Fibre Optic Accelerometer Lever Mechanism Cross-Axis Sensitivity
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Solution Overview
Problem
Fibre optic accelerometers face challenges with cross-axis sensitivity and limited frequency range due to electromagnetic interference and nonlinear acceleration-strain characteristics, making accurate vibration measurements difficult, especially in high-voltage environments.
Innovation Solution
The design incorporates a moving mass that moves only along the measurement direction, coupled with a suspension system and optical fibre arranged to minimize cross-axis sensitivity, using a pivoting arm and flexible hinges to amplify or reduce strain, and multiple measurement sections for accurate strain measurement, allowing for improved sensitivity and frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bigger moving mass is used to increase the inertia force and strain in the fibre, then the sensitivity of the accelerometer is improved, but the eigenfrequency of the accelerometer decreases, limiting the frequency range it can measure
Solution Approach 1:
A lever mechanism is introduced as an intermediary between the moving mass and the optical fibre. The lever amplifies the displacement of the moving mass, allowing a smaller mass to generate sufficient strain in the fibre while maintaining the ability to measure higher frequencies. The lever acts as a mechanical amplifier that decouples the mass requirement from the strain output.
Solution Approach 2:
The system changes the mechanical parameters by introducing a lever with a specific arm ratio. This transforms the relationship between mass, displacement, and strain, allowing optimization of both sensitivity and frequency response by adjusting the lever geometry rather than simply increasing mass.
2Measurement precision
If a lever mechanism is used to amplify strain in the optical fibre, then the sensitivity is improved, but cross-talk between translational and rotational accelerations increases, deteriorating performance
Solution Approach 1:
The lever mechanism is designed with asymmetric mounting: it is rigidly attached to the moving mass at one end and pivotally connected to the housing at the other end, with the pivot axis perpendicular to the measurement direction. This asymmetric configuration allows the lever to amplify strain in the measurement direction while being insensitive to rotational accelerations, thereby reducing cross-talk.
Solution Approach 2:
The solution moves the pivot connection to a different dimensional orientation by positioning the pivot axis perpendicular to both the measurement direction and the lever arm. This spatial arrangement decouples the measurement axis from rotational interference, allowing strain amplification without cross-axis sensitivity.
3Measurement precision
If the moving mass is pivotally mounted to achieve a lever effect, then sensitivity is improved, but the accelerometer becomes harder to calibrate due to nonlinear acceleration-strain characteristics
Solution Approach 1:
The lever arm is designed to operate within a limited angular range where the small angle approximation holds, ensuring that sin(θ) ≈ θ. This partial action approach maintains linearity between acceleration and strain output, simplifying calibration while still achieving the desired sensitivity amplification through the lever ratio.
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 configuration reduces cross-axis sensitivity, enabling accurate and reliable acceleration measurements over a wide frequency range and amplitude, while minimizing the impact of electromagnetic interference.
Implementation Method 1
an optical fibre that is connected at a fibre connection point that is coupled to the movable mass, wherein the optical fibre comprises a measurement section for measuring the movement of the moving mass
Implementation Method 2
a measurement section, such as a Fibre Bragg Grating, and an input spectrum of light in the fibre are provided. By measuring a change of the spectrum on the opposing side of the fibre, or by measuring a reflected spectrum of light, the imposed strain can be determined.
Data Source
AI summary
Accelerometer for measuring acceleration along a measurement direction including a moving mass which is moving with respect to a frame member only along the measurement direction, a suspension system for suspending the moving mass in the frame member while substantially limiting movement of the moving mass along only the measurement direction, and an optical fibre that is connected at a fibre connection point that is coupled to the movable mass. The optical fibre is arranged between the moving mass and the frame member and includes a measurement section for measuring the movement of the moving mass along the measurement direction.