Closed Loop Scale Factor Estimation for Hemispherical Resonator Gyroscopes
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Solution Overview
Problem
Existing hemispherical resonator gyroscopes face scale factor degradation over time and temperature due to dependencies on various sources, and the closed loop scale factor error correction technique using a deterministic 125 Hz square-wave modulation signal limits bandwidth and introduces errors due to correlation with inertial rate inputs.
Innovation Solution
Implementing a closed loop scale factor estimator that uses a non-uniform rate signal, such as a pseudo-random modulation signal, to estimate the force-to-rebalance scale factor by comparing the measured flex angle with a demodulation angle signal, reducing correlation with inertial rate inputs and allowing for higher bandwidth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a deterministic 125 Hz square-wave modulation signal is used for closed loop scale factor estimation, then scale factor errors can be corrected, but the bandwidth of the gyro output is limited and large transients occur when inertial rate inputs are correlated with the modulation signal
Solution Approach 1:
The patent transforms the static, deterministic modulation signal into a dynamic, random modulation signal. The random modulation signal changes continuously over time with unpredictable characteristics, allowing the system to adapt to different operating conditions and avoid the bandwidth limitations and correlation issues associated with fixed-frequency deterministic signals.
Solution Approach 2:
The patent changes the fundamental parameter of the modulation signal from deterministic to random. This parameter change fundamentally alters the signal characteristics, eliminating the fixed frequency component that causes bandwidth limitations and correlation with inertial rate inputs, while maintaining the ability to estimate scale factor through correlation techniques.
2Measurement precision
If a deterministic 125 Hz square-wave modulation signal is used for closed loop scale factor estimation, then scale factor errors can be corrected, but large transients occur when inertial rate inputs are correlated with the modulation signal
Solution Approach 1:
By using a random modulation signal instead of a deterministic one, the system becomes dynamic and unpredictable in its modulation pattern. This prevents systematic correlation with inertial rate inputs that could cause large transients, thereby improving the reliability of the system output while maintaining scale factor estimation accuracy.
Solution Approach 2:
The patent converts the potential harm of signal correlation into a benefit by using random modulation. The randomness ensures that correlation with inertial rate inputs becomes negligible, transforming what could be a source of large transients and errors into a robust method that eliminates such issues while maintaining estimation accuracy.
3Measurement precision
If Force to Rebalance mode is used to provide high performance angular rate data, then angular rate measurement capability is improved, but scale factor degrades over time and with temperature due to dependencies on multiple sources
Solution Approach 1:
The patent implements a closed-loop feedback mechanism where the random modulation signal is used to continuously estimate and correct the scale factor. The system measures the response to the random modulation, calculates the scale factor error, and applies correction to maintain accurate angular rate measurements despite drift in the Force to Rebalance mode components.
Solution Approach 2:
The system performs self-calibration by using the random modulation signal to automatically detect and correct its own scale factor errors. The closed loop scale factor estimator continuously monitors and adjusts the scale factor without external intervention, allowing the Force to Rebalance mode to maintain high performance while compensating for its own degradation over time and temperature.
Data Source
AI summary
A closed loop scale factor estimator of an apparatus in one example is configured to compare a measured flex angle of a hemispherical resonator gyroscope (HRG) with a demodulation angle signal to estimate a force-to-rebalance (FTR) scale factor for the HRG, wherein the demodulation angle signal corresponds to an integral of a non-uniform rate signal applied to the HRG.