Optical Fiber Strain Sensors for Torsion and Multi-Axis Measurement
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Solution Overview
Problem
Current strain measurement technologies, such as electrical and mechanical extensometers, suffer from low resolution, dynamic, and precision issues, are affected by electromagnetic noise, unstable, prone to corrosion, and cannot measure strains in objects with non-cylindrical shapes or those subjected to torsion, and are expensive due to the large number of sensors required.
Innovation Solution
A system comprising optical sensors arranged in specific geometric configurations within fiber optic cables, connected to an interrogator machine and computer, allowing for precise measurement of strains along multiple axes and torsion in two- or three-dimensional objects, with sensors positioned to maximize distance from the neutral axis and capable of withstanding harsh environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrical or mechanical extensometers are used for strain measurement, then measurement capability is provided, but resolution, dynamic range, and precision are low
Solution Approach 1:
The patent replaces electrical and mechanical extensometers with optical fiber sensors that use light propagation characteristics (Bragg wavelength shifts) to measure strain. This substitution eliminates the mechanical and electrical components that limit precision and stability, providing high-resolution measurements without electromagnetic interference or corrosion issues.
Solution Approach 2:
The invention changes the measurement parameter from electrical resistance or mechanical displacement to optical wavelength characteristics. By monitoring changes in Bragg wavelength of light reflected from the optical fiber sensor, the system achieves superior measurement precision and dynamic range compared to traditional extensometers.
2Measurement precision
If electrical or mechanical extensometers are used, then strain measurement is possible, but electromagnetic noise affects measurements
Solution Approach 1:
The patent substitutes electrical sensing systems with optical fiber-based sensing. Since optical fibers transmit light rather than electrical signals, they are inherently immune to electromagnetic noise, eliminating the interference problem that plagues electrical extensometers in electromagnetic environments.
3Duration of action of stationary object
If electrical or mechanical extensometers are used, then strain measurement is provided, but corrosion affects device longevity
Solution Approach 1:
The invention changes the material composition and sensing mechanism from electrical/mechanical components susceptible to corrosion to optical fiber sensors made of glass or plastic that are chemically inert. This material substitution eliminates corrosion issues and extends device service life in harsh environments.
4Measurement precision
If a tube with optical fibers is used for strain measurement, then measurement capability is provided, but only strain along tube's neutral axis is measured, not real object strain
Solution Approach 1:
The patent divides the measurement function into multiple independent optical fiber sensors positioned at different locations and orientations on the object. By segmenting the measurement capability across multiple sensors, the system can capture the full strain state (including principal strains and shear strains) rather than just strain along a single neutral axis.
Solution Approach 2:
The invention transitions from one-dimensional strain measurement (along a single axis) to multi-dimensional strain measurement by positioning sensors in different spatial orientations and locations. This allows measurement of strain components in multiple directions, enabling accurate determination of the complete strain state on the object surface.
5Device complexity
If uniform strain assumption is made for measurement, then simplified measurement is possible, but non-uniform strains are not properly measured
Solution Approach 1:
The patent applies segmentation by placing multiple discrete optical fiber sensors at different locations on the object. This segmentation of the measurement field allows detection of strain variations across the object surface, enabling accurate measurement of non-uniform strain distributions without requiring complex measurement systems.
6Measurement precision
If fibers are positioned on inner tube surface along neutral axis, then tube strain measurement is possible, but torsion measurement is not permitted
Solution Approach 1:
The invention adds dimensional diversity to sensor positioning by placing optical fiber sensors at various orientations and locations on the object surface, including positions that are sensitive to torsional deformation. This multi-dimensional sensor arrangement enables detection of torsion in addition to other strain components.
7Measurement precision
If a large number of sensors are used for comprehensive strain measurement, then complete strain state is measured, but measurement cost becomes very expensive
Solution Approach 1:
The patent makes each optical fiber sensor multi-functional by positioning them to simultaneously measure multiple strain components (principal strains, shear strains, and torsion) through strategic orientation and location. This universality allows a reduced number of sensors to perform comprehensive strain state measurement, lowering overall system cost.
Solution Approach 2:
The invention maximizes the information content from each sensor by utilizing three-dimensional sensor placement and orientation. Each sensor is positioned and angled to capture multiple strain components, effectively increasing the measurement dimensionality without proportionally increasing sensor quantity.
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 system provides high-resolution, dynamic, and precise strain measurements, capable of detecting flexion, compression, dilatation, and torsion in various objects without the limitations of traditional methods, while being cost-effective and resistant to corrosion and environmental hazards.
Implementation Method 1
at least one group of optical sensors to be applied on said object according to a predetermined geometric configuration, each of said optical sensors being provided within at least one fiber optic cable
Data Source
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AI summary
The present invention relates to a system for measuring and monitoring strains of a two- or tri-dimensional object, comprising at least one group of optical sensors to be applied on said object according to a predetermined geometric configuration, said at least one group comprising a number of sensors at least equal to the number of dimensions of said object, each of said optical sensors being provided within at least one fiber optic cable, an optical interrogator machine (M) for generating a light signal at a given frequency to be sent in said at least one fiber optic cable, and for receiving response signals from said optical sensors and for determining the wavelength's displacement of said optical sensors from their nominal value or calibration value determined at the time of fixing the fiber optic cable on the object itself when it is in rest condition, i.e. when said object is not subjected to any to any external force; and a computer (C) for calculating the object's strain with respect to at least one of two or three reference axes X, Y and Z; said computer (C) being connectable to said interrogator machine (M) and receiving data concerning the displacement's wavelength of each of said optical sensors with respect to their calibration values.