WO2000047967A1 - Capteur a fibres optiques et dispositif optique pour detecter des deformations et/ou des contraintes - Google Patents

Capteur a fibres optiques et dispositif optique pour detecter des deformations et/ou des contraintes Download PDF

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Publication number
WO2000047967A1
WO2000047967A1 PCT/IT1999/000025 IT9900025W WO0047967A1 WO 2000047967 A1 WO2000047967 A1 WO 2000047967A1 IT 9900025 W IT9900025 W IT 9900025W WO 0047967 A1 WO0047967 A1 WO 0047967A1
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WO
WIPO (PCT)
Prior art keywords
fibre
optical
fibres
laid
sensor according
Prior art date
Application number
PCT/IT1999/000025
Other languages
English (en)
Inventor
Sergio Leali
Original Assignee
Pllb Elettronica S.P.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pllb Elettronica S.P.A. filed Critical Pllb Elettronica S.P.A.
Priority to PCT/IT1999/000025 priority Critical patent/WO2000047967A1/fr
Priority to AU25453/99A priority patent/AU2545399A/en
Publication of WO2000047967A1 publication Critical patent/WO2000047967A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/08—Testing mechanical properties
    • G01M11/083—Testing mechanical properties by using an optical fiber in contact with the device under test [DUT]
    • G01M11/086—Details about the embedment of the optical fiber within the DUT
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/22—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers
    • G01L5/226—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers to manipulators, e.g. the force due to gripping
    • G01L5/228—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers to manipulators, e.g. the force due to gripping using tactile array force sensors

Definitions

  • This invention relates to a fibre optics sensor and an optical apparatus for detecting and measuring physical stresses and/or strains in a flat and/or tubular and/or irregularly shaped surface.
  • the invention relates to a fibre optics sensor for detecting and measuring physical stresses and/or strains in a flat and/or tubular and/or irregularly shaped surface, being of a type which comprises at least one sensing optical fibre and a back-up member for said at least one fibre.
  • the invention further relates to an optical apparatus for detecting and measuring mechanical stresses and/or strains in flat or tubular surfaces, being of a type which comprises at least one fibre optics sensor according to the invention, and a plurality of transmitters and receivers connected according to the following:
  • each sensor fibre is supplied a constant optical power from an transmitter
  • a receiver is connected to each fibre, on the opposite side from the transmitter side thereof.
  • the invention relates, particularly but not exclusively, to a fibre optics sensor for detecting and measuring mechanical stresses and/or strains in flat or tubular surfaces, and the following description is given with reference to this field of application for convenience of explanation only.
  • Sensors employing optical fibres have been developed which have specialized structures according to application, and can detect and locate mechanical stresses, or stresses of another nature (e.g., temperature).
  • FBG Fibre Bragg Grating technology
  • Known sensors of this type are essentially local sensors arranged to detect physical stresses or mechanical loads at given spots on a structure corresponding to the positions where the sensors have been placed.
  • the underlying technical problem of this invention is to provide a fibre optics sensor adapted to detect mechanical stresses, even when these are spread over a large area, the sensor having such structural and functional features as to overcome the limitations of similar sensors provided in the prior art .
  • the concept behind this invention provides for the use, as the sensors, of a plurality of optical fibres having a determined geometric structure, and for the fibre optics sensor to include a plastic back-up member, in particular a tape, wherein the fibres are embedded.
  • Figure 1 shows schematically a possible embodiment of a fibre optics sensor according to the invention
  • Figure 2 shows an embodiment of the sensor of Figure 1
  • Figure 3 shows a second embodiment of the fibre optics sensor according to the invention
  • Figure 4 shows a further embodiment of the sensor of Figure 1;
  • Figure 5 schematically illustrates the phenomenon of the light power of an optical fibre becoming attenuated through bends in the optical fibre;
  • Figure 6 is an exemplary plot of the qualitative evolution of the light power attenuation through an optical fibre versus its radius of curvature
  • Figures 7A and 7B are respective schematic views of an optical fibre, under normal conditions and in the presence of mechanical strain
  • Figures 8A and 8B are respective schematic views of an optical fibre, under normal conditions and in the presence of mechanical strain due to its component parts having different coefficients of thermal expansion;
  • Figure 9 is a mathematical schematic of the sensor of this invention as formed of two bundles of optical fibres
  • Figure 10 is a three-dimensional view of a surface to which a sensor according to the invention can be mounted;
  • Figure 11 shows schematically an optical apparatus for measuring strain which incorporates a sensor according to the invention
  • Figure 12 illustrates an application of the strain measuring optical apparatus of Figure 11 to a tubular structure
  • Figure 13 illustrates an application of the strain measuring optical apparatus of Figure 11 to a tubular structure
  • Figure 14 illustrates an application to a flat structure with scan-laid optical fibres of the strain measuring optical apparatus shown in Figure 11;
  • Figure 15 illustrates an application to a flat structure, with spiral-laid optical fibres of the strain measuring optical apparatus shown in Figure 11.
  • a fibre optics sensor according to this invention is generally shown schematically at 1.
  • the presence of physical stresses or strains can be detected by measuring the attenuation in light power through the optical fibres of the sensor, while the points of application of such stresses/strains can be located in two ways, namely:
  • Sensors can be considered which comprise a plurality of optical fibres in a layout shaped as a grid, solenoid, twisting, spiral or another type of geometry.
  • optical fibres used in the making of this sensor are laid over a bi-dimensional surface and divided basically into two sets, as follows:
  • 1st set fibres extending along a first direction
  • 2nd set fibres extending along a second direction across the first.
  • Both fibre sets lie close to the surface, so that the fibres will follow any deformations produced in the surface by mechanical stresses.
  • the fibre optics sensor 1 comprises, as shown schematically in Figure 1, N H fibres laid along a first direction (FO) , and N v fibres laid along a second direction (FV) across the first, above a surface 2 which may be of very large area.
  • a fibre optics sensor 1 comprises a "tape" 3 formed from a very thin, e.g. about 1 mm thick, pliable plastic material having plural optical fibres embedded therein which extend in the longitudinal direction of the tape (corresponding to the FO fibres) and in the transverse direction of the tape (corresponding to the FV fibres) .
  • the senor 1 uses optical fibres which are evenly distributed over a large surface.
  • optical fibres which are evenly distributed over a large surface.
  • single mode fibres may be used, such as those normally employed for telecommunications and hence available at reasonable prices.
  • the auxiliary fibres FA can be terminated at one end of the tape 3 for measuring the optical power attenuation therethrough.
  • the fibres may be laid in a straight-line pattern, as has been assumed above, or a sinusoidal pattern, as shown in Figure 4 for the fibre section 4, or other more complex patterns . In this way, the responsiveness of the sensor 1 to straining forces in the surface 2, or mere pressure forces acting on the surface 2, is improved.
  • Figure 5 illustrates how the attenuation increase originates in consequence of the deformation undergone by a fibre F, and highlights points A, B and C where a light loss is experienced.
  • Losses can be of two types, namely: a loss by reflection, PR, at the transition point of the curvature, and a loss by absorption, PA (bending absorption) in the region where the fibre is subject to deformation.
  • the change in optical attenuation as the fibre deformation varies can be evaluated by means of appropriate algorithms, a most widely used of such algorithms being that known as FD-BPM (Finite Difference Beam Propagation Method) and described, for example, in Yevick, D. and Hermansson, B, "Spli-Step Finite Difference Analysis of Rib Waveguides", Electronic Letters, No. 7, 1989.
  • FD-BPM Finite Difference Beam Propagation Method
  • the optical attenuation, as expressed in dB's, of a fibre is a linear function of the fibre length and can increase, all the other conditions being the same, depending on deformations coming under the "bending" headin .
  • a ⁇ is the overall attenuation of the fibre F, considered to have a constant length.
  • a most probable value is picked from the aggregate of the values provided by the inverse function 3 " , once a value for the variable AA ⁇ is given
  • the fibre F shown in these Figures has a cylindrical configuration with a core, having a diamater Deo, which is surrounded by a cladding, having a diameter Del and an outer protective layer 7.
  • FIG 8B Shown schematically in Figure 8B is a possible deformation induced in the fibre F as a result of a temperature gradient T1-T2 being applied to the fibre, in particular with T1>T2.
  • fibre F has an optical attenuation of Adb
  • this attenuation will increase by ⁇ Adb in the presence of a deformation, as defined - for example - by a function F(S) .
  • A is the coefficient of attenuation due to bending
  • D co is the core diameter
  • NA is a numerical aperture
  • R is the bending radius of curvature.
  • the coefficient of attenuation, A-. can be used to calculate the loss along the longitudinal axis, s, by the following expression:
  • P is the optical power within the fibre, at an abscissa s.
  • Fibre HI a set of fibres: Fibre HI,..., Fibre Hn, arranged horizontally;
  • Fibre VI a set of fibres: Fibre VI,..., Fibre VM, arranged vertically.
  • Fibre VI a set of fibres: Fibre VI,..., Fibre VM, arranged vertically.
  • an overall optical attenuation can be determined in accordance with the following formal correspondence : Fibre Hi: corresponding attenuation A Hi ;
  • Fibre Vj corresponding attenuation A vj .
  • each fibre will undergo bending, assuming a geometric configuration defined by a function F Hi (z) ' or F vj (z) , according to whether the fibre is horizontal or vertical.
  • K is a proportionality constant.
  • the actual deformation can be found fairly easily by making attenuation measurements continually over time.
  • Another instance of the strained surface being immediate to determine is that of a concentrated strain for, in this case, variations in attenuation will only occur at some of the vertical fibres and some of the horizontal fibres.
  • Figure 11 illustrates schematically an embodiment of an optical apparatus for measuring strains in a flat surface by a sensor according to the invention, and using transmitters and receivers connected in the following manner :
  • each fibre is supplied a constant optical power, from an transmitter TX connected through a transmit system 8 which comprises a splitter and plural distribution fibres; on the far side from the transmission side, a receiver RX is connected to each fibre through a receive system 9 which comprises essentially a plurality of pick-up fibres;
  • the optical power values measured by the receivers RX are reported to a central optical system (OS) which will calculate the attenuation through each fibre, considering that the transmitted powers are constant .
  • OS central optical system
  • a second embodiment of the optical apparatus for strain measurements according to the invention concerns the application of this sensor for controlling stresses and strains occurring in a tubular structure 11, e.g. a gas pipeline.
  • the horizontal fibres FO of the sensor would be laid along the tubular structure 11, and the vertical fibres FV would be wound ring-like around the tubular structure 11.
  • a raceway 12 placed on top of the tubular structure 11, for example, contains an optical fibre 13 adapted to distribute the optical power to the individual vertical fibres, and a bus 14 for supplying the receivers and picking up measurement data of the power received on each wound fibre (vertical fibre FV) .
  • optical apparatus for measuring strain and/or intrusion can be embodied to either monitor a flat surface or a pipeline 15, using a single sensing optical fibre 16, which may include sets of horizontal fibres FO, for example, and measuring the reflected power by means of an OTDR 17.
  • the strains can be located from anomalies detected by the OTDR 17.
  • This embodiment of the optical apparatus for strain measurements is useful especially where the strains do not vary sharply over time.
  • the measurements then can be made cyclically by the OTDR 17, and the OTDR can be shared by several sensing optical fibres 16.
  • a sensing optical fibre 16 may be wound spirally around the structure and connected through an optical switch 18 at one end of the OTDR 17, as shown in Figure 13.
  • the spiral-wound optical fibre 16 may comprise a single fibre, or alternatively a set of fibres embedded, for example, in a plastic tape, to provide a substantially solenoid-like configuration.
  • the reflected power measurement made by the OTDR 17 connected to the spiral-wound sensing optical fibre 16 via the optical switch 18 enables the detection of mechanical stresses, producing a concentrated deformation in the pipeline 15, to be detected even a distance away from the point where the measurement is taken.
  • the strain-measuring optical apparatus of this invention may further comprise a sensing optical fibre 19 laid scan- like over a flat surface 20 to be monitored, as shown in Figure 14, into a substantially serpentine con iguration.
  • a measurement of reflected optical power would be made by the OTDR 17.
  • the fibre optics sensor and optical apparatus for measuring strains can be used in many situations where the occurrence of mechanical stresses, abnormal displacements, pressure from intrusions, etc. in a structure however long is to be monitored.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Optical Transform (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

L'invention concerne un capteur à fibres optiques permettant de détecter et de mesurer des déformations et/ou des contraintes physiques sur une superficie (2) plate et/ou tubulaire et/ou de forme irrégulière. Ce capteur, qui est du type comprenant au moins une fibre optique de détection et un support pour cette fibre (3), se caractérise par le fait qu'au moins une fibre optique de détection est placée selon une disposition géométrique donnée. Ce capteur est par ailleurs muni d'organes conçus pour détecter toute atténuation de la puissance optique réfléchie dans ladite fibre, ainsi que des organes de calcul destinés à reconstituer les déformations et/ou les contraintes de ladite superficie (2), à partir de la valeur de l'atténuation de la puissance optique dans la fibre optique.
PCT/IT1999/000025 1999-02-08 1999-02-08 Capteur a fibres optiques et dispositif optique pour detecter des deformations et/ou des contraintes WO2000047967A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/IT1999/000025 WO2000047967A1 (fr) 1999-02-08 1999-02-08 Capteur a fibres optiques et dispositif optique pour detecter des deformations et/ou des contraintes
AU25453/99A AU2545399A (en) 1999-02-08 1999-02-08 Optical fibers sensor and optical device for detecting stress and/or strain

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IT1999/000025 WO2000047967A1 (fr) 1999-02-08 1999-02-08 Capteur a fibres optiques et dispositif optique pour detecter des deformations et/ou des contraintes

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WO2000047967A1 true WO2000047967A1 (fr) 2000-08-17

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102005010344A1 (de) * 2005-03-07 2006-09-21 CCS Technology, Inc., Wilmington Vorrichtung zum Biegen eines Lichtwellenleiters sowie Anordnung und Verfahren zum Dämpfen von Licht in einem Lichtwellenleiter
GB2435689A (en) * 2006-03-02 2007-09-05 Insensys Ltd Monitoring hollow structures
CN106198365A (zh) * 2016-06-28 2016-12-07 大连理工大学 一种基于分布式应变测量的管道内腐蚀监测方法
CN114812424A (zh) * 2022-05-13 2022-07-29 天津大学 一种天然冰场冰层可视化安全监测系统及方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4692610A (en) * 1986-01-30 1987-09-08 Grumman Aerospace Corporation Fiber optic aircraft load relief control system
US4733068A (en) * 1986-04-07 1988-03-22 Rockwell International Corporation Crossed fiber optic tactile sensor
US4781056A (en) * 1985-03-07 1988-11-01 Sopha Praxis Optical device for strain detection, method for the measurement of strain by means of the said device and their application to scales
US4886361A (en) * 1987-05-12 1989-12-12 Versuchsanstalt fur Luft Flat tactile sensor
EP0357253A2 (fr) * 1988-08-16 1990-03-07 Gec-Marconi Limited Capteur à fibres optiques
DE19625730A1 (de) * 1996-06-27 1998-01-02 Teves Gmbh Alfred Verwendung einer Berührungssensormatrix als Sensor in Kraftfahrzeugen

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4781056A (en) * 1985-03-07 1988-11-01 Sopha Praxis Optical device for strain detection, method for the measurement of strain by means of the said device and their application to scales
US4692610A (en) * 1986-01-30 1987-09-08 Grumman Aerospace Corporation Fiber optic aircraft load relief control system
US4733068A (en) * 1986-04-07 1988-03-22 Rockwell International Corporation Crossed fiber optic tactile sensor
US4886361A (en) * 1987-05-12 1989-12-12 Versuchsanstalt fur Luft Flat tactile sensor
EP0357253A2 (fr) * 1988-08-16 1990-03-07 Gec-Marconi Limited Capteur à fibres optiques
DE19625730A1 (de) * 1996-06-27 1998-01-02 Teves Gmbh Alfred Verwendung einer Berührungssensormatrix als Sensor in Kraftfahrzeugen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
HASTINGS M C ET AL: "Integration of the finite element and beam propagation methods to determine performance of microbend sensors", TENTH INTERNATIONAL CONFERENCE ON OPTICAL FIBRE SENSORS CONFERENCE, GLASGOW, UK, 11-13 OCT. 1994, PROCEEDINGS OF THE SPIE - THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, 1994, USA, PAGE(S) 376 - 379, ISSN: 0277-786X, XP002117508 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102005010344A1 (de) * 2005-03-07 2006-09-21 CCS Technology, Inc., Wilmington Vorrichtung zum Biegen eines Lichtwellenleiters sowie Anordnung und Verfahren zum Dämpfen von Licht in einem Lichtwellenleiter
DE102005010344B4 (de) * 2005-03-07 2007-05-31 CCS Technology, Inc., Wilmington Vorrichtung zum Biegen eines Lichtwellenleiters sowie Anordnung zum Dämpfen von Licht in einem Lichtwellenleiter
GB2435689A (en) * 2006-03-02 2007-09-05 Insensys Ltd Monitoring hollow structures
GB2435689B (en) * 2006-03-02 2009-04-08 Insensys Ltd Structural monitoring
CN106198365A (zh) * 2016-06-28 2016-12-07 大连理工大学 一种基于分布式应变测量的管道内腐蚀监测方法
CN114812424A (zh) * 2022-05-13 2022-07-29 天津大学 一种天然冰场冰层可视化安全监测系统及方法

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