~?D~?controller is reduced by about12%.The experimental prototype is built and the experiment is verified.The experimental prototype is processed and assembled,the software and hardware platform are built and debugged.The passive force and the active force of the driven unit in the zero-stiffness magnetic levitation micro-motion stage are measured.Finally,a single degree of freedom positioning experiment is performed to verify the accuracy of the electromagnetic modeling and the feasibility of the servo system.