【作者】 张赫；

【导师】 寇宝泉；

【作者基本信息】 哈尔滨工业大学 ， 电机与电器， 2014， 博士

【摘要】 多自由度磁悬浮微动台具有定位精度高、响应速度快、无摩擦、兼容真空环境等优点,在半导体光刻系统、超精密测量、生物芯片技术等现代精密、超精密装备领域具有广阔的应用前景,近年来受到了学术界和工业界的广泛关注。本文在总结国内外现有微动台结构形式优缺点的基础上,提出一种集成化的磁悬浮微动台方案,该结构方案将洛伦兹平面电机与磁悬浮重力补偿器进行结合,具有结构紧凑、推力线性度高、隔振性能好、表面温升低等特点。本文以该种多自由度磁悬浮微动台为研究对象,通过理论分析、数值计算与实验验证,围绕磁悬浮微动台数学模型建立、推力波动抑制、法向刚度优化、电磁结构设计、表面温升抑制等方面对其展开研究。本文首先介绍所提出磁悬浮微动台方案的基本结构和六自由度运行原理。采用等效磁荷与磁荷镜像相结合的方法对洛伦兹平面电机三维气隙磁场进行解析,通过分析各洛伦兹驱动单元之间的位置关系和对平面电机各向推力的贡献,推导考虑线圈端部出力的洛伦兹平面电机各向推力表达式。基于等效电流法建立所提出圆筒型Halbach次级结构磁悬浮重力补偿器的数学模型,包括气隙磁场、静态悬浮力、动态悬浮力以及法向刚度的表达式。上述工作为后续微动台的力特性优化分析与电磁设计方法总结奠定理论基础。为实现高精度定位,磁悬浮微动台应具有较低的推力波动和较好的低频隔振性能,为此,本文分别对洛伦兹平面电机的推力特性以及磁悬浮重力补偿器的法向刚度特性展开研究。首先,分析洛伦兹驱动单元推力波动的产生机理,总结水平位移、法向位移及俯仰偏转对推力的影响规律,提出一种非等高Halbach永磁阵列,旨在通过增强端部磁场以减小电机的推力波动。其次,分别对传统次级结构和Halbach次级结构两种被动磁悬浮单元的悬浮力和法向刚度进行分析与比较,总结悬浮力和法向刚度随径向气隙长度、永磁环厚度、永磁环高度以及Halbach永磁阵列高度比的变化规律。研究发现,当刚度低至一定程度时会发生零刚度偏移的现象,本文通过分析永磁体的“增去磁效应”,揭示该现象的产生机理并提出修正磁悬浮重力补偿器零刚度位置的具体方案。考虑到洛伦兹平面电机与磁悬浮重力补偿器在磁路上的独立性,本文对二者的电磁设计方法分别展开研究。首先,明确洛伦兹平面电机的设计原则,推导洛伦兹驱动单元的主要尺寸关系式,确定洛伦兹驱动单元的主要尺寸。利用所建立的数学模型,总结各参数对电机性能的影响规律,为洛伦兹平面电机初级与次级结构参数的电磁设计提供参考。研制一台洛伦兹平面电机样机,搭建洛伦兹平面电机静态推力/转矩测试平台,开展平面电机推力/转矩线性度、推力波动的实验研究。其次,基于磁悬浮重力补偿器的技术指标与结构特点,给出其设计原则与设计流程。利用解析法与有限元计算相结合的方法,提出一种磁悬浮重力补偿器的半解析数学模型,实现对悬浮力和法向刚度的变化规律进行准确预测,突破传统解析法在低刚度场合中应用的瓶颈。研制一台磁悬浮重力补偿器样机,搭建悬浮力测试平台,开展悬浮力随轴向位移、径向位移、线圈电流变化规律的实验研究,对有效行程内的法向刚度曲面进行拟合。在超精密定位系统中,为了降低微动台对测量系统环境的影响,微动台的表面温升受到较为严格的限制。本文利用三维有限元模型分别对洛伦兹平面电机和磁悬浮重力补偿器的温度场进行分析,并提出具有针对性的冷却方案。首先,通过线圈冷却单元的温升及冷却实验对水套式冷却结构的冷却能力进行评估。其次,提出洛伦兹平面电机的水套式冷却结构,并利用分流板实现对各冷却支路流阻的平均分配。然后,对比分析不同结构材料对电机表面温升的影响并进行相关的实验验证。最后,针对磁悬浮重力补偿器的结构特点,提出在四个线圈附近均设置水道槽的冷却结构方案,建立其温度场仿真模型并开展相关实验研究,为磁悬浮重力补偿器在超精密定位场合中的应用奠定技术基础。更多还原

【Abstract】 Multi-degree-of-freedom(Multi-DOF) magnetic levitation fine stages have advantages of high positioning accuracy, fast response, no friction and vacuum compatibility. They have broad application prospects in modern precision, ultra-precision equipment domains such as semiconductor photolithography processing, ultra precise measurement, and biological chip technology. In recent years, magnetic levitation fine stages have attracted widespread attention in academic research and industrial applications. Based on the summary of the existing configurations of fine stages, a new integrated scheme for magnetic levitation fine stage is presented in this thesis, which combines the Lorentz planar motor and the magnetic levitation gravity compensator. The novel fine stage has some advantages such as compact structure, high force linearity, low vertical stiffness, low surface temperature rise, and so on. Taking the multi-DOF fine stage as the research object, the modeling of accurate analytical model, suppression of force ripple, optimization of vertical stiffness, study of electromagnetic design method and suppression of surface temperature rise are researched in this thesis. The research method is based on the combination of theoretical analysis, numerical calculation and experimental verification.The basic configuration and six-DOF driving unit of the magnetic levitation fine stage is introduced. Based on the equivalent charge model and image method, the accurate analytical expression of the 3D air-gap magnetic field for Lorentz planar motor is derived. The position relationship and the contribution to force of each driving unit is discussed. The complete force expressions for the Lorentz planar motor that considers the coil end force are established. Based on the equivalent current model, the mathematical model of the proposed cylindrical magnetic levitation gravity compensator with Halbach secondary structure is built, which include the expressions of air-gap magnetic field, static levitation force, dynamic levitation force and vertical stiffness. The above analysis lays a theoretical foundation for the force characteristic optimization and design method research of the fine stage.To achieve high-precision positioning, the magnetic levitation fine stage should have low force ripple and good vibration isolation performance. Therefore, the force characteristic of the Lorentz planar motor and the vertical stiffness of the magnetic levitation gravity compensator are further studied. The leading cause of the force ripple in Lorentz driving unit is described, and the influence of horizontal displacement, vertical displacement and pitching/deflection angle on the force are summarized. To enhance the end magnetic field and reduce the force ripple, a new Halbach magnet with unequal thickness is presented. The levitation force and stiffness from two types of passive magnetic levitation units which includes conventional secondary and Halbach secondary, respectively, are analyzed and compared. The variation rules of the levitation force and stiffness with radial air-gap length, magnet thickness, magnet height and height ratio of Halbach array are summarized. It can be found that the zero-stiffness point will shift when the stiffness is low enough. In this thesis, the "magnetization increasing and demagnetization effect" of permanent magnets is adopted to theoretically explain the phenomenon and put forward several means to adjust the zero-stiffness point.The electromagnetic design method for Lorentz planar motor and magnetic levitation gravity compensator are researched respectively on account of the independentability of the magnetic circuit. The design principles for the Lorentz planar motor are first given. The main dimensions’ equation of the driving unit is derived, and the three main dimensions are determined. According to the established mathematical model, the influence of parameters on the motor performance is studied, which provides an important reference for the design of primary and secondary of Lorentz planar motor. A prototype of Lorentz planar motor is manufactured and the static force/torque testing platform is set up. The force/torque linearity and force ripple of the prototype are tested. Based on the specifications and features of the magnetic levitation gravity compensator, the related design principles and flow chart are given. To solve the problem that classical analytical model is not valid in the low stiffness applications, a semi-analytical model for the magnetic levitation gravity compensator is proposed. A prototype of magnetic levitation gravity compensator is manufactured and the levitation force testing platform is set up. The levitation forces characteristics of the prototype as a function of axial displacement, radial displacement and coil current are are tested, respectively. Finally, the vertical stiffness within the effective motion range is calculated.In high-precision positioning systems, the surface temperature rise of the fine stage is strictly restricted to reduce its influence on the measuring system. The 3D temperature field finite element models for the Lorentz planar motor and the magnetic levitation gravity compensator are built, and the specific cooling systems are designed. For the Lorentz planar motor, the temperature rise and cooling experiments of the coil cooling unit are completed to evaluate the cooling capacity of the water-jaclet type cooling structure first. The cooling structure of the Lorentz planar motor is then proposed, and the separation plate is presented to achieve equal distribution for the three cooling branches. Finally, the influence of structural material on the temperature rise of coil part is analyzed using finite element method, and the analysis results are verified by the experiment. For the magnetic levitation gravity compensator, the cooling mode setting water channel slots near four coils is proposed. In addition, the temperature field simulation model is built and the relevant experiments are completed, which lays a technology foundation for the use of magnetic levitation gravity compensator in the high-precision positioning applications.更多还原