Micromachined Tuning Fork Gyroscopes With Ultra-High Sensitivity And Shock Rejection
University of California System: University of California, Irvine
posted on 05/23/2011
University researchers have designed a family of new dual mass and quadruple mass tuning fork architectures addressing the limitations of the conventional designs. In the dual mass design, the spurious in-phase drive-mode is shifted above the operational frequency to improve the response characteristics.
These new ultra-high resolution tuning fork gyroscope architectures provide a path to silicon MEMS-based gyrocompassing and inertial navigation systems.
Unlike conventional tuning fork gyroscopes, the proposed architecture prioritizes the quality factor of the sense-mode by mechanical design, where the linearly coupled anti-phase sense-mode is balanced in both the linear momentum as well as moment of reaction forces (torque) in order to minimize dissipation of energy through the substrate and enable ultra-high mechanical sensitivity to the input angular rate.
The second, quadruple mass design builds upon the dual mass architecture by coupling together two dual mass devices to achieve completely symmetric, mode-matched mechanical structure with ultra-high quality factor in both the drive- and the sense-mode. The quadruple mass design of the sensor element preserves the ultra-high sensitivity of the dual mass design. At the same time, the quadruple mass design provides complete mechanical rejection of external vibrations and shocks along both drive and sense axes, and improved robustness to fabrication imperfections and temperature induced frequency drifts.
File Number: 19585
The operation of micromachined vibratory gyroscopes is based on a transfer of energy between two modes of vibration caused by the Coriolis effect. When the drive- and sense-mode resonant frequencies are equal, or mode-matched, the sensor output is increased proportionally to the sense-mode quality factor. Anti-phase driven tuning fork architectures are often used due to their ability to reject common mode acceleration inputs. Conventional tuning fork designs with linear anti-phase drive-modes present several major drawbacks: presence of the parasitic low-frequency structural mode of in-phase vibrations, limitation of the maximal achievable sense-mode quality factor by approximately half of the drive-mode quality factor due to substrate energy dissipation caused by the torque imbalance, and difficulty of maintaining mode-matched condition over the practical temperature ranges.
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