Study On Key Technologies Of Rocking Mass Microgyroscope

The Rocking Mass Micro-Gyroscope (RMG) adopts an axisymmetric Foucaultpendulum vibratory structure and a centrosymmetric rocking mass post, whoseoperational modes are the perpendicular degeneration modes of the axisymmetric elasticbody. RMG has some important advantages, such as equal natural frequency of theoperational modes without modes matching, large inertia mass, high sensitivity, andthus has the potential to be the high performance microgyroscope which can befabricated in batches. The study on RMG has been greatly developed abroad, but therelated products and technologies are forbidden by the western countries. Therefore,researching the RMG technologies to improve our microgyroscope technologies is ofgreat importance.The study on RMG technology abroad mainly focused on vibratory structureimproving, fabrication process optimizing, and control method innovating, hardlyinvolved its structure design theory. In this dissertation, we explore a novel rockingmass microgyroscope, which operates based on the method of entirely differentialelectrostatic force actuating and capacitance sensing. The prototype of RMG isfabricated by MEMS process, traditional precision mechanical machining and precisionadherence technologies. RMG has the advantages as simple fabrication process, highprecision, low cost, and also has the potential to be fabricated in batches.In this dissertation, we present the structure design theory, energy loss mechanism,dynamics analysis, MEMS fabrication process, and performance test of the micro-gyroscope. The main content includes:1. The differential whole structure of RMG is designed, the mechanics of itsvibratory structure are analyzed, and the natural frequency analytical model of itsoperational modes is deduced. The theoretical models of the microgyroscope’s interfacecapacitance, actuating momentum, and feedback momentum are also deduced. Based onthe analyzed mechanics and electrics results of the microgyroscope, the detailed naturalfrequency analytical model of its operational modes are derived to provide thetheoretical basis for its structure design.2. All the energy loss mechanisms of RMG are studied, and their theoretical modelof vibratory damping (Q-factors) are respectively deduced, including squeeze-film airdamping, support loss, thermoelastic damping, energy loss of the base, and surface loss.The squeeze-film air damping will badly restrain the Q-factors of the microgyroscope inatmospheric air, and the microgyroscope must be packaged in low vacuum. The supportloss will mainly affect the Q-factors of the microgyroscope in vacuum, and the ratio ofthe thickness between the support structure and the vibratory structure must be designedas larger as possible to improve its Q-factors. 3. The dynamic characteristic of RMG is studied. The Coriolis momentumtheoretical model of the microgyroscope are deduced, then the dynamic differentialequations are built, and the steady-state responses of the actuating mode and sensingmode are derived finally. The analytical model of the structural sensitivity of themicrogyroscope is derived, based on its Q-factor theoretical model and steady-stateresponse results. The whole structure of RMG is optimized, and the parameters of thevibratory structure are achieved, by analyzing the influences of different parameters onthe structural sensitivity.4. The fabrication process of RMG is studied. Based on the strucaturalcharacteristics of RMG, the fabrication process is divided into four parts, such as siliconstructure, Pyrex base (including metal electrodes), rocking mass post, and supportingpart. The MEMS fabrication processes of the silicon structure and Pyrex base arestudied respectively, a kind of single crystal silicon anisotropic wet etching processbased on pre-buried mask method is designed, and the hole in the center of the Pyrexbase is fabricated by using the UV laser dicing technology. The assembly process ofRMG is optimized, and then the prototype is fabricated and encapsulated in low vacuumby using metal tube welding technology. Finally, the operational modes of theprototypes in atmospheric air and in vacuum are characterized respectively.5. The RMG prototype is theoretically validated. The special mode test circuit andCoriolis siginal test circuit of RMG are designed and fabricated. The mode frequencyresponse curves and Coriolis signal of RMG prototype are tested. The tested resultsindicate that: the structure design theory, energy loss mechanism, dynamics theory,and structural parameter optimization method in this dissertation are valid; the MEMSfabrication processes are feasible.