Hemispherical Resonator Gyroscope N=3 Vibration Pattern
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Solution Overview
Problem
Hemispherical resonator gyroscopes (HRGs) face challenges with noise from cross-talk and bias instability due to the coupling of drive signals, particularly in N=2 vibration patterns, which affect the accuracy of rotation measurement.
Innovation Solution
The HRG system employs a symmetrical annular arrangement of electrodes to generate a non-integer N=3 vibration pattern, using a controller to generate phase-disparate forcer signals that electrostatically force a resonator into a periodic motion, thereby improving decoupling of vibratory energy and reducing noise and bias instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If N=2 vibration pattern is used in HRG, then the resonator can be excited at fundamental resonant frequency, but noise from cross-talk and bias instability increase due to coupling of drive signals
Solution Approach 1:
The patent transitions from the conventional N=2 vibration pattern to an N=3 vibration pattern, creating an asymmetric change in the vibratory mode. This asymmetry in the vibration pattern fundamentally alters the spatial distribution of antinodes and nodes, thereby decoupling the drive signals and eliminating the cross-talk noise that plagues N=2 patterns. The N=3 pattern inherently provides better separation between drive and sense axes, improving measurement precision without sacrificing resonant frequency excitation efficiency.
Solution Approach 2:
The patent changes the vibration pattern parameter from N=2 to N=3, which modifies the fundamental characteristics of the resonator's vibratory behavior. This parameter change affects the number of antinodes and nodes, their angular separation, and the coupling between different axes. By selecting N=3, the system achieves a configuration where drive signals are naturally decoupled, reducing bias instability and cross-talk noise while maintaining effective resonant frequency excitation.
2Reliability
If symmetrical annular arrangement of electrodes is used, then decoupling of vibratory energy is improved, but device complexity increases due to multiple phase-disparate forcer signals
Solution Approach 1:
The patent divides the electrode system into multiple segments arranged symmetrically in an annular configuration. Each electrode or electrode pair is assigned a specific phase-disparate forcer signal, creating segmented control zones around the resonator. This segmentation allows independent control of different vibratory modes and facilitates precise decoupling of vibratory energy. The symmetrical arrangement ensures balanced distribution of control authority, improving reliability while the modular segmented structure makes the complexity manageable through systematic signal generation.
Solution Approach 2:
The patent employs periodic forcer signals with specific phase disparities applied to the symmetrical electrode arrangement. These periodic signals are generated at the resonant frequency and are phase-shifted relative to each other to create the desired N=3 vibration pattern. The periodic nature of these signals simplifies the control architecture compared to aperiodic or randomly modulated signals, as they can be generated using standard oscillators and phase shifters, thereby reducing the practical complexity despite the multiple signals required.
3Measurement precision
If N=3 vibration pattern is implemented, then noise and bias instability are reduced, but manufacturing precision requirements increase for electrode arrangement
Solution Approach 1:
The patent employs local quality by creating regions of different electrode properties or configurations within the symmetrical annular arrangement. Specific electrodes or electrode pairs may have slightly different geometries, positions, or electrical characteristics optimized for their local role in generating the N=3 pattern. This allows compensation for manufacturing tolerances and ensures that the overall symmetrical arrangement achieves the desired vibration decoupling even with practical manufacturing variations, reducing the stringency of precision requirements.
Solution Approach 2:
The patent incorporates feedback mechanisms that monitor the actual vibration pattern and electrode performance, then adjust the forcer signals or electrode configurations to maintain optimal N=3 operation. This feedback compensates for deviations caused by manufacturing imperfections in the electrode arrangement. By continuously measuring the vibratory response and adjusting control parameters, the system can achieve high measurement precision despite variations in electrode positioning or geometry that would otherwise require extremely tight manufacturing tolerances.
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 enhances the accuracy of rotation measurement by mitigating noise and bias instability, allowing for higher measurement bandwidth and improved quadrature control without altering the physical structure of existing HRGs.
Implementation Method 1
configured to electrostatically force a resonator into a substantially periodic N=3 motion based on a plurality of forcer signals applied to the plurality of electrodes
Implementation Method 2
In a fundamental or N=2 mode, the displacement of points on the vibrating resonator is in the form of a standing wave with antinodes and nodes that are separated by 45° in the circumferential direction
Implementation Method 3
In response to an applied angular rate about an input axis parallel to the tines of the tuning fork, Coriolis forces cause the tines to vibrate out of plane along a sense axis
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
One example includes a hemispherical resonator gyroscope (HRG). The HRG includes a sensing system comprising a plurality of electrodes arranged in a symmetrical annular arrangement about a sensitive axis and configured to electrostatically force a resonator into a substantially periodic motion based on a plurality of forcer signals applied to the plurality of electrodes. The plurality of electrodes are configured to provide an indication of rotation about a sensitive axis of the HRG. The HRG also includes a controller configured to generate the plurality of forcer signals in a phase-disparate manner to provide the substantially periodic motion in a vibration pattern such that a ratio of the plurality of electrodes and the vibration pattern is a non-integer number, and to measure the rotation about the sensitive axis of the HRG in response to the plurality of forcer signals.