Gyroscope Q-Factor Measurement via AGC Override
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Solution Overview
Problem
Vibrating structure gyroscopes face challenges in determining the quality-factor (Q-factor) of their resonators due to interactions with support electronics, making it difficult to differentiate between signals for rate measurement and Q-factor measurement, which affects scale factor errors and accuracy, especially in inductive gyroscopes where magnetic field strength variations are common.
Innovation Solution
The method involves overriding the automatic gain control (AGC) unit to set a fixed amplitude for the primary drive signal, allowing the resonant structure to resonate, and measuring the resulting resonance using the sense electrode, enabling independent determination of the Q-factor, which can indicate physical degradation and be used to separate variations in Q from magnetic field changes, thus improving scale factor compensation and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the automatic gain control (AGC) unit is used to maintain constant amplitude of the resonant structure, then the resonator can operate at optimal amplitude, but it becomes difficult to determine the Q-factor because the AGC masks the natural decay of oscillations
Solution Approach 1:
The patent implements periodic switching between AGC-enabled operation and AGC-disabled measurement intervals. During predetermined time intervals, the AGC unit is switched off to allow natural oscillation decay, enabling Q-factor measurement. This periodic action resolves the contradiction by alternating between stable operation mode and measurement mode, allowing both reliable operation and accurate Q-factor determination.
2Measurement precision
If the AGC unit is overridden to apply a fixed amplitude primary drive signal for Q-factor measurement, then independent determination of Q-factor is enabled, but the normal automatic amplitude control is disrupted
Solution Approach 1:
The system dynamically adjusts the AGC unit's operation based on the desired function. During normal operation, the AGC unit actively maintains constant amplitude. During Q-factor measurement intervals, the AGC unit is temporarily overridden with a fixed amplitude signal. This dynamic switching resolves the contradiction by adapting the control mode to the current operational requirement.
3Measurement precision
If scale factor errors are compensated by adjusting the primary drive signal, then measurement accuracy improves, but it becomes difficult to distinguish whether changes are due to Q-factor variations or magnetic field degradation
Solution Approach 1:
The patent segments the factors affecting scale factor into two distinct components: Q-factor variations and magnetic field degradation. By independently measuring Q-factor during AGC-disabled intervals and monitoring the primary drive signal adjustments during normal operation, the system can separate and independently compensate for each factor. This segmentation resolves the contradiction by providing distinct measurement pathways for each source of variation.
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 allows for accurate compensation of scale factor errors throughout the gyroscope's life by separating Q-factor variations from magnetic degradation, reducing errors and improving overall accuracy, while also serving as an early indicator for maintenance needs.
Implementation Method 1
allowing the resonant structure to resonate, and measuring the resulting resonance using the sense electrode
Implementation Method 2
inductive gyroscopes
Implementation Method 3
When the gyroscope rotates, a Coriolis force is exerted on the vibrating mass, and this force may cause the mass to oscillate in a secondary mode of vibration
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A vibrating structure gyroscope (30) comprises a resonant structure (10) arranged to vibrate under stimulation from a primary drive electrode. A drive system is arranged to vibrate the vibrating structure at a resonance frequency. An automatic gain control unit (34) varies an amplitude of a primary drive signal (PD). A controller (44) operates the gyroscope (30) such that in a first mode of operation, the automatic gain control unit (34) varies an amplitude of the drive signal (PD) between an operating range defined by upper and lower bounds. The controller (44) may also operate the gyroscope (30) in a second mode operation, in which the automatic gain control unit (34) sets the amplitude of the drive signal (PD) to a predetermined level outside of the operating range. When the gyroscope (3) is operated in the second mode of operation, the controller (44) measures an amplitude of a primary sense signal (PP) after a predetermined time period, determines an oscillation cycle count during said predetermined time period, and determines a quality-factor of the gyroscope (30) from said measured amplitude and oscillation cycle count.