Research On The Dynamic Coupling Characteristics And Vibration Sensitivity Of MEMS Tuning Fork Gyroscopes

MEMS(Micro-Electro Mechanical Systems)vibrational gyroscopes are a kind of inertial sensors for measuring angular rate,which are based on an energy transfer of two vibrational modes with the Coriolis effects.MEMS gyros are widely used in the fields of military and civilian areas,due to their small size,light weight,low cost,low power consumption and so on.With the improvement of the performance of micro gyros,its application occasion is more widely and the application environment is getting worse.Due to the exsiting of the coupling and the external vibration,the dynamic coupling problems and vibration output are induced.Therefore,it is necessary to study how to suppress or eliminate the dynamic coupling and the vibration sensitivity to improve the performance of the micro gyroscope.Based on the above background,the research object is focused on the tuning fork gyroscope(TFG)which is designed by our research group in this thesis.Trough theoretical model,simulation and experiments,the dynamic coupling characteristics and vibration sensitivity are investigated from structural and electrical aspects,which provide important theoretical basis and reference value for the design optimization of high performance micromachined gyroscope.The main work and contributions are summarized as follows:(1)Considering the micro gyroscope by the coupling stiffness force,coupling damping force and the inertial force caused by external acceleration,the general dynamic equation of single mass micro gyros with two degrees of freedom,dual mass tuning fork gyros with four degrees of freedom and quad mass tuning fork gyros are established.This can provide a theoretical premise for the dynamic modeling of micro gyros.At the same time,the problems such as quadrature coupling,in-phase and anti-phase coupling,mode ordering and vibration sensitivity are analyzed,which provides a theoretical basis for solving the corresponding problems.(2)In order to realize the decoupling of the quadrature coupling of the TFGs,two decoupling methods are presented,which is structural decoupling and electrical decoupling.First,the quadrature coupling output is derived,and the relationship between the quadrature coupling output and the stiffness coupling coefficient of the spring is set up.Structural decoupling method is realized by reducing the stiffness coupling coefficient.Then,by using the energy method,the stiffness coupling coefficient of single folded beam is solved,which is verified by simulation.The key parameters are given to reduce the stiffness coupling coefficient of elastic beam.Meanwhile,electrical decoupling method is realized by using the quadratural coupling elimination electrodes.The electro-static force induced by the elimination electrodes is deduced,and the dynamics equation is established of the quadrature coupling output.The quadrature coupling elimination strategy by controlling the quadrature coupling stiffness of a mass is proposed,which was verified by electrostaticstructure coupling simulation and experiments.(3)Since the in-phase and anti-phase coupling has an effect on the vibration sensitivity and the quality factor of the TFGS,two methods of structural decoupling and electrical decoupling are proposed to suppress or eliminate the coupling.First,a two degree of freedom vibration model is set up,and the analytical solution of vibration output induced by the imbalance of the stiffness of TFGs is given by using the matrix perturbation method.By increasing the stiffness difference ratio and the width of the elastic beam,the structural coupling can be realized,which proves that the decoupling can effectively reduce the vibration sensitivity of TFGs through the verification of the finite element simulation and experiments.Based on electrostatic negative stiffness effect,the stiffness match method is proposed to decouple in-phase and anti-phase coupling.Then,a theoretical model of the common-mode vibration output is established.Taking advantage of the coordinate transformation method,the analytical expression is obtained,which were verified through the sine sweep vibration tests.In addition,considering the substrate damping,three degrees of freedom vibration model of TFG has been established.The in-phase and anti-phase mode quality factor are given under ideal and non-ideal conditions.Therefore,the proposed stiffness match method can make the anti-phase mode quality factor reach the maximum value,which was verified by experimental tests.(4)Because there is a trade-off between the sensitivity and vibration sensitivity,the novel anchor ring beam coupling type of TFG and anchor diamond beam coupling type are designed.In order to investigate the mode ordering and vibration sensitivity of the TFGs with anchor coupling type,the anchor coupling type is simplified as the anchored coupled model.Through the coordinate transformation method,the mode ordering and vibration sensitivity of the TFG with anchor coupling type is calculated,which were verified with the finite element simulation.At the same time,compared with the anchor coupling and direct coupling type,the anchor coupling type of TFGs can structurally improve the mode ordering and greatly reduce the vibration senistivity without sacrificing sensitivity.(5)Considering the dynamic coupling characteristics,vibration sensitivity and mode ordering,a micromachined tuning fork gyroscope with an anchored lever coupling mechanism is designed.First,the structure optimization,simulation and electrodes design are presented,and the four degree of freedom coupled vibration model of the proposed TFG is establised.The dynamics response characteristics are analyzed.Then,by using SOG processing technology,the TFGs were fabricated,which were packaged with LCC-44 package.Based on embededd FPGA,the digital control circuit with CORDIC and LMS algorithms are used to realize the closed-loop drive and open loop detection of TFGs.Finally,the performance parameters were measured by the experiments.