MEMS Gyroscope Self-Test via Sideband Demodulation
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Solution Overview
Problem
Conventional gyroscopes face instability and complex self-testing due to rapid phase shifts near resonance frequencies, and existing self-test methods using pilot tones are unreliable in the presence of external vibrations.
Innovation Solution
A microelectromechanical gyroscope with a force-feedback system that includes a sideband signal doubly modulated from a primary oscillation signal, allowing for self-testing by comparing the demodulated signal with the primary oscillation signal, providing a reliable single signal criterion for operation verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If force-feedback is implemented to maintain resonance in secondary oscillation mode, then signal-to-noise ratio is enhanced, but device complexity increases
Solution Approach 1:
The patent implements a force-feedback system that uses the amplitude and phase information from the sense signal to generate a counter-force through force-feedback transducers. This feedback mechanism maintains resonance in the secondary oscillation mode by actively compensating for frequency deviations, thereby enhancing the signal-to-noise ratio while managing the complexity through systematic control architecture
Solution Approach 2:
The patent replaces mechanical rotation stimulus with electrical signals that are fed through the signal path and transmitted via the MEMS part. This substitution allows self-testing without requiring physical rotation, reducing mechanical complexity while maintaining testing effectiveness
2Ease of operation
If pilot tones are used for self-testing the secondary system, then operation verification is enabled, but reliability decreases in presence of external vibrations
Solution Approach 1:
The patent introduces sideband signals as intermediary test signals that are modulated onto the primary oscillation frequency. These sideband signals serve as mediators between the primary resonator and secondary system testing, allowing verification of secondary system operation while being distinguishable from external vibrations through their specific frequency characteristics
Solution Approach 2:
The patent applies preliminary damping through force-feedback before introducing test signals. This preliminary action widens the bandwidth of the secondary resonator, making the system more robust against external vibrations and ensuring that test signals can be reliably distinguished from environmental disturbances
3Measurement precision
If primary and secondary resonant frequencies are matched for maximal signal-to-noise ratio, then measurement precision improves, but instability increases due to rapid phase shifts
Solution Approach 1:
The force-feedback system continuously monitors the phase and amplitude of the secondary oscillation and adjusts the counter-force to maintain stable resonance. This active feedback control stabilizes the phase relationship between primary and secondary oscillations, preventing the rapid phase shifts that would otherwise occur when frequencies are matched
Solution Approach 2:
The patent dynamically adjusts the resonant frequencies of the primary and secondary modes to maintain optimal matching while stability is maintained through force-feedback control. The system can shift operating parameters to avoid instability regions while preserving the benefits of frequency matching for signal-to-noise ratio
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach stabilizes the secondary resonant frequency, reduces instability, and enhances self-test reliability by filtering out external disturbances, ensuring accurate operation even in the presence of vibrations.
Implementation Method 1
The Coriolis masses are typically set to oscillate in resonance in its primary oscillation mode in order to achieve a large amplitude with a relatively small actuating force
Implementation Method 2
Coriolis masses should preferable also be easily actuated into a secondary oscillation mode (which may also be called the sense oscillation mode) by the Coriolis force when the gyroscope undergoes angular rotation
Implementation Method 3
For a maximal signal-to-noise ratio, the Coriolis masses should be operated in resonance also in their secondary oscillation mode
Implementation Method 4
Force-feedback can help to maintain resonance in the secondary oscillation mode because it dampens the secondary resonance and gives the frequency response a sufficiently wide bandwidth
Data Source
AI summary
A microelectromechanical gyroscope which comprises one or more Coriolis masses driven by a drive transducer and a force-feedback system. The force-feedback circuit comprises first and second sideband modulators and the self-test circuit comprises first and second sideband demodulators.