Distributed curvature, strain and temperature sensing system and sensing calculation method thereof

Abstract

The invention provides a distributed curvature, strain and temperature sensing system and a sensing calculation method thereof, and relates to the technical field of sensors, and the sensing system comprises an optical fiber unit, a Brillouin optical time domain analyzer BOTDA, a distributed optical fiber temperature measurement system DTS, a first optical fiber switcher and a second optical fiber switcher. The optical fiber unit is composed of three spiral optical fibers and a central optical fiber and can sense various physical quantities such as curvature, strain and temperature. The system carries out dynamic measurement through a time division multiplexing technology, firstly, the DTS is used for measuring the temperature along the optical fiber unit, and then the BOTDA is used for measuring the strain of the optical fiber unit. Collected temperature data is not only used for temperature feedback of the optical fiber unit, but also provides temperature compensation for strain measurement. Through an equation set in the sensing solution method, the curvature radius, the curvature direction, the torsional strain and the tensile strain of the optical fiber unit can be accurately solved, and the shape information of the optical fiber unit can be restored through the curvature radius and the curvature direction.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a distributed curvature, strain and temperature sensing system and a sensing solution method thereof. Background Art

[0002] Coal mining machine cables work in complex working conditions and harsh environments, requiring them to have a high degree of safety and dynamic reliability. Studies have shown that the quality of cable development and the harsh working environment are the main factors affecting their service life and dynamic reliability. During the operation of the coal mining machine, the cable is frequently subjected to bending, dragging, squeezing, twisting, and impact by coal blocks, which shortens its service life and increases the risk of short circuits and grounding accidents.

[0003] Cable damage has a significant impact on the efficiency of coal mining machines and the safety of underground power supply systems. However, due to the harsh working environment, cables are easily damaged, affecting production safety. Compared with other underground equipment, the intelligent development of cables is relatively lagging, lacking real-time monitoring and status feedback methods.

[0004] Therefore, there is an urgent need for a sensing system and a solution method that can monitor the cable temperature, strain and curvature to monitor the tooling status of the cable to ensure production safety underground. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a distributed curvature, strain and temperature sensing system and a sensing solution method thereof;

[0006] The present invention is achieved through the following technical solutions:

[0007] In one aspect, a distributed curvature, strain and temperature sensing system comprises: an optical fiber unit, a Brillouin optical time domain analyzer BOTDA, a distributed optical fiber temperature measurement system DTS, a first optical fiber switcher and a second optical fiber switcher;

[0008] The optical fiber unit comprises four tight-buffered single-mode optical fibers, which are fused end to end to form a whole, and the two ends after fusion are respectively connected to the output end of the first optical fiber switch and the output end of the second optical fiber switch; the measuring light source of the Brillouin optical time domain analyzer BOTDA is connected to the input 1 of the first optical fiber switch, the pumping light source of the Brillouin optical time domain analyzer BOTDA is connected to the input 1 of the second optical fiber switch, and the measuring light source of the distributed optical fiber temperature measurement system DTS is connected to the input 2 of the first optical fiber switch.

[0009] The four tight-buffered single-mode optical fibers specifically include three spiral optical fibers and one central optical fiber, which are formed by extrusion of an outer sheath (3), wherein the three spiral optical fibers (2) are distributed around the central optical fiber, and the axis of the central optical fiber (1) coincides with the overall axis of the optical fiber unit;

[0010] The sensing system measures the temperature and strain information of the optical fiber by time division multiplexing. In each measurement cycle, the first optical fiber switch and the second optical fiber switch are first switched to input 2. At this time, the distributed optical fiber temperature measurement system DTS is connected to the optical fiber unit. The temperature along the optical fiber unit is measured by using the distributed optical fiber temperature measurement system DTS. After the temperature measurement is completed, the first optical fiber switch and the second optical fiber switch are both switched to input 1. At this time, the optical fiber unit is connected to the Brillouin optical time domain analyzer BOTDA to measure the strain of the optical fiber. One temperature measurement and one strain measurement constitute one measurement cycle, and each measurement cycle is repeated to form a dynamic measurement process.

[0011] On the other hand, a distributed curvature, strain and temperature sensing solution method is implemented based on the aforementioned distributed curvature, strain and temperature sensing system, specifically including a curvature, strain, temperature solution method and a shape restoration method.

[0012] The curvature, strain and temperature calculation method is specifically as follows: the strain of the central optical fiber and the three spiral optical fibers on a normal plane of the optical fiber unit, the temperature at the normal plane and the position of the normal plane are input, and the curvature radius, curvature direction, torsional strain and tensile strain of the entire optical fiber unit on the normal plane are solved, as shown in the following formula:

[0013] eps1=coe_wl*[(r / R)*sin(α-β1+rol_ang)+eps_l]+coe_n*eps_n+eps_T

[0014] eps2=coe_wl*[(r / R)*sin(α-β2+rol_ang)+eps_l]+coe_n*eps_n+eps_T

[0015] eps3=coe_wl*[(r / R)*sin(α-β3+rol_ang)+eps_l]+coe_n*eps_n+eps_T

[0016] eps4=eps_l+eps_T

[0017] where:

[0018] rol_ang=2π*flg*(position / pitch)

[0019] coe_wl=pitch 2 / (pitch 2 +(2πr) 2 )

[0020] coe_n=2πr*pitch / (pitch2 +(2πr) 2 )

[0021] Wherein: eps1, eps2, eps3 are the strain values ​​of the three spiral fibers at the normal plane, eps4 is the strain value of the central fiber at the normal plane, and the strain of the central fiber and the three spiral fibers is directly measured by the Brillouin optical time domain analyzer BOTDA; β1, β2 and β3 are the initial azimuths of the three spiral fibers, rol_ang is the angle of rotation of the three spiral fibers relative to the initial normal plane, flg is the spiral direction of the three spiral fibers, flg = 1 for right-handed rotation and flg = -1 for left-handed rotation, coe_w1 is the strain weight of the spiral fiber under bending and tensile strain, coe_n is the strain weight of the spiral fiber under torsional strain, position is the distance from the starting point along the center line of the normal plane, eps_T is the thermal strain, which is calculated from the temperature measured by the distributed optical fiber temperature measurement system DTS, r is the twisting radius of the spiral fiber, pitch is the intercept of the spiral fiber, eps_1 is the tensile strain of the fiber unit, eps_n is the torsional strain of the fiber unit, R is the bending radius of the fiber unit, and α is the direction of the curvature vector;

[0022] BOTDA and DTS are used to collect a set of temperature and fiber strain information on the normal plane respectively, and the tensile strain, torsional strain, bending radius and bending angle of each point along the fiber unit can be solved by bringing them into the strain-curvature model equation with temperature compensation.

[0023] The shape restoration method is implemented based on a shape restoration algorithm, and the centerline shape of the optical fiber unit is restored based on a zero-torsion frame; specifically, as shown in the following formula:

[0024] for(int i=0;i<m;i++)

[0025] K i =1 / R i , α i =arctan(K2 / K1);

[0026] T i+1 =T i +l*(K1 i *N1 i +K2 i *N2 i );

[0027] N1 i+1 =N1 i -l*K1 i *T i ;

[0028] N2i+1 =N2 i -l*K2 i *T i ;

[0029] P i+1 =P i +0.5l(T i+1 +T i );

[0030] Where: m is the total number of discrete points, i is the number of the current discrete point, R0~R m and α0~α1 are a set of curvatures and curvature directions respectively, P0~P m is the position of each tangent vector, that is, the position of the point on the restored curve, 1 is the distance between each point, K0~K m is the curvature of each point, K10~K1 m and K20~K2 m The curvature component of each point on the frame, N10~N1 m and N20~N2 m The two normal vectors of the zero torsion frame at each point, T0~T m The tangent vector at each point;

[0031] The beneficial effects of adopting the above technical solution are:

[0032] The present invention provides a distributed curvature, strain and temperature sensing system and a sensing solution method thereof. The present invention can not only simultaneously measure the curvature, strain and temperature of an optical fiber unit, but also provide an accurate temperature compensation function to ensure the accuracy of strain measurement. Through reasonable structural design and measurement cycle control, the present invention realizes the ability of dynamic monitoring, has strong adaptability and has broad application prospects. Its system design is simple and reliable, suitable for long-term stable operation in complex and harsh environments, and greatly improves the practicality and reliability of the sensing system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the connection structure of a distributed curvature, strain and temperature sensing system in an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the structure of an optical fiber unit in an embodiment of the present invention;

[0035] Among them, 1-central optical fiber, 2-helical optical fiber, 3-outer sheath;

[0036] Figure 3 Flow chart of the solution process in the embodiment of the present invention. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0038] On the one hand, a distributed curvature, strain and temperature sensing system, e.g. Figure 1 As shown, it includes: an optical fiber unit, a Brillouin optical time domain analyzer BOTDA, a distributed optical fiber temperature measurement system DTS, a first optical fiber switcher and a second optical fiber switcher;

[0039] The optical fiber unit comprises four tight-buffered single-mode optical fibers for sensing, which are fused end to end to form a whole, and the two ends after fusion are respectively connected to the output end of the first optical fiber switch and the output end of the second optical fiber switch; the measuring light source of the Brillouin optical time domain analyzer BOTDA is connected to the input 1 of the first optical fiber switch, the pumping light source of the Brillouin optical time domain analyzer BOTDA is connected to the input 1 of the second optical fiber switch, and the measuring light source of the distributed optical fiber temperature measurement system DTS is connected to the input 2 of the first optical fiber switch.

[0040] like Figure 2 As shown, the four tight-buffered single-mode optical fibers specifically include three spiral optical fibers and one central optical fiber, which are formed by extrusion of an outer sheath (3), wherein the three spiral optical fibers (2) are distributed around the central optical fiber, and the axis of the central optical fiber (1) coincides with the overall axis of the optical fiber unit. The unique structure composed of the three spiral optical fibers and the central optical fiber makes the optical fiber unit sensitive to the axial load (tension, compression), radial load (bending) and torsional load it is subjected to.

[0041] It is worth noting that the sequence of head-to-tail fusion splicing does not need to be fixed, but the sequence needs to be recorded. Since the present invention fuses four optical fibers into one, and the measurement data output by BOTDA is the strain value of each measurement point and the position of the measurement point in the optical fiber. Similarly, the output of DTS is the temperature value of each measurement point and the position of the measurement point in the optical fiber. Therefore, when measuring temperature and strain, it is necessary to use the recorded connection sequence to determine the actual position of each data point in the optical fiber unit using the measurement point position.

[0042] The sensing system measures the temperature and strain information of the optical fiber by time division multiplexing. In each measurement cycle, the first optical fiber switch and the second optical fiber switch are first switched to input 2. At this time, the distributed optical fiber temperature measurement system DTS is connected to the optical fiber unit. The temperature along the optical fiber unit is measured by using the distributed optical fiber temperature measurement system DTS. After the temperature measurement is completed, the first optical fiber switch and the second optical fiber switch are both switched to input 1. At this time, the optical fiber unit is connected to the Brillouin optical time domain analyzer BOTDA to measure the strain of the optical fiber. One temperature measurement and one strain measurement constitute one measurement cycle, and each measurement cycle is repeated to form a dynamic measurement process. The temperature information collected by the DTS is not only used as temperature feedback of the optical fiber unit, but also provides data support for temperature compensation for strain measurement.

[0043] On the other hand, a distributed curvature, strain and temperature sensing solution method, such as Figure 3 As shown, it is implemented based on the aforementioned distributed curvature, strain and temperature sensing system, specifically including curvature, strain, temperature solution method and shape restoration method.

[0044] The curvature, strain, and temperature calculation method is specifically as follows: when the structural parameters of the optical fiber unit are known, the strain of the central optical fiber and the three spiral optical fibers on a normal plane of the optical fiber unit, the temperature at the normal plane, and the position of the normal plane are input to solve the curvature radius, curvature direction, torsional strain, and tensile strain of the entire optical fiber unit on the normal plane. Due to the special structure of the optical fiber unit, the load on the optical fiber unit at this point can be determined by measuring the strain in the optical fiber on a normal plane. Therefore, a strain-curvature model with temperature compensation can be established in this embodiment, as shown in the following formula:

[0045] eps1=coe_wl*[(r / R)*sin(α-β1+rol_ang)+eps_l]+coe_n*eps_n+eps_T

[0046] eps2=coe_wl*[(r / R)*sin(α-β2+rol_ang)+eps_l]+coe_n*eps_n+eps_T

[0047] eps3=coe_wl*[(r / R)*sin(α-β3+rol_ang)+eps_l]+coe_n*eps_n+eps_T

[0048] eps4=eps_l+eps_T

[0049] where:

[0050] rol_ang=2π*flg*(position / pitch)

[0051] coe_wl=pitch 2 / (pitch 2 +(2πr) 2 )

[0052] coe_n=2πr*pitch / (pitch 2 +(2πr) 2 )

[0053] Wherein: eps1, eps2, eps3 are the strain values ​​of the three spiral fibers at the normal plane, eps4 is the strain value of the central fiber at the normal plane, and the strain of the central fiber and the three spiral fibers is directly measured by the Brillouin optical time domain analyzer BOTDA; β1, β2 and β3 are the initial azimuths of the three spiral fibers, rol_ang is the angle of rotation of the three spiral fibers relative to the initial normal plane at the normal plane, flg is the spiral direction of the three spiral fibers, flg = 1 for right-handed rotation and flg = -1 for left-handed rotation, coe_w1 is the strain weight of the spiral fiber under bending and tensile strain, coe_n is the strain weight of the spiral fiber under torsional strain, position is the distance from the starting point along the center line of the normal plane, eps_T is the thermal strain, which is calculated from the temperature measured by the distributed optical fiber temperature measurement system DTS, r is the twisting radius of the spiral fiber, pitch is the intercept of the spiral fiber, eps_1 is the tensile strain of the fiber unit, eps_n is the torsional strain of the fiber unit, R is the bending radius of the fiber unit, and α is the direction of the curvature vector;

[0054] BOTDA and DTS are used to collect a set of temperature and fiber strain information on the normal plane respectively, and the tensile strain, torsional strain, bending radius and bending angle of each point along the fiber unit can be solved by bringing them into the strain-curvature model equation with temperature compensation.

[0055] The shape restoration method is implemented based on the shape restoration algorithm, which is an iterative process. The centerline shape of the optical fiber unit is restored based on the zero torsion frame. The curvature and curvature direction are input to obtain the iterative process curve. The curve can be restored by the position of each point on the iterative process curve. In this embodiment, the curvature-shape model of the optical fiber unit can be established based on the zero torsion frame of the curve. The model can recursively restore the shape information of the curve point by point through discrete points through the curvature (1 / R) and curvature direction (α) obtained by the strain-curvature model equation with temperature compensation. The specific formula is as follows:

[0056] for(int i=0;i<m;i++)

[0057] K i =1 / Ri , α i =arctan(K2 / K1);

[0058] T i+1 =T i +l*(K1 i *N1 i +K2 i *N2 i );

[0059] N1 i+1 =N1 i -l*K1 i *T i ;

[0060] N2 i+1 =N2 i -l*K2 i *T i ;

[0061] P i+1 =P i +0.5l(T i+1 +T i );

[0062] Where: m is the total number of discrete points, i is the number of the current discrete point, R0~R m and α0~α1 are a set of curvatures and curvature directions respectively, P0~P m is the position of each tangent vector, that is, the position of the point on the restored curve, 1 is the distance between each point, K0~K m is the curvature of each point, K10~K1 m and K20~K2 m The curvature component of each point on the frame, N10~N1 m and N20~N2 m The two normal vectors of the zero torsion frame at each point, T0~T m The tangent vector at each point.

[0063] The above description is only a preferred embodiment of the present disclosure and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the above-mentioned inventive concept. For example, the above-mentioned features are replaced with the technical features with similar functions disclosed in the embodiments of the present disclosure (but not limited to) to form a technical solution.

Claims

1. A distributed curvature, strain and temperature sensing system, characterized in that: include: Optical fiber unit, Brillouin optical time domain analyzer BOTDA, distributed optical fiber temperature measurement system DTS, first optical fiber switcher and second optical fiber switcher; The optical fiber unit comprises four tight-buffered single-mode optical fibers, which are fused end to end to form a whole, and the two ends after fusion are respectively connected to the output end of the first optical fiber switch and the output end of the second optical fiber switch; the measuring light source of the Brillouin optical time domain analyzer BOTDA is connected to the input 1 of the first optical fiber switch, the pumping light source of the Brillouin optical time domain analyzer BOTDA is connected to the input 1 of the second optical fiber switch, and the measuring light source of the distributed optical fiber temperature measurement system DTS is connected to the input 2 of the first optical fiber switch.

2. A distributed curvature, strain and temperature sensing system according to claim 1, characterized in that: The four tight-buffered single-mode optical fibers specifically include three spiral optical fibers and one central optical fiber, which are formed by extrusion of an outer sheath (3), wherein the three spiral optical fibers (2) are distributed around the central optical fiber, and the axis of the central optical fiber (1) coincides with the overall axis of the optical fiber unit.

3. A distributed curvature, strain and temperature sensing system according to claim 1, characterized in that: The sensing system uses time division multiplexing to measure the temperature and strain information of the optical fiber. In each measurement cycle, the first optical fiber switch and the second optical fiber switch are first switched to input 2. At this time, the distributed optical fiber temperature measurement system DTS is connected to the optical fiber unit. The distributed optical fiber temperature measurement system DTS is used to measure the temperature along the optical fiber unit. After the temperature measurement is completed, the first optical fiber switch and the second optical fiber switch are both switched to input 1. At this time, the optical fiber unit is connected to the Brillouin optical time domain analyzer BOTDA to measure the strain of the optical fiber.

4. A distributed curvature, strain and temperature sensing system according to claim 3, characterized in that: Each measurement cycle consists of one temperature measurement and one strain measurement, and each measurement cycle is repeated to form a dynamic measurement process.

5. A distributed curvature, strain and temperature sensing solution method, implemented based on the distributed curvature, strain and temperature sensing system of claim 1, characterized in that: Specifically, it includes curvature, strain, temperature solution methods and shape restoration methods; The curvature, strain and temperature calculation method is specifically as follows: Use BOTDA and DTS to collect a set of temperature and fiber strain information on the normal plane respectively, and bring them into the strain-curvature model equation with temperature compensation to solve the tensile strain, torsional strain, bending radius and bending angle of each point along the fiber unit. The shape restoration method is implemented based on a shape restoration algorithm, and restores the centerline shape of the optical fiber unit based on a zero-twist frame.

6. A distributed curvature, strain and temperature sensing solution method according to claim 5, characterized in that: The strain-curvature model equation with temperature compensation is specifically as follows: the strains of the central optical fiber and the three spiral optical fibers on a normal plane of the optical fiber unit, the temperature at the normal plane and the position of the normal plane are input, and the curvature radius, curvature direction, torsional strain and tensile strain of the entire optical fiber unit on the normal plane are solved, as shown in the following formula: eps1=coe_wl*[(r / R)*sin(α-β1+rol_ang)+eps_l]+coe_n*eps_n+eps_T eps2=coe_wl*[(r / R)*sin(α-β2+rol_ang)+eps_l]+coe_n*eps_n+eps_T eps3=coe_wl*[(r / R)*sin(α-β3+rol_ang)+eps_l]+coe_n*eps_n+eps_T eps4=eps_l+eps_T where: rol_ang=2π*flg*(position / pitch) coe_wl=pitch 2 / (pitch 2 +(2πr) 2 ) coe_n=2πr*pitch / (pitch 2 +(2πr) 2 ) Wherein: eps1, eps2, eps3 are the strain values ​​of the three spiral fibers at the normal plane, eps4 is the strain value of the central fiber at the normal plane, and the strains of the central fiber and the three spiral fibers are directly measured by the Brillouin optical time domain analyzer BOTDA; β1, β2 and β3 are the initial azimuth angles of the three spiral fibers, rol_ang is the rotation angle of the three spiral fibers relative to the initial normal plane, flg is the spiral direction of the three spiral fibers, flg = 1 for right-handed rotation and flg = -1 for left-handed rotation, coe_ wl is the strain weight of the helical optical fiber caused by bending and tensile strain, coe_n is the strain weight of the helical optical fiber caused by torsional strain, position is the distance from the starting point along the center line of the normal plane, eps_T is the thermal strain, which is calculated from the temperature measured by the distributed optical fiber temperature measurement system DTS, r is the twisting radius of the helical optical fiber, pitch is the intercept of the helical optical fiber, eβs_1 is the tensile strain of the optical fiber unit, eps_n is the torsional strain of the optical fiber unit, R is the bending radius of the optical fiber unit, and α is the direction of the curvature vector.

7. A distributed curvature, strain and temperature sensing solution method according to claim 5, characterized in that: The shape restoration algorithm is specifically shown in the following formula: for(int i=0;i<m;i++) K i =1 / R i ,α i =arctan(K2 / K1); T i+1 =T i +l*(K1 i *N1 i +K2 i *N2 i ); N1 i+1 =N1 i -*K1 i *T i ; N2 i+1 =N2 i -l*K2 i *T i ; P i+1 =P i +0.5l(T i+1 +T i ); Where: m is the total number of discrete points, i is the number of the current discrete point, R0~R m and α0~α1 are a set of curvatures and curvature directions respectively, P0~P m is the position of each tangent vector, that is, the position of the point on the restored curve, 1 is the distance between each point, K0~K m is the curvature of each point, K10~K1 m and K20~K2 m The curvature component of each point on the frame, N10~N1 m and N20~N2 m The two normal vectors of the zero torsion frame at each point, T0~T m The tangent vector at each point.

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