Design And Study Of Multi-axis Magnetically Levitated Positioning System Based On Lorenz Force Actuator

In the area of ultra-precision machining, such as semiconductor processing, bio-engineering, and aerospace component manufacturing, the accuracy of controlling, pro-cessing, and assembling are micro or nanometer grade, therefore, the positioning equip-ments with the corresponding accuracy level are necessary to ensure the precision. The traditional positioning device can not eliminate the inherent friction, which results in the shortcomings like low motion accuracy, less degree of freedom, and so on; another available micro-motion device actuated by piezoelectric material is able to realize the positioning accuracy of nanometer grade in different motional direction, but still suffers from the drawbacks including short stroke, low respond speed, and so on. Currently, magnetically levitated positioning technology is considered as a promising method to maintain high positioning accuracy, long stroke, multiple degrees of freedom, and high respond frequency. As a kind of direct current driving actuator, Lorenz force actuator possesses the advantages of excellent controllability, high motion resolution, and flexure design structure, which is suitable to provide the accurate and adjustable motion for magnetically levitated system. In this case, this thesis has mainly studied the design and simulation method of multi-axis magnetically levitated system based on Lorenz force actuator, and the achieved research results contain four aspects below.(1) A calculation method for solving the output magnetic force of cylindrical Lorenz force actuator is proposed, and this method is employed in the design of magnetically levitated system in order to guarantee the performance of the system. Based on the Lorenz integral equation and the numerical integration method, this thesis obtains the expression for the force-position relationship of the actuator. Additionally, employing the cylindrical Lorenz force actuator, a single axis magnetically levitated system is de-signed. The motion range of the moving part in the system is decided depending on the force-position relationship solved by the proposed calculation method, in which the magnetically levitated system is open-loop stable, meanwhile, the relationship is also employed in the system to realize the linearity, which produces the desired control ef-fect. The testing results demonstrate the excellent precision of the proposed calculation method used for solving the magnetic force produced by the Lorenz force actuator, and the designed single-axis magnetically levitated system has good dynamic and steady characteristics.(2) A design method of driving system used for the compact multi-axis magnetically levitated positioning system capable of positioning down to micron in several millimeter travel range is proposed. Utilizing eight cylindrical Lorenz force actuators possess the same structure to provide the vertical levitated force and horizontal propulsion, the levitated stage is able to be controlled accurately; employing three eddy gauges and three laser displacement sensors to construct the sensing system; combining the magnetic force model with the location of each actuator, the current-wrench transferring matrix for the levitated system is obtained to realize the decoupling between different actuators in the controller. The experimental results illustrate the positioning system realizes the 2.8?m and 4?m resolution of horizontal and vertical translation respectively with the travel volume of 2mm×2mm×2mm, and the 100?rad and 80?rad resolution in horizontal and vertical rotating respectively with the rotating range of 80mrad×80mrad×40mrad.(3) A parallel simulation method used for solving the characteristics of the Lorenz force actuator is proposed to maintain the simulation efficiency and simulation accuracy. With the magnetic node, Gaussian quadrature, and coordinate transformation, this the-sis derives the universal wrench model for the Lorenz force actuator, which obtains the solution of dynamic characteristics due to various kinestates of magnetically levitated system. Aiming at the large-scale parallelism in this model, all of these calculation modules are implemented on the graphics processing unit (GPU) in a massively parallel framework to realize the significant acceleration. In the experiment, compared with the finite element method software and a boundary element method software package, the testing results demonstrate that the computation efficiency of the proposed par-allel wrench model achieves the dramatic improvement with the sufficient calculation accuracy, generality, and robustness.(4) A hardware-in-the-loop emulator for the magnetically levitated system is pro-posed for the on-line testing of the matching controller in the multi-axis magnetically levitated positioning system. Benefited from the computation method of magnetic force aforementioned, and the parallelism and pipeline in the execution of FPGA program, this thesis decreases the computation cycle of one sampling point to 100?s in the sim-ulation; with the circuit states and the dynamic states solving modules, the real-time mathematical model of the single axis magnetically levitated system and 6 degree of freedom magnetically levitated stage, which are able to interface with the real con-troller, are constructed for the hardware-in-the-loop simulation. In the experiment, the proposed hardware-in-the-loop emulating method is proved to be able to reflect the real effects of the controller well via comparing the outputs of the emulator with the practical results of the real magnetically levitated system.This thesis conducts a comprehensive study of the application of Lorenz force actu-ator in the magnetically levitated positioning system, and some research achievements about the magnetically levitated system design and simulation have been obtained. These achievements possess great practical value and theoretical significance for the development of corresponding positioning device in the ultra precision machining and the improvement of emulator aiming at the multi-axis magnetically levitated system in the commercial software respectively.