Long-distance continuous strain grating array sensing network and sensing optical cable preparation method

Abstract

The application provides a long-distance continuous strain grating array sensing network and a sensing optical cable preparation method, and belongs to the technical field of distributed optical fiber sensing. The long-distance continuous strain grating array sensing network adopts an innovative large-capacity fiber grating array strain sensing optical cable structure, and can realize accurate measurement of long-distance continuous spatial strain distribution. The core feature of the optical cable is that two adjacent fixed points form a large-span strain sensing unit, a pre-stress is applied to the fiber segment between the fixed points, and a fiber grating is written, thereby forming an independent strain sensing unit. When the sensing optical cable is combined with the measured object, no additional tension needs to be applied, and each strain sensing unit can accurately perceive the strain change of the region between the two fixed points. Through unique structural design, multiple sensing units can be connected in series to form a linear array strain sensing network with large capacity, continuous distribution and no measurement blind area, thereby significantly improving the spatial resolution and measurement accuracy of long-distance strain monitoring.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of distributed optical fiber sensing technology, in particular to a long-distance continuous strain grating array sensing network and a built-in prestressed sensing optical cable preparation method. BACKGROUND

[0002] The service state of large-scale engineering structures is constantly changing, and changes beyond a certain limit will cause accidents, threatening people's lives and property safety. Strain can understand the deformation of the structure under load from a microscopic perspective. By measuring and analyzing the strain of materials or structures, key parameters such as mechanical properties, health status, and durability can be evaluated.

[0003] The existing strain sensing network is mainly point-type strain gauges, which need to be installed one by one in engineering applications, and then networked through communication cables. More importantly, each sensor can only detect the strain change at the installation point and cannot monitor the strain between points, resulting in a monitoring blind area, so it is difficult to form a continuous distributed sensing network. As the scale of the sensing network increases, the system complexity and cost increase dramatically, and the reliability decreases sharply. Therefore, only by laying strain gauges at several important positions for spatial sampling measurement, the automation degree is low, the measurement cost is high, and it is difficult to achieve full coverage, high efficiency, and high precision of engineering structure service state detection. Optical fiber sensors based on Brillouin scattering can achieve long-distance distributed sensing, but due to the limitation of stimulated Brillouin scattering effect, the strain monitoring accuracy at a single point is only a few tens of micro-strains, and the system is complex and has poor real-time performance, making it difficult to meet the needs of high-demand monitoring occasions.

[0004] Existing distributed optical fiber sensing technology and grating array sensing technology can use cabling as a sensing probe. However, to achieve strain detection function, the strain of the measured body needs to be effectively transmitted to the sensitive element. In engineering implementation, the sensitive element needs to be pre-tensioned and then tightly attached to the measured body. However, due to manufacturing process problems, it is difficult to pre-tension, such as Chinese patent "Internal fixed-point type ultra-weak optical fiber grating strain optical cable" (publication number: CN110632719A), which can only be tensioned on site to realize strain sensing function, seriously affecting installation efficiency and engineering quality, and it is difficult to ensure the consistency of each measurement point. In addition, when applying this type of strain optical cable to structures made of non-reinforced concrete, asphalt, glass steel, and other non-fixed point gel materials, it is difficult to achieve tensioning and solidification during construction, thereby greatly limiting the application of distributed strain sensing optical cable. SUMMARY

[0005] Therefore, it is necessary to provide a long-distance continuous strain grating array sensing network and a built-in prestressed sensing optical cable preparation method to solve the technical problem that the sensing optical cable needs to be tensioned at the construction measurement site to realize the strain sensing function, which limits the application scene, use efficiency and measurement accuracy of the cabled optical fiber.

[0006] To solve the above problems, in a first aspect, the present application provides a long-distance continuous strain grating array sensing network, which adopts a fiber grating array strain sensing optical cable structure, comprising: a tensioned optical fiber and an elastic sleeve;

[0007] The tensioned optical fiber is engraved with equidistantly distributed ultra-weak reflectivity fiber gratings;

[0008] The tensioned optical fiber is built-in in the elastic sleeve, and the tensioned optical fiber is fixedly connected with the elastic sleeve through evenly spaced fixing points to form a sensing optical cable; the sensing optical cable has prestress and an ultra-weak reflectivity fiber grating between any two adjacent fixing points, and forms a strain sensing unit; the sensing optical cable has a plurality of strain sensing units, forming a long-distance continuous strain sensing network.

[0009] In a possible implementation, the fixed connection between the tensioned optical fiber and the elastic sleeve can adopt any one of the following: adhesion, low-temperature glass welding and metal fastening.

[0010] In a possible implementation, the ultra-weak reflectivity fiber grating has a certain gap distribution with the elastic sleeve.

[0011] In a possible implementation, it further comprises an inner protective layer and an outer protective layer.

[0012] The inner protective layer is wrapped around the elastic sleeve, and the inner protective layer has a reinforcing rib inside, which is tightly attached to the elastic sleeve.

[0013] The outer protective layer is wrapped around the inner protective layer.

[0014] In a possible implementation, the outer protective layer comprises a metal sheath layer and a rubber sheath layer; the metal sheath layer is wrapped around the inner protective layer, and the rubber sheath layer is wrapped around the metal sheath layer.

[0015] In a possible implementation, the outer surface of the metal sheath layer has an embossed pattern.

[0016] In a second aspect, the present application provides a built-in prestressed sensing optical cable preparation method for preparing the long-distance continuous strain grating array sensing network as described in any one of the above aspects, comprising:

[0017] The speed of the fiber paying-off wheel and the fiber taking-up wheel is controlled to tension the optical fiber to obtain a pre-strained optical fiber structure; the fiber paying-off wheel is used to release the optical fiber from a reel, and the fiber taking-up wheel is used to wind the optical fiber released by the paying-off wheel onto the reel;

[0018] After the pre-strained optical fiber structure is fixed on the elastic belt, the winding mechanism is controlled to wind the elastic belt into an elastic tube to wrap the pre-strained optical fiber structure, to obtain an internal pre-stress sensing optical cable.

[0019] In a possible implementation, the fixing of the pre-strained optical fiber structure on the elastic belt comprises:

[0020] The dispensing mechanism is controlled to dispense to fix the pre-strained optical fiber structure on the elastic belt.

[0021] In a possible implementation, after the internal pre-stress sensing optical cable is obtained, the method further comprises:

[0022] The injection molding machine is controlled to extrude to wrap the internal pre-stress sensing optical cable, to perform secondary encapsulation on the internal pre-stress sensing optical cable.

[0023] In a possible implementation, the method further comprises:

[0024] After the initial optical fiber structure is fixed on the elastic belt, the wrapping mechanism is controlled to wind the elastic belt to form a spiral armor tube to wrap the initial optical fiber, to obtain the initial optical fiber structure;

[0025] After the initial optical fiber is fixed on the spiral armor tube, the speed of the fiber paying-off wheel and the fiber taking-up wheel is controlled to tension the initial optical fiber structure, and the extrusion mechanism is controlled to extrude the initial optical fiber structure after tensioning, to obtain a sensing optical cable.

[0026] The beneficial effects of the present application are: in order to solve the problem that the cabling optical fiber needs to be tensioned on site during the strain measurement process, the sensing network provided by the present application adopts a large-capacity fiber grating array strain sensing optical cable structure, which can realize accurate measurement of long-distance continuous spatial strain distribution, the large-capacity fiber grating array continuous large-span strain sensing optical cable adopts a multi-layer composite structure design, the sensing optical fiber is stably coupled with the elastic sleeve through uniformly distributed fixed points, and two adjacent fixed points form a large-span strain sensing unit. A pre-stress is applied to the fiber segment between the fixed points and a fiber grating is written, forming an independent strain sensing unit. The built-in pre-stressed large-span strain sensing unit can accurately perceive the strain change of the region between the two fixed points when the sensing optical cable is combined with the measured object without additional tension. A plurality of built-in pre-stressed large-span strain sensing units are connected in series to form a linear array strain sensing network with large capacity, continuous distribution and no measurement blind area. The present application solves the problem that the optical cable cannot be fixed and tensioned in special application scenarios such as concrete and asphalt without reinforcement, and ensures the consistency and reliability of all measurement points of the large-capacity sensing network through the pre-tensioned built-in pre-stressed optical cable structure for stress measurement.

[0027] Further, the optical fiber is tensioned by controlling the speed of the optical fiber pay-off wheel and the optical fiber take-up wheel to obtain a pre-strained optical fiber structure; the optical fiber pay-off wheel is used to release the optical fiber from the reel, and the optical fiber take-up wheel is used to wind the optical fiber released by the pay-off wheel onto the reel; and after the pre-strained optical fiber structure is fixed on the elastic belt, the elastic belt is curled into an elastic tube by the winding mechanism to wrap the pre-strained optical fiber structure, thereby obtaining a built-in pre-stressed sensing optical cable. Thus, the pre-stressed optical fiber structure after tensioning is maintained and fixed by the elastic sleeve to form a built-in pre-stressed sensing optical cable, solving the problem that the optical cable cannot be fixed and tensioned in special application scenarios such as concrete and asphalt without reinforcement, and ensuring the consistency and reliability of all measurement points of the large-capacity sensing network through the pre-tensioned built-in pre-stressed optical cable structure for stress measurement. The sensing optical cable prepared by the built-in pre-stressed sensing optical cable preparation method has built-in pre-stress and can be directly used for engineering measurement without the need for tensioning before measurement, improving the measurement efficiency and not being limited by the application scenario. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The structure schematic diagram of an embodiment of the long-distance continuous strain grating array sensing network provided by the present application;

[0029] Figure 2 The sensing optical cable cross-sectional structure schematic diagram in the long-distance continuous strain grating array sensing network provided by the present application;

[0030] Figure 3 Method flow chart of an embodiment of the method for preparing the built-in pre-stressed sensing optical cable provided by the present application;

[0031] Figure 4 Structure schematic diagram of an embodiment of the sensing optical fiber and elastic sleeve curing and packaging in the method for preparing the built-in pre-stressed sensing optical cable provided by the present application;

[0032] Figure 5 Method flow chart of another embodiment of the method for preparing the built-in pre-stressed sensing optical cable provided by the present application;

[0033] Figure 6 Structure schematic diagram of an embodiment of the built-in pre-strain cable method in the method for preparing the built-in pre-stressed sensing optical cable provided by the present application. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present application will be specifically described below in combination with the accompanying drawings, wherein the drawings form a part of the present application, and are used to explain the principles of the embodiments of the present application, and are not used to limit the scope of the present application.

[0035] Before the embodiments are shown, the following terms are explained.

[0036] Built-in pre-stress: refers to the stress applied in advance in the structure or material during the preparation process. Such stress already exists in the initial state of the structure, and is usually used to improve the performance of the structure or to achieve a specific function.

[0037] Optical fiber tensioning: refers to stretching the optical fiber by external force during the preparation process to make it produce a certain strain (elongation deformation), so that the optical fiber is in a stretched state.

[0038] Sensing optical cable: a kind of optical cable integrated with optical fiber sensors, used to measure the changes of physical quantities (such as strain, temperature, pressure, etc.). The sensing optical cable senses the changes of the external environment through the changes of the optical properties of the optical fiber (such as light intensity, phase, wavelength, etc.), and converts these changes into measurable signals.

[0039] In one specific embodiment of the present application, a long-distance continuous strain grating array sensing network is provided, which adopts a fiber grating array strain sensing optical cable structure, please refer to Figure 1 , which comprises: a tensioned optical fiber and an elastic sleeve;

[0040] The tensioned optical fiber is engraved with equidistantly distributed ultra-weak reflectivity fiber gratings;

[0041] The tensioned optical fiber is embedded in the elastic sleeve, and the tensioned optical fiber is fixedly connected with the elastic sleeve through evenly spaced consolidation points to form a sensing optical cable; the sensing optical cable has a pre-stress and an ultra-weak reflectivity fiber grating between any two adjacent consolidation points on the sensing optical cable, and forms a strain sensing unit; the sensing optical cable has a plurality of strain sensing units, forming a long-distance continuous strain sensing network.

[0042] In the embodiment, the long-distance continuous strain grating array sensing network prepared by the preparation method of the pre-stressed sensing optical cable has a large-capacity fiber grating array strain sensing optical cable structure, and can realize accurate measurement of long-distance continuous spatial strain distribution. The large-capacity fiber grating array continuous large-span strain sensing optical cable adopts a multi-layer composite structure design. The sensing optical fiber is stably coupled with the elastic sleeve through evenly distributed consolidation points. Two adjacent consolidation points form a large-span strain sensing unit. A pre-stress is applied to the fiber segment between the fixed nodes, and a fiber grating is written, forming an independent strain sensing unit. The pre-stressed large-span strain sensing unit is embedded. When the sensing optical cable is fixedly combined with the measured object, no additional tension needs to be applied. Each strain sensing unit can accurately sense the strain change of the region between the two consolidation points. The pre-stressed large-span strain sensing unit is connected in series to form a linear array strain sensing network with large capacity, continuous distribution and no measurement blind area.

[0043] It should be noted that the writing method of the grating is not limited here.

[0044] It should be noted that the tensioned optical fiber structure is wrapped with an elastic sleeve, and the tensioned optical fiber structure with pre-strain after tensioning is fixed in the elastic sleeve. The elastic sleeve has a high elastic modulus and good flexibility, which can effectively maintain the pre-strain state of the optical fiber and prevent the optical fiber from shrinking in the subsequent processing or use process. At the same time, the elastic sleeve also has excellent bending performance, which can maintain the structural integrity when winding or bending without damaging the optical fiber, thereby forming a pre-stressed sensing optical cable. In a specific embodiment, the elastic sleeve is a metal tube. The metal elastic sleeve is used to wrap the tight-fitting fiber grating array sensing optical fiber. The metal elastic sleeve can be a longitudinally wrapped formed armored structure with a metal strip, or a spiral armored structure formed by winding a metal strip.

[0045] Further, the tensioned optical fiber and the elastic sleeve are connected through the consolidation points. The consolidation points can be pasted, low-temperature glass welding, metal fastening, etc. In the embodiment, the consolidation points are tightly combined with the sensing optical fiber by using high-strength adhesive. Specifically, the consolidation points are fixed on the elastic sleeve by spacing glue injection through a glue injection mechanism.

[0046] Further, the ultra-weak reflectivity fiber grating is located between two adjacent fixed points, and the ultra-weak reflectivity fiber grating is distributed between every two adjacent fixed points. The fiber segment between the two adjacent fixed points is pre-stressed, and one grating is arranged to form one strain sensing unit. When the sensing cable is cured on the measured object, each strain sensing unit can sense the strain change of the region between the two fixed points, thereby forming a large-capacity, continuous and blind-area-free linear array strain sensing network.

[0047] In order to improve the strain detection accuracy, in some embodiments of the present application, the ultra-weak reflectivity fiber grating has a certain gap distribution between the elastic sleeve.

[0048] It should be noted that the fiber and the sleeve in the sensing unit are in a loose sleeve structure, so that the fiber grating is freely suspended and the stress is uniformly distributed, thereby improving the strain detection accuracy. A plurality of spaced and continuously distributed freely suspended fiber gratings can form a continuous sensing unit array, thereby realizing large gauge length, continuous and blind-area-free distributed strain detection.

[0049] In order to further improve the tensile strength and compressive strength of the cable, in some embodiments of the present application, please refer to Figure 1 , which further comprises an inner protective layer and an outer protective layer.

[0050] The inner protective layer wraps the elastic sleeve, and the inner protective layer has a reinforcing rib inside.

[0051] The outer protective layer wraps the inner protective layer.

[0052] It should be noted that the outer protective layer is used to improve the strength of the sensing fiber, so that the tensile performance is better when the sensing fiber is subjected to bending and flexing, and the strain can be effectively transmitted from the plastic pipe layer to the sensing fiber. The outer protective layer comprises a metal sheath and a rubber sheath, and the rubber sheath is preferably made of high-density polyethylene (HDPE) material. The metal sheath is preferably formed by longitudinally wrapping a metal strip with a pressure pattern. The pressure patterned metal sheath can effectively reduce the relative sliding of the inner and outer sheath rubber layers, and improve the strain transmission efficiency.

[0053] Further, in order to improve the accuracy of fiber strain measurement and the reliability of installation, different cross-sectional structures of the outer protective layer can be selected according to different application scenarios. For example, for direct-buried application scenarios, a circular cross-sectional structure is selected, and the number of layers and the structural strength of the outer protective layer can be increased according to the actual stress environment, thereby increasing the mechanical strength of the cable to make the cable have higher stability during the installation process. For example, for surface-mounted application scenarios, in order to avoid the cable from being twisted, as shown in Figure 2 , square, trapezoidal, D-shaped and other cross-sectional structures can be selected. On the one hand, the installation direction of the cable can be ensured to be consistent, and on the other hand, the contact area can be increased to ensure the stability of the installation.

[0054] It should be noted that the inner sheath layer is used to wrap the metal elastic sleeve, and the inner sheath is preferably made of high-density polyethylene (HDPE) material and has a reinforcing member, and the reinforcing member is preferably made of phosphorized steel wire, which is used to improve the tensile strength of the optical cable. The inner sheath is tightly wrapped on the metal elastic sleeve by an extrusion molding process, so as to realize effective transmission of strain.

[0055] In the embodiment, by arranging the inner sheath layer and the outer sheath layer, not only the structural strength of the optical cable is improved, but also the convenience and reliability of the optical cable installation are improved through the design of the materials and structures of the inner sheath layer and the outer sheath layer.

[0056] Based on the long-distance continuous strain grating array sensing network, the embodiment of the application further provides a preparation method of the built-in prestressed sensing optical cable, please refer to Figure 3 , which comprises the following steps:

[0057] S301, control the speed of the optical fiber pay-off reel and the optical fiber take-up reel to tension the optical fiber, and obtain a pre-strained optical fiber structure; wherein the optical fiber pay-off reel is used to release the optical fiber from the reel, and the optical fiber take-up reel is used to wind the optical fiber released by the pay-off reel onto the reel;

[0058] It should be noted that if the optical fiber is not tensioned, the optical fiber is in a relaxed state and cannot measure the tensile strain. Therefore, in order to detect the tensile strain in the project, the optical fiber needs to be tensioned. On the one hand, the size of the tension force is related to the characteristics of the optical fiber (mechanical fracture damage). On the other hand, the measurement range of the strain after the optical fiber is tensioned should be consistent with the existing strain sensor. Therefore, the degree of tension of the optical fiber is also related to the measurement range of the optical fiber strain sensor.

[0059] In the embodiment, by designing the relatively placed optical fiber pay-off reel and the optical fiber take-up reel as the tool and carrier for tensioning the optical fiber, large-scale and high-efficiency tensioning of the optical fiber can be realized, while the continuity of large-scale optical fiber stretching is ensured. And by controlling the pay-off speed to control the stretching amount of the optical fiber, on the one hand, the purpose of automatic tensioning of the optical fiber is realized, and on the other hand, the stability of large-scale optical fiber stretching and the consistency of optical fiber process parameters are ensured by controlling the speed consistency. Specifically, the preferred pre-stretching amount is 1500~2500.

[0060] In a specific embodiment, the pay-off speed is controlled to control the stretching amount of the optical fiber, and the stretching amount is generally controlled to be between 1.5%~2.5%.

[0061] Further, the pre-strained optical fiber structure is an optical fiber with built-in prestress after tensioning.

[0062] S302, after fixing the pre-strained fiber structure on the elastic belt, the winding mechanism is controlled to wind the elastic belt into an elastic tube to wrap the pre-strained fiber structure, so as to obtain the pre-stress sensing optical cable.

[0063] It should be noted that the pre-strained fiber structure is wrapped by the elastic sleeve, and the pre-strained fiber structure is fixed inside the elastic sleeve. The elastic sleeve has high elastic modulus and good flexibility, which can effectively maintain the pre-strained state of the optical fiber and prevent the optical fiber from shrinking in the subsequent processing or use process. At the same time, the elastic sleeve also has excellent bending performance, which can maintain the structural integrity when winding or bending without damaging the optical fiber, thereby forming the pre-stress sensing optical cable.

[0064] It should be noted that the pre-strained fiber structure is wrapped by the elastic sleeve, and the pre-strained fiber structure is fixed inside the elastic sleeve. The elastic sleeve has high elastic modulus and good flexibility, which can effectively maintain the pre-strained state of the optical fiber and prevent the optical fiber from shrinking in the subsequent processing or use process. At the same time, the elastic sleeve also has excellent bending performance, which can maintain the structural integrity when winding or bending without damaging the optical fiber, thereby forming the pre-stress sensing optical cable.

[0065] In a specific embodiment, the elastic sleeve is a metal tube. The metal elastic sleeve is used to wrap the tight-fitting fiber grating array sensing optical fiber, and the metal elastic sleeve can be a longitudinally wrapped formed armored tube structure with a pressed metal strip, or a spiral armored structure formed by winding a metal strip.

[0066] In summary, the pre-stress sensing optical cable preparation method provided by the embodiments of the present application solves the problem that the cable optical fiber needs to be tensioned on site during strain measurement. The present application provides a pre-stress sensing optical cable preparation method, which first controls the speed of the fiber unwinding wheel and the fiber winding wheel to tension the optical fiber, thereby obtaining a pre-strained fiber structure. The fiber unwinding wheel is used to release the optical fiber from the reel, and the fiber winding wheel is used to wind the released optical fiber from the reel onto the reel. After fixing the pre-strained fiber structure on the elastic belt, the winding mechanism is controlled to wind the elastic belt into an elastic tube to wrap the pre-strained fiber structure, thereby obtaining the pre-stress sensing optical cable. The elastic sleeve maintains and fixes the pre-stressed fiber structure after tensioning, thereby forming the pre-stress sensing optical cable. This solves the problem of fixing the optical cable for tensioning in special application scenarios such as concrete and asphalt without reinforcement. The stress measurement is performed by the pre-tensioned pre-stress sensing optical cable structure, which ensures the consistency and reliability of all measurement points in the large-capacity sensing network.

[0067] In some embodiments of the present application, the fixing of the pre-strained fiber structure on the elastic belt comprises:

[0068] The point gluing mechanism is controlled to fix the pre-strained fiber structure on the elastic belt.

[0069] It should be noted that the optical fiber structure is connected with the elastic band through the adhesive formed consolidation point. In other embodiments, the consolidation point can be a welding or other fixing means to connect the pre-strained optical fiber structure and the elastic sheet at a fixed position. The consolidation points are distributed along the optical fiber structure to ensure that the optical fiber remains in a pre-strained state during subsequent processing or use, preventing the optical fiber from retracting. As a connection point, the consolidation point can transmit external forces (such as stretching and bending) from the elastic sheet to the optical fiber, allowing the optical fiber to sense and respond to external strain changes. In practical applications, the design and distribution of the consolidation points need to be optimized according to the pre-strain requirements of the optical fiber, the material properties of the elastic sheet, and the specific application scenarios to ensure that the performance and functionality of the sensing optical cable meet the requirements.

[0070] The consolidation points can be uniformly distributed or non-uniformly distributed. In different embodiments, the distribution of the consolidation points can be selected according to actual needs.

[0071] In a specific embodiment, the optical fiber is parallel to the metal band, preferably referring to Figure 4 The optical fiber can be fixed to the metal band using a dispensing mechanism to maintain the pre-tension strain of the optical fiber using the mechanical strength of the metal band.

[0072] To prevent damage to the optical cable from external environments (such as moisture, oil, acid and alkali substances, high voltage electric field, etc.), in some embodiments of the present application, after obtaining the built-in pre-stressed sensing optical cable, further comprising:

[0073] Controlling the injection molding machine to extrude and wrap the built-in pre-stressed sensing optical cable to perform secondary packaging on the built-in pre-stressed sensing optical cable.

[0074] It should be noted that the secondary packaging can effectively reduce the influence of external environmental changes (such as temperature, humidity, mechanical vibration, etc.) on the performance of the optical cable, ensuring the stability and reliability of the sensor in complex environments. In the packaging process, the secondary packaging can maintain the pre-stress state of the fiber Bragg grating, preventing the fiber Bragg grating from relaxing or deforming and causing chirp, thereby ensuring the measurement accuracy of the sensor.

[0075] In a specific embodiment, to further improve the tensile strength and compressive strength of the optical cable, the outer sheath of the secondary packaging is composed of a metal armor tube and a rubber sheath. The rubber sheath is preferably made of high-density polyethylene (HDPE) material, and the metal armor tube is preferably formed by longitudinally wrapping a corrugated metal band. The corrugated metal armor tube can effectively reduce the relative sliding of the inner and outer rubber layers, improving the strain transmission efficiency. Depending on different application scenarios, the outer sheath can have different cross-sectional structures, such as a circular cross-section for direct burial applications and a square, trapezoidal, or D-shaped cross-section for surface-mounted applications.

[0076] In order to expand the application scenarios of the built-in pre-stressed optical cable, in some embodiments, referring to Figure 5 , the application further comprises:

[0077] S501, after fixing the initial optical fiber structure on the elastic belt, the wrapping mechanism is controlled to wrap the elastic belt to form a spiral armor tube to wrap the initial optical fiber, so as to obtain an initial optical fiber structure;

[0078] S502, after fixing the initial optical fiber on the spiral armor tube, the speed of the fiber pay-off reel and the fiber take-up reel is controlled to tension the initial optical fiber structure, and the extrusion mechanism is controlled to extrude the tensioned initial optical fiber structure, so as to obtain a sensing optical cable.

[0079] In this embodiment, the initial optical fiber is first wrapped with an elastic sleeve, and then the elastic sleeve and the initial optical fiber are synchronously tensioned, and the high elastic modulus and good flexibility of the elastic sleeve are used to keep the tensioned optical fiber from shrinking back.

[0080] In a specific embodiment, the optical fiber is first broadcasted in parallel with the metal belt, the metal belt is wound to form a spiral armor tube to wrap the optical fiber by the wrapping mechanism, then the spiral armor tube with the optical fiber is broadcasted to the dispensing mechanism, the optical fiber is adhered in the spiral armor tube by interval dispensing, and the spiral armor size is generally 1.2-5.0 mm. Then the spiral armor tube with the adhered optical fiber is tensioned and broadcasted to the extrusion mechanism, referring to Figure 6 , the spiral armor tube is kept in a tensioned state by the extrusion process, so that the optical fiber between two adjacent adhesive points in the armor tube is also in a tensioned state. Optionally, a reinforcing member can be added in the inner sheath, and the material can be selected from, for example, phosphorized steel wire, FRP, etc.

[0081] Therefore, the spiral armor tube and the tensioning and extrusion process in this embodiment are more suitable for optical fiber protection and general sensor applications.

[0082] The above is only a preferred specific embodiment of the application, but the protection scope of the application is not limited thereto, and any changes or replacements within the technical range disclosed by the application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the application.

Claims

1. A method for preparing a built-in prestressed sensing optical cable for preparing a long-distance continuous strain grating array sensing network, characterized in that: The long-distance continuous strain grating array sensing network adopts a fiber grating array strain sensing cable structure, which includes: a tensioned optical fiber, an elastic sleeve, an inner sheath, and an outer sheath; the inner sheath is wrapped around the elastic sleeve, and has reinforcing ribs inside the inner sheath, which are made of phosphated steel wire. The inner sheath is tightly wrapped around the elastic sleeve through an extrusion molding process, and the inner sheath is made of high-density polyethylene (HDPE); the outer sheath is wrapped around the inner sheath, and the outer sheath includes a metal armor tube and a rubber sheath, and the rubber sheath is made of high-density polyethylene (HDPE); The tensioned optical fiber is inscribed with equally spaced and distributed ultra-weak reflectivity fiber Bragg gratings; The tensioned optical fiber is embedded in the elastic sleeve, and the tensioned optical fiber is solidified and connected to the elastic sleeve through evenly spaced solidification points to form a sensing optical cable. The elastic sleeve wraps the tensioned optical fiber and fixes the tensioned optical fiber with pre-strain after tensioning inside the elastic sleeve. There is pre-stress and an ultra-weak reflectivity fiber Bragg grating between any two adjacent solidification points on the sensing optical cable. When the sensing optical cable is solidified and bonded to the measured object, no additional tension is required. Each strain sensing unit accurately senses the strain changes in the area between the two solidification points. The sensing optical cable has multiple strain sensing units, forming a long-distance continuous strain sensing network. The preparation method comprises: Controlling the speed of the optical fiber payout wheel and the optical fiber take-up wheel to tension the optical fiber to obtain an optical fiber structure with pre-strain; wherein the optical fiber payout wheel is used to release the optical fiber from the reel, and the optical fiber take-up wheel is used to wind the optical fiber released by the payout wheel onto the reel; After the glue dispensing mechanism is controlled to dispense glue to fix the pre-strained optical fiber structure on the elastic band, the wrapping mechanism is controlled to roll the elastic band into an elastic tube to wrap the pre-strained optical fiber structure, thereby obtaining a built-in prestressed sensing optical cable; or; After the initial optical fiber is fixed on the elastic band, the wrapping mechanism is controlled to wrap the elastic band to form a spiral armor tube to wrap the initial optical fiber, thereby obtaining an initial optical fiber structure; After the initial optical fiber is fixed on the spiral armor tube, the speeds of the optical fiber pay-off wheel and the optical fiber take-up wheel are controlled to tension the initial optical fiber structure, and the extrusion mechanism is controlled to extrude the tensioned initial optical fiber structure to obtain a sensor optical cable.

2. The method for preparing a built-in prestressed sensing optical cable according to claim 1, wherein: The curing connection between the tensioned optical fiber and the elastic sleeve can be achieved by any one of gluing, low-temperature glass welding, and metal fastening.

3. The method for preparing a built-in prestressed sensing optical cable according to claim 2, wherein: There is a certain gap distribution between the ultra-weak reflectivity optical fiber Bragg grating and the elastic sleeve.

4. The method for preparing a built-in prestressed sensing optical cable according to claim 1, wherein: After getting the built-in prestressed sensing cable, it also includes: The injection molding machine is controlled to extrude and wrap the built-in prestressed sensing optical cable, and the built-in prestressed sensing optical cable is encapsulated with a second protection package.

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