Improving the frequency stability of capacitive ring-based Coriolis Vibrating Gyroscopes

Arifin, D; Mcwilliam, S

Abstract

MEMS capacitively operated ring-based Coriolis vibratory gyroscopes are used to measure angular rate. Under standard operating conditions the ring is driven into resonance and Coriolis coupling generates a response that is proportional to the applied angular rate. In practice capacitive devices are susceptible to electrostatic nonlinearities due to narrow capacitive gaps which potentially degrades the quality of the measurement. One issue is that large amplitude drive responses yield multi-harmonic response which distorts the sense output causing the rate output to vary periodically (i.e. frequency instability). In this research it is shown that this frequency instability can be negated relatively easily by incorporating additional harmonics in the drive force. To implement such an approach it is necessary to use a voltage distribution to generate the appropriate electrostatic forces to eliminate or reduce the multi-frequency mechanical response of the ring. A mathematical model is used to quantify the effects of the implementation of the voltage distribution in terms of discrete Fourier transform of the ring response and the calculated Allan deviation. It is shown that the proposed implementation approximates linear behaviour by reducing the multi-harmonic response by orders of magnitude. 1. Introduction MEMS ring-based Coriolis Vibratory Gyroscopes (CVG's) are conventionally operated within linear operating regimes where the operational drive and sense modes are linearly coupled by the Coriolis force in the presence of an angular rate [1]. The sense displacement amplitude is proportional to the angular rate, which is a key feature enabling the device to operate as an angular rate sensor. Within the linear operating regime, standard CVG operation involves the sense mode vibration exhibiting the following important characteristics. First, the angular rate sensitivity of the sense displacement amplitude scales proportionally with the drive displacement amplitude. As such, implementing larger drive displacement amplitudes is conventionally desirable to maximize the quality of the device rate output through signal-to-noise ratio (SNR) enhancements [2, 3]. Second, the sense mode vibrates in phase/antiphase relative to the drive mode, resulting in zero quadrature sense displacement component due to the degeneracy of the ring flexural modes [4]. MEMS ring-based CVG's are commonly operated capacitively due to compatibility with most microfabrication processes [1]. However, the electrostatic forces in capacitive MEMS CVG's are known to be nonlinear [5-8]. The electrostatic nonlinearities are particularly strong for these miniaturized devices due to the narrow capacitive gaps between the ring and electrodes. Electrostatic nonlinearities cause the dynamics of the drive and sense modes to deviate from the previously discussed characteristics expected in standard linear device operation [5]. As such, electrostatic nonlinearities are commonly

Citation

Arifin, D., & Mcwilliam, S. (2024, July). Improving the frequency stability of capacitive ring-based Coriolis Vibrating Gyroscopes. Presented at 14th International Conference on Recent Advances on Structural Dynamics, Southampton, UK

• Presentation Conference Type: Edited Proceedings
• Conference Name: 14th International Conference on Recent Advances on Structural Dynamics
• Start Date: Jul 1, 2024
• End Date: Jul 3, 2024
• Acceptance Date: Apr 30, 2024
• Deposit Date: Nov 14, 2024
• Journal: Journal of Physics: Conference Series
• Print ISSN: 1742-6588
• Electronic ISSN: 1742-6596
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Public URL: https://nottingham-repository.worktribe.com/output/41910674
• Related Public URLs: https://www.southampton.ac.uk/rasd/index.page