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WO2018158678A1 - Procédé et système de mesure de forces - Google Patents

Procédé et système de mesure de forces Download PDF

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Publication number
WO2018158678A1
WO2018158678A1 PCT/IB2018/051218 IB2018051218W WO2018158678A1 WO 2018158678 A1 WO2018158678 A1 WO 2018158678A1 IB 2018051218 W IB2018051218 W IB 2018051218W WO 2018158678 A1 WO2018158678 A1 WO 2018158678A1
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WO
WIPO (PCT)
Prior art keywords
optical
polarization
signal
components
βρτοτ
Prior art date
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Ceased
Application number
PCT/IB2018/051218
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English (en)
Inventor
Silvio Abrate
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Istituto Superiore Mario Boella
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Istituto Superiore Mario Boella
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Filing date
Publication date
Application filed by Istituto Superiore Mario Boella filed Critical Istituto Superiore Mario Boella
Publication of WO2018158678A1 publication Critical patent/WO2018158678A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/344—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells using polarisation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
    • G01D5/35341—Sensor working in transmission
    • G01D5/35345—Sensor working in transmission using Amplitude variations to detect the measured quantity
    • 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
    • G01L1/243—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 using means for applying force perpendicular to the fibre axis

Definitions

  • the present invention relates to force measurement.
  • the present invention relates to measurement of mechanical forces such as, for example, transversal forces (pressure) and rotational forces (torsion) applied to an optical fiber.
  • the present invention relates to measurement of forces by means of optical transducers. Even more in detail, the present invention relates to measurement of forces by means of optical transducers and/or sensors comprising optical fibers.
  • the present invention relates to a method and a system for measuring forces, said system comprising optical transducers and/or sensors and/or optical fiber sensors.
  • optical transducers known in the art are based on the consideration that forces, in particular mechanical forces such as pressure or torsion forces, can be measured and/or detected by evaluating the effects caused on the light transmitted through an optical path by a force acting, whether directly or indirectly, upon said optical path.
  • the principle of operation of most optical transducers known in the art exploits the variation occurring in the photocurrent detected at the output of an optical path as a function of the optical signal attenuation generated by the variation in the optical connection or by signal interference, which are controlled by the force to be detected. It is in fact always possible to establish a relationship between the photocurrent detected at the output of an optical path and the mechanical stress acting upon the optical path.
  • some known optical transducers utilize the variation occurring in the polarization of optical fibers due to microstresses induced and caused by an external force applied thereto.
  • optical transducers are based on interference of two orthogonal polarization modes, and hence require special, highly birefringing fibers and very precise mechanical enclosures. More in detail, the known optical transducers are based on the detection of polarization variations in the light beam transmitted through a birefringing optical fiber.
  • optical signal at the output of the optical path can be converted into a current and/or voltage measurement, it will also be possible to establish a relationship between the measured current or voltage and the force acting upon the optical path.
  • force detection principle may appear to be rather general, it has nevertheless proven to be very reliable for detecting and/or measuring forces, in particular mechanical forces such as, for example, pressure and torsion forces.
  • Document EP 1 748 284 Bl describes an optical transducer for detecting forces acting upon the transducer.
  • the transducer comprises an optical path adapted to transmit optical signals, wherein the optical path comprises sensor means adapted to modify the transmission of the optical signals along the optical path as a result of a force acting upon them; the optical path further comprises polarization scrambling means adapted to render the polarization of the optical signals entering the sensor means parallel to a first predefined direction, the sensor means being also adapted to modify the polarization of the optical signals entering the sensor means as a result of a force acting upon them; the transducer further comprises polarizing means adapted to collect the optical signals exiting the sensor means and having an axis of polarization parallel to a predefined direction, so as to allow only those optical signals which have a polarization that is parallel to the axis of polarization to exit the polarizing means.
  • an optical path e.g. an optical fiber
  • the optical transducer 1 of Figure la comprises also polarization scrambling means la, sensor means lb and polarizing means lc.
  • the polarization scrambling means la, the sensor means lb and the polarizing means lc may comprise, or even be defined by, one or more loops laa, lbb and lcc, respectively, of the optical fiber If
  • reference numeral 5 identifies a force and/or a mechanical stress (e.g. a pressure force or a rotation force) acting upon the transducer 1, in particular upon the sensor means lb of the transducer 1.
  • a mechanical stress e.g. a pressure force or a rotation force
  • polarization scrambling means refers to means suitable for modifying the polarization of an optical signal 2a (e.g. a luminous signal) entering the polarization scrambling means la (after having entered the optical path or optical fiber If), so as to render the polarization of the optical signal exiting the polarization scrambling means parallel to a predefined axis or a predefined direction.
  • optical signal 2a e.g. a luminous signal
  • polarizing means refers to means suitable for emitting optical signals with a predefined polarization.
  • the polarizing means lc of Figure la may comprise an axis of polarization parallel to a predefined direction, so as to allow only those optical signals which have a polarization parallel to said axis of polarization to exit the polarizing means lc, while any optical signals having a polarization that is not parallel to the axis of polarization of the polarizing means will be either absorbed or reflected.
  • the polarizing means lc included in the optical transducer 1 of Figure la behave like some sort of optical filter, because only those optical signals which have a polarization parallel to the axis of polarization can propagate along the polarizing means lc and be emitted, whereas any optical signals having a polarization that is not parallel to the axis of polarization of the polarizing means lc will be absorbed, and therefore neither transmitted/propagated along the polarizing means nor emitted from the polarizing means lc.
  • the optical signal 2a entering the optical path If normally comprises different components having as many different characteristics, in particular as many different wavelengths and polarizations, it can also be appreciated that only those components entering the polarizing means lc which have a polarization that is parallel to the axis of polarization will be propagated and transmitted through the polarizing means lc and then emitted.
  • sensor means refers to means adapted to modify the transmission of optical signals entering the sensor means lb.
  • the expression "sensor means” indicates means adapted to modify the polarization of optical signals entering the sensor means lb as a function of a force (e.g. pressure or torsion, or even a mechanical stress) acting upon the sensor means.
  • a force e.g. pressure or torsion, or even a mechanical stress
  • the sensor means lb comprise one or more loops lbb of an optical fiber
  • the forces acting upon the sensor means will be able to deform or even damage one or more loops of the optical fiber; the microdeformations ensuing in the fiber as a result of the mechanical stress acting upon the fiber will produce variations in the polarization of the optical signals transmitted and propagated through the sensor means.
  • the variations in the polarization of the optical signals can be related to the forces or stresses acting upon the sensor means lb.
  • the polarization scrambling means la are programmed to define the optical signals 2b exiting the optical transducer 1; in other words, through the polarization scrambling means la, the polarization of the optical signal 2a entering the optical path If will be modified until the polarization of the optical signal exiting the polarization scrambling means la will be parallel to a predefined direction.
  • the polarization of the optical signal exiting the polarization scrambling means la may be made parallel to the axis of polarization of the polarizing means lc.
  • the polarization of the optical signal exiting the polarization scrambling means la may be made orthogonal to the axis of polarization of the polarizing means lc.
  • the former case i.e.
  • the optical signal 2b exiting the optical path If (from the polarizing means lc) will essentially correspond to the optical signal 2a at the input of the optical path If or, in other words, the intensity of the output optical signal 2b will substantially correspond to that of the input optical signal 2a, except for negligible power losses due to inevitable imperfections of the optical path. It follows, therefore, that the maximum or most intense optical signal 2b will be collected at the output of the optical transducer 1.
  • the transmission of the optical signals along the optical path If will be modified as a result of the force or stress 5.
  • the polarization of the optical signals exiting the polarization scrambling means will change because of the force 5, e.g. due to microdeformations produced in the sensor means lb (e.g. in a portion of one or more loops lbb).
  • the polarization of the optical signal exiting the polarization scrambling means la has been made parallel to the axis of polarization of the polarizing means lc
  • the polarization of at least some components of the optical signal exiting the sensor means lb will no longer be parallel to the axis of polarization of the polarizing means lc.
  • the intensity of the optical signal 2b exiting the polarizing means lc (the optical path If) will be lower than the intensity of the optical signal 2a entering the optical path If and exiting the polarization scrambling means la.
  • the difference between the intensities of the optical signals 2b and 2a will depend on the intensity of the force 5 applied to the sensor means lb, so that it will be possible to relate the difference between the output signal 2b and the input signal 2a to the intensity of the force 5.
  • the polarization of the optical signal exiting the polarization scrambling means la is made orthogonal to the axis of polarization of the polarizing means lc
  • at least some components of the optical signal exiting the sensor means lb will have a polarization that will no longer be orthogonal to the axis of polarization of the polarizing means lc because of the force or stress 5 acting upon the sensor means lb. It will then be possible to collect the optical signal 2b exiting the optical transducer 1 (the polarizing means) and establish a relationship between the intensity or power of the signal 2b and the intensity of the force or stress 5 acting upon the transducer 1.
  • the polarization scrambling means la may comprise a first portion of the optical fiber If; in particular, the polarization scrambling means may comprise one or more loops laa of the optical fiber If Likewise, the sensor means lb may comprise a second portion of the optical fiber If; in particular, the sensor means lb may comprise one or more loops lbb of the optical fiber If
  • reference numerals 6a and 6b identify an optical signal emitter device and an optical signal receiver device, respectively.
  • the device 6a generates and/or emits optical signals that enter the optical path If and propagate or are transmitted through the optical path defined by the polarization scrambling means la, the sensor means lb and the polarizing means lc, and may be partially or totally absorbed by the polarizing means lc.
  • the resulting optical signals at the output of the polarizing means lc are received and/or collected by the receiver device 6b.
  • the device 6a may comprise a current or voltage generator connected to a laser light source; likewise, the receiver device 6b may comprise an amplified photodetector with a photodiode followed by a low-noise amplifier.
  • the receiver device 6b may comprise an amplified photodetector with a photodiode followed by a low-noise amplifier.
  • Figures la and lb schematically represent the principle of operation of a known optical transducer and provide a schematic view of the electric layout of a measuring device making use of the known transducer of Figure la;
  • FIG. 2a,2b,2c,2d and 2e show a detail of the receiver according to the present invention and graphs illustrating the trend of the powers outputted by the receiver. Detailed description
  • the present invention has proven particularly advantageous when used for detecting and/or measuring transversal and rotational forces, such as, for example, pressure and torsion forces. For this reason, the following will describe some examples wherein embodiments of an optical transducer according to the present invention are used for detecting and/or measuring pressure and torsion forces.
  • optical transducers according to the present invention is not limited to detecting or measuring pressure or torsion forces; on the contrary, the optical transducers according to the present invention can also be used for measuring and/or detecting different forces acting thereupon.
  • the present invention is therefore useful also for measuring all such forces, and the transversal (pressure) and/or rotational (torsion) forces described below will represent forces of any kind acting upon the transducers.
  • patent EP 1 748 284 Bl describes a solution that stands out as an evolution providing simplification and, in perspective, a reduction in the costs to be incurred for implementing a measurement system.
  • one embodiment of the measurement system according to the present invention uses an optical source on the source side, e.g. a single-mode laser. More in detail, said single-mode laser must not rigorously be one with known polarization. Therefore, the transmitter side can use a less complex source. This is because the polarization controller and/or the polarizer employed in the known solution described in patent EP 1 748 284 Bl are no longer necessary, and a simpler source can be used.
  • the sensitive fiber used for implementing the optical path and the sensor means remains unchanged from the known solution.
  • the sensitive fiber is selected among single-mode optical fibers.
  • a polarizing beam splitter (PBS) device is used, i.e. a device having one input IN and two separate outputs Ul and U2.
  • the splitter device PBS has one input IN, whereat the signal arrives from the optical path, which signal comprises two polarization components x and y along the two main axes of the fiber, and two outputs Ul and U2. On the first output branch Ul there is the component x, and on the second output branch U2 there is the component y of the signal.
  • the two outputs Ul and U2 of the splitter device PBS are connected to two receiver devices, e.g. two photodiodes PD1 and PD2, which convert the optical signal into an electric signal.
  • the two electric signals outputted by the photodiodes PD1 and PD2 can be processed in a simple manner, e.g. by means of a direct voltage or current measurement.
  • the signal inputted to the splitter device PBS will have a total power ⁇ flowing along the fiber.
  • the total power ⁇ is split between the two fundamental polarizations, i.e. the components x and y, which are parallel to the two main axes of the fiber. Therefore, each component x and y will have a corresponding power Px and Py, and the sum of the two powers will always be equal to the total power.
  • the total power ⁇ is the sum of the powers of the two signal components x and y of the main axes of the fiber.
  • the total power ⁇ can also be expressed as:
  • a stress of any kind acting upon the fiber will result in changes in all the other relationships between the coefficients a and ⁇ .
  • Other relationships are possible as well.
  • the electric signals outputted by the photodiodes PDl and PD2 are proportional to the respective powers Px and Py associated with the different components x and y.
  • the output signal of the photodiode PDl will be proportional to the power Px, while the output signal of the photodiode PD2 will be proportional to the power Py.
  • a high-pass filter whether analogue or digital
  • a low-pass filter whether analogue or digital
  • said two outputs Ul and U2 may change over time as a consequence of the stresses undergone by the sensitive fiber that constitutes the optical path.
  • the incoming signal x+y is split according to its two fundamental polarizations, parallel to the main axes of the fiber, resulting in two power components
  • Such components x and y of the signal are received by the two photodiodes PD1 and PD2, which measure their respective powers Px and Py (see graphs in Figures 2b and 2c).
  • the sum of the powers Px and Py of the two components x and y of the signal is always constant (except for negligible losses).
  • the ratio (or difference or product) between the powers Px and Py of the two components x and y of the signal will change because of external stresses.
  • the solution proposed herein which comprises the splitter device PBS and the two photodiodes PD1 and PD2, can be easily implemented as integrated optics (e.g. silicon photonics). This is because at present polarization control is hardly implementable as integrated optics, e.g. on platforms such as silicon.
  • integrated optics e.g. silicon photonics
  • the device PBS and the photodiodes PD1 and PD2 are classic discrete components that can be more easily implemented as an integrated optical circuit.
  • all three discrete components can be implemented on a single platform, i.e. on a single integrated device implemented as integrated optics. This will result in a reduction in the space required for implementation and in lower costs.
  • the three components may be implemented separately and then used for building the system.
  • the PBS and one photodiode are integrated on the same device, whereas the second photodiode is a separate component.
  • the implementations described herein are based on the assumption that all the fiber in use is sensitive.
  • a laser is used on the transmitter side which has a polarization-maintaining (PM) output, followed by a PM fiber section with polarization tuned to the laser output (it is just a matter of purchasing the proper fiber, since no polarizer is needed between the two).
  • PM fiber is a fiber wherein symmetry is broken to such an extent (i.e. it has such an elliptical core) that one polarization along a main axis is maintained up to the exit. Since the second polarization is never excited, no scattering of the PMD polarization modes occurs.
  • the PM fiber will then be connected to the portion of sensitive fiber, followed by the splitter device PBS and the two photodiodes PD1 and PD2.
  • the connection between them can be effected by means of sections of optical fiber of any length. In this manner, the interrogator will be kept at a distance from the section of sensitive fiber.
  • the photodiodes may be located at a distance of kilometres from the PBS.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)
  • Optical Transform (AREA)

Abstract

L'invention concerne un système de détection de forces agissant sur un transducteur optique (1), comprenant une source de signal optique conçue pour émettre des signaux optiques (2a, 2b), un transducteur (1), disposé sur un trajet optique (1f), conçu pour propager les signaux optiques (2a, 2b), des moyens capteurs (1b) disposés sur le trajet optique (1f) et conçus pour modifier la transmission des signaux optiques (2a, 2b) le long du trajet optique (1f) consécutivement à une contrainte (5) agissant sur ces derniers, le système comprenant un récepteur équipé d'un diviseur de faisceau polarisant (PBS) destiné à diviser le signal optique entrant (x,y,PTOT) en deux composantes (U1,U2,αPTOT,βPTOT) à envoyer à deux dispositifs récepteurs (PD1, PD2), chaque dispositif récepteur (PD1, PD2) convertissant le signal optique reçu en un signal électrique correspondant, et la somme des puissances (αPTOT,βPTOT) des deux composantes (U1,U2) du signal étant toujours constante, en l'absence d'une contrainte, les autres relations entre les puissances (αPTOT,βPTOT) des deux composantes (U1,U2) du signal étant également constantes, et en présence d'une contrainte, les autres relations entre les puissances (αPTOT,βPTOT) des deux composantes (U1,U2) du signal variant.
PCT/IB2018/051218 2017-02-28 2018-02-27 Procédé et système de mesure de forces Ceased WO2018158678A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT102017000022654 2017-02-28
IT102017000022654A IT201700022654A1 (it) 2017-02-28 2017-02-28 Procedimento e sistema per misurare forze

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WO2018158678A1 true WO2018158678A1 (fr) 2018-09-07

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4495411A (en) * 1982-10-27 1985-01-22 The United States Of America As Represented By The Secretary Of The Navy Fiber optic sensors operating at DC
US5028130A (en) * 1988-09-22 1991-07-02 U.S. Philips Corporation Method of stress-optical force measurement and measurement device for performing the method

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4495411A (en) * 1982-10-27 1985-01-22 The United States Of America As Represented By The Secretary Of The Navy Fiber optic sensors operating at DC
US5028130A (en) * 1988-09-22 1991-07-02 U.S. Philips Corporation Method of stress-optical force measurement and measurement device for performing the method

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