Ultrahigh-precision fiber grating displacement sensor

Abstract

The utility model provides an ultrahigh-precision fiber grating displacement sensor, which can realize high-precision displacement measurement, is provided with double-end outgoing lines, and can realize multi-sensor series monitoring. Comprising a housing and an optical fiber arranged in the housing, the optical fiber is engraved with a strain grating and a temperature compensation grating which are connected through an optical cable, two ends of the housing are provided with wire pressing terminals, the wire pressing terminals are sleeved with protective sleeves, the inner bottom surface of the housing is oppositely provided with temperature compensation terminals and adjusting terminals at intervals, and the temperature compensation grating is arranged on the temperature compensation terminals. The strain grating is arranged between the temperature compensation terminal and the adjusting terminal, the adjusting terminal is movably arranged in the stretching direction of the strain grating, an outer pipe is installed at the outer end of the housing, a pull rod used for being connected with a measured piece is arranged in the outer pipe, the pull rod moves in the axial direction of the outer pipe, and a steel wire rope connected with the adjusting terminal penetrates through the housing and the outer pipe and then is connected with one end of a spring. The other end of the spring is connected with the pull rod.

Description

Technical Field

[0001] The utility model relates to the field of optical fiber grating sensors, in particular to an ultra-high precision optical fiber grating displacement sensor. Background Art

[0002] Fiber Bragg grating (FBG) sensor technology originated in the mid-1980s, when scientists discovered that a periodic refractive index modulation structure could be written into optical fibers using ultraviolet light, forming a so-called fiber Bragg grating (FBG). This grating structure effectively reflects specific wavelengths of light while transmitting others, making it useful for applications such as wavelength selection and filtering. Subsequently, it was discovered that the reflected wavelength of a FBG shifts when subjected to external strain or temperature changes. FBGs began to be used to measure physical quantities such as strain and temperature, and since their invention, they have been widely used in the field of fiber-optic sensing.

[0003] Displacement detection is one of the most fundamental measurement techniques used in construction monitoring and long-term health monitoring of major engineering structures such as bridges, tunnels, dams, underground projects, and slopes. Currently, the displacement meters commonly used in civil engineering are mostly resistance strain gauges and vibrating wire displacement meters. However, these traditional displacement meters have limitations due to their poor electromagnetic interference resistance, lightning strike resistance, limited transmission distance, and low long-term stability and reliability. Fiber Bragg grating (FBG) sensors, however, are gaining increasing attention due to their advantages, including electromagnetic interference resistance, corrosion resistance, electrical insulation, high sensitivity, low cost, and good compatibility with conventional optical fibers.

[0004] Fiber Bragg gratings (FBGs) have the advantages of being compact, explosion-proof, electrically insulated, resistant to electromagnetic interference, highly accurate, reliable, and environmentally adaptable, making them suitable for use in complex working environments. Chinese patent number CN111537119B, "A High-Precision Fiber Bragg Grating Displacement Meter with Temperature Compensation," states that the FBG and pull rod are coaxial, allowing for single-ended wiring and preventing the use of multiple sensors in series for monitoring. Furthermore, this structure utilizes a fiber optic base and FBG structure, with the base fixed at only one end and the other directly connected to a spring. This approach is susceptible to vibration during use, leading to inaccurate test results. Furthermore, the process of gluing the optical fiber to the base limits the fiber's displacement to the base, preventing ultra-high-precision monitoring. In the Chinese patent "A Fiber Bragg Grating Displacement Meter" with patent number ZL 201120286959.8, a steel wire rope and a fixed pulley are used to cleverly realize the conversion between the displacement to be measured and the displacement of the free end of the equal-strength beam. However, this method has a complex structure and high risks in field application. At the same time, this method is to stick the entire optical fiber to the equal-strength beam, which will cause the accuracy of the optical fiber to be limited by the equal-strength beam, resulting in low accuracy.

[0005] In summary, the detection accuracy of existing fiber Bragg grating displacement sensors is low and cannot meet the ultra-high precision requirements. At the same time, many existing fiber Bragg grating displacement sensors are single-ended and cannot realize multi-sensor series monitoring. Therefore, it is particularly important to produce a high-precision fiber Bragg grating sensor with double-ended output. Utility Model Content

[0006] In response to the above problems, the present invention provides an ultra-high precision fiber Bragg grating displacement sensor, which can achieve high-precision displacement measurement and has double-ended output lines, enabling multi-sensor series monitoring.

[0007] The utility model adopts the following technical solution: an ultra-high precision fiber Bragg grating displacement sensor, comprising a cover shell, an optical fiber arranged in the cover shell, a strain grating and a temperature compensation grating connected by an optical cable engraved on the optical fiber, crimping terminals are provided at both ends of the cover shell, a protective sleeve is sheathed on the outside of the crimping terminal, a temperature compensation terminal and an adjustment terminal are arranged on the bottom surface of the cover shell at intervals, the temperature compensation grating is arranged on the temperature compensation terminal, the strain grating is arranged between the temperature compensation terminal and the adjustment terminal, the adjustment terminal is movably arranged along the tensile direction of the strain grating, an outer tube is provided at the outer end of the cover shell, a pull rod for connecting to a measured piece is provided in the outer tube, and the pull rod moves axially along the outer tube, a wire rope connected to the adjustment terminal passes through the cover shell and the outer tube and is connected to one end of a spring, and the other end of the spring is connected to the pull rod.

[0008] Furthermore, the crimping terminal and the outer tube are both threadedly connected to the cover; the cover comprises a bottom shell and an upper cover, the bottom shell is a frame-shaped structure with an opening at the top, and the upper cover is detachably assembled on the top of the bottom shell;

[0009] Furthermore, the temperature compensating terminal and the regulating terminal are both Z-shaped, and the temperature compensating terminal and the regulating terminal are symmetrically arranged in the housing;

[0010] Furthermore, the temperature compensation terminal and the adjustment terminal are both assembled to the bottom surface of the housing through fasteners. The bottom surface of the adjustment terminal is provided with a waist-shaped hole. The adjustment terminal is slidably assembled between the waist-shaped hole and the fastener. The adjustment terminal is provided with a fixing hole. One end of the steel wire rope is fixed in the fixing hole.

[0011] Furthermore, the tail end of the outer tube is provided with an internal thread, the limiting tube is threadedly connected to the inner side of the outer tube, and the tail end of the pull rod is sleeved in the limiting tube;

[0012] Furthermore, the outer tube and the limiting tube are provided with notches, and a limiting hole is provided on the pull rod at the position corresponding to the notch, and the limiting post passes through the notch and is threadedly connected to the limiting hole; the tail end of the pull rod is provided with an internal thread to connect with the measured object;

[0013] Furthermore, the lead wire crimped with the crimping terminal is led out from the protective cover, the lead wire is an armored optical cable, and the protective cover is made of PVC rubber;

[0014] Furthermore, the temperature compensating terminal, the adjusting terminal and the spring are all made of 316L stainless steel; the wire pressing terminal, the cover, the steel wire rope, the outer tube, the pull rod, the limit tube and the limit column are all made of 304 stainless steel.

[0015] The beneficial effect of the present invention is that the pull rod connected to the measured object moves axially along the outer tube, and the pull rod is connected to the adjustment terminal provided with the strain grating through the spring and the steel wire rope. The displacement of the measured object will drive the spring and the steel wire rope to deform, and then pull the adjustment terminal to cause it to deform. The stretching and compression of the strain grating affects the wavelength change of the internal light, and ultimately can reflect the external displacement change with high precision. In addition, the temperature compensation grating can perform temperature compensation on the strain grating, thereby eliminating the influence of temperature on displacement monitoring, and has good use value. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a three-dimensional structural diagram of the utility model;

[0017] Figure 2 It is the main view of the utility model;

[0018] Figure 3 yes Figure 2 AA section view.

[0019] Figure 4 It is a structural diagram of the adjustment terminal in the utility model.

[0020] Explanation of the accompanying symbols: 1. Wire crimping terminal; 2. Protective cover; 3. Bottom shell; 4. Upper cover; 5. Temperature compensation grating; 6. Temperature compensation terminal; 7. Strain grating; 8. Fastener; 9. Adjustment terminal; 10. Wire rope; 11. Outer tube; 12. Spring; 13. Pull rod; 14. Limiting tube; 15. Limiting column; 16. Notch; 17. Limiting hole; 91. Strain grating pasting surface; 92. Fixing hole; 93. Waist-shaped hole. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] like Figures 1 to 4 As shown, the utility model is an ultra-high precision fiber Bragg grating displacement sensor, comprising a housing, an optical fiber arranged in the housing, a strain grating 7 and a temperature compensation grating 5 connected by an optical cable are engraved on the optical fiber, the temperature compensation grating 5 and the strain grating 7 are two grating areas on the same optical fiber, both ends of the housing are equipped with a wire pressing terminal 1, the outer sleeve of the wire pressing terminal 1 is covered with a protective cover 2 for protecting the fixed lead, the wire pressing terminal 1, the lead and the protective cover 2 are each two, ensuring that the sensor has two-end outlets, thereby realizing series monitoring of the sensor; the bottom surface of the housing is relatively spaced apart with a temperature compensation terminal 6 and an adjustment terminal 9, the temperature compensation grating 5 is attached to the temperature compensation terminal 6, and the strain grating 7 is arranged on the temperature compensation terminal 6. The strain grating 7 is suspended between the terminal 6 and the adjustment terminal 9. The strain grating 7 is fixedly pasted, that is, one end of the strain grating 7 is pasted and fixed on the temperature compensation terminal 6, and the other end of the strain grating 7 is pasted on the strain grating pasting surface 91 of the adjustment terminal 9; the adjustment terminal 9 is movably arranged along the tensile direction of the strain grating 7, and the outer end of the cover is equipped with an outer tube 11. The outer tube 11 is provided with a pull rod 13 for connecting to a test piece (not shown in the figure), and the pull rod 13 moves axially along the outer tube 11. The wire rope 10 connected to the adjustment terminal 9 passes through the cover and the outer tube 11 and is connected to one end of a spring 12. The other end of the spring 12 is connected to the pull rod 13 by welding.

[0023] The crimping terminal 1 and the outer tube 11 are both threadedly connected to the cover; the cover includes a bottom shell 3 and an upper cover 4. The bottom shell 3 is a frame-shaped structure with an opening at the top. The upper cover 4 can be detachably assembled on the top of the bottom shell 3 to ensure sealing and protect internal key components.

[0024] The temperature compensating terminal 6 and the adjusting terminal 9 are both Z-shaped and are symmetrically arranged in the cover; the temperature compensating terminal 6 and the adjusting terminal 9 are both assembled to the bottom surface of the cover by fasteners 8 (such as screws), and a waist-shaped hole 93 is provided on the bottom surface of the adjusting terminal 9. The adjusting terminal 9 is slidably assembled between the waist-shaped hole 93 and the fastener 8. A fixing hole 92 is provided on the adjusting terminal 9, and one end of the wire rope 10 is fixed to the fixing hole 92.

[0025] An internal thread is provided at the tail end of the outer tube 11, and the limiting tube 14 is threadedly connected to the outer tube 11. The tail end of the pull rod 13 is sleeved in the limiting tube 14. The limiting tube 14 is used to limit the pull rod 13 to prevent it from being pulled out of the outer tube 11; a notch 16 is provided on the outer tube 11 and the limiting tube 14, and a limiting hole 17 is provided on the pull rod 13 corresponding to the position of the notch 16. The limiting column 15 passes through the notch 16 and is threadedly connected to the limiting hole 17. The limiting column 15 is used to limit the pull rod 13 when it is compressed, pressing the pull rod 13 into the outer tube 11 to avoid damaging the internal structure; an internal thread is provided at the tail end of the pull rod 13 to connect with the test piece.

[0026] The strain grating 7 uses a high-strength femtosecond grating with a wavelength variation of up to 30nm, which can ensure the resolution accuracy of the sensor reaches 0.3%. 00 (0.3 per ten thousand); the temperature compensating grating 5 is used to compensate for the deviation of the strain grating 7 caused by the influence of temperature, thereby ensuring the accuracy of the sensor measurement; the lead wire (not shown in the figure) crimped with the wire crimping terminal 1 is led out from the protective cover 2, the lead wire is an armored optical cable, the lead wire is used to protect the internal optical fiber, and the protective cover 2 is made of PVC rubber; the temperature compensating terminal 6, the adjustment terminal 9, and the spring 12 are all made of 316L stainless steel; the wire crimping terminal 1, the cover, the wire rope 10, the outer tube 11, the pull rod 13, the limit tube 14 and the limit column 15 are all made of 304 stainless steel, thereby ensuring the corrosion resistance of the sensor and increasing its service life.

[0027] The utility model has a simple overall structure and is quick to install. It can monitor the displacement of cracks, landslides, etc., and reflects the external displacement changes through the stretching and compression of the high-strength strain grating 7. The strain grating 7 is a femtosecond grating, which is sensitive and has high precision, solving the problems of low precision and inaccurate measurement of existing sensors. At the same time, all accessories are made of rust-proof and waterproof materials, which overcomes the problems of condensation and electromagnetic interference inside the sensor in humid air, greatly prolongs the service life of the sensor, and improves the reliability of the sensor. Specifically, when using it, first connect the fiber Bragg grating displacement sensor to the measured object, and then Then, when there are external displacement changes such as cracks, the external displacement will act on the pull rod 13, and the adjustment terminal 9, wire rope 10, spring 12 and pull rod 13 are connected together. When the pull rod 13 is displaced, it will cause the spring 12 and wire rope 10 to deform, and then pull the adjustment terminal 9 to deform, and then stretch / compress the strain grating 7, affecting the wavelength change of the internal light, and finally reflecting the external displacement change, providing a large amount of ultra-high precision data for subsequent displacement monitoring; and the temperature compensation grating 5 can perform temperature compensation on the high-strength strain grating 7 to eliminate the influence of temperature on displacement monitoring.

[0028] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed within the present invention. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0029] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. An ultra-high-precision fiber Bragg grating displacement sensor, comprising a housing and an optical fiber disposed within the housing, characterized in that: The optical fiber is engraved with a strain grating and a temperature compensation grating connected by an optical cable, and both ends of the cover are equipped with a wire crimping terminal, and the outside of the wire crimping terminal is covered with a protective sleeve. The inner bottom surface of the cover is provided with a temperature compensation terminal and an adjustment terminal. The temperature compensation grating is provided on the temperature compensation terminal, and the strain grating is provided between the temperature compensation terminal and the adjustment terminal. The adjustment terminal is movably provided along the tensile direction of the strain grating. The outer end of the cover is provided with an outer tube, and a pull rod for connecting to the test piece is provided in the outer tube, and the pull rod moves axially along the outer tube. The steel wire rope connected to the adjustment terminal passes through the cover and the outer tube and is connected to one end of the spring, and the other end of the spring is connected to the pull rod.

2. The ultra-high precision fiber Bragg grating displacement sensor according to claim 1, characterized in that: The crimping terminal and the outer tube are both threadedly connected to the cover shell; the cover shell includes a bottom shell and an upper cover, the bottom shell is a frame-shaped structure with an opening on the top, and the upper cover can be detachably assembled on the top of the bottom shell.

3. The ultra-high precision fiber Bragg grating displacement sensor according to claim 1, characterized in that: The temperature compensating terminal and the regulating terminal are both Z-shaped, and the temperature compensating terminal and the regulating terminal are symmetrically arranged in the cover.

4. The ultra-high precision fiber Bragg grating displacement sensor according to claim 1, characterized in that: The temperature compensation terminal and the adjustment terminal are both assembled on the bottom surface of the cover shell through fasteners. The bottom surface of the adjustment terminal is provided with a waist-shaped hole. The adjustment terminal is slidably assembled between the waist-shaped hole and the fastener. The adjustment terminal is provided with a fixing hole, and one end of the steel wire rope is fixed in the fixing hole.

5. The ultra-high precision fiber Bragg grating displacement sensor according to claim 1, characterized in that: The tail end of the outer tube is provided with an internal thread, the limiting tube is threadedly connected to the inner side of the outer tube, and the tail end of the pull rod is sleeved in the limiting tube.

6. The ultra-high precision fiber Bragg grating displacement sensor according to claim 5, characterized in that: Notches are provided on the outer tube and the limiting tube, and a limiting hole is provided on the pull rod corresponding to the notch position. The limiting column passes through the notch and is threadedly connected to the limiting hole; the tail end of the pull rod is provided with an internal thread to connect with the measured part.

7. The ultra-high precision fiber Bragg grating displacement sensor according to claim 1, characterized in that: The lead wire crimped with the crimping terminal is led out from the protective cover. The lead wire is an armored optical cable, and the protective cover is made of PVC rubber.

8. The ultra-high precision fiber Bragg grating displacement sensor according to claim 6, characterized in that: The temperature compensation terminal, adjustment terminal, and spring are all made of 316L stainless steel; the wire pressing terminal, cover, wire rope, outer tube, pull rod, limit tube, and limit column are all made of 304 stainless steel.

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