| 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.
|
PDF Full Text Request