Three-Axis FBG Accelerometer Structure With Single Core Mass
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Solution Overview
Problem
Existing three-directional accelerometers require multiple one-directional accelerometers, increasing mass, cost, and space, while current FBG accelerometers are limited to single-direction sensing.
Innovation Solution
A three-layered frame design with a single core mass and three sets of spring leaves and FBG's, each perpendicular to the others, allowing for three-directional sensing with reduced mass and volume, and adjustable natural frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple conventional accelerometers are used for three-directional measurement, then measurement capability is improved, but cost and device volume increase
Solution Approach 1:
The patent combines three separate acceleration sensing functions into a single integrated device by using one core mass connected to three sets of spring leaves oriented along three mutually perpendicular directions. Each direction has its own FBG sensor, but they share the common core mass and frame structure, thereby achieving three-directional measurement with fewer components than three separate accelerometers.
Solution Approach 2:
The patent extends the sensing capability from one-dimensional to three-dimensional by adding spring leaf sets and FBG sensors along three mutually perpendicular directions (X, Y, Z axes). This dimensional expansion allows the single device to measure acceleration components in all three spatial directions simultaneously.
2Reliability
If FBG accelerometers are used, then sensing stability and sensitivity are improved, but directional sensing capability is limited
Solution Approach 1:
The patent segments the sensing function by creating three independent sensing channels along three perpendicular directions. Each channel consists of dedicated spring leaves and FBG sensors that independently measure acceleration in their respective direction, allowing the system to maintain FBG stability while achieving multi-directional capability.
Solution Approach 2:
The patent transitions from single-directional to three-directional sensing by arranging spring leaf sets and FBG sensors along three mutually perpendicular axes. This spatial arrangement enables the FBG-based device to capture acceleration components in X, Y, and Z directions simultaneously while preserving the inherent stability of FBG technology.
3Volume of stationary object
If a single core mass is used for three-directional sensing, then device volume is reduced, but structural complexity increases
Solution Approach 1:
The patent applies local quality by making each set of spring leaves significantly thinner in the direction perpendicular to their sensing plane compared to their width within the plane. This anisotropic design allows each spring leaf set to be primarily responsive to vibration in one specific direction, reducing cross-axis interference and simplifying the overall structural analysis despite the three-dimensional configuration.
4Measurement precision
If spring leaves with small thickness are used, then directional sensitivity is improved, but mechanical strength decreases
Solution Approach 1:
The patent employs composite materials for the spring leaves, specifically using fiber-reinforced plastic (FRP) or carbon fiber reinforced plastic (CFRP). These composite materials provide high specific strength (strength-to-weight ratio) and can be tailored to exhibit appropriate stiffness and strength characteristics despite the thin cross-sectional dimensions required for directional sensitivity.
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
The new design achieves three-directional acceleration measurement with reduced mass and volume, simplified installation, and adjustable natural frequency, utilizing FBG's for stable and sensitive strain sensing.
Implementation Method 1
the section of the optic fiber 100 with refraction index variation at a period of Λ is called an FBG 103. When continuous and wide-band light 104 enters the optic fiber core 101 that includes the FBG 103, only light 105 with a special wavelength that meets the Bragg condition is reflected
Implementation Method 2
exposing a 1-20 mm long optic fiber 100, which includes an optic fiber core 101 coated by an acrylic layer 102, under high energy ultraviolet light that causes permanent periodic variations of the refraction index in that part of the optic fiber 100
Implementation Method 3
The spring leaves 5, 12 and 17 are made of metal or fiber-reinforced plastic and individually connect the core mass 1, the innermost sub-frame 4, the intermediate sub-frame 11 and the outermost sub-frame 23
Implementation Method 4
The inertia causes the mass 202 to vibrate, and induces the two FBG's 205 to contract and extend, respectively
Data Source
AI summary
Provided herein are a three-directional accelerometer and a method for manufacturing the same. The three-directional accelerometer includes a three-layer frame, a core mass, three sets of spring leaves and three sets of optic fiber Bragg gratings (FBG's). The spring leaves that react to seismic motion of the mass are aligned perpendicular to one another in three dimensions. The spring leaves are significantly smaller in thickness than width, thus creating significant differences in moments of inertia, making the spring leaves sensitive only to mass vibration or acceleration in one direction. One set of FBG is responsible for sensing the corresponding mass vibration in one direction. The natural frequency in any direction can be adjusted by varying the mass/dimensions of the core mass, corresponding frame and stiffness of the spring leaves.