摘要
随着机器人等高新技术的发展,能够实现三自由度运动的永磁球形电动机成为了研究热点。但是,该类电机特有的球形结构,无法照搬传统电机的研究方法与经验,其研究具有开拓性和前沿性。目前,永磁球形电动机还处于理论探索阶段,主要研究内容局限为电磁模型、运动学模型及动力学模型的理论推导与计算。从当前的研究结果来看,电机的力能指标不高,矩角特性需要改进。
本论文提出了一种Halbach阵列永磁球形电动机,给出了其基本结构和工作原理。应用球谐函数理论,对Halbach阵列永磁球形电动机磁场的基波和谐波分量进行了分析,得到了磁场解析模型。研究了Halbach阵列永磁球形电动机转子磁体厚度、磁体纬度角及磁化方式对气隙磁场的影响。并与平行充磁磁体结构产生的磁场进行了比较分析,研究结果表明Halbach阵列永磁球形电动机可以明显改善球形电动机的性能。
作为对解析法的一个验证及补充,本论文基于有限元法对永磁球形电动机不同转子磁体结构产生的磁场进行了分析,有限元法得到的结果与解析法得到的结果是一致的。分析了不同磁体结构转子磁体厚度、转子芯磁导率及定子芯磁导率对气隙磁场的影响,并对不同转子磁体结构产生的磁场谐波含量进行了比较。采用解析法得到了Halbach阵列永磁球形电动机的反电动势模型和转矩模型。对不同转子磁体结构永磁球形电动机产生的转矩进行了比较分析,并将有限元法与解析法得到的转矩结果进行了对比。最后就球面Halbach阵列磁极的实现方法进行了讨论。
根据球面转子磁极的空间分布特点,提出了几种球面多层Halbach阵列转子磁体结构。对球面多层Halbach阵列转子磁体结构的充磁方案及其磁化规律进行了详细的讨论。采用有限元法对各种球面多层Halbach阵列转子磁体结构产生的磁场分布进行了比较,并讨论了磁体结构参数对磁场分布的影响。
基于磁场解析模型,研究了Halbach阵列永磁球形电动机转子的位置检测问题。采用三维磁感应强度传感器测量气隙磁场的三个分量,根据电机的磁场模型和旋转变换关系,建立了磁场三维测量值与电机转子旋转角度的关系,进而辨识出电机转子的位置信息。
Widespread application of the robot and manipulator has necessitated the development of the motors which are capable of making multi-DOF motion. The PM spherical motor becomes a new research direction of the PM motor. It is not suitable to copy indiscriminately the research method and experience of the traditional PM motor for the PM spherical motor. The research on the PM spherical motor, a pioneering study and advanced subject, is in theory exploration stage at present. The main research contents are limited on magnetic model, kinematics and dynamics analysis. The current research results indicate that lower energy index and poor torque-angle characteristic are disadvantages of the PM spherical motor.
Halbach array can be applied into the PM spherical motor in order to improve the motor performance. A design concept of a Halbach array PM spherical motor is proposed. The fundamental principle of the Halbach array PM spherical motor is demonstrated. By using the Laplace equation and correct boundary conditions, the magnetic field is formulated. Harmonic components of magnetic field alongφandθdirection are studied. A study is made on the variations of air gap magnetic field with parallel magnetization directions along different spatial positions in each magnet segment. Magnetization angles and arrangement mode of magnetic poles are also studied, which lay a foundation for optimum design of the Halbach array PM spherical motor. A comparison is made between the Halbach array PM spherical motor and the conventional parallel magnet array spherical motor in terms of spherical harmonic components and amplitude of air gap flux density, which shows that, compared with the latter, the Halbach array PM spherical motor is more effective in improving air gap magnetic field distribution.
In order to validate the analytical method, magnetic field analysis with FEM is offered. The effects of magnet thickness, the permeability of rotor core and stator core on air gap magnetic field are also studied. A comparison is made among different magnet structures in terms of spherical harmonic components. The results produced by analytical method and finite element method are basically in agreement.
Three-dimensional (3-D) torque model and back-EMF model of the Halbach array PM spherical motor are given in order to study the motor characteristics furthermore. The torque models produced by different magnet structures are compared and the results are validated by FEM. In the end, two manufacturing methods of Halbach array magnets are also discussed.
According to the structural characteristics of the spherical magnetic poles, some kinds of Halbach array spherical magnets with multi-layer poles which can be applied to the PM spherical motor are proposed. The magnetization mechanisms of the Halbach array spherical magnets with multi-layer poles are studied. The magnetic fields produced by different Halbach array spherical magnets with multi-layer poles are analyzed using FEM. The effects of magnetization directions of some magnets and the magnet thickness on the magnetic field are also discussed, which can lay a theoretical foundation for the optimization design of magnets.
Based on the magnetic field model and 3-D magnetic field measurement, a position identification method is presented. The analysis results of the positioning process show that the rotor position can be determined by the rotation angles of the motor, which revolve around three reference axis of the stator. Furthermore, the coordinates of the point, where the magnetic field are measured, are obtained from the rotation angles. According to the magnetic field model and the rotation transformation theory, the nonlinear relationship between the measured value of magnetic flux density and the rotation angles is obtained. So by solving the nonlinear equation, the rotation angles are obtained and the rotor position is identified. The validity is verified through the simulation.
引文
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