Vibratory Ring Gyroscope Tuning via Laser-Ablated Holes
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Solution Overview
Problem
Vibratory ring gyroscopes face challenges in accurately matching and aligning primary and secondary mode frequencies due to imperfections in ring structures, leading to quadrature bias errors and performance constraints, particularly influenced by temperature variations and anisotropic stresses.
Innovation Solution
A method involving the formation of fine tuning holes on or near the neutral axis of the vibratory ring structure, strategically positioned to reduce the frequency split between target and offset normal modes, combined with coarse tuning, allows for precise alignment and frequency matching using laser ablation techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If material is removed from the neutral axis to tune the ring structure, then the manufacturing process becomes simpler, but the frequency matching precision is insufficient
Solution Approach 1:
The patent applies local quality by creating tuning holes at specific locations (radial nodes of the target mode) rather than uniform material removal. This localized modification allows precise control over which mode frequencies are adjusted, enabling both simple manufacturing (drilling holes) and high precision (frequency matching within 0.1 Hz) by concentrating the tuning effect exactly where needed in the ring structure.
2Reliability
If the ring structure is made geometrically perfect with isotropic material, then the primary and secondary modes are perfectly matched in frequency, but real-world imperfections cause misalignment and quadrature bias errors
Solution Approach 1:
The patent applies preliminary anti-action by proactively compensating for the harmful effects of manufacturing imperfections before they cause performance degradation. During fabrication, tuning holes are strategically placed at radial nodes to pre-correct frequency mismatches and misalignments, counteracting the inevitable anisotropies and geometric deviations that occur in real silicon ring structures, thereby eliminating quadrature bias errors before they affect gyroscope operation.
3Manufacturing precision
If coarse tuning holes are formed at radial anti-nodes, then the frequency split is reduced to a low level, but fine precision alignment requires additional fine tuning holes at specific angular offsets
Solution Approach 1:
The patent applies segmentation by dividing the tuning process into two distinct stages: coarse tuning using holes at radial anti-nodes to achieve bulk frequency alignment, and fine tuning using holes at radially offset positions to achieve precise angular alignment. This segmentation allows each stage to address specific alignment requirements independently, reducing the frequency split to very low levels (0.05-0.1 Hz) while maintaining a systematic and manageable hole placement strategy.
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 enables enhanced accuracy in balancing vibratory ring structures, significantly reducing quadrature bias errors and improving gyroscope performance by achieving precise frequency matching and alignment, even across varying temperatures.
Implementation Method 1
forming the pair of fine tuning holes in the vibratory ring structure at the determined angular separation
Data Source
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AI summary
A method of tuning a vibratory ring structure includes determining an angular spacing for a pair of fine tuning holes of substantially the same size, located on or near the neutral axis of the vibratory ring structure, the angular offset being selected to reduce to an acceptable level the frequency split between the target normal mode and a further normal mode which is angularly offset relative to the target normal mode, and forming the pair of fine tuning holes in the vibratory ring structure at the determined angular spacing. A ring structure, for example, a gyroscope, tuned or balanced in this manner, is also disclosed.