Angular Rate Sensor Support Structure with Variable Thickness
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Solution Overview
Problem
Existing angular rate sensors face challenges in achieving robustness without compromising performance, as thinner support legs enhance isolation but make the sensor vulnerable to shocks, while thicker legs increase quadrature bias and degrade performance by bringing unwanted resonant modes closer to the Cos 2θ mode.
Innovation Solution
The supporting structures are split into orthogonal portions with different thicknesses, with radial portions being thicker than circumferential portions, increasing the frequency of unwanted resonant modes without affecting the Cos 2θ mode's resonant frequency or Q factor, and incorporating fillets to reduce stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the support legs are made thinner to enhance isolation and improve performance, then the Q factor increases, but the sensor becomes vulnerable to shocks and loses robustness
Solution Approach 1:
The support structure is designed with non-uniform thickness: thinner portions (first thickness) provide isolation for high Q factor, while thicker portions (second thickness) at critical locations provide shock resistance. This local differentiation allows simultaneous optimization of both performance and robustness.
Solution Approach 2:
The support legs feature asymmetric thickness distribution with different thicknesses in different regions. The first thickness is smaller than the second thickness, creating an asymmetric structure that optimizes both vibration isolation and mechanical strength.
2Reliability
If the support legs are thickened to increase robustness and survive shocks, then reliability improves, but the Q factor decreases and performance is degraded
Solution Approach 1:
Instead of uniformly thickening the support legs, the invention applies increased thickness only at specific critical locations where shock resistance is needed, while maintaining thin sections for vibration isolation. This localized thickening preserves the Q factor while improving robustness.
Solution Approach 2:
The support legs are segmented into different thickness regions: a first thickness for isolation and a second thickness for strength. This segmentation allows independent optimization of performance and robustness characteristics.
3Reliability
If the legs are thickened to make the sensor more robust, then shock resistance improves, but the quadrature bias increases and performance degrades
Solution Approach 1:
The support structure uses localized thickening only where mechanically necessary for shock resistance, rather than uniform thickening. This minimizes the impact on quadrature bias while maintaining robustness.
4Reliability
If the legs are thickened and stiffened to restrict translational mode movement, then shock resistance improves, but unwanted resonant modes move closer in frequency to the Cos 2θ mode causing undesirable dynamics
Solution Approach 1:
The non-uniform thickness distribution selectively stiffens critical regions while leaving other regions flexible. This maintains adequate frequency separation between modes while providing necessary shock resistance.
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 design enhances the sensor's robustness by reducing stress under shock and maintaining high performance by keeping unwanted modes far from the Cos 2θ mode frequency, ensuring the sensor can withstand greater shocks without degrading its sensitivity.
Implementation Method 1
When the sensor undergoes rotation about an axis perpendicular to the plane of the annular resonator, Coriolis forces are generated which couple energy into the secondary vibration mode (in-plane)
Implementation Method 2
The annular resonator is driven into a cos 2θ mode of vibration at resonance by primary drive transducers that excite the primary vibration mode (in-plane)... supported on the lower glass substrate by compliant supporting structures
Implementation Method 3
the radial portions are thicker than the circumferential portions. This lowers the peak leg stress, e.g. caused when shock in shear excites the translational mode, and increases the frequency of unwanted resonant modes without affecting the resonant frequency or the Q factor of the Cos 2θ mode used for sensing
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
An annular resonator (100) for a vibrating structure angular rate sensor comprises a planar annular member (202) that lies in the X-Y plane and one or more supporting structures (204) arranged to flexibly support the annular member (202) in the X-Y plane. The one or more supporting structures (204) each comprise a radial portion (206), extending radially from the annular member (202) and having a first thickness in the X-Y plane, and a circumferential portion (208), extending circumferentially from the radial portion (206) and having a second thickness in the X-Y plane, wherein the first thickness is greater than the second thickness.