Gyroscope Frequency-Feedback Circuit for Phase Locking
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Solution Overview
Problem
Conventional gyroscopes without force-feedback face challenges in matching primary and secondary resonant frequencies, leading to instability and reduced signal-to-noise ratio, and existing frequency-feedback systems lack practical methods for generating pilot tones and estimating frequency response, making them susceptible to external vibrations.
Innovation Solution
The implementation of a sideband signal doubly modulated from a primary oscillation signal, demodulated and compared with the original phase to adjust the secondary resonant frequency, ensuring stability and accuracy by locking the phase shift to -π at the primary resonant frequency, thereby enhancing the signal-to-noise ratio and robustness against frequency mismatches and external vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If force-feedback is implemented to damp secondary resonance, then bandwidth is widened and signal-to-noise ratio is enhanced, but device complexity increases
Solution Approach 1:
The patent implements force-feedback by feeding back the sense signal to the force-feedback transducer through a feedback path. The feedback signal is generated by multiplying the sense signal with a drive signal, creating a counter-force that dampens secondary resonance and stabilizes the Coriolis mass, thereby improving measurement precision while managing complexity through systematic signal processing
Solution Approach 2:
The patent introduces an intermediary feedback path that includes a feedback transducer and signal processing circuitry. This intermediary system processes the sense signal and generates an appropriate feedback force, acting as a mediator between the detection system and the Coriolis mass to achieve resonance damping without directly modifying the mass structure
2Measurement precision
If pilot tones are used for frequency response estimation, then frequency matching can be achieved, but susceptibility to external vibrations increases
Solution Approach 1:
The patent applies preliminary action by pre-modulating the drive signal with pilot tones before it acts on the Coriolis mass. This allows the system to establish known reference frequencies in advance, enabling accurate frequency response estimation and matching while the system operates, rather than attempting to measure and adjust after disturbances occur
Solution Approach 2:
The patent converts the potential harm of external vibrations into a benefit by using modulation techniques that embed pilot tones within the drive signal. The system processes these modulated signals through demodulation and correlation to extract frequency information, transforming what could be interference into a useful reference for frequency matching and stabilization
3Ease of manufacture
If secondary resonant frequency is allowed to drift, then manufacturing tolerances are easier to meet, but phase shift instability increases
Solution Approach 1:
The patent employs feedback control where the sense signal, containing information about secondary resonance frequency, is processed and fed back to adjust the drive signal. This continuous feedback mechanism automatically compensates for frequency drift caused by manufacturing tolerances or environmental changes, maintaining stable phase shift relationships without requiring extremely tight manufacturing controls
Solution Approach 2:
The patent utilizes parameter changes by modulating the drive signal frequency and phase based on the processed sense signal. The system dynamically adjusts the drive parameters to track and match the secondary resonant frequency, allowing the operating parameters to adapt to manufacturing variations while maintaining optimal performance and phase stability
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 feedback loop, reduces phase shift instability, and maintains a high signal-to-noise ratio by ensuring the secondary resonant frequency closely matches the primary oscillation frequency, even in the presence of external vibrations, thus improving the accuracy and reliability of the gyroscope.
Implementation Method 1
a drive transducer which receives as input a drive signal and actuates the Coriolis mass into primary oscillation movement at a primary oscillation frequency Fprim
Implementation Method 2
drive transducers which are coupled to the Coriolis mass
Implementation Method 3
The Coriolis mass typically oscillates in resonance in its primary oscillation mode in order to achieve a high amplitude with limited generating force
Implementation Method 4
The Coriolis masses can 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 5
the force-feedback transducers may be configured to generate a counter-force which is closely synchronized with the secondary oscillation, so that the amplitude of the secondary oscillation in the Coriolis mass is reduced almost to zero
Implementation Method 6
It is well known that the resonant frequency of a mechanical resonator can be lowered electrically by changing the bias voltage present at electrodes attached to the resonating mass
Data Source
Figure 1~2a
Figure 2b~2c
Figure 2d~2f
AI summary
A microelectromechanical gyroscope comprising a force-feedback circuit with a sideband modulator configured to impart to a mechanical oscillator a modulated force-feedback signal, and a frequency-feedback circuit which receives from the oscillator a modulated sense signal and is configured to keep the phase of the secondary resonant frequency of the oscillator equal to its primary oscillation frequency.