GB2592274A - Optical fiber grating acceleration sensor - Google Patents

Optical fiber grating acceleration sensor Download PDF

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Publication number
GB2592274A
GB2592274A GB2002584.7A GB202002584A GB2592274A GB 2592274 A GB2592274 A GB 2592274A GB 202002584 A GB202002584 A GB 202002584A GB 2592274 A GB2592274 A GB 2592274A
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United Kingdom
Prior art keywords
arm
optical fiber
leaf spring
grating
measuring device
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Legal status (The legal status 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 status listed.)
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GB2002584.7A
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GB202002584D0 (en
Inventor
Zhang Hua
Hu Binxin
Song Guangdong
Zhu Feng
Wang Jiqiang
Liu Tongyu
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Laser Inst Of Shandong Academy Of Science
Laser Institute of Shandong Academy of Science
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Laser Inst Of Shandong Academy Of Science
Laser Institute of Shandong Academy of Science
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Priority to GB2002584.7A priority Critical patent/GB2592274A/en
Publication of GB202002584D0 publication Critical patent/GB202002584D0/en
Publication of GB2592274A publication Critical patent/GB2592274A/en
Pending legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P15/093—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by photoelectric pick-up
    • 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
    • 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
    • G01D5/35306—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 an interferometer arrangement
    • G01D5/35309—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 an interferometer arrangement using multiple waves interferometer
    • G01D5/35316—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 an interferometer arrangement using multiple waves interferometer using a Bragg gratings
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P2015/0805—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration
    • G01P2015/0822—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass
    • G01P2015/0825—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass for one single degree of freedom of movement of the mass
    • G01P2015/0828—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass for one single degree of freedom of movement of the mass the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

Disclosed is an optical fibre grating acceleration sensor, which includes: a housing (1). a sensing component (2) provided in the housing (1) and a computing unit (3). The sensing component (2) includes: a leaf spring (21) connected to a bottom of the housing (1 ); a mass (22) connected to a top of the leaf spring (21 ); a beam (23), including a first arm (231) and a second arm (232), wherein the first arm (231) and the second arm (232) are connected via a rotating member (233) fixed on a sidewall of the housing (1), and one end of the second arm (232) far from the rotating member (233) is connected to the top of the mass (22); and an optical fibre measuring device (24) suspended above the beam (23), which includes a grating measuring device (241) and an optical fibre (242) connected respectively to the grating measuring device (241) and the computing unit (3). The computing unit (3) computes an acceleration of a structure to be measured according to a drift of the light parameter of the grating measuring device (241).

Description

OPTICAL FIBER GRATING ACCELERATION SENSOR
FIELD OF THE INVENTION
[0001] The present invention relates to the field of vibration monitoring technologies, and in particular, to an optical fiber grating acceleration sensor.
BACKGROUND OF THE INVENTION
[0002] For some large-scale geologic configuration with complex environment, for example, tunnels and mines, etc., vibration monitoring needs to be carried out periodically, and sensors for measuring vibration parameters are buried inside the geologic configuration in advance. When a seismic wave is generated in the geologic configuration, the seismic wave will be transmitted to the sensor, and the sensor will be able to measure the vibration parameter, so that a latent seismic activity may be found, thereby attaining the object of prewarning and disaster prevention.
[0003] Acceleration is one of the general vibration parameters, and it is used for reflecting the impact force of a seismic wave. At present, an optical fiber grating acceleration sensor is often employed to measure an acceleration. Optical fiber grating has the advantages of electromagnetic interference resistance, explosion-proof and high-temperature resistance, and it may be adapted to the complex and harsh environment of a geologic configuration. When an optical fiber grating acceleration sensor buried inside a geologic configuration detects a vibration signal, the light parameter of the optical fiber grating will change correspondingly, and the vibration acceleration of a large-scale structural engineering will be acquired by demodulating the change of the light parameter.
[0004] Fig.1 shows a structure of an optical fiber grating acceleration sensor, wherein an optical fiber grating 101 is adhered to the surface of a fixed end (Fi) of a cantilever beam 201, the free end (Fr) of the cantilever beam 201 is flexibly connected to a mass structure 301, and the vibration of the mass structure 301 makes the cantilever beam 201 bend, so that the central wavelength of the optical fiber grating 101 will drift. By detecting the drift of the central wavelength, the vibration acceleration of the geologic configuration can be computed. However, because the optical fiber grating 101 is directly adhered to the cantilever beam 201, the mechanical properties of the cantilever beam 201 will cause the grating period of the optical fiber grating 101 to change axially, that is, a grating chirp phenomenon will occur, which causes an inaccurate measurement result.
SUMMARY OF THE INVENTION
[0005] The present invention provides an optical fiber grating acceleration sensor, thereby solving the problem of low accuracy of acceleration measurement.
[0006] In the first aspect of the invention, there provides an optical fiber grating acceleration sensor, which includes: a housing, a sensing component provided in the housing, and a computing unit; wherein the sensing component includes: [0007] a leaf spring connected to the bottom of the housing, which is plate-shaped elastic member formed by stacking at least one layer of spring steel; [0008] a mass connected to the top of the leaf spring; [0009] a beam, which includes a first arm and a second arm, wherein the first arm and the second arm are connected via a rotating member, the rotating member is fixed to the sidewall of the housing, and one end of the second arm far from the rotating member is connected to the top of the mass; [0010] an optical fiber measuring device suspended above the beam, which includes a grating measuring device, and an optical fiber connected respectively to the grating measuring device and the computing unit.
[0011] The computing unit is configured to compute the acceleration of a structure to be measured according to a drift of the light parameter of the grating measuring device.
[0012] In the first aspect, the sensor is placed in the structure to be measured, when the structure to be measured vibrates due to external factors, the sensor vibrates with the structure to be measured, so that the mass vibrates under the action of an inertial force, and the first arm in the beam is driven to make a certain angular displacement around the rotating member, so that the grating measuring device will deform due to being stretched, thus the light parameter of the grating will drift, and the acceleration of the structure to be measured may be demodulated according to the drift of the light parameter. In the invention, the optical fiber grating is suspended in the housing, and no grating chirp phenomenon or reflected wave multimodal phenomenon will appear. The second arm is connected to the leaf spring via a mass, and the leaf spring is an elastic member with relatively large size and stiffness, thus the lateral vibration interference to the mass may be lowered, and the interference vibration in the leaf spring is transmitted to the second arm after being attenuated by the mass, so that the lateral vibration interference to the second arm is greatly lowered, the measurement precision of unidirectional vibration acceleration is increased, the frequency band is wide, and it has a high sensitivity and a large frequency response range.
[0013] In the second aspect of the invention, there provides an optical fiber grating acceleration sensor, which includes: a housing, a sensing component provided in the housing, and a computing unit; wherein the sensing component includes: [0014] a leaf spring connected to the bottom of the housing, which is plate-shaped elastic member formed by stacking at least one layer of spring steel; [0015] a beam, which includes a first arm and a second arm, wherein the first arm and the second arm are connected via a rotating member, the rotating member is fixed to the sidewall of the housing, the second arm is connected to the top of the leaf spring, and the length of the leaf spring and the length of the first arm are both less than that of the second arm; [0016] an optical fiber measuring device suspended above the beam, which includes a grating measuring device, and an optical fiber connected respectively to the grating measuring device and the computing unit.
[0017] The computing unit is configured to compute the acceleration of a structure to be measured according to a drift of the light parameter of the grating measuring device. [0018] In the second aspect, the second arm is a long arm, and a leaf spring is connected to the bottom of the long arm, and the leaf spring has large size and stiffness, which can provide a more stable support to the second arm and lower the lateral vibration interference in the vibration of the second arm, so that the measurement precision of unidirectional vibration acceleration is increased, the frequency band is wide, and it has a high sensitivity and a large frequency response range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In order to more clearly illustrate the technical solutions of the embodiments of the invention or of the prior art, the drawings needed in the description of the embodiments or the prior art will be briefly introduced below. Apparently, the drawings in the description below are only some embodiments of the invention, and other drawings may also be obtained by one of ordinary skills in the art according to these drawings without creative work.
[0020] Fig.1 is a structural representation of an optical fiber grating acceleration
sensor of the prior art;
is a structural representation of an optical fiber grating acceleration in Embodiment 1 of the invention; is an equivalent force model of the sensor shown in Embodiment 1; is a structural representation of an optical fiber grating acceleration in Embodiment 2 of the invention; and is an equivalent force model of the sensor shown in Embodiment 2.
[0021] Fig.2 sensor shown [0022] Fig.3 [0023] Fig.4 sensor shown [0024] Fig.5 [0025] In the drawings: 1 housing; 2 sensing component; 21 leaf spring; 22 mass; 23 beam; 231 first arm; 232 second arm; 233 rotating member; 24 optical fiber measuring device; 241 grating measuring device; 242 optical fiber; 25 bolt; 3 computing unit.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0026] The technical solutions in the embodiments of the invention will be described clearly and fully below in conjunction with the drawings in the embodiments of the invention. Apparently, the embodiments described are only a part of the embodiments of the invention, rather than being the whole embodiments. All the other embodiments obtained by one of ordinary skills in the art based on the embodiments of the invention without creative work pertain to the protection scope of the invention.
[0027] As shown in Fig.2, an optical fiber grating acceleration sensor according to Embodiment 1 of the invention may be buried inside a structure to be measured, for measuring an acceleration parameter a structure to be measured. The sensor overall includes a housing 1, a computing unit 3, and a sensing component 2 provided inside the housing 1. The housing 1 is configured to encapsulate the sensing component 2, and the sensing component 2 is configured to convert the vibration of the structure to be measured into the change of grating strain. Moreover, the light parameter of the grating on which strain occurs will also change. The light parameter may be wavelength, frequency, phase or polarization, etc. For different types of gratings, the light parameter sensitive to strain may be different. For example, Fiber Bragg Grating (FBG) may be selected as the specific grating. The computing unit 3 may be an external light signal demodulation device, and it is configured to demodulate the light parameter detected so as to obtain the acceleration of the structure to be measured.
[0028] In Fig.2, the sensing component 2 includes a leaf spring 21 fixedly connected to the bottom of the housing 1, a beam 23 connected to the top of the leaf spring 21 and an optical fiber measuring device 24 connected to the beam 23, wherein the optical fiber measuring device 24 is suspended above the beam 23.
[0029] The optical fiber measuring device 24 includes a grating measuring device 241 of which a light parameter changes when a structure to be measured vibrates, and an optical fiber 242 connected respectively to the grating measuring device 241 and the computing unit 3. The grating measuring device 241 may be a grating dedicated to acceleration measurement. In other possible implementation modes, the grating measuring device 241 is formed by directly engraving the grating into the fiber core of the optical fiber 242.
[0030] The beam 23 includes a first arm 231 and a second arm 232, wherein the first arm 231 and the second arm 232 are connected via a rotating member 233 fixed on the sidewall of the housing 1, and an end A of the first arm 231 is connected to the grating measuring device 241. If the mode that the grating is engraved into the optical fiber 242 is employed, the end A of the first arm 231 will be directly connected with the optical fiber 242, and in such a case, the optical fiber 242 and the grating have the same deformation. The beam 23 employs an L-shaped beam, and the second arm 232 is parallel to the optical fiber measuring device 24. If the vibration inertia of the second arm 232 is to be increased, a mass 22 may be additionally connected to the end B of the second arm 232.
[0031] The housing 1, the leaf spring 21 and the second arm 232 may be connected as a whole via a bolt 25, so that the housing 1, the leaf spring 21 and the beam 23 form a vibration sensing and transmitting structure in z direction. The vibration sensing and transmitting structure employs the leaf spring 21 as a support base and realizes rigid connection via a bolt 25, so that the vibration sensing and transmitting structure may be prevented from generating non-z direction displacement due to an external vibration, the measurement precision of acceleration may be increased, and structure stability may be ensured. Additionally, in such a bolt connection mode, it is convenient for removing and replacing a component. The housing 1, the leaf spring 21 and the second arm 232 are not limited to being connected via a bolt, and other rigid connection modes may also be employed, for example, the leaf spring 21 may be welded to the bottom of the housing 1, and the second arm 232 may be welded to the top of the leaf spring 21.
[0032] It is found by the inventors in practical application that, when the second arm 232 is supported by a common spring, because the size and elastic stiffness of the spring are both small, the support to the second arm 232 by the spring will not be stable enough, and the spring will be very sensitive to vibration. When the vibration of the structure to be measured is transmitted to the housing 1 and then transmitted to the second arm 232 via the spring, not only the second arm 232 and the mass 22 will vibrate up and down along z direction, but also lateral vibration interference will occur in the horizontal plane. That is, the mass 22 not only generates a displacement Ax, in z direction, but also generates a lateral displacement Ax due to lateral vibration interference. Thus the strain of the grating measuring device 241 will be a result of the combined action of Ax, and Air,. The strain generated on on the grating measuring device 241 will change its light parameter, thus a deviation will occur between the acceleration demodulated from the light parameter and the actual acceleration generated by the z direction vibration, which causes an inaccurate computation of the vibration acceleration in z direction.
[0033] Therefore, in this embodiment, a leaf spring 21 is employed to support the second arm 232. The leaf spring 21 is also referred to as a plate spring, which is a plate-shaped elastic member formed by stacking at least one layer of spring steel. The leaf spring 21 may be provided with large length and width, as well as a large elastic stiffness. The leaf spring 21 can provide a more stable support to the second arm 232 and have a stronger lateral vibration interference resistance. Because the leaf spring 21 is directly connected to the second arm 232, the length L" of the leaf spring 21 should be less than the length 112 of the second arm 232, thus the obstruction of the leaf spring 21 to the rotating member 233 may be eliminated, and it may be guaranteed that the rotating member 233 can freely drive the first arm 231 to rotate under the drive of the vibration of the second arm 232, and the strain of the grating can conform to the actual vibration, thereby ensuring the measurement accuracy of the grating measuring device 241.
[0034] Preferably, the length L" of the leaf spring 21 is 4/5 of the length L, of the second arm 232, that is, a length difference of scale 0.2 is reserved. By such a design, not only flexible rotation of the rotating member 233 can be guaranteed, but also the leaf spring 21 and the second arm 232 can have a large contact area, so that the affect of interference vibration can be lowered greatly. The leaf spring 21 may be provided at any location on the bottom of the second arm 232, for example, at a location on the bottom of the second arm 232 near the mass 22. Preferably, in this embodiment, the leaf spring 21 is provided at the center of the bottom of the second arm 232. By such a configuration, the leaf spring 21 can more stably support the second arm 232, and the leaf spring 21 can more uniformly transmit the vibration, so that the lateral vibration interference to the second arm 232 and the mass 22 can be further lowered, and the accuracy of acceleration measurement of vibration in z direction can be increased. In Embodiment 1, the length 1_, of the second arm 232 is the distance from the axle center C of the rotating member 233 to the mass 22 (end B).
[0035] When vibration occurs in the environment of a structure to be measured, an acting force will be applied on the sensor by the structure to be measured, and the acting force will be transmitted to the second arm 232 via the housing 1 and the leaf spring 21 sequentially. The second arm 232 has a certain mass, and it vibrates because of inertia. The vibration of the second arm 232 will drive the first arm 231 to generate a certain angular displacement around the rotating member 233, so that a strain will be generated to the grating measuring device 241 due to being stretched, so that the light parameter of the grating measuring device 241 will drift, thus the computing unit 3 may demodulate the acceleration of the structure to be measured according to the drift of the light parameter.
[0036] A component such as a bearing and a rotating shaft, etc., may be employed as the rotating member 233. In this embodiment, the bearing is preferred. The bearing is configured to connect and support a mechanical rotating body (that is, the beam 23). It can lower the frictional coefficient in the rotation of the first arm 231, ensure a revolving precision of the first arm 231 and increase the mechanical sensitivity of the beam 23.
Moreover, it is favorable for lowering the loss of vibration during transfer, thereby improving the measurement precision of the sensor.
[0037] Fig.3 shows an equivalent force model of the sensor in Embodiment 1. The displacement generated by the second arm 232 is Ax, , the displacement generated by the grating in the grating measuring device is Ax,, L, is the length of the first arm 231, and L, is the length of the second arm 232, wherein the length L, of the first arm 231 is less than the length 112 of the second arm 232, that is, the first arm 231 is a short arm, and the second arm 232 is a long arm. By such a design, the displacement Ax, generated by the second arm 232 may be less than the displacement Aoc, generated by the grating, that is, the deformation of the grating measuring device 241 due to stretching may be reduced, which is equivalent to signal reduction. Thus the sensor may be buried inside a structure to be measured with strong vibration, for example, railway and tunnel, etc., so that the deformation of grating in the grating measuring device 241 may be limited, and the grating may be prevented from being broken due to excessive stretching or bending.
[0038] As shown in Fig.4, an optical fiber grating acceleration sensor according to Embodiment 2 of the invention includes a housing 1, a computing unit 3, and a sensing component 2 provided inside the housing 1. The housing 1 is configured to encapsulate the sensing component 2, and the sensing component 2 is configured to convert the vibration of the structure to be measured into the change of grating strain. The light parameter of the grating on which strain occurs will also change. The light parameter may be wavelength, frequency, phase or polarization, etc. For different types of gratings, the light parameter sensitive to strain may be different, and Fiber Bragg Grating (FBG) may be selected as the grating. The computing unit 3 may be an external demodulation device, and it is configured to demodulate the light parameter detected so as to obtain the acceleration of the structure to be measured.
[0039] In Fig.4, the sensing component 2 includes a leaf spring 21 connected to the bottom of the housing 1, a mass 22 connected to the top of the leaf spring 21, a beam 23 connected to the top of the mass 22, and an optical fiber measuring device 24 connected to the beam 23, wherein the optical fiber measuring device 24 is suspended above the beam 23.
[0040] The optical fiber measuring device 24 includes a grating measuring device 241 of which a light parameter changes when a structure to be measured vibrates, and an optical fiber 242 connected respectively to the grating measuring device 241 and the computing unit 3. In other possible implementation modes, the grating is engraved into the fiber core of the optical fiber 242. The beam 23 includes a first arm 231 and a second arm 232, wherein the first arm 231 and the second arm 232 are connected via a rotating member 233 fixed on the sidewall of the housing 1. One end of the second arm 232 far from the rotating member 233 (that is, end B) is connected to the top of the mass 22, and the end A of the first arm 231 is connected to the grating measuring device 241. If the mode that the grating is engraved into the optical fiber 242 is employed, the end A of the first arm 231 will be directly connected with the optical fiber 242. In such a case, the optical fiber 242 and the grating have the same deformation.
[0041] The housing 1, the leaf spring 21, the mass 22 and the second arm 232 may be connected as a whole via a bolt 25, so that the housing 1, the leaf spring 21, the mass 22 and the beam 23 form a vibration sensing and transmitting structure in z direction. The vibration sensing and transmitting structure employs the leaf spring 21 as a support base and realizes rigid connection via a bolt 25, so that the vibration sensing and transmitting structure may be prevented from generating non-z direction displacement due to an external vibration, the measurement precision of acceleration may be increased, and structure stability may be ensured. Additionally, in such a bolt connection mode, it is convenient for removing and replacing a component. The housing 1, the leaf spring 21, the mass 22 and the second arm 232 are not limited to being connected via a bolt, and other rigid connection modes may also be employed, for example, the leaf spring 21 may be welded to the bottom of the housing 1, the mass 22 may be welded to the top of the leaf spring 21, and one end of the second arm 232 far from the rotating member 233 (that is, end B) may be welded to the top of the mass 22.
[0042] The leaf spring 21, the mass 22 and the second arm 232 are connected sequentially from the bottom to the top along z direction. After a force is applied on the sensor buried inside the structure to be measured, vibration (resonance) is generated on the leaf spring-mass 21, 22 structure. The leaf spring 21 has a lateral vibration interference resistance, so that the lateral vibration interference to the mass 22 directly connected with the leaf spring 21 may be lowered, and the mass 22 almost vibrates up and down along z direction. In comparison with the structure of Embodiment 1 in which the leaf spring 21 and the second arm 232 are connected directly, in Embodiment 2, after the remaining lateral vibration of the leaf spring 21 is transmitted to the mass 22, a certain degree of attenuation will be generated. Thus when the mass 22 transmits the vibration to the second arm 232 again, the lateral vibration interference to the second arm 232 will be further lowered, that is, the lateral vibration interference attenuates gradually from the bottom to the top, and the strain of the grating is approximately the action result of the displacement Ax, of the mass 22 in z direction, so that the accuracy and reliability of the acceleration measurement in z direction may be improved, and at the same time, the leaf spring 21 can also improve the sensitivity and frequency 30 response range of the sensor.
[0043] Because the second arm 232 and the leaf spring 21 are connected via the mass 22, the leaf spring 21 will not affect the rotation of the rotating member 233, thus the size of the leaf spring 21 may not be specifically defined. The larger the size of the leaf spring 21 is, the larger the stiffness will be, and the more stable the supporting performance will be, and hence the stronger the lateral vibration interference resistance will be. The length of the leaf spring 21 is less than or equal to that of the housing 1, the width of the leaf spring 21 is less than or equal to that of the housing 1, the height of the leaf spring 21 depends on the number of spring steel layers stacked, and the height of the leaf spring 21 is less than that of the housing 1. The length and width of the housing 1 are the inside dimensions of the housing 1, that is, the external dimensions with the thickness of the housing 1 being subtracted.
[0044] Preferably, in Embodiment 2, the width of the leaf spring 21 is equal to that of the housing 1, and the length of the leaf spring 21 is equal to that of the housing 1, which is equivalent to that the housing 1 is used for limiting the leaf spring 21, so that the leaf spring 21 can truly vibrate in z direction only, thereby limiting the freedom of movement of the leaf spring 21, the mass 22 and the second arm 232. By such a size design, the lateral interference to the mass 22 may be totally eliminated, thus the deviation of acceleration measurement may be further lowered, and the measurement precision of unidirectional vibration acceleration of the sensor may be increased.
[0045] Components such as a bearing and a rotating shaft, etc., may be employed as the rotating member 233. In this embodiment, the bearing is preferred. The bearing is configured to connect and support a mechanical rotating body (that is, the beam 23), and it can lower the frictional coefficient in the rotation of the first arm 231, ensure a revolving precision of the first arm 231 and increase the mechanical sensitivity of the beam 23. Moreover, it is favorable for lowering the loss of vibration during transmission, thereby improving the measurement precision of the sensor.
[0046] The beam 23 employs an L-shaped beam, so that the beam 23 is equivalent to a lever mechanism. The rotating member 233 is equivalent to a lever fulcrum, so that a dynamic balance mechanism is established inside the housing 1 for vibration 30 transmission. As shown in Fig.4, the second arm 232 is vertically connected to the mass
II
22, so that the second arm 232 keeps in a horizontal position, that is, the second arm 232 is a fixed arm, thus the second arm 232 will suffer vibration in z direction together with the mass 22, the inertial force of vibration may function as a driving force of the rotating member 233, so that the rotating member 233 drives the first arm 231 to generate a certain angular displacement. That is, the first arm 231 is a power arm for stretching the grating measuring device 241. When the optical fiber measuring device 24 is suspended along a direction parallel to the second arm 232, deformation in a horizontal direction occurs to the grating in the grating measuring device 241, that is, a leftward tension strain is generated on the grating in Fig.4, so that the displacement Ax, of the mass 22 in z direction is converted into a displacement Ax, of the grating in horizontal direction, and Ay, makes the light parameter of the grating measuring device 241 drift, and acceleration of the structure to be measured may be obtained by demodulating the light parameter [0047] Fig.5 is an equivalent force model of the sensor structure shown in Fig.4. It is given that the elastic coefficient of the leaf spring 21 is k1, the elastic modulus of the optical fiber 242 is E", the lateral area of the optical fiber 242 is 4, and the length between fixed points A and M of the optical fiber 242 is L, then the elastic coefficient of the optical fiber 242 will be: 1r2 = E2*4/L, the resultant force applied to the sensor is F, the displacement of the mass 22 in z direction is Ax,, then the total stiffness k of the system is: k=F/ Ax, , and the resultant force F may be resolved into a component force F, acting on the leaf spring 21 and a component force F, acting on the second arm 232 by the mass 22, wherein F, makes the leaf spring 21 and the mass 22 to generate a displacement Ax,, and after.fr, transmitted by the mass 22 is acted on the second arm 232, under the action of the L-shaped beam, F, is generated in the optical fiber 242, wherein FT makes the grating measuring device 241 generate a displacement Ax2, that is, F, is a component of 13. Because the displacement of the grating measuring device 241 and the mass 22 is small, it may be regarded that 12, and F., is always vertical to the action line, then: = Axi (1) = k2Ax, (2) [0048] According to lever principle and the geometric property of an L-shaped beam, it may be obtained that: F2L, ='31 (3) Ax, = Ax, 13 [0049] Wherein, L, is the length of the first arm 231. [ is the length of the second arm 232. The length L, of the second arm 232 is the distance between the axle center C of the rotating member 233 and the central axis Lc of the mass 22 in x direction, the length L, of the second arm 232 is greater than zero, thus a space in x direction exists between the mass 22 and the rotating member 233, and the mass 22 will not affect the rotation of the rotating member 233. By subsequent computation, it may be obtained that:
A
az, -aa-, F, = -I 1 F -L, k2Ax2 -L2 [0050] It may be known from formula (5) that, when the length L, of the first arm 231 is greater than the length L, of the second arm 232, that is, when the first arm 231 is a long arm and the second arm 232 is a short arm, the L-shaped beam may function to amplifying a signal, thereby improving the measurement precision of the sensor. The resultant force 1= 14; +13, then it may be obtained that: kAx, = k,Ax, L2 (4) (7) [0051] From formula (7), the total stiffness k of the sensor may be obtained as: k= (8) L2 [0052] It may be known from formula (8) that, the total stiffness k of the sensor is related to the elastic coefficient of the leaf spring 21 and the optical fiber 242 and the arm length of the L-shaped beam. In this embodiment, Fiber Bragg Grating (FBG) is selected as the grating in the grating measuring device 241. When no affect of temperature is considered, the central wavelength of FBG has a linear relationship with strain. It is given that the strain of FBG is s, the offset of the leaf spring 21 is p, wherein p = k =, ma / k, the mass of the mass 22 is m, with a unit of Kg, and acceleration of the structure to be measured is a, then: L, L, ma 61= -p = 1.2 k [0053] Fiber Bragg Grating (FBG) has a strain sensing feature of: AA AB (10) [0054] Wherein, AX is wavelength drift of the grating measuring device 241, 2" is initial wavelength of the grating measuring device 241, Pe is effective elastooptical coefficient of the optical fiber 242, which generally has a value of 0.22, then a relationship between acceleration a of the structure to be measured and wavelength drift AX may be obtained as: Li ma k [0055] After receiving a detection signal from the grating measuring device 241, the computing unit 3 may compute acceleration a of the structure to be measured according to the wavelength drift AX via formula (11), wherein the acceleration is the acceleration corresponding to the vibration signal in z direction.
[0056] The sensitivity S of the sensor is the wavelength drift on unit acceleration, then the sensitivity S will be shown by formula (12): (9) L, ma (12) AA)4 PC) L k S = - 2 =2(1 a a L2 ki k2 LL, )2 [0057] The resonance frequency co, of the sensor is shown by formula (13): mik _ ik1L22 + k,L,2 (13) mL22 [0058] In this embodiment, the length L, of the first arm 231 is greater than the length L. of the second arm 232, that is, the first arm 231 is a long arm, the second arm 232 is a short arm. The sensor is buried inside a structure to be measured with weak external vibration. For example, it is applied to the microseism monitoring of an ore structure, and an optical fiber grating acceleration sensor is buried inside an ore structure to which a microseism activity occurs. It may be known from the above formula (5) that, when the length L, of the first arm 231 is greater than the length L, of the second arm 232, the L-shaped beam may function to amplify a signal, thus an external weak vibration signal may be amplified inside the sensor. Because lateral vibration interference is eliminated by the sensor of Embodiment 2, it is the vibration signal in z direction that is amplified, rather than the interference vibration signal in non-z direction. Therefore, for a structure to be measured with microseism, the measurement precision of unidirectional vibration acceleration may also be improved.
[0059] It may be known from formula (12) and formula (13) that, when the length L, of the first arm 231 is greater than the length L, of the second arm 232, the sensitivity S and the resonance frequency ro, of the sensor can also be increased, so that the performance of the sensor can be further improved. Additionally, in the invention, the optical fiber measuring device 24 is suspended inside the housing 1, thus no grating chirp phenomenon or reflected wave multimodal phenomenon will appear, it has a good lateral interference resistance, and the measurement precision of unidirectional vibration acceleration may be improved.
[0060] Reference may be made to each other for the same pad in Embodiment 1 and Embodiment 2.
[0061] Other embodiments of the invention will readily occur to those skilled in the art after reading and practicing the invention disclosed herein. The invention intends to cover any variations, usages or adaptability changes, which conform to the general principles of the invention and include common sense or conventional technical means of the art that are not disclosed n the invention. The illustrations and embodiments are exemplary only, and the true scope and spirit of the invention are defined by the appended claims.
[0062] It should be understood that, the invention is not limited to the exact structures I 0 described above and shown in the drawings, and various modifications and variations may be made without departing from the scope thereof. The scope of the invention is merely limited by the claims appended.

Claims (10)

  1. WHAT IS CLAIMED IS: 1. An optical fiber grating acceleration sensor, comprising: a housing (1), a sensing component (2) provided in the housing (1), and a computing unit (3); wherein the sensing component (2) comprises: a leaf spring (21) connected to a bottom of the housing (1), which is a plate-shaped elastic member formed by stacking at least one layer of spring steel; a mass (22) connected to a top of the leaf spring (21); a beam (23), comprising a first arm (231) and second arm (232), wherein the first arm (231) and the second arm (232) are connected via a rotating member (233), the rotating member (233) is fixed on a sidewall of the housing (1), and one end of the second arm (232) far from the rotating member (233) is connected to a top of the mass (22); an optical fiber measuring device (24) suspended above the beam (23), comprising a grating measuring device (241), and an optical fiber (242) connected respectively to the grating measuring device (241) and the computing unit (3); the computing unit (3) is configured to compute an acceleration of a structure to be measured according to a drift of a light parameter of the grating measuring device (241).
  2. 2. The optical fiber grating acceleration sensor according to claim 1, wherein the length of the first arm (231) is greater than that of the second arm (232).
  3. 3. The optical fiber grating acceleration sensor according to claim 1 or 2, wherein the computing unit (3) computes an acceleration of a structure to be measured according to the formula below: L, ma AX = -Pe) -L2 k wherein AX is a wavelength drift of the grating measuring device (241), AR is an initial central wavelength of the grating measuring device (241), Pe is an effective elastooptical coefficient of the optical fiber (242), m is a mass of the mass (22) with a unit of Kg, k is a total stiffness of the optical fiber grating acceleration sensor, a is an acceleration of a structure to be measured, L, is a length of the first arm (231), and L, is a length of the second arm (232); the total stiffness k of the optical fiber grating acceleration sensor is: k = k, + k2( -41 wherein k is an elastic coefficient of the leaf spring (21), and k, is an elastic coefficient of the optical fiber (242)
  4. 4. The optical fiber grating acceleration sensor according to any preceding claim, 5 wherein the beam (23) employs an L-shaped beam, and the second arm (232) is parallel to the optical fiber measuring device (24).
  5. 5. The optical fiber grating acceleration sensor according to any preceding claim, wherein the rotating member (233) employ a bearing.
  6. 6. The optical fiber grating acceleration sensor according to any preceding claim, wherein a width of the leaf spring (21) is equal to that of the housing (1), and a length of the leaf spring (21) is equal to that of the housing (1).
  7. 7, The optical fiber grating acceleration sensor according to any preceding claim, wherein the housing (1), the leaf spring (21), the mass (22) and the second arm (232) are connected as a whole via a bolt (25).
  8. 8. An optical fiber grating acceleration sensor, comprising: a housing (1), a sensing component (2) provided in the housing (1), and a computing unit (3); wherein the sensing component (2) comprises: a leaf spring (21) connected to a bottom of the housing (1), which is a plate-shaped elastic member formed by stacking at least one layer of spring steel; a beam (23), comprising a first arm (231) and second arm (232), wherein the first arm (231) and the second arm (232) are connected via a rotating member (233), the rotating member (233) is fixed on a sidewall of the housing (1), the second arm (232) is connect to a top of the leaf spring (21), and a length of the leaf spring (21) and a length of the first arm (231) are both less than that of the second arm (232); and an optical fiber measuring device (24) suspended above the beam (23), comprising a grating measuring device (241), and an optical fiber (242) connected respectively to the grating measuring device (241) and the computing unit (3); and the computing unit (3) is configured to compute an acceleration of a structure to be measured according to a drift of a light parameter of the grating measuring device (241).
  9. 9. The optical fiber grating acceleration sensor according to any preceding claim, wherein a length of the leaf spring (21) is 4/5 of that of the second arm (232).
  10. 10. The optical fiber grating acceleration sensor according to any preceding claim, wherein the leaf spring (21) is provided at the center of the bottom of the second arm (232).
GB2002584.7A 2020-02-24 2020-02-24 Optical fiber grating acceleration sensor Pending GB2592274A (en)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19939583A1 (en) * 1999-02-24 2000-09-14 Siemens Ag Bragg grating device to measure mechanical force, e.g. for vibration sensor
CN104515587A (en) * 2013-09-26 2015-04-15 同方威视技术股份有限公司 Fiber grating vibration sensor
US20150135832A1 (en) * 2013-11-13 2015-05-21 Intuitive Surgical Operations, Inc. Integrated fiber bragg grating accelerometer in a surgical instrument
WO2016182431A1 (en) * 2015-05-08 2016-11-17 Fugro Technology B.V. Optical sensor device, sensor apparatus, cable and method of manufacturing
CN107946887A (en) * 2018-01-03 2018-04-20 常州工学院 A kind of fiber grating dual laser and device based on special equivalent phase shift
CN108982916A (en) * 2018-07-04 2018-12-11 石家庄铁道大学 A kind of high-sensitivity optical fiber grating acceleration transducer

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19939583A1 (en) * 1999-02-24 2000-09-14 Siemens Ag Bragg grating device to measure mechanical force, e.g. for vibration sensor
CN104515587A (en) * 2013-09-26 2015-04-15 同方威视技术股份有限公司 Fiber grating vibration sensor
US20150135832A1 (en) * 2013-11-13 2015-05-21 Intuitive Surgical Operations, Inc. Integrated fiber bragg grating accelerometer in a surgical instrument
WO2016182431A1 (en) * 2015-05-08 2016-11-17 Fugro Technology B.V. Optical sensor device, sensor apparatus, cable and method of manufacturing
CN107946887A (en) * 2018-01-03 2018-04-20 常州工学院 A kind of fiber grating dual laser and device based on special equivalent phase shift
CN108982916A (en) * 2018-07-04 2018-12-11 石家庄铁道大学 A kind of high-sensitivity optical fiber grating acceleration transducer

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