This paper studies a design approach that yields robust vibratory MEMS gyroscopes. The design is based on multiple drive-mode resonators with incrementally spaced frequencies, distributed symmetrically around the center of a supporting frame. These resonators are structurally constrained in the tangential direction with respect to the supporting frame. In the presence of an angular rotation rate about the z-axis, a harmonic Coriolis force is induced on each proof mass. These force vectors lie in the tangential direction, generating a resultant torque on the supporting frame. The net Coriolis torque excites the supporting frame into torsional oscillation about the z-axis, which is capacitively detected to generate angular rate measurement. Two batches of prototypes have been fabricated using in-house single crystal silicon on insulator (SCS-SOI) bulk-micromachining and EFABTM process commercially available from Microfabrica. Wideband drive operation was demonstrated in SOI devices. EFAB process yielded 850 Hz devices with quality factor 250 in air (bandwidth 3 Hz) and 850 in vacuum. Increase of temperature from 25o to 125oC shifts the resonant frequency down by roughly bandwidth, while quality factor drops by 8%. Parasitics model associated with EFAB consists of only a lumped capacitor and is simpler than two-parametric parasitics circuit in SOI devices. Nonlinear parametric excitation of motion at resonant frequency by super-harmonic AC voltage was experimentally characterized. This actuation method provides high amplitude of motion and separates motion from parasitics in frequency domain. The actuation method can potentially further improve the bandwidth and gain characteristics of distributed mass gyroscope.
This paper reports a design concept for MEMS gyroscopes that shifts the complexity of the design from control architecture to system dynamics, utilizing the passive disturbance rejection capability of the 4-DOF dynamical system. Specifically, a novel wide-bandwidth micromachined gyroscope design approach based on increasing the degrees-of-freedom of the oscillatory system by the use of two independently oscillating interconnected proof masses is presented along with preliminary experimental demonstration of implementation feasibility. With the concept of using a 4-DOF system, inherent disturbance rejection is achieved due to the wide operation frequency range of the dynamic system, providing reduced sensitivity to structural and thermal parameter fluctuations. Thus, less demanding active control strategies are required for operation under presence of perturbations. The fabricated prototype dual-mass gyroscopes successfully demonstrated a dramatically wide driving frequency range within where the drive direction oscillation amplitude varies insignificantly without any active control, in contrast to the conventional gyroscopes where the mass has to be sustained in constant amplitude oscillation in a very narrow frequency band. Mechanical amplification of driven mass oscillation by the sensing element was also experimentally demonstrated, providing large oscillation amplitudes, which is crucial for sensor performance.
This paper reports a novel micromachined gyroscope design with inherent disturbance-rejection capabilities. The proposed approach is based on increasing the degrees-of-freedom (DOF) of the oscillatory system by the use of two independently oscillating proof masses. Utilizing dynamical amplification in the 4-DOF system, inherent disturbance rejection is achieved, providing reduced sensitivity to structural and thermal parameter fluctuations and damping changes over the operating time of the device. In the proposed system, the first mass is forced to oscillate in the drive direction, and the response of the second mass in the orthogonal direction is sensed. The response has two resonant peaks and a flat region between peaks. Operation is in the flat region, where the gain is insensitive to frequency fluctuations. Simulations indicate over 15 times increase in the bandwidth of the system due to the use of the proposed architecture. In addition, the gain in the operation region has low sensitivity to damping changes. Consequently, by utilizing the disturbance-rejection capability of the dynamical system, improved robustness is achieved, which can relax tight fabrication tolerances and packaging requirements and thus result in reducing production cost of micromachined gyroscopes.
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