Asphalt pavement fiber grating vertical displacement device and manufacturing method

Abstract

This invention discloses a fiber optic grating vertical displacement device for asphalt pavement and its manufacturing method, belonging to the field of road engineering structural health monitoring technology. The displacement device includes a high-strength 42CrMo material housing, a load-bearing compression spring, and a tension spring sensing component. The load-bearing compression spring provides the main body's load-bearing stiffness, while the fiber optic grating and tension spring work together to sense displacement. An equivalent stiffness matching design dynamically matches the overall modulus of the displacement device with the asphalt pavement material. This invention employs a decoupled load-sensing stiffness structure design, which, compared to traditional displacement devices, offers higher measurement accuracy, stronger resistance to electromagnetic interference, and longer service life under harsh environments such as high-temperature construction and heavy-load operation of asphalt pavements. It enables high-precision, long-term real-time online monitoring of pavement settlement and deformation.

Description

Technical Field

[0001] This invention relates to the field of road engineering structural health monitoring technology, and in particular to a fiber optic grating vertical displacement device for asphalt pavement and its manufacturing method. Background Technology

[0002] In the field of road engineering, the vertical displacement of asphalt pavement (i.e., the settlement or permanent deformation of the pavement structural layers) is a key mechanical indicator for evaluating pavement service performance, structural bearing capacity, and long-term durability. Accurate, long-term, and real-time acquisition of this displacement data is of significant engineering importance for pavement design verification, construction quality control, operational health monitoring, and preventative maintenance decisions.

[0003] Existing technologies, such as the evaluation method for the co-deformation of embedded fiber Bragg grating sensors and asphalt pavement disclosed in CN113916147A, are limited to laboratory evaluation and can only point out co-deformation problems and propose post-hoc correction methods. Summary of the Invention

[0004] The purpose of this invention is to provide a fiber optic grating vertical displacement device and manufacturing method for asphalt pavement, which solves the technical problem that traditional displacement devices cannot simultaneously achieve high-precision measurement, long-term durability and anti-interference capability under the harsh environment of high-temperature construction and heavy-load service on asphalt pavement.

[0005] The present invention is implemented as follows: The present invention provides a vertical displacement device for fiber optic gratings on asphalt pavement, including an upper housing and a lower housing that are relatively movable. A load-bearing compression spring and a tension spring sensing component are provided between the upper housing and the lower housing. The tension spring sensing component is arranged along the central axis of the load-bearing compression spring. The tension spring sensing component includes a tension spring connected vertically and a fiber optic grating sensing component. A transmission optical fiber is fixedly provided inside the fiber optic grating sensing component. The transmission optical fiber extends from one side of the lower housing for connection with a fiber optic grating demodulation device. The fiber optic grating sensing component includes an elastic bearing part. A fiber optic grating is provided on the transmission optical fiber and the fiber optic grating is placed inside the elastic bearing part.

[0006] The relatively movable structure of the upper and lower shells provides a physical basis for the vertical deformation of the displacement device; the load-bearing compression spring bears the main stiffness generated by the external load, and the tension spring sensing component is arranged along the central axis, so that the sensing path coincides with the force path, avoiding interference from off-center loading or torsion on the measurement accuracy; the fiber optic grating is placed in the elastic bearing part to ensure that the grating and the elastic body deform together, directly converting the displacement into a wavelength drift signal, realizing high-sensitivity and electromagnetic interference-resistant accurate measurement; the transmission optical fiber is led out from the side of the lower shell, which facilitates on-site wiring and protection, and improves the convenience of engineering installation.

[0007] A further technical solution of the present invention is: one end of the tension spring is detachably connected to the upper housing, the other end of the tension spring is connected to the fiber optic grating sensing component, and the end of the fiber optic grating sensing component away from the tension spring is connected to the lower housing.

[0008] The upper end of the tension spring is detachably connected to the upper housing, and the lower end is connected to the lower housing via a sensing component, forming a complete force transmission chain from the upper housing → tension spring → sensing component → lower housing. This ensures that the relative displacement between the upper and lower housings is entirely converted into the tensile deformation of the tension spring, which is then accurately sensed by the fiber optic grating. The detachable connection facilitates on-site replacement or repair of the tension spring, reducing maintenance costs and improving the maintainability of the displacement equipment. The tension spring is pre-stretched during assembly, ensuring that it remains under tension throughout the entire monitoring range. This ensures that whether there is road subsidence (upper housing closer to lower housing) or rebound arching (upper housing farther from lower housing), the fiber optic grating can sense strain changes and output continuous wavelength drift signals. The pre-stretch amount is 15% to 25% of the tension spring's working range.

[0009] A further technical solution of the present invention is: a connecting groove is provided on the fiber optic grating sensing component along the axial direction, and the transmission optical fiber is arranged along the connecting groove.

[0010] The axially oriented connecting slot provides a precise positioning channel for the transmission optical fiber, ensuring that the optical fiber remains in the central axis position during the tension or compression of the tension spring, avoiding additional strain interference caused by optical fiber bending or twisting; at the same time, the connecting slot structure also facilitates the installation and fixation of the optical fiber, improving assembly consistency and the reliability of mass production.

[0011] A further technical solution of the present invention is: to form the elastic bearing portion by opening multiple transverse grooves along both sides of the fiber optic grating sensing component.

[0012] The design of multiple transverse grooves enables the elastic support part to form a flexible structure similar to a spring sheet. Under the action of the tension spring, this area can generate uniform and repeatable axial strain, so that when the fiber grating is pasted or fixed in this area, the grating can obtain a strain response with good linearity. The transverse groove structure effectively reduces the overall stiffness of the elastic support, avoids generating additional resistance to the deformation of the tension spring, and ensures accurate transmission of displacement-strain.

[0013] A further technical solution of the present invention is that the transverse grooves on both sides are arranged in an intersecting manner.

[0014] The cross-shaped transverse grooves make the stress distribution of the elastic bearing part more symmetrical and uniform when subjected to axial tension, reducing the bending or torsional stress components, so that the fiber grating only senses pure axial strain, thereby improving the linearity between wavelength drift and displacement.

[0015] A further technical solution of the present invention is: a lateral cable outlet port is provided on one side of the lower housing, a metal protective tube is provided at the lateral cable outlet port, the transmission optical fiber is led out from the metal protective tube, and the transmission optical fiber and the metal protective tube are encapsulated together.

[0016] The side-outlet port, in conjunction with the metal protective tube, provides a rigid protective channel against pressure and bending for the fragile optical fiber lead-out section. The encapsulation treatment between the optical fiber and the metal protective tube effectively blocks the direct damage to the optical fiber caused by the high-temperature asphalt slurry or external force of the rolling machinery during the asphalt mixture paving process. At the same time, it prevents moisture or dust from entering the internal cavity along the optical fiber, ensuring the survival rate and long-term sealing of the displacement equipment in harsh construction environments.

[0017] A further technical solution of the present invention is: a high-temperature resistant protective sleeve is fitted on the transmission optical fiber outside the lower housing.

[0018] The high-temperature resistant protective sleeve on the outside of the outer shell provides a second layer of thermal and mechanical protection for the optical fiber, which can withstand the high temperature radiation of 160~180℃ during asphalt pavement paving and the shear impact of aggregate compaction. The sleeve and the internal metal protective tube form a continuous protective chain, ensuring that the entire optical fiber from the inside of the displacement equipment to the external demodulation equipment is in a reliable protected state, which greatly improves the survivability of the system during the construction period.

[0019] A further technical solution of the present invention is: the upper housing includes an upper pressure plate and a connecting hole structure, the center of the lower surface of the upper pressure plate is a top limiting area, the connecting hole structure is located in the top limiting area, and the connecting hole structure is detachably connected to the tension spring.

[0020] The upper bearing plate provides a large bearing surface that is in direct contact with the road structure layer, ensuring that the vertical load of the road surface can be evenly transferred to the inside of the displacement equipment; the detachable connection between the connecting hole structure and the tension spring ensures the coaxiality of the force transmission and facilitates assembly and maintenance.

[0021] A further technical solution of the present invention is: the lower housing includes a lower pressure plate and a lower housing cover placed on the lower pressure plate.

[0022] The lower bearing plate serves as the bottom support surface for the displacement equipment, enabling the entire displacement equipment to be stably embedded in the base layer or subbase layer, preventing tilting or sinking during use. The mating structure between the lower cover of the housing and the lower bearing plate provides a closed mounting base for the internal sensing components, while ensuring reliable mechanical coupling between the lower housing and the substructure of the road surface, ensuring that external vertical displacement can be effectively transmitted to the internal sensing system.

[0023] A further technical solution of the present invention is: a housing cover is provided on the outer periphery of the bottom of the upper pressure plate, and an accommodating space is formed between the housing cover and the housing bottom cover.

[0024] The upper and lower covers of the housing cooperate to form a closed enclosure, which encloses all the precision components such as the load-bearing compression spring, tension spring sensing components, and fiber optic grating, effectively isolating them from direct contact with external asphalt mixture, moisture, and dust. At the same time, the relative sliding fit between the upper and lower covers ensures the vertical free movement of the upper and lower housings, while also providing lateral limiting and anti-tilting functions, enabling the displacement device to maintain stable measurement performance even under complex road surface stress conditions.

[0025] In this invention, the upper and lower shells together form the outer casing. The cylindrical outer casing, especially the upper pressure plate, can evenly distribute and withstand enormous vertical pressure when subjected to vehicle traffic, preventing stress concentration and structural damage. The robust cylindrical outer casing provides reliable protection for the internal precision sensing components, such as fiber optic gratings and tension springs, effectively resisting the high temperatures during asphalt paving and the crushing damage from heavy machinery. When the road surface experiences a slight vertical displacement, the external "load-bearing shield" accurately transmits this displacement to the internal "sensing core." Because the tension spring is very soft, it faithfully follows the deformation and converts the displacement into strain of the fiber optic grating, thereby achieving high-precision measurement.

[0026] This invention also provides a method for manufacturing a vertical displacement device for asphalt pavement fiber optic gratings, comprising the following steps:

[0027] S1. Parameter matching and selection design: Based on the standard axle load and material modulus of asphalt pavement, determine the stiffness requirements of displacement equipment, select the specifications of load-bearing compression springs and tension springs, and determine the wavelength-strain calibration relationship of fiber optic gratings;

[0028] S2. Housing assembly processing: Processing the upper housing, lower housing, and side cable outlet ports;

[0029] S3. Assembly of tension spring sensing component: The lower end of the tension spring is connected to the upper end of the fiber optic grating sensing component. The transmission optical fiber is fixed at the position of the axis of the fiber optic grating sensing component. The transmission optical fiber is fixed in the connecting groove of the fiber optic grating sensing component by high temperature resistant epoxy adhesive. The adhesive length is not less than 10mm, so that the fiber optic grating segment is positioned in the middle of the effective working section of the elastic bearing part.

[0030] S4. Coaxial assembly: Install the load-bearing compression spring into the lower housing, and then install the tension spring sensing component inside the load-bearing compression spring, keeping the two coaxial;

[0031] S5. Pre-stretch assembly: Cover the transmission optical fiber with the armor sheath and pass it out from the lower housing side to the outlet port; connect the upper end of the tension spring to the upper housing, apply a pre-stretch force to the tension spring so that its elongation reaches 15% to 25% of the working range, and then assemble the upper housing and lower housing and lock them in the pre-stretch position.

[0032] S6. Calibration and Protection: Perform displacement-wavelength calibration on the assembled displacement equipment and apply anti-corrosion and high-temperature resistant treatment to the outer shell surface.

[0033] The beneficial effects of this invention are as follows: The invention provides a physical basis for vertical deformation of the displacement device through the relatively movable structure of the upper and lower shells; the load-bearing compression spring bears the main stiffness generated by the external load, and the tension spring sensing component is arranged along the central axis, so that the sensing path coincides with the force path, avoiding interference from off-center loading or torsion on the measurement accuracy; the fiber optic grating is placed in the elastic bearing part, ensuring that the grating and the elastic body deform together, directly converting the displacement into a wavelength drift signal, realizing high-sensitivity and electromagnetic interference-resistant accurate measurement; the transmission optical fiber is led out from the side of the lower shell, which facilitates on-site wiring and protection, and improves the convenience of engineering installation.

[0034] The manufacturing method of this invention involves: S1 Precisely selecting the load-bearing compression spring and tension spring according to the road load to dynamically match the overall modulus of the displacement device with the road material, ensuring that the sensor is in the optimal linear response range; S2-S4 Coaxial assembly to ensure that the load-bearing path and sensing path are highly coincident, avoiding off-center loading errors and ensuring that the fiber optic grating is accurately located within the effective working section of the elastic bearing part, achieving precise linear transmission of displacement-strain; S5 An armored protective layer is fitted on the transmission optical fiber, passing through the lateral outlet port of the lower shell, effectively resisting high-temperature rolling and impact during paving, preventing moisture and dust intrusion, and ensuring structural integrity and sealing under harsh construction environments; S6 Eliminating assembly errors through whole-machine calibration, combined with anti-corrosion and high-temperature resistant coating treatment, enabling the displacement device to meet the requirements of high-temperature construction and long-term heavy-load service of asphalt pavement, achieving high-precision long-term real-time monitoring of road settlement. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the vertical displacement device for asphalt pavement fiber optic gratings provided by the present invention;

[0036] Figure 2 This is a three-dimensional view of the load-bearing compression spring provided by the present invention;

[0037] Figure 3 This is a front view of the tension spring sensing component provided by the present invention;

[0038] Figure 4 This is a left view of the tension spring sensing assembly provided by the present invention;

[0039] Figure 5This is a top view of the tension spring sensing component provided by the present invention.

[0040] Reference numerals: 1. Upper housing; 11. Upper pressure plate; 12. Top limiting area; 13. Connecting hole structure; 14. Upper cover of housing; 2. Lower housing; 21. Lower cover of housing; 22. Side cable outlet port; 23. Lower pressure plate; 3. Tension spring sensing component; 31. Tension spring; 32. Fiber optic grating sensing component; 33. Transmission fiber; 34. Elastic bearing part; 35. Fiber optic grating; 36. Metal protective tube; 4. Load-bearing compression spring. Detailed Implementation

[0041] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0042] Example 1:

[0043] like Figure 1-5 The illustrated fiber Bragg grating vertical displacement device for asphalt pavement includes a relatively movable upper housing 1 and a lower housing 2. A load-bearing compression spring 4 and a tension spring sensing component 3 are provided between the upper housing 1 and the lower housing 2. The tension spring sensing component 3 is arranged along the central axis of the load-bearing compression spring 4. The tension spring sensing component 3 includes a tension spring 31 connected vertically and a fiber Bragg grating sensing component 32. A transmission fiber 33 is fixedly installed inside the fiber Bragg grating sensing component 32. The transmission fiber 33 extends from one side of the lower housing 2 for connection with a fiber Bragg grating demodulation device. The fiber Bragg grating sensing component 32 includes an elastic bearing portion 34. A fiber Bragg grating 35 is provided on the transmission fiber 33 and placed inside the elastic bearing portion 34. The tension spring 31 has a pre-tension amount in the installed state, so that the tension spring 31 is always in a tensile working state, and the pre-tension amount is configured to make the Bragg wavelength of the fiber Bragg grating 35 located in a preset wavelength range.

[0044] The relatively movable structure of the upper and lower shells provides a physical basis for the vertical deformation of the displacement device; the load-bearing compression spring 4 bears the main stiffness generated by the external load, and the tension spring sensing component 3 is arranged along the central axis, so that the sensing path coincides with the force path, avoiding interference from off-center loading or torsion on the measurement accuracy; the fiber optic grating 35 is placed in the elastic bearing part 34 to ensure that the grating and the elastic body deform together, directly converting the displacement into a wavelength drift signal, realizing high-sensitivity and electromagnetic interference-resistant accurate measurement; the transmission optical fiber is led out from the side of the lower shell, which facilitates on-site wiring and protection, and improves the convenience of engineering installation.

[0045] In this embodiment, one end of the tension spring 31 is detachably connected to the upper housing 1, the other end of the tension spring 31 is connected to the fiber optic grating sensing component 32, and the end of the fiber optic grating sensing component 32 away from the tension spring 31 is connected to the lower housing 2.

[0046] The upper end of the tension spring 31 is detachably connected to the upper housing, and the lower end is connected to the lower housing through the sensing component, forming a complete force transmission chain from the upper housing → tension spring → sensing component → lower housing. This ensures that the relative displacement between the upper and lower housings can be completely converted into the tensile deformation of the tension spring, which can then be accurately sensed by the fiber optic grating. The detachable connection method facilitates on-site replacement or repair of the tension spring, reduces maintenance costs, and improves the service maintainability of the displacement equipment.

[0047] In this embodiment, the fiber optic grating sensing component 32 has a connecting groove along the axial direction, and the transmission optical fiber 33 is arranged along the connecting groove.

[0048] The connecting slot opened along the axial direction provides a precise positioning channel for the transmission optical fiber 33, ensuring that the optical fiber is always in the central axis position during the tension or compression of the tension spring, avoiding additional strain interference caused by the bending or twisting of the optical fiber; at the same time, the connecting slot structure also facilitates the installation and fixing of the optical fiber, improving assembly consistency and the reliability of mass production.

[0049] In this embodiment, multiple transverse slots are formed along both sides of the fiber optic grating sensing component 32 to form the elastic support portion 34.

[0050] The design of multiple transverse grooves enables the elastic bearing part 34 to form a flexible structure similar to a spring sheet. Under the action of the tension spring, this area can generate uniform and repeatable axial strain, so that when the fiber grating 35 is pasted or fixed in this area, the grating can obtain a strain response with good linearity. The transverse groove structure effectively reduces the overall stiffness of the elastic bearing body, avoids generating additional resistance to the deformation of the tension spring 31, and ensures accurate transmission of displacement-strain.

[0051] In this embodiment, the transverse grooves on both sides are arranged in an intersecting manner.

[0052] The cross-shaped transverse grooves make the stress distribution of the elastic bearing part 34 more symmetrical and uniform when it is subjected to axial tension, reducing the bending or torsional stress components, so that the fiber grating 35 only senses pure axial strain, thereby improving the linearity between wavelength drift and displacement.

[0053] In this embodiment, a lateral cable outlet port 22 is provided on one side of the lower housing 2, and a metal protective tube 36 is provided at the lateral cable outlet port 22. The lateral cable outlet port 22 is a cylindrical through hole with an inner diameter of 8 mm and an axial depth of 18 mm. The metal protective tube 36 has an outer diameter of 5 mm and a wall thickness of 1 mm. The metal protective tube 36 is inserted into the lateral cable outlet port 22 to a depth of not less than 10 mm. The annular gap between the metal protective tube 36 and the lateral cable outlet port 22 is filled and sealed with high-temperature resistant epoxy resin. The transmission optical fiber 33 is led out from the metal protective tube 36, and the transmission optical fiber 33 is encapsulated with the metal protective tube 36.

[0054] The side outlet port 22, together with the metal protective tube 36, provides a rigid protective channel that is resistant to pressure and bending for the fragile optical fiber lead-out section. The encapsulation treatment between the optical fiber and the metal protective tube effectively blocks the direct damage to the optical fiber caused by the high temperature asphalt slurry or external force of the rolling machinery during the asphalt mixture paving process. At the same time, it prevents moisture or dust from entering the internal cavity along the optical fiber, ensuring the survival rate and long-term sealing of the displacement equipment in harsh construction environments.

[0055] In this embodiment, a high-temperature resistant protective sleeve is fitted onto the transmission optical fiber 33 outside the lower housing 2.

[0056] The high-temperature resistant protective sleeve on the outside of the outer shell provides a second layer of thermal and mechanical protection for the optical fiber, which can withstand the high temperature radiation of 160~180℃ during asphalt pavement paving and the shear impact of aggregate compaction. The sleeve and the internal metal protective tube form a continuous protective chain, ensuring that the entire optical fiber from the inside of the displacement equipment to the external demodulation equipment is in a reliable protected state, which greatly improves the survivability of the system during the construction period.

[0057] In another embodiment, the transmission optical fiber 33 is fitted with an armored sheath that passes through the side outlet port 22.

[0058] In this embodiment, the upper housing 1 includes an upper pressure plate 11 and a connecting hole structure 13. The center of the lower surface of the upper pressure plate 11 is a top limiting area 12. The connecting hole structure 13 is located in the top limiting area 12 and is detachably connected to the tension spring 31.

[0059] The upper bearing plate 11 provides a large bearing surface that is in direct contact with the road structure layer, ensuring that the vertical load of the road can be evenly transmitted to the inside of the displacement equipment; the detachable connection between the connecting hole structure 13 and the tension spring ensures the coaxiality of the force transmission and facilitates assembly and maintenance.

[0060] In this embodiment, the lower housing 2 includes a lower pressure plate 23 and a lower housing cover 21 placed on the lower pressure plate 23.

[0061] The lower pressure plate 23 serves as the bottom support surface of the displacement device, which can stably embed the entire displacement device in the base layer or subbase layer to prevent tilting or sinking during use. The mating structure between the lower cover 21 of the housing and the lower pressure plate 23 provides a closed mounting base for the internal sensing components, while ensuring reliable mechanical coupling between the lower housing and the substructure of the road surface, ensuring that external vertical displacement can be effectively transmitted to the internal sensing system.

[0062] In this embodiment, a housing cover 14 is provided on the outer periphery of the bottom of the upper pressure plate 11, and an accommodating space is formed between the housing cover 14 and the housing cover 21.

[0063] The upper cover 14 and the lower cover 21 of the housing cooperate to form a closed receiving space, which encloses all the precision components such as the load-bearing compression spring 4, the tension spring sensing component 3, and the fiber optic grating 35, effectively isolating them from direct contact with external asphalt mixture, moisture, and dust. At the same time, the relative sliding fit between the upper and lower covers ensures the vertical free movement space of the upper and lower housings, and also plays a role in lateral limiting and anti-tilting, so that the displacement device can maintain stable measurement performance under complex road surface stress conditions.

[0064] In this invention, the upper and lower shells together form the outer casing. The cylindrical outer casing, especially the upper pressure plate, can evenly distribute and withstand enormous vertical pressure when subjected to vehicle traffic, preventing stress concentration and structural damage. The robust cylindrical outer casing provides reliable protection for the internal precision sensing components, such as fiber optic gratings and tension springs, effectively resisting the high temperatures during asphalt paving and the crushing damage from heavy machinery. When the road surface experiences a slight vertical displacement, the external "load-bearing shield" accurately transmits this displacement to the internal "sensing core." Because the tension spring is very soft, it faithfully follows the deformation and converts the displacement into strain of the fiber optic grating, thereby achieving high-precision measurement.

[0065] In this embodiment, a single load-bearing compression spring 4 is vertically arranged at the center of the inner part of the displacement device housing to provide the main body bearing stiffness for vertical deformation of the displacement device.

[0066] In this embodiment, the working range of the tension spring 31 is 25mm; the transmission optical fiber 33 is arranged vertically along the central axis of the fiber optic grating sensing component 32, and the fiber optic grating 35 inside it, which senses strain, is arranged in the middle of the elastic bearing part of the tension spring sensing component, and is in a state of coordinated deformation with the tension spring 31; the transmission optical fiber 33 runs downward to the bottom of the displacement device, and is led out through the lateral outlet port 22 provided on the side of the lower housing 2, for connecting to the external fiber optic grating demodulation device.

[0067] In this embodiment, the outer dimensions of the main body of the displacement device are 104mm in height and φ125mm in maximum diameter; the pressure surface area of ​​the upper pressure plate 11 is 12271.85mm²; the total working range of the displacement device is 25mm; under a pressure of 0.7MPa, the total bearing force of the internal bearing spring 4 is 8590.3N, and the corresponding vertical equivalent modulus of the entire displacement device is 3.03MPa.

[0068] In this embodiment, the tension spring 31 is made of spring steel with a free length of 25mm and a stiffness coefficient k=0.37N / mm. Under the 25mm limit working range, the spring tension is 9.25N, corresponding to a displacement measurement sensitivity of 39.3pm / mm for the fiber optic grating 35.

[0069] In this embodiment, the tension spring 31 has a pre-tension of 5mm after assembly, corresponding to an initial pre-tightening force of approximately 1.85N; the initial Bragg wavelength of the fiber grating 35 is set in the middle of the demodulation equipment's range, thereby ensuring that when the road surface undergoes vertical displacement changes within a range of ±5mm, the fiber grating 35 is always under tension, and the wavelength drift direction maintains a monotonic correspondence with the displacement direction.

[0070] In this embodiment, the load-bearing compression spring 4 is made of 55CrSi or 50CrVA material, with structural specifications of 14mm wire diameter, 95mm outer diameter, 88mm free height, and 28mm pitch; its spring stiffness coefficient k=357N / mm, and under a limit displacement of 25mm, the maximum elastic force that a single compression spring can withstand is 8925N, and the maximum shear stress τ of the compression spring material is 847MPa, which is less than the yield strength of the material of 1100MPa.

[0071] Example 2:

[0072] A method for manufacturing a fiber optic grating vertical displacement device for asphalt pavement as described in Embodiment 1 includes the following steps:

[0073] S1. Parameter matching and selection design: Based on the standard axle load and material modulus of asphalt pavement, determine the stiffness requirements of displacement equipment, select the specifications of load-bearing compression spring 4 and tension spring 31, and determine the wavelength-strain calibration relationship of fiber optic grating 35.

[0074] S2. Housing assembly processing: Processing the upper housing 1, lower housing 2 and side cable outlet 22;

[0075] S3. Assembly of tension spring sensing component 3: The lower end of tension spring 31 is connected to the upper end of fiber optic grating sensing component 32. The transmission fiber 33 is fixed at the position of the axis of the fiber optic grating sensing component 32. The transmission fiber 33 is fixed in the connecting groove of fiber optic grating sensing component 32 by high temperature resistant epoxy adhesive. The adhesive length is not less than 10mm, so that the fiber optic grating 35 segment is positioned in the middle of the effective working segment of elastic bearing part 34.

[0076] S4. Coaxial assembly: Install the load-bearing compression spring 4 into the lower housing 2, and then install the tension spring sensing component 3 inside the load-bearing compression spring 4, keeping the two coaxial;

[0077] S5. Pre-stretch assembly: The transmission optical fiber 33 is fitted with an armored sheath and passed through the lower housing 2 side to the outlet port 22; the upper end of the tension spring 31 is connected to the upper housing 1, and a pre-stretch force is applied to the tension spring 31 so that its elongation reaches 15% to 25% of the working range. Then the upper housing 1 and the lower housing 2 are assembled and locked in the pre-stretch position.

[0078] S6. Calibration and Protection: Perform displacement-wavelength calibration on the assembled displacement equipment and apply anti-corrosion and high-temperature resistant treatment to the outer shell surface.

[0079] The manufacturing method of this invention involves: S1 Precisely selecting the load-bearing compression spring 4 and tension spring 31 according to the road load to dynamically match the overall modulus of the displacement device with the road material, ensuring that the sensor is in the optimal linear response range; S2-S4 Coaxial assembly to ensure that the load-bearing path and sensing path are highly coincident, avoiding off-center loading errors and ensuring that the fiber optic grating 35 is accurately located within the effective working section of the elastic bearing part 34, achieving precise linear transmission of displacement-strain; S5 The transmission optical fiber 33 is fitted with an armored protective layer that passes through the lateral outlet port 22 of the lower shell 2, effectively resisting high-temperature rolling and impact during paving, preventing moisture and dust intrusion, and ensuring structural integrity and sealing under harsh construction environments; S6 Eliminating assembly errors through whole-machine calibration, combined with anti-corrosion and high-temperature resistant coating treatment, enabling the displacement device to meet the requirements of high-temperature construction and long-term heavy-load service of asphalt pavement, achieving high-precision long-term real-time monitoring of road settlement.

[0080] In this embodiment, in step S3, the transmission optical fiber 33 is fixed to the fiber optic grating sensing component 32 using an adhesive bonding process, so that the fiber optic grating 35 segment is located within the effective working segment of the tension spring 31.

[0081] In another embodiment, in S5, a metal protective tube is embedded in the side outlet port 22, and the transmission optical fiber 33 is led out through the metal protective tube. At the innermost part of the outlet channel, near the fusion splice and the bare optical fiber, high-temperature resistant silicone rubber is first injected as a stress buffer layer. The outside of the channel is filled with high-temperature resistant epoxy resin for potting and sealing. The transmission optical fiber 33 outside the outer shell is covered with an armored sheath, and the end of the armored sheath is embedded in high-temperature resistant epoxy resin for stress anchoring.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A vertical displacement device for fiber optic gratings on asphalt pavement, characterized in that: The device includes a relatively movable upper housing (1) and a lower housing (2). A load-bearing compression spring (4) and a tension spring sensing assembly (3) are provided between the upper housing (1) and the lower housing (2). The tension spring sensing assembly (3) is arranged along the central axis of the load-bearing compression spring (4). The tension spring sensing assembly (3) includes a tension spring (31) connected vertically and a fiber optic grating sensing assembly (32). A transmission fiber (33) is fixedly provided inside the fiber optic grating sensing assembly (32). The transmission fiber (33) extends from one side of the lower housing (2) for connection with a fiber optic grating demodulation device. The fiber grating sensing component (32) includes an elastic support part (34), and a fiber grating (35) is provided on the transmission fiber (33). The fiber grating (35) is placed in the elastic support part (34). The tension spring (31) has a pre-tension amount in the installed state, so that the tension spring (31) is always in a tensile working state within the measurement range. The pre-tension amount corresponds to the extension amount of the tension spring being 15% to 25% of its working range, and the pre-tension amount is configured to make the Bragg wavelength of the fiber grating (35) located in a preset wavelength range.

2. The fiber optic grating vertical displacement device for asphalt pavement according to claim 1, characterized in that: One end of the tension spring (31) is detachably connected to the upper housing (1), and the other end of the tension spring (31) is connected to the fiber optic grating sensing assembly (32). The end of the fiber optic grating sensing assembly (32) away from the tension spring (31) is connected to the lower housing (2).

3. The fiber optic grating vertical displacement device for asphalt pavement according to claim 2, characterized in that: The fiber optic grating sensing component (32) has a connecting groove along the axial direction, and the transmission optical fiber (33) is arranged along the connecting groove.

4. The fiber optic grating vertical displacement device for asphalt pavement according to claim 1, characterized in that: Multiple transverse slots are formed on both sides of the fiber optic grating sensing component (32) to form the elastic support portion (34).

5. The fiber optic grating vertical displacement device for asphalt pavement according to claim 4, characterized in that: The transverse grooves on both sides are arranged in an intersecting pattern.

6. The fiber optic grating vertical displacement device for asphalt pavement according to claim 1, characterized in that: The lower housing (2) has a lateral cable outlet port (22) on one side, and a metal protective tube (36) is provided at the lateral cable outlet port (22). The transmission optical fiber (33) is led out from the metal protective tube (36), and the transmission optical fiber (33) is encapsulated with the metal protective tube (36).

7. The vertical displacement device for asphalt pavement fiber optic gratings according to claim 6, characterized in that: A high-temperature resistant protective sleeve is fitted onto the transmission optical fiber (33) outside the lower housing (2).

8. The fiber optic grating vertical displacement device for asphalt pavement according to claim 1, characterized in that: The upper housing (1) includes an upper pressure plate (11) and a connecting hole structure (13). The center of the lower surface of the upper pressure plate (11) is a top limiting area (12). The connecting hole structure (13) is located in the top limiting area (12). The connecting hole structure (13) is detachably connected to the tension spring (31). The lower housing (2) includes a lower pressure plate (23) and a lower cover (21) placed on the lower pressure plate (23).

9. The fiber optic grating vertical displacement device for asphalt pavement according to claim 8, characterized in that: The upper pressure plate (11) has a shell cover (14) on its outer periphery at the bottom, and a receiving space is formed between the shell cover (14) and the shell cover (21).

10. A method for manufacturing a vertical displacement device for asphalt pavement fiber optic gratings as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Parameter matching and selection design: Based on the standard axle load and material modulus of asphalt pavement, determine the stiffness requirements of displacement equipment, select the specifications of load-bearing compression spring (4) and tension spring (31), and determine the wavelength-strain calibration relationship of fiber optic grating (35); S2. Outer shell assembly processing: Process the upper shell (1), lower shell (2) and side cable outlet (22); S3. Assembly of tension spring sensing component (3): The lower end of tension spring (31) is connected to the upper end of fiber optic grating sensing component (32). The transmission fiber (33) is fixed at the position of the axis line through which the transmission fiber (33) passes. The transmission fiber (33) is fixed in the connecting groove of fiber optic grating sensing component (32) by high temperature resistant epoxy adhesive. The adhesive length is not less than 10mm, so that the fiber optic grating (35) segment is positioned in the middle of the effective working segment of the elastic bearing part (34). S4. Coaxial assembly: Install the load-bearing compression spring (4) into the lower housing (2), and then install the tension spring sensing component (3) inside the load-bearing compression spring (4) to keep them coaxial; S5. Pre-stretch assembly: The transmission optical fiber (33) is covered with an armored sheath and passes through the lower housing (2) to the outlet port (22); the upper end of the tension spring (31) is connected to the upper housing (1), and a pre-stretch force is applied to the tension spring (31) so that its elongation reaches 15% to 25% of the working range. Then the upper housing (1) and the lower housing (2) are assembled and locked in the pre-stretch position. S6. Calibration and Protection: Perform displacement-wavelength calibration on the assembled displacement equipment and apply anti-corrosion and high-temperature resistant treatment to the outer shell surface.

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