Gyroscope Scale Factor Stability via Harmonic Ratio Feedback
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Solution Overview
Problem
Capacitive ring gyroscope sensors face a charge trapping effect that leads to a reduction in scale factor accuracy over time, causing unacceptable errors and making it difficult to achieve the required stability for high-performance applications.
Innovation Solution
The solution involves generating primary drive signals using a ratio of the second harmonic frequency amplitude over the fundamental frequency amplitude, which helps to compensate for changes in the scale factor due to charge trapping, thereby stabilizing the sensor's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional primary drive signal generation methods are used, then the sensor can operate, but the scale factor accuracy deteriorates over time due to charge trapping effects
Solution Approach 1:
The patent implements feedback by detecting the second harmonic frequency amplitude and using it to adjust the primary drive signal amplitude. The system continuously monitors the ratio of second harmonic to fundamental frequency amplitude and dynamically adjusts the drive signal to maintain optimal operating conditions, compensating for charge trapping effects and preventing scale factor drift over time.
Solution Approach 2:
The patent changes the operating parameter by utilizing the second harmonic frequency amplitude as a control parameter. Instead of using conventional drive signal amplitudes alone, the system adjusts the primary drive signal based on the detected second harmonic content, which changes in response to charge trapping conditions. This parameter change enables real-time compensation for accuracy degradation.
2Manufacturing precision
If additional transducers are added to compensate for frequency split, then frequency matching improves, but device complexity increases
Solution Approach 1:
The patent applies self-service by using the sensor's own existing transducers to detect and compensate for frequency split. The primary pick-off transducer detects both the fundamental frequency and second harmonic frequency, and this information is used to adjust the primary drive signal. This eliminates the need for additional external transducers while maintaining frequency matching compensation.
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 results in a five-fold improvement in the stability of the scale factor over time, maintaining accuracy within 0.03% over a period of ten hours at elevated temperatures, compared to conventional methods which show a 0.15% change in sixteen hours.
Implementation Method 1
When a direct current (DC) signal offset is applied between a capacitor plate of an additional transducer and the planar silicon ring, an electrostatic force is generated that acts as a negative spring
Implementation Method 2
When the gyroscope is rotated around an axis normal to the plane of a planar silicon ring that forms the gyroscope, Coriolis forces are generated which couple energy into the other vibration mode
Implementation Method 3
at least one primary drive transducer arranged to cause the ring structure to oscillate in a primary mode substantially at the resonant frequency of the primary mode
Data Source
AI summary
An angular velocity sensor or gyroscope has a ring and a primary drive transducer arranged to cause the ring to oscillate in a primary mode substantially at the resonant frequency of the primary mode of the ring. A primary control loop receives primary pick-off signals from the primary pick-off transducer and provides primary drive signals to the primary drive transducer so as to maintain resonant oscillation of the ring. The primary control loop includes a demodulator arranged to determine the amplitude of the fundamental frequency of the primary pick-off signals and a demodulator arranged to determine the amplitude of the second harmonic frequency of the primary pick-off signals and a drive signal generator arranged to produce the primary drive signals with an amplitude that is dependent on a ratio of the amplitude of the second harmonic frequency of the primary pick-off signal over the amplitude of the fundamental frequency of the primary pick-off signal as derived by a divider.