【作者】 刘武；

【导师】 陈文元；

【作者基本信息】 上海交通大学 ， 微电子学与固体电子学， 2009， 博士

【摘要】 抗磁悬浮转子微器件中转子自由悬浮,从根本上消除了大多数微惯性器件的检测质量块通过支撑梁与衬底相连而存在的接触摩擦的影响,可用于高精度的微惯性器件。结合抗磁体和永磁体的抗磁悬浮具有室温下工作、无源、自主稳定悬浮以及适宜在微器件尺度下使用等优点,其根据原理可以分成抗磁转子悬浮和抗磁稳定永磁转子悬浮。本文是首次对抗磁悬浮转子微器件用于惯性传感器所涉及的工作机理、制作工艺和悬浮转子旋转驱动测控电路进行的系统研究。全文主要研究内容和结论如下:对抗磁悬浮系统进行了电磁场和动力学分析,以深入理解抗磁悬浮转子微器件的悬浮和稳定的原理,以及其用作惯性传感器的原理。首先运用电磁场理论详细推导了抗磁悬浮中电磁场矢量、电磁力和电磁力矩的求解方程,稳定悬浮的充要条件,并论证了其在微器件中应用的优势;接着对自由悬浮刚体运动和悬浮微转子小角度运动进行了动力学分析,说明了悬浮刚体转子高速旋转时的陀螺效应;然后设计了两种抗磁悬浮原理的器件结构以及转子的旋转驱动方案;最后对微器件用作惯性传感时转子线加速度、角速度与其位置的关系进行了分析。对抗磁悬浮微器件中转子的悬浮、稳定和旋转进行了系统的仿真分析。(1)使用ANSOFT的MAXWELL 3D有限元软件包分析了抗磁转子悬浮微器件的悬浮问题,具体包括:首先分析了永磁体的不同布置形式的影响,并确定了采用同心内外永磁磁环、磁化方向沿轴向且相反的布置方案;接着对悬浮高度与悬浮力的关系、转子悬浮平衡位置高度与永磁体厚度的关系、转子悬浮力与内外永磁体环外侧径向尺寸比值的关系、转子悬浮力与永磁体外环径向尺寸的关系进行了分析;最后通过分析可得在设计的结构参数下抗磁转子为稳定悬浮。(2)采用等效电流环表示永磁体和映像电流表示抗磁效应的解析法,对抗磁稳定永磁转子悬浮系统进行了分析,其中对盘形永磁转子进行了静力学、动力学研究,对齿形永磁转子进行了静力学研究,研究结果表明在设计的结构参数下盘形和齿形永磁转子为稳定悬浮。(3)对基于轴向变电容微电机原理的转子旋转驱动相关问题进行了研究,具体包括:分析确定了旋转驱动相关的转子和定子结构参数、驱动电压的加载方式,使用MAXWELL 3D有限元软件包分析了旋转电容、驱动力矩与转子转角的关系以及涡流阻尼,另外还对空气阻尼的影响进行了分析。对抗磁悬浮微器件的制作工艺进行了研究。(1)抗磁转子悬浮微器件包括定子和转子。定子由加工好的硅基底微结构单元和环形永磁组合体装配而成。硅片上微结构采用MEMS工艺制作,环形永磁体和齿形热解石墨转子采用精密加工工艺得到。目前,该器件制作已成功完成。(2)抗磁稳定永磁转子悬浮微器件包括上定子、下定子和转子,其中齿形永磁转子采用精密加工工艺,定子采用MEMS工艺。为实现该器件的制作,本文首次对基底材料为热解石墨的多层结构的MEMS工艺进行了研究,它包括热解石墨基底的处理方法,用于转子重力平衡的环形永磁体的制作以及定子器件整个工艺制作流程。文中研究了分离式和整体式两种方案,目前,分离式微器件已制作完成,而整体式由于工艺复杂,工艺实验研究还在进行之中。对悬浮转子旋转驱动测控电路进行了系统研究,研究工作分为微电容检测和旋转驱动控制两方面内容。(1)微电容检测使用电荷积分和锁定放大器原理,具体电路包括载波发生电路、电荷积分放大器、交流放大、模拟乘法器解调电路以及低通滤波。微电容检测研究工作中首先设计了使用DDS芯片的正弦载波发生电路。接着对前置放大器进行了噪声分析,由分析结果得到该电路理论上的检测分辨率为在1.5KHz带宽下可以达到78aF,对应的角度检测分辨率为0.0053o。然后,使用Orcad软件分析了设计的实际检测电路的动态响应以及存在的相位滞后。最后设计了转子转速的获取电路。(2)悬浮转子的旋转驱动是基于轴向变电容静电微电机原理。首先分析了固定频率、变频率开环驱动模式下的动态响应。然后,根据电容变化的特点提出了变驱动力矩、平稳驱动力矩和最大驱动力矩的三种闭环控制逻辑,并研究了变驱动力矩控制中理想模型,考虑低通滤波器和补偿器影响的模型下转子的动态响应响应情况。研究结果表明低通滤波器引起的相位滞后将影响转子所能达到的最高转速,为提高闭环下的最高转速可以增加补偿器。最后设计了驱动电路。对抗磁悬浮器件进行了相关实验。实验研究内容主要是抗磁转子悬浮微器件的实验,具体包括:(1)悬浮实验:测量了不同厚度永磁体时转子的悬浮高度,通过悬浮稳定性实验验证了转子的悬浮稳定性,并说明了稳定区间;(2)电容检测实验:测试了制作的用于检测转子高速旋转差分电容电路的性能;(3)旋转驱动实验:测试了固定频率、变频率开环驱动作用下转子转速与驱动电压的关系。另外,对抗磁稳定永磁转子悬浮器件进行了宏观模拟悬浮实验。本文为抗磁悬浮转子微器件真正成为高精度惯性传感器的进一步深入研究提供了良好的基础。更多还原

【Abstract】 Diamagnetic levitation micro device with free rotor can cancel the effect of contact friction, which exist in majority micro inertial device whose proof mass is connect with substrate by flexible beams, has the ability to be used as high resolution micro inertial device. The diamagnetic levitation, which consists of diamagnetic material and permanent magnet, has the advantage of working under room temperature, no energy input, self stable levitation and suitable scale down effect for MEMS (MicroElectroMechanical Systems) device. According to the principle, the diamagnetic levitation can be divided into diamagnetic rotor levitation and diamagnetic stable permanent magnet rotor levitation. The dissertation work discussed herein mainly focus on the system study of the working principle, fabrication process and rotor testing and control circuit for its rotating drive, for the diamagnetic levitation micro device using as inertial sensor. The main research content and results of this dissertation are as follows:For understanding the principle of the stable levitation of rotor in the diamagnetic levitation micro device and it’s using as inertial sensor, the electromagnetic field analysis and dynamic analysis have been done. Firstly, based on the electromagnetic field theory, the solution equations of electromagnetic field vectors, forces and torques in the diamagnetic system have been derived in detail and the advantage of diamagnetic system for dimension scale down micro device have been proved. Then, the dynamic analysis has been made on the common motion characteristic of free rotor and the small angular deflection motion of free rotor around its null position, which shows the gyroscope effect of high speed rotating rigid rotor. And then the structure of diamagnetic rotor levitation micro device and diamagnetic stable permanent magnet rotor levitation micro device and their electrode arrangement have been designed. Lastly the relationships between the linear accelerator signal, angular velocity signal and their position have been analyzed when the levitation device with free rotor is used as inertial sensor.The system analysis of levitation, stability and rotation of diamagnetic levitation micro device has been carried out. (1) The diamagnetic rotor levitation system has been analyzed, using the FEM analysis software Ansoft MAXWELL 3D. Firstly, four kinds of permanent magnets arrangements have been studied and the scheme with two concentric ring-shaped magnets has been chosen, whose magnetization directions are both along the thickness but opposite to each other. The relationship between levitation height and levitating force, the relationship between levitation balance height and permanent magnets thickness, the relationship between levitating force and the dimension ratio of inner and outer permanent magnets and the relationship between levitating force and the outer permanent magnets size have been studied in detail, respectively. The results show that the diamagnetic rotor can be stably levitated. (2) Using the equivalent surface current denotes PM and image current denotes diamagnetic effect method, the author put forward the analytic model of diamagnetic stable permanent magnet rotor levitation system, in which the rotor is disc shape or gear shape. The static analysis has been done for two kinds of rotor shapes. Because of the computational resource limitation, the dynamic analysis has been implemented only for the disc shape rotor. The result shows the permanent magnet rotor can be stably levitated. (3) The relative problems of rotor rotating drive which based on variable capacitance axial-drive micro motor principle have been studied. Those problems include structure parameters, driving voltage loading, the relationship between rotating capacitance, driving torque and rotor angle, the eddy current damp and air damp.The fabrication process of diamagnetic micro device has been studied. (1) The diamagnetic rotor levitation micro device is composed of rotor and stator. The stator was assembled by the micro structure die on the silicon and two concentric ring-shaped permanent magnets. The micro structure was fabricated by MEMS process. The PMs and rotor were fabricated by Micro electro discharge machine. The fabrication of the device has been done successfully. (2) The diamagnetic stable permanent magnet rotor levitation micro device consists of rotor, up stator and down stator. The rotor was fabricated by conventional precise manufacture and the stators were fabricated by MEMS process. For realizing the fabrication of the device, the MEMS process of multi layer structure on the pyrolytic graphite substrate has been studied for the first time. The study of process is composed of pyrolytic graphite substrate preparing, ring shape PM electroplating and the process flow of the device. Two fabrication schemes have been studied, that are separated scheme and integrative bonded scheme. At present, the separated mode micro device has been fabricated. However, the fabrication experiment of integrative bonded mode micro device is still being studied for its complicated process.The systemic study of the detecting and control circuit for the levitated rotor rotating has been carried out. The study work has two aspects that are weak capacitance sensing and rotating drive control. (1) The principle of weak capacitance sensing is based on the charge integral amplifier and Lock-In amplifier. The practical circuit is composed of sine carrier wave generation, charge integral amplifier, AC amplifier, analog multiplier demodulator, and low pass filter. Firstly, the DDS chip has been used for generating the sine carrier wave. Then the noise analysis of front end amplifier has been carried out. According to the analysis result, when the bandwidth is 1.5 KHz, the resolution of the sensing circuit is 78aF corresponds to 0.0053 angle degree under ideal condition. And then, using the Orcad software, the dynamic response of the designed detecting circuit and its phase lag has been analyzed. Lastly, the rotation speed acquiring circuit of rotor has been designed. (2) The rotating drive of the levitated rotor is based on axial variable capacitance electrostatic micro motor principle. Firstly, the dynamic analysis of the fixed frequency and variable frequency open loop drive has been implemented. Then, according to the vary characteristic of differential capacitance, three kinds of close loop control logic, which are variable torque drive, smooth torque drive and maximal torque drive, have been brought forward, respectively. In addition, the dynamic analyses of rotor, whose control logic is variable torque drive, were done under ideal model, with low pass filter and compensator. The results of the analysis show that the phase lag causing by the low pass filter would affect the highest speed of the rotor, and the compensator can increase the speed limit. Lastly, the driving circuit has been designed.The experimental investigation for the diamagnetic levitation device was conducted. The mostly experimental studies were conducted for the diamagnetic rotor levitation micro device, which are (1) levitation experiment that are the test of the levitated height under different thickness of PMs, and the stable test which proves the stability of the rotor and declare the stable region; (2) capacitance detection experiment that test the performance of the fabricated differential capacitance sensing circuit using for high speed rotated rotor; (3) rotating drive experiment that test the relationship between the rotation speed and driving voltage under fixed and variable frequency open loop drive. In addition, the levitation experiment was conducted for the macro diamagnetic stable permanent magnet rotor device.The works achieved in this dissertation have provided good basis for the further research of the diamagnetic levitation micro device with levitated rotor become high resolution inertial sensor.更多还原