Processing Tolerance Analysis And Optimal Design Of MEMS Gyroscope

MEMS gyroscope has been applied widely in low precision inertial navigation and attitude determination systems for its smaller volume, lower power consumption, lower cost and some other features compared with traditional gyroscope. Measuring accuracy of MEMS gyroscope is great affected by bulk-silicon manufacture processing error, and the processing error effect on gyroscope performance is related with the gyroscope structure, so the analysis of processing tolerance and the gyroscope structure optimal design are very important.In this paper, the dynamic model of Z-axis linear vibration MEMS gyroscope was established firstly, and then the dynamic equations of drive and detect direction were attained by Lagrange Principle. Some coupling terms were discarded and the simplified kinetic equations of Z-axis gyroscope were achieved. The expression of driven displacement related with driving force, the quality factor, the mechanical sensitivity related with modal frequency, the bandwidth and other important gyroscope characteristics were obtained by solving the simplified kinetic equation. The drive and detection mechanism of electrostatic comb capacitive, electrostatic tuning, the support beam stiffness and its matrix expressions were analyzed overall.The theoretical error caused by coupling term can be ignored. Based on gyroscope dynamic and electrostatic drive theory, the effects on the gyroscope caused by center offset of mass, structure deviation of capacitor, structure deviation of beam and residual stress were analyzed. The expression of relative error and interaction term caused by processing error was listed.The model simulated calculation of important component and the entire gyroscope were done used ANSYS software. The model analysis of two folding support beam structures indicated that the stiffness of folding beam meet the design requirements; the simulation data of comb capacitor indicated that the capacitance is more sensitive for variation of comb width; the comb operated in normal voltage range can be anti-adsorption. The gyroscope mode analysis and stiffness calculations of 3D and 2D model show that gyroscope mode frequency satisfied matching constraints, stiffness meet the decoupling requirements and modal analysis of 2D have approximate result with 3D modal analysis. The overload results of 3D and 2D model show that the gyroscope anti-overload requirement has been satisfied.From relative processing error expression of different gyroscope structures, the interaction term expressions caused by process error, gyroscope simulation data and structural parameters combined with gyroscope technology targets, the different processing tolerance ranges were calculated.According to the gyroscope dynamics and simulation results, the major MEMS gyroscope performance requirements were determined. The target constraints and design constraints were both taken into account, the length and width of beam structure were set as design variables, the optimal design of gyroscope structure was completed based on different objective functions used optimal component in ANSYS.