Optical fiber inclination angle sensor, inclination angle of two-dimensional inclination angle measuring device and method

Abstract

The invention provides an optical fiber tilt angle sensor and a two-dimensional tilt angle measuring device and method. The optical fiber tilt angle sensor comprises a light source assembly and a sensing probe, the light source assembly is configured to generate four paths of polarized light and output to the sensing probe; the sensing probe comprises a cuboid shell, a mass ball, four stress rods and four long-period fiber gratings; the mass ball is fixed on the top surface of the shell through a connecting piece; the first end of the stress rod is fixed on the mass ball, and the second end of the stress rod abuts against one long-period fiber grating; the four periodic fiber gratings are respectively arranged on four inner side surfaces of the shell; when the long-period fiber bragg grating is subjected to transverse stress of the stress rod, the polarization mode of one path of received polarized light is separated, and a transmission spectrum signal with two loss wave crest spectrums with different wavelengths is output; wherein the wavelength difference between the two loss peak spectrums is used for determining the inclination angle. Compared with an existing device, the optical fiber tilt angle sensor has very high sensitivity and stability.

Description

Technical Field

[0001] The present application relates to the technical field of optical fiber tilt sensors, and in particular to an optical fiber tilt sensor, a two-dimensional tilt measurement device and a method. Background Art

[0002] At present, most fiber optic inclination sensors use short-period fiber Bragg gratings as sensing elements, and use the axial stretching of its structure to cause changes in reflection wavelength to detect external physical quantities. The disadvantages of this sensing scheme are: long-term axial stretching of the overall structure of the fiber Bragg grating will cause mechanical fatigue, thereby affecting the stability of the sensor, and the mass block is directly fixed to the fiber Bragg grating and strain unit. Even in the non-working state, the gravity of the mass block will cause mechanical fatigue of the fiber Bragg grating and strain unit; in addition, the short-period fiber Bragg grating is easily affected by temperature, causing its reflection wavelength to change, resulting in errors in the sensor's inclination measurement. Summary of the invention

[0003] In view of this, the present application provides a fiber optic tilt sensor, a two-dimensional tilt measurement device and a method to solve the technical problems of low sensitivity, poor stability and low measurement accuracy in existing devices.

[0004] In a first aspect, an embodiment of the present application provides a fiber optic tilt sensor, including a light source assembly and a sensor probe;

[0005] The light source assembly is configured to generate four polarized lights and output them to the sensing probe;

[0006] The sensing probe comprises: a rectangular shell, a mass ball, four stress rods and four long-period fiber gratings; the rectangular shell is placed on the measured plane; the mass ball is fixed on the top surface of the rectangular shell through a connector; the first end of the stress rod is fixed on the mass ball; the second end of the stress rod is against a long-period fiber grating; two opposite stress rods are on the same plane; the four period fiber gratings are respectively arranged on the four inner side surfaces of the rectangular shell; when the long-period fiber grating is subjected to the lateral stress of the stress rod, it separates the polarization mode of the received polarized light and outputs a transmission spectrum signal with two loss peak spectra of different wavelengths; wherein the wavelength difference between the two loss peak spectra is used to determine the inclination angle of the measured plane.

[0007] In one possible implementation, the light source assembly includes a broadband light source, an isolator, a polarizer, a polarization controller, and a fiber coupler arranged on an optical path;

[0008] The broadband light source is used to emit broadband light;

[0009] The isolator is used to isolate the broad-spectrum light;

[0010] The polarizer is used to convert broadband light into polarized light;

[0011] The polarization controller is used to adjust the polarization state of polarized light;

[0012] The optical fiber coupler is used to divide polarized light into four polarized lights, and transmit the four polarized lights to corresponding long-period optical fiber gratings through transmission optical fibers.

[0013] In a possible implementation, the connecting member is a steel wire rope; a first end of the steel wire rope is fixed to the top surface of the rectangular parallelepiped shell, and a second end of the steel wire rope is fixed to the mass ball.

[0014] In a possible implementation, two stress rods that are oppositely disposed are on a first plane, and another two stress rods that are oppositely disposed are on a second plane, and the first plane is perpendicular to the second plane.

[0015] In one possible implementation, the four long-period fiber gratings include: a first long-period fiber grating and a third long-period fiber grating that are arranged opposite to each other, and a second long-period fiber grating and a fourth long-period fiber grating that are arranged opposite to each other; wherein the first long-period fiber grating and the third long-period fiber grating respectively measure a first inclination angle of the measured plane rotating counterclockwise and clockwise around a first direction, and the second long-period fiber grating and the fourth long-period fiber grating respectively measure a second inclination angle of the measured plane rotating counterclockwise and clockwise around a second direction.

[0016] In a second aspect, an embodiment of the present application provides a two-dimensional tilt angle measurement device, including: an optical fiber tilt angle sensor, a spectrometer and an electronic device according to an embodiment of the present application;

[0017] The spectrometer is used to collect four transmission spectrum signals output by four long-period fiber gratings, detect the wavelength difference of two loss peak spectra in at most two transmission spectrum signals and send them to the electronic device;

[0018] The electronic device is used to calculate the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two spectrum signals.

[0019] In a third aspect, an embodiment of the present application provides a two-dimensional inclination measurement method, which is applied to a two-dimensional inclination measurement device of an embodiment of the present application, and the method includes:

[0020] The light source assembly generates four polarized lights and transmits them to corresponding long-period fiber gratings of the sensing probe respectively;

[0021] When the mass ball is tilted, at most two stress rods apply lateral stress to the corresponding long-period fiber grating;

[0022] The long-period fiber grating to which the transverse stress is applied separates the polarization mode of the polarized light and outputs a transmission spectrum signal having two loss peak spectra of different wavelengths to the spectrometer;

[0023] The spectrometer collects four transmission spectrum signals output by four long-period fiber gratings, detects the wavelength difference between two loss peak spectra in at most two transmission spectrum signals, and sends the difference to the electronic device;

[0024] The electronic device calculates the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two transmission spectrum signals.

[0025] In a possible implementation, the light source assembly generates four polarized lights and transmits them to corresponding long-period fiber gratings of the sensing probe respectively; comprising:

[0026] The broadband light source emits broadband light;

[0027] The isolator isolates the passing broad-spectrum light;

[0028] The polarizer converts the broad spectrum light into polarized light;

[0029] The polarization controller adjusts the polarization state of the polarized light;

[0030] The optical fiber coupler divides polarized light into four polarized lights, and transmits the four polarized lights to corresponding long-period optical fiber gratings through transmission optical fibers.

[0031] In a possible implementation, when at most two transmission spectrum signals include a transmission spectrum signal output by the first long-period fiber grating or a transmission spectrum signal output by the third long-period fiber grating;

[0032] Calculating the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two transmission spectrum signals; comprising:

[0033] Detecting a first wavelength difference between two loss peak spectra from a transmission spectrum signal output by the first long-period fiber grating or the third long-period fiber grating;

[0034] The absolute value of the first wavelength difference is substituted into a predetermined first function to obtain a first inclination angle of the measured plane; the first function represents the corresponding relationship between the first inclination angle and the absolute value of the first wavelength difference.

[0035] In a possible implementation, when at most two transmission spectrum signals include a transmission spectrum signal output by the second long-period fiber grating or a transmission spectrum signal output by the fourth long-period fiber grating;

[0036] Calculating the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two transmission spectrum signals; comprising:

[0037] Detecting a second wavelength difference between two loss peak spectra from a transmission spectrum signal output by the second long-period fiber grating or the fourth long-period fiber grating;

[0038] The absolute value of the second wavelength difference is substituted into a predetermined second function to obtain a second inclination angle of the measured plane; the second function represents the corresponding relationship between the second inclination angle and the absolute value of the first wavelength difference.

[0039] The optical fiber tilt sensor of the present application has the advantages of simple structure, insensitivity to temperature, and little influence of lateral crosstalk, and at the same time has very high sensitivity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of the structure of the optical fiber tilt sensor according to an embodiment of the present application;

[0041] Figure 2 This is a schematic diagram of the structure of a light source assembly according to an embodiment of the present application;

[0042] Figure 3 A schematic diagram of a two-dimensional inclination angle measuring device according to an embodiment of the present application;

[0043] Figure 4 A flow chart of a two-dimensional inclination angle measurement method according to an embodiment of the present application;

[0044] FIG5( a ) is a schematic diagram of the optical fiber tilt sensor of an embodiment of the present application when it is not tilted;

[0045] FIG5( b ) is a schematic diagram of the optical fiber tilt sensor according to an embodiment of the present application being tilted.

[0046] Figure ID:

[0047] 100: optical fiber tilt sensor; 101: light source assembly; 102: sensing probe;

[0048] 103: cuboid shell; 104: mass ball; 105: connector

[0049] 106: stress rod; 107: long period fiber grating; 108: transmission fiber;

[0050] 200: two-dimensional inclination measuring device; 201: spectrometer; 202: electronic equipment. DETAILED DESCRIPTION

[0051] Various aspects and features of the present application are described herein with reference to the accompanying drawings.

[0052] It should be understood that various modifications may be made to the embodiments of the present application. Therefore, the above description should not be considered as limiting, but only as an example of an embodiment. Other modifications within the scope and spirit of the present application will occur to those skilled in the art.

[0053] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present application and, together with the general description of the present application given above and the detailed description of the embodiments given below, serve to explain the principles of the present application.

[0054] These and other characteristics of the present application will become apparent from the following description of a preferred form of embodiment given as a non-limiting example with reference to the accompanying drawings.

[0055] It should also be understood that although the present application has been described with reference to some specific examples, those skilled in the art will be able to readily implement many other equivalent forms of the present application.

[0056] The above and other aspects, features and advantages of the present application will become more apparent in view of the following detailed description when taken in conjunction with the accompanying drawings.

[0057] Specific embodiments of the present application are described hereinafter with reference to the accompanying drawings; however, it should be understood that the embodiments applied for are merely examples of the present application, which may be implemented in a variety of ways. Well-known and / or repeated functions and structures are not described in detail to avoid unnecessary or redundant details that obscure the present application. Therefore, the specific structural and functional details applied for herein are not intended to be limiting, but merely serve as a basis and representative basis for the claims to teach those skilled in the art to use the present application in a variety of ways with substantially any suitable detailed structure.

[0058] This specification may use the phrases "in one embodiment," "in another embodiment," "in yet another embodiment," or "in other embodiments," all of which may refer to one or more of the same or different embodiments according to the present application.

[0059] First, the design concept of the embodiments of the present application is briefly introduced.

[0060] At present, high-precision inclination measurement is increasingly used in aerospace, civil construction, and mechanical safety, and is an important part of scientific research and infrastructure construction. At the same time, inclination sensors are also used in the measurement of the posture of objects, such as leveling of engineering machinery and equipment, long-distance ranging instruments, radar vehicle platform detection, tower cranes, CNC machine tools, and other fields. In the field of civil engineering, with the improvement of structural health monitoring requirements, the requirements for the accuracy and technical level of inclination monitoring are also getting higher and higher. As a key part of structural tilt monitoring, the sensing performance of the inclination sensor directly affects the accuracy of the inclination measurement. At present, the widely used traditional inclination sensors use electromagnetic and capacitive effects as basic principles to convert the inclination into electrical signal output, but this type of sensor is extremely susceptible to electromagnetic interference and has measurement deviations in complex electromagnetic environments.

[0061] Compared with traditional sensors, fiber optic tilt sensors have the advantages of light weight, small size, high sensitivity, and anti-electromagnetic interference. Fiber optic tilt sensors are mainly divided into fiber Bragg grating type and fiber interferometric tilt sensors. Fiber grating tilt sensors are mainly made of fiber Bragg grating (FBG). When the tilt angle changes, the refractive index of the FBG grating area is changed to cause the wavelength drift of the reflection spectrum. The tilt angle is measured by analyzing the wavelength drift. Fiber interferometric tilt sensors are constructed based on the principle of optical interference, mainly including Michelson interferometry, Mach-Zehnder interferometry, and FP interferometry.

[0062] At present, most fiber optic tilt sensors are designed with short-period fiber grating (FBG), and the probe sensing principle is based on the fiber grating coupled mode theory. The fiber grating coupled mode theory is: short-period fiber grating is a reflective bandpass filter. When the light wave passes through the fiber grating, the fiber grating will reflect the narrow spectrum component that satisfies the Bragg wavelength λ as the central wavelength. The calculation formula of the Bragg central reflection wavelength λ is: λ=2n eff Λ, where Λ is the grating spacing, n eff is the effective refractive index of the fiber core. Any physical change in the two parameters will cause a shift in the reflected wavelength λ, thereby realizing inclination sensing by detecting the change in the reflected wavelength. The short-period fiber Bragg grating (FBG) is installed on the strain unit (cantilever beam), and the strain unit is directly deformed by the movement of the mass block, causing the short-period fiber Bragg grating (FBG) to axially stretch and cause the wavelength to change. When working, the short-period fiber Bragg grating is in an axially stretched state for a long time, which is easy to cause mechanical fatigue and affect the stability of the sensor.

[0063] In addition, during the design of the sensor structure, a reference fiber Bragg grating is usually installed around the fiber Bragg grating used for sensing. This fiber Bragg grating is only used to measure temperature changes. The results measured by the reference fiber Bragg grating are then used to correct the measurement results of the sensing fiber Bragg grating to offset the influence of temperature on the fiber Bragg grating, thereby achieving temperature compensation. The defect of this design is that it requires the addition of an additional fiber Bragg grating, which not only makes the optical path structure more complicated, but also makes the overall cost higher.

[0064] In order to solve the above technical problems, the optical fiber inclination sensor of the present application adopts long-period fiber grating (LPFG, Long-period Fiber Grating). Long-period fiber grating belongs to transmission-type fiber grating. The sensing principle is based on the lateral strain sensing principle of long-period fiber grating. The inclination sensing is actually achieved by detecting the change in the wavelength difference between the two loss peaks of the transmission spectrum.

[0065] In terms of structural design, the long-period fiber grating of the present application is separated from the mass ball structure and interacts with it through the stress rod only when working. In addition, the stress rod only applies lateral pressure to the grating area of ​​the long-period fiber grating. Based on the high-sensitivity sensing characteristics of the lateral strain of the long-period fiber grating, only a very small lateral pressure is needed to realize the sensing function. This design scheme has little impact on the overall structure of the optical fiber and fiber grating.

[0066] When the external temperature causes the central wavelength of the long-period fiber grating to drift, since what is detected is the spectral spacing in the transmission spectrum, that is, the wavelength difference, even if the temperature causes the wavelength to drift, the two are subtracted to offset the drift, thereby achieving a temperature-insensitive design.

[0067] The sensor probe design of this application is based on the principle of optical fiber sensing. The detected inclination angle is calculated by detecting the wavelength difference of the two loss peaks of the transmission spectrum. Four LPFGs are installed on the designed rectangular shell to achieve two-dimensional inclination angle detection in different tilt directions. The sensor is simple in design, insensitive to temperature, and has little influence from lateral crosstalk. It also has very high sensitivity and stability, and can achieve autonomous, fast and accurate sensing and detection of inclination angle values ​​in complex and harsh environments. It can be applied to technical fields such as leveling of engineering machinery and equipment, long-distance ranging instruments, radar vehicle platform detection, tower cranes, CNC machine tools, etc. In addition, except for metal structural parts, the sensor probe adopts an all-optical design. The optical path and devices are integrated by optical fiber, with strong anti-electromagnetic interference ability, high precision, and strong reliability, and can be applied to complex and harsh environments.

[0068] The inclination measuring device of the present application detects the inclination of the sensor in two directions through two pairs of long-period fiber gratings, and can calculate the inclination in the corresponding direction in real time according to the wavelength difference detected by the spectrometer, that is, realizes two-dimensional inclination detection with different degrees of freedom.

[0069] The inclination angle measurement method of the present application is based on the long-period fiber grating lateral strain sensing principle. By establishing the corresponding relationship between the spectral wavelength spacing of the loss peak and the inclination angle, the influence of optical path loss and temperature drift on the sensing accuracy is avoided, thereby improving the inclination angle measurement accuracy.

[0070] After introducing the application scenarios and design concepts of the embodiments of the present application, the technical solutions provided by the embodiments of the present application are described below.

[0071] like Figure 1 As shown, an embodiment of the present application provides a fiber optic tilt sensor, including a light source assembly 101 and a sensor probe 102;

[0072] The light source assembly 101 is configured to generate four polarized lights and output them to the sensing probe;

[0073] The sensing probe 102 comprises: a rectangular parallelepiped housing 103, a mass ball 104, four stress rods 106 and four long period fiber gratings 107, wherein the four long period fiber gratings include: LPFG1, LPFG2, LPFG3 and LPFG4; the rectangular parallelepiped housing 103 is placed on the measured plane; the mass ball 104 is fixed on the top surface of the rectangular parallelepiped housing 103 through a connector 105; the first end of the stress rod 106 is fixed on the mass ball 104; the second end of the stress rod 105 is against a long period fiber grating 107; two opposite stress rods 105 are on the same plane; the four period fiber gratings 107 are respectively arranged on the four inner side surfaces of the rectangular parallelepiped housing 103; when the long period fiber grating 107 is subjected to the lateral stress of the stress rod, it separates the polarization mode of the received polarized light and outputs a transmission spectrum signal with two loss peak spectra of different wavelengths; wherein the wavelength difference between the two loss peak spectra is used to determine the inclination of the measured plane.

[0074] like Figure 2 As shown, the light source assembly 101 includes a broadband light source, an isolator, a polarizer, a polarization controller and a fiber coupler arranged on an optical path, wherein the broadband light source is used to emit broadband light; the isolator is a passive optical device that only allows unidirectional light to pass through, and is used to isolate the broadband light; the polarizer is used to convert the broadband light into polarized light; the polarization controller is used to adjust the polarization state of the polarized light; the fiber coupler, also known as a splitter, is a component that splits the optical signal from one optical fiber to multiple optical fibers; it is used to split the polarized light into four polarized lights, and transmit the four polarized lights to the corresponding long-period fiber gratings through the transmission optical fiber.

[0075] For example, a broadband light source emits broadband light, which passes through an isolator to a polarizer, is converted into polarized light after passing through the polarizer, and then is polarized by a polarization controller to adjust the polarization state, and is divided into four polarized lights after passing through a fiber coupler. The four polarized light waves pass through transmission fibers and reach four long-period fiber gratings ( Figure 1 When the measured plane is not tilted and the two inclination angles are both 0°, the mass ball is in a natural vertical state, and the four groups of long-period fiber gratings are not subjected to the lateral stress of the stress rod.

[0076] Preferably, the shell 105 is made of copper or aluminum. The mass ball 107 is made of lead. The stress rod 105 is a cylindrical metal rod made of copper or iron.

[0077] In one embodiment of the present application, the connecting member is a steel wire rope; the first end of the steel wire rope is fixed to the top surface of the rectangular shell, and the second end of the steel wire rope is fixed to the mass ball.

[0078] In one embodiment of the present application, two stress rods disposed opposite to each other are on a first plane, and another two stress rods disposed opposite to each other are on a second plane, and the first plane is perpendicular to the second plane.

[0079] In one embodiment of the present application, the four long-period fiber gratings include: a first long-period fiber grating and a third long-period fiber grating that are arranged opposite to each other, and a second long-period fiber grating and a fourth long-period fiber grating that are arranged opposite to each other; wherein the first long-period fiber grating and the third long-period fiber grating respectively measure a first inclination angle of the measured plane rotating counterclockwise and clockwise around a first direction, and the second long-period fiber grating and the fourth long-period fiber grating respectively measure a second inclination angle of the measured plane rotating counterclockwise and clockwise around a second direction.

[0080] Exemplarily, the first long-period fiber grating can be set to measure the first inclination angle (positive value) of the measured plane rotating counterclockwise around the first direction, and the third long-period fiber grating can measure the first inclination angle (negative value) of the measured plane rotating clockwise around the first direction. The first long-period fiber grating can also be set to measure the first inclination angle (negative value) of the measured plane rotating clockwise around the first direction, and the third long-period fiber grating can measure the first inclination angle (positive value) of the measured plane rotating counterclockwise around the first direction.

[0081] Similarly, the second long-period fiber grating can be set to measure the second inclination angle (positive value) of the measured plane rotating counterclockwise around the second direction, and the fourth long-period fiber grating measures the second inclination angle (negative value) of the measured plane rotating clockwise around the second direction. The second long-period fiber grating can also be set to measure the second inclination angle (negative value) of the measured plane rotating clockwise around the second direction, and the fourth long-period fiber grating measures the second inclination angle (positive value) of the measured plane rotating counterclockwise around the second direction.

[0082] When the measured plane is tilted and the sensing probe is in working state, the mass ball tilts due to the influence of gravity, and applies lateral stress to the opposing long-period fiber grating through the stress rod.

[0083] Exemplarily, the stress rod that offsets the first long-period fiber grating is set as the first stress rod, the stress rod that offsets the second long-period fiber grating is set as the second stress rod, the stress rod that offsets the third long-period fiber grating is set as the third stress rod, and the stress rod that offsets the fourth long-period fiber grating is set as the fourth stress rod. Then, when the mass ball tilts, the first stress rod and the third stress rod selectively apply lateral stress, and / or the second stress rod and the fourth stress rod selectively apply lateral stress.

[0084] The long-period fiber grating of this embodiment is prepared on a single-mode optical fiber by a point-by-point writing method. The preparation method is flexible, and the fiber grating length, period, refractive index, profile and other parameters can be adjusted online, and a fiber grating of any length can be produced.

[0085] The long-period fiber grating of this embodiment is separated from the mass ball structure and interacts with it through the stress rod only when it is working. In addition, the stress rod only applies lateral pressure to the grating area of ​​the long-period fiber grating. Based on the high-sensitivity sensing characteristics of the lateral strain of the long-period fiber grating, only a very small lateral pressure is needed to realize the sensing function, and the overall structure of the optical fiber and the fiber grating is slightly affected.

[0086] Based on the same inventive concept, Figure 3 As shown, an embodiment of the present application provides a two-dimensional inclination measurement device, and the two-dimensional inclination measurement device 200 includes: the optical fiber inclination sensor 100 of the above embodiment, a spectrometer 201 and an electronic device 202;

[0087] The spectrometer 201 is used to collect transmission spectrum signals output by four long-period fiber gratings, detect the wavelength difference of two loss peak spectra in at most two transmission spectrum signals and send it to the electronic device;

[0088] The electronic device 202 is used to calculate the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two spectrum signals.

[0089] Exemplarily, the sensing probe of this embodiment is based on the transverse strain sensing principle of long-period fiber grating. When the long-period fiber grating is not subjected to transverse strain force, after the wide-spectrum light passes through the long-period fiber grating, due to the long-period fiber grating mode coupling theory, the spectrometer only detects one loss peak spectrum, and the wavelength corresponding to the loss peak spectrum is λ0; when the long-period fiber grating is subjected to transverse pressure, the polarization mode of the light wave is separated, forming two different coupling center wavelengths λ1 and λ2 corresponding to the same grating, which are reflected in the transmission spectrum of the grating as two loss peak spectra. The spectral wavelength spacing between the two loss peaks can be detected by the spectrometer, that is, the absolute value of the wavelength difference Δλ=|λ2-λ1|. When the transverse stress gradually increases, the spectral wavelength spacing in the transmission spectrum also gradually increases. Therefore, when the tilt sensor is in a tilted state, the larger the tilt angle, the greater the transverse stress applied to the long-period fiber grating, and the electronic device can calculate the tilt angle according to Δλ and the pre-fitted function.

[0090] The sensing probe of this embodiment has the advantage of being insensitive to temperature. When the external temperature causes the central wavelength of the long-period fiber grating to drift, since the spectrometer detects the spectral wavelength spacing between the two loss peaks, that is, the wavelength difference Δλ=|λ2-λ1|, even if the temperature causes the wavelength to drift, both wavelengths drift, and the drift is offset after subtraction, thereby solving the problem of wavelength drift caused by temperature.

[0091] Based on the same inventive concept, the present application provides a two-dimensional inclination angle measurement method, which is applied to the two-dimensional inclination angle measurement device of the above embodiment, such as Figure 4 As shown, the method includes:

[0092] Step 301: the light source assembly generates four polarized lights and transmits them to corresponding long-period fiber gratings of the sensing probe respectively;

[0093] Exemplarily, when the mass sphere is not tilted, a long-period fiber grating receives one polarized light channel respectively and outputs a transmission spectrum signal to the spectrometer, and the spectrometer detects only one loss peak spectrum from each transmission spectrum signal.

[0094] Step 302: when the mass ball is tilted, at most two stress rods apply lateral stress to the corresponding long-period fiber grating;

[0095] Exemplarily, when the measured plane rotates counterclockwise or clockwise around a first direction at a first inclination angle, the first stress rod applies transverse stress to the first long-period fiber grating, or the third stress rod applies transverse stress to the third long-period fiber grating; and / or when the measured plane rotates counterclockwise or clockwise around a second direction at a second inclination angle, the second stress rod applies transverse stress to the second long-period fiber grating, or the fourth stress rod applies transverse stress to the fourth long-period fiber grating.

[0096] Step 303: the long-period fiber grating to which the transverse stress is applied separates the polarization mode of the polarized light, and outputs a transmission spectrum signal having two loss peak spectra of different wavelengths to a spectrometer;

[0097] For example, when a long-period fiber grating is subjected to lateral pressure, the polarization mode of the light wave is separated, forming two different coupling center wavelengths λ1 and λ2 corresponding to the same grating, which is reflected in the transmission spectrum of the grating as two loss peak spectra.

[0098] Step 304: the spectrometer collects transmission spectrum signals output by four long-period fiber gratings, detects the wavelength difference of two loss peak spectra in at most two transmission spectrum signals, and sends the difference to the electronic device;

[0099] Exemplarily, the spectrometer can detect the spectral wavelength spacing between the two loss peaks, ie, the absolute value of the wavelength difference Δλ=|λ2-λ1|, from the received transmission spectrum signal.

[0100] Step 305: The electronic device calculates the first tilt angle and / or the second tilt angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two transmission spectrum signals.

[0101] In one embodiment of the present application, the light source assembly generates four polarized lights and transmits them to corresponding long-period fiber gratings of the sensing probe respectively; comprising:

[0102] The broadband light source emits broadband light;

[0103] The isolator isolates the passing broad-spectrum light;

[0104] The polarizer converts the broad spectrum light into polarized light;

[0105] The polarization controller adjusts the polarization state of the polarized light;

[0106] The optical fiber coupler divides polarized light into four polarized lights, and transmits the four polarized lights to corresponding long-period optical fiber gratings through transmission optical fibers.

[0107] In one embodiment of the present application, when at most two transmission spectrum signals include a transmission spectrum signal output by the first long-period fiber grating or a transmission spectrum signal output by the third long-period fiber grating;

[0108] Calculating the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two transmission spectrum signals; comprising:

[0109] Detecting a first wavelength difference between two loss peak spectra from a transmission spectrum signal output by the first long-period fiber grating or the third long-period fiber grating;

[0110] The absolute value of the first wavelength difference is substituted into a predetermined first function to obtain a first inclination angle of the measured plane; the first function represents the corresponding relationship between the first inclination angle and the absolute value of the first wavelength difference.

[0111] The first function is fitted by the following steps:

[0112] Placing the sensing probe on a plurality of measured planes with different first inclination angles, wherein the first inclination angles are all positive values;

[0113] For each first tilt angle, the electronic device detects a first wavelength difference between two loss peak spectra in a transmission spectrum signal output by the first long-period fiber grating;

[0114] The absolute values ​​of multiple sets of first wavelength differences and first inclination angles are used as fitting data to obtain a first function through fitting, wherein the first function is a linear function or a quadratic function.

[0115] In one embodiment of the present application, when at most two transmission spectrum signals include a transmission spectrum signal output by the second long-period fiber grating or a transmission spectrum signal output by the fourth long-period fiber grating;

[0116] Detecting a second wavelength difference between two loss peak spectra from a transmission spectrum signal output by the second long-period fiber grating or the fourth long-period fiber grating;

[0117] The absolute value of the second wavelength difference is substituted into a predetermined second function to obtain a second inclination angle of the measured plane; the second function represents the corresponding relationship between the second inclination angle and the absolute value of the first wavelength difference.

[0118] The second function is fitted by the following steps:

[0119] Placing the sensing probe on a plurality of measured planes with different second inclination angles, wherein the second inclination angles are all positive values;

[0120] For each second tilt angle, the electronic device detects a second wavelength difference between two loss peak spectra in a transmission spectrum signal output by the second long-period fiber grating;

[0121] The absolute values ​​of the multiple sets of second wavelength differences and the second inclination angles are used as fitting data to obtain a second function by fitting, and the second function is a linear function or a quadratic function.

[0122] The specific implementation process of this application is described below in conjunction with a specific application scenario.

[0123] FIG5(a) is a schematic diagram of the fiber optic tilt sensor when it is not tilted. FIG5(b) is a schematic diagram of the fiber optic tilt sensor when it is tilted; when the measured plane is tilted and the tilt angle is θ, the mass ball 104 is subjected to the combined effect of the steel wire rope 105, the stress rod 106 and gravity. At this time, part of the gravity of the mass ball 104 acts on the long-period fiber grating LPFG through the stress rod and exerts lateral stress on it. Based on the transverse strain sensing principle of the long-period fiber grating, at this time, the spectrometer detects that the single loss peak spectrum in the transmission spectrum signal of the long-period fiber grating becomes two loss peak spectra. The wavelengths of the two loss peak spectra correspond to λ1 and λ2 respectively. The spectrometer can detect the spectral wavelength spacing between the loss peaks, that is, the wavelength difference Δλ=|λ2-λ1|. When the tilt angle θ increases, the corresponding α value (α=90°-θ) decreases, and the lateral strain force value is F=G×cos(90°-θ), where G is the gravity of the mass ball. As the lateral strain increases, the spectral wavelength spacing in the transmission spectrum also gradually increases. When the optical fiber tilt sensor is in an up and down vibration state, the larger the tilt angle, the greater the lateral stress applied to the long-period fiber grating. The tilt angle can be sensed by calculating the tilt value by detecting the spectral wavelength spacing in the transmission spectrum.

[0124] In addition, although the operations of the method of the present application are described in a specific order in the drawings, this does not require or imply that the operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps.

[0125] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A fiber optic tilt sensor, characterized in that: Including a light source assembly and a sensor probe; The light source assembly is configured to generate four polarized lights and output them to the sensor probe; The sensing probe comprises: a rectangular shell, a mass ball, four stress rods and four long-period fiber gratings; the rectangular shell is placed on the measured plane; the mass ball is fixed on the top surface of the shell through a connector; the first end of the stress rod is fixed on the mass ball; the second end of the stress rod is against a long-period fiber grating; two opposite stress rods are on the same plane; the four period fiber gratings are respectively arranged on the four inner side surfaces of the rectangular shell; when the long-period fiber grating is subjected to the lateral stress of the stress rod, it separates the polarization mode of the received polarized light and outputs a transmission spectrum signal with two loss peak spectra of different wavelengths; wherein the wavelength difference between the two loss peak spectra is used to determine the inclination angle of the measured plane.

2. The optical fiber tilt sensor according to claim 1, characterized in that: The light source assembly comprises a broadband light source, an isolator, a polarizer, a polarization controller and a fiber coupler arranged on an optical path; The broadband light source is used to emit broadband light; The isolator is used to isolate the broad-spectrum light; The polarizer is used to convert broadband light into polarized light; The polarization controller is used to adjust the polarization state of polarized light; The optical fiber coupler is used to divide polarized light into four polarized lights, and transmit the four polarized lights to corresponding long-period optical fiber gratings respectively through transmission optical fibers.

3. The optical fiber tilt sensor according to claim 1, characterized in that: The connecting member is a steel wire rope; the first end of the steel wire rope is fixed on the top surface of the rectangular parallelepiped shell, and the second end of the steel wire rope is fixed on the mass ball.

4. The optical fiber tilt sensor according to claim 1, characterized in that: Two stress rods arranged opposite to each other are on a first plane, and another two stress rods arranged opposite to each other are on a second plane, wherein the first plane is perpendicular to the second plane.

5. The optical fiber tilt sensor according to claim 4, characterized in that: The four long-period fiber gratings include: a first long-period fiber grating and a third long-period fiber grating that are arranged opposite to each other, and a second long-period fiber grating and a fourth long-period fiber grating that are arranged opposite to each other; wherein the first long-period fiber grating and the third long-period fiber grating respectively measure a first inclination angle of a measured plane rotating counterclockwise and clockwise around a first direction, and the second long-period fiber grating and the fourth long-period fiber grating respectively measure a second inclination angle of a measured plane rotating counterclockwise and clockwise around a second direction.

6. A two-dimensional inclination measuring device, characterized in that: include: The optical fiber tilt sensor, spectrometer and electronic device according to any one of claims 1 to 5; The spectrometer is used to collect four transmission spectrum signals output by four long-period fiber gratings, detect the wavelength difference of two loss peak spectra in at most two transmission spectrum signals and send them to the electronic device; The electronic device is used to calculate the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two spectrum signals.

7. A two-dimensional inclination measurement method, characterized in that: Applied to the two-dimensional inclination measuring device according to claim 6, the method comprises: The light source assembly generates four polarized lights and transmits them to the corresponding long period fiber gratings of the sensing probe respectively; When the mass ball is tilted, at most two stress rods apply lateral stress to the corresponding long-period fiber grating; The long-period fiber grating to which the transverse stress is applied separates the polarization mode of the polarized light and outputs a transmission spectrum signal having two loss peak spectra of different wavelengths to the spectrometer; The spectrometer collects four transmission spectrum signals output by four long-period fiber gratings, detects the wavelength difference of two loss peak spectra in at most two transmission spectrum signals, and sends the difference to the electronic device; The electronic device calculates the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two transmission spectrum signals.

8. The two-dimensional inclination angle measurement method according to claim 7, characterized in that: The light source assembly generates four polarized lights and transmits them to corresponding long-period fiber gratings of the sensing probe respectively; comprising: The broadband light source emits broadband light; The isolator isolates the passing broad-spectrum light; The polarizer converts the broad spectrum light into polarized light; The polarization controller adjusts the polarization state of the polarized light; The optical fiber coupler divides polarized light into four polarized lights, and transmits the four polarized lights to corresponding long-period optical fiber gratings through transmission optical fibers.

9. The two-dimensional inclination angle measurement method according to claim 7, characterized in that: When at most two transmission spectrum signals include a transmission spectrum signal output by the first long-period fiber grating or a transmission spectrum signal output by the third long-period fiber grating; Calculating the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two transmission spectrum signals; comprising: Detecting a first wavelength difference between two loss peak spectra from a transmission spectrum signal output by the first long-period fiber grating or the third long-period fiber grating; The absolute value of the first wavelength difference is substituted into a predetermined first function to obtain a first inclination angle of the measured plane; the first function represents the corresponding relationship between the first inclination angle and the absolute value of the first wavelength difference.

10. The two-dimensional inclination angle measurement method according to claim 7, characterized in that: When at most two transmission spectrum signals include a transmission spectrum signal output by the second long-period fiber grating or a transmission spectrum signal output by the fourth long-period fiber grating; Calculating the first inclination angle and / or the second inclination angle of the measured plane based on the wavelength difference between two loss peak spectra in at most two transmission spectrum signals; comprising: Detecting a second wavelength difference between two loss peak spectra from a transmission spectrum signal output by the second long-period fiber grating or the fourth long-period fiber grating; The absolute value of the second wavelength difference is substituted into a predetermined second function to obtain a second inclination angle of the measured plane; the second function represents the corresponding relationship between the second inclination angle and the absolute value of the first wavelength difference.

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