A sensitized adjustable-precision fiber grating micro-displacement sensor and a sensing method thereof

Abstract

The application discloses a kind of sensitized adjustable precision fiber grating micro-displacement sensor and its sensing method, including sensor shell, movable lever mechanism, measuring device.In movable lever mechanism: hollow sleeve rod is sleeved on cylindrical guide rail by sliding support, cylindrical guide rail is connected with fixed support fixed rod, and the other end is fixed in the inner wall of shell, sliding support can move along cylindrical guide rail, short rotary lever is hinged with sliding support and long rotary lever respectively, long rotary lever is hinged with fixed support and circular arc toothed curve rod respectively.Measuring device: strip-shaped toothed plate is closely engaged with circular arc toothed curve rod, strip-shaped toothed plate is fixed with equal strength beam, and two gratings are respectively located on the tension and compression surface of equal strength beam.Finally, the micro displacement of the external to be measured is converted into the displacement of circular arc toothed curve rod, which drives the bending of equal strength beam, and the displacement change quantity after amplification is obtained by fiber grating.The application can measure micro displacement, and has the advantages of simple structure, convenient use and high precision.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic grating sensing technology, and relates to an enhanced-sensitivity, adjustable-precision fiber optic grating micro-displacement sensor and its sensing method. Background Technology

[0002] Since the 1970s and 80s, fiber optic sensing technology, a novel sensing technology that uses light as a carrier and optical fiber as a medium to sense various external objects and perform precise quantitative measurement and monitoring of multiple parameters in time and space, has developed rapidly and been widely applied. Due to its advantages such as strong resistance to electromagnetic interference, ability to correct for ambient temperature, small size and light weight, ease of industrial production and reusability, it has gradually replaced traditional sensing technologies in various fields such as medicine, materials, hydraulic engineering, construction, and mining.

[0003] Existing displacement sensors often directly transmit actual displacement to deformation detection mechanisms, but for some minute displacements, they may have insufficient accuracy, leading to large errors in the measurement results. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of the prior art mentioned above. By providing a range-adjustable fiber optic grating micro-displacement sensor and its sensing method, it relies on a mechanical transmission structure to amplify the minute external displacement, thereby achieving accurate measurement.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A sensitivity-enhanced, adjustable-precision fiber Bragg grating micro-displacement sensor, comprising a sensor housing 1, a movable lever mechanism within the housing, and a measuring device; wherein:

[0007] The sensor housing 1 is a cuboid box. A through hole 13 is provided at the rear end of one long side plate of the box for mounting a hollow sleeve rod 8. A fixed support rod 12 is fixed at the rear end of the other side plate of the box. The fixed support rod 12 corresponds to the through hole 13, and a fixed support 6, a cylindrical guide rail 10, a sliding support 7, and a hollow sleeve rod 8 are sequentially arranged between the fixed support rod 12 and the through hole 13. Two fiber optic through holes 14 and 15 are provided on the short front side plate of the box for passing through optical fibers 21. An equal-strength beam fixing plate 11 is fixed in the middle of the inner surface of the front front plate of the box. The equal-strength beam fixing plate 11 is arranged along the length of the box, and its top is fixedly connected to the bottom of the equal-strength beam 2.

[0008] The movable lever mechanism is the main structure of this invention, primarily comprising: a cylindrical guide rail 10, a fixed support 6, a sliding support 7, a hollow sleeve rod 8, a long rotating rod 4, a short rotating rod 5, and a fixed support fixing rod 12. The hollow sleeve rod 8 is inserted into the sensor housing 1 through the through hole 13 and then sleeved onto the cylindrical guide rail 10 via the sliding support 7. The hollow sleeve rod 8 and the sliding support 7 are fixedly connected, and the diameter of the central through hole of the hollow sleeve rod 8 and the sliding support 7 is larger than the outer diameter of the cylindrical guide rail 10. The other end of the cylindrical guide rail 10 is connected to one end of the fixed support fixing rod 12 via the fixed support 6, and the other end of the fixed support fixing rod 12 is fixed to the inner surface of the long side plate of the sensor housing 1. After installation, the hollow sleeve rod 8, the cylindrical guide rail 10, and the fixed support fixing rod 12 are arranged parallel to the wide side direction of the sensor housing 1. The sliding support 7 has a through hole 71 at its center and is mounted on the cylindrical guide rail 10, allowing it to move back and forth along the guide rail 10, which is also the direction of displacement measurement. The fixed support 6 has blind holes on both sides of its center, for mounting the ends of the fixed support rod 12 and the cylindrical guide rail 10 respectively. The other end of the cylindrical guide rail 10 is connected to the hollow sleeve rod 8. The short rotating rod 5 has holes at both ends and is hinged to the sliding support 7 and the long rotating rod 4 via pins. The long rotating rod 4 has a hole at one end, which is hinged to the fixed support 6 via a pin, and this end can rotate around the pin. The other end of the long rotating rod 4 is fixedly connected to one side of the arc-shaped toothed rod 3. A groove is left in the middle of the long rotating rod 4 as a space for hinged connection with the short rotating rod 5. A series of parallel and equidistant pin holes 42 are provided on both sides of the groove. The short rotating rod 5 changes its range by connecting different pin holes 42. The sliding support 7 only generates displacement along the cylindrical guide rail 10, so that the movement direction of the sliding support 7 is consistent with the measurement direction, which refers to the axial direction of the cylindrical guide rail 10.

[0009] The measuring device includes an arc-shaped toothed rod 3, a strip-shaped toothed plate 9, an equal-strength beam 2, an optical fiber 21, and a first grating 22 and a second grating 23 on the optical fiber, meaning the invention includes two fiber optic grating sensors. When the sliding support 7 moves, it drives the long and short rotating rods to rotate. The arc-shaped toothed rod 3, connected to the end of the long rotating rod 4, rotates around the fixed support 6, amplifying the displacement of the sliding support 7 into the rotation distance of the arc-shaped toothed rod 3. This then converts the small external displacement to be measured into the displacement of the sliding support 7 through the hollow pressure rod 8. The sliding support 7, the long rotating rod 4, the short rotating rod 5, and the arc-shaped toothed rod 3 constitute a sliding body. The top of the strip-shaped toothed plate 9 is tightly engaged with the other side of the arc-shaped toothed rod 3, and the bottom of the strip-shaped toothed plate 9 is fixedly connected to the equal-strength beam 2. The first grating 22 and the second grating 23 are located on the tension and compression surfaces of the equal-strength beam 2, respectively. The first grating 22 and the second grating 23 are connected to an external optical signal demodulation device via optical fiber 21 passing through fiber optic holes 14 and 15, respectively, to convert the optical signal into an electrical signal. The two gratings have equal strain sensitivities but opposite signs, and different temperature and strain sensitivities; therefore, temperature and strain can be separated using an external temperature compensation method. After the arc-shaped toothed rod 3 undergoes displacement, the strip-shaped toothed plate 9 causes the equal-strength beam 2 to bend. The amplified displacement change is then measured using a fiber optic grating attached to the equal-strength beam 2.

[0010] Furthermore, the connections between the long rotating rod 4 and the fixed support 6, the short rotating rod 5 and the sliding support 7, and the short rotating rod 5 and the long rotating rod 4 are all pin connections, ensuring free rotation between the components. Specifically: the long rotating rod 4 has a long rotating rod pin hole 41 at its end, which is connected to the fixed support pin hole 61 of the fixed support 6 by a pin. The short rotating rod 5 is a rod-shaped structure, with a short rotating rod pin hole 51 and a short rotating rod pin hole 52 at its two ends, respectively. The short rotating rod pin hole 51 is connected to the long rotating rod pin hole 42 by a pin, and the short rotating rod pin hole 52 is connected to the sliding support pin hole 72 of the sliding support 7 by a pin.

[0011] Furthermore, the fixed support 6 is a cylindrical structure with a fixed support blind hole 62 at the center and a fixed support pin hole 61 on the side wall. The fixed support blind hole 62 is used to install the end of the cylindrical guide rail 10.

[0012] Furthermore, the hollow sleeve rod 8 includes a top circular protrusion and a hollow sleeve rod post 82. The outer diameter of the circular protrusion is larger than the diameter of the through hole 13 at the rear end of the side plate of the box. The hollow sleeve rod post 81 is sleeved with the cylindrical guide rail 10.

[0013] Furthermore, the pin holes reserved in the middle of the long rotating rod 4 for connecting with the short rotating rod 5 are a series of equidistant through holes on both sides, serving as pin holes 42 for the long rotating rod. By connecting with different pin holes, the length of the lever arm is adjusted, thereby changing the efficiency of the linear displacement from the sliding support 7 to the arc-shaped toothed rod 3, thus achieving the purpose of changing the range. Furthermore, the sliding support 7 is a rotating structure with a central circular through hole 71. The diameter of the through hole 71 is slightly larger than the diameter of the cylindrical guide rail 10, and the two are lubricatedly fitted together. The bottom of the sliding support 7 is fixedly connected to the hollow sleeve rod 8. That is, the cylindrical guide rail 10 is fitted onto the hollow sleeve rod 8, and the bottom of the sliding support 7 is fixedly connected to the hollow sleeve rod 8, with the two moving synchronously.

[0014] Furthermore, the arc-shaped toothed rod 3 and the strip-shaped toothed plate 9 are tightly meshed by teeth, simplifying the geometric model so that the arc and the straight line are tangent to each other.

[0015] Furthermore, the arc-shaped toothed rod 3 has a fixed blind hole 31 on one side for mounting the end of the long rotating rod 4.

[0016] Furthermore, the top of the box is provided with a top plate.

[0017] A sensing method for a sensitivity-enhanced, adjustable-precision fiber Bragg grating micro-displacement sensor includes the following steps:

[0018] Step 1, Installation and Fixing: Before operation, ensure the annular protrusion of the hollow sleeve rod 8 is tightly pressed against the surface to be monitored, guaranteeing that external micro-displacements are completely converted into displacements of the sliding body. Generally, the sensor housing can be completely fixed to a plane perpendicular to the surface to be monitored using a U-shaped groove or other methods.

[0019] The second step is temperature compensation: the first fiber grating 22 is attached to the tension surface of the equal strength beam 2, ensuring that it is parallel to the axis of the equal strength beam 2; the second fiber grating 23 is attached to the compression surface of the equal strength beam 2, and the two gratings have different properties.

[0020] The third step is displacement measurement: For this mechanism, by measuring the center wavelength drift of the first fiber grating 22 and the second fiber grating 23, the axial strain of the first grating caused solely by the bending of the equal-strength beam 2 can be calculated.

[0021] For the first fiber grating 22, the calculation is performed according to the following formula:

[0022]

[0023] Where, Δλ B1 λ is the change in the center wavelength of the fiber grating. B1 P is the center wavelength of the grating; e1α1 and ζ1 are the effective photoelastic coefficient, thermal expansion coefficient and thermo-optic coefficient of the grating, respectively. They are all constants related to the grating material. When selecting, the material constants of the first and second gratings should be different. ε1 and ΔT1 are the axial displacement and temperature change of the grating, respectively.

[0024] For the second fiber grating 23, the axial strain and temperature variables are obtained using the same formula:

[0025]

[0026] The meanings of each letter are explained in the same way as in formula (1).

[0027] Combining the measurement data of the two gratings above, and according to the external temperature compensation method, ε represents the axial strain of the grating. Since they have the same value but opposite signs, the temperature and strain can be separated using the following equation:

[0028]

[0029] Among them, K B1,T K B2,T These are the temperature sensitivities of the two gratings, K. B1,s K B2,s The sensitivities of the two gratings to strain are calculated using the following formulas:

[0030] K B,T =α+ζ

[0031] K B,s =1-P e

[0032] Step 4, Displacement Amplification: For the displacement transmitted to the sliding support 7 via the hollow sleeve 8, the principle is explained using the following geometric model (e.g. Figure 12 As shown):

[0033] The movable lever mechanism has an initial state during installation, such that the initial distance between the sliding support 7 and the fixed support 6 is l0, and the initial installation angle between the long rotating rod and the cylindrical guide rail 10 is θ0. One of the series of pin holes 42 on the long rotating rod is selected as the initial installation position, such that the installation position of the short rotating rod 5 on the long rotating rod 4 is b from the fixed support 6. Furthermore, the lengths of the long rotating rod 5 and the short rotating rod 4, R and a respectively, remain constant throughout the installation process.

[0034] Taking the displacement under pressure as an example, the hollow sleeve rod 8 moves into the sensor, and the displacement generated by the sliding support 7 after being compressed is Δl. The movable lever mechanism drives the short rotating rod 5 and the long rotating rod 4 to rotate, and after rotation, the angle between the long rotating rod 4 and the cylindrical guide rail 10 is θ1.

[0035] a, b, R, l0, and θ0 represent the short rotating rod, Δl represents the sliding support, and θ1 represents the long rotating rod. According to the cosine theorem, the initial installation angle θ0 can be determined by the lengths of the three sides:

[0036]

[0037] After the sliding support 7 transmits the external displacement, it moves a distance Δl along the cylindrical guide rail 10, and the position of the sliding support 7 becomes (l0-Δl). Similarly, the angle θ1 of the long rotating rod 4 can be determined as follows:

[0038]

[0039] At this point, the rotational linear displacement of the arc-shaped toothed crank 3 connected to the far end of the long rotating rod 4 can be determined as follows:

[0040]

[0041] Using the above method, the short rotating rod 5 can be connected to different pin hole positions on the long rotating rod 4 to adjust the connection length b of the long rotating rod 4 during installation, thereby achieving the purpose of changing the displacement amplification efficiency.

[0042] The beneficial effects of this invention are as follows:

[0043] This invention incorporates a mechanical linkage mechanism within the sensor. By adjusting the initial position of the rotating rod during installation, the displacement transmitted from the external environment to the sliding support 7 can be amplified. This improves the sensor's accuracy and enables the measurement of minute displacements. The invention features a simple structure, ease of use, and high precision. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0045] Figure 2 This is a schematic diagram of the sensor housing in this invention;

[0046] Figure 3 This is a schematic diagram of the medium-strength beam and fiber optic grating of the present invention;

[0047] Figure 4 This is a schematic diagram of the arc-shaped toothed rod in this invention;

[0048] Figure 5 This is a schematic diagram of the long rotating rod 4 in this invention;

[0049] Figure 6 This is a schematic diagram of the short rotating rod 5 in this invention;

[0050] Figure 7 This is a schematic diagram of the fixed support in this invention;

[0051] Figure 8 This is a schematic diagram of the sliding support in this invention;

[0052] Figure 9 This is a schematic diagram of the hollow sleeve rod in this invention;

[0053] Figure 10 This is a schematic diagram of the strip-shaped toothed plate in this invention;

[0054] Figure 11 This is a schematic diagram of the cylindrical guide rail in this invention;

[0055] Figure 12 This is a schematic diagram of the geometric model of a movable lever mechanism.

[0056] In the diagram: 1. Sensor housing; 11. Equal strength beam fixing plate; 12. Fixed support fixing rod; 13. Hollow sleeve rod through hole; 14, 15. Fiber optic through holes; 2. Equal strength beam; 21. Fiber optic cable; 22. First fiber optic grating; 23. Second fiber optic grating; 3. Arc-shaped toothed rod; 31. Fixed blind hole; 4. Long rotating rod; 41. Long rotating rod pin hole one; 42. Long rotating rod pin hole two; 5. Short rotating rod; 51. Short rotating rod pin hole one; 51. Short rotating rod pin hole two; 6. Fixed support; 61. Fixed support pin hole; 62. Fixed support blind hole; 7. Sliding support; 71. Sliding support through hole; 72. Sliding support pin hole; 8. Hollow sleeve rod; 81. Hollow sleeve rod column; 9. Strip toothed plate; 10. Cylindrical guide rail. Detailed Implementation

[0057] The present invention will be further described below with reference to a specific embodiment and accompanying drawings. This embodiment is a part of the embodiments of the present invention, while all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present application.

[0058] See Figure 1 As shown, a sensitive, adjustable-precision fiber Bragg grating micro-displacement sensor is disclosed. The overall structure of the sensor includes a sensor housing 1, a movable lever mechanism, a measuring device, and a guiding device inside the housing; wherein:

[0059] The sensor housing 1 is a cuboid box: a through hole 13 is opened at the rear end of one long side plate of the box for installing a hollow sleeve rod 8; a fixed support rod 12 is fixed at the rear end of the other side plate of the box, the fixed support rod 12 corresponds to the through hole 13, and a fixed support 6, a cylindrical guide rail 10, a sliding support 7, and a hollow sleeve rod 8 are arranged sequentially between the fixed support rod 12 and the through hole 13. Two optical fiber through holes 14 and 15 are provided on the short side plate at the front end of the box for passing through optical fibers 21; an equal strength beam fixing plate 11 is fixed in the middle of the inner surface of the front end plate of the box, the equal strength beam fixing plate 11 is arranged along the length of the box, and its top is fixed to the bottom of the equal strength beam 2.

[0060] The movable lever mechanism is the main structure of this invention, primarily comprising: a cylindrical guide rail 10, a fixed support 6, a sliding support 7, a hollow sleeve rod 8, a long rotating rod 4, a short rotating rod 5, and a fixed support fixing rod 12. The hollow sleeve rod 8 is inserted into the sensor housing 1 through the through hole 13 and then sleeved onto the cylindrical guide rail 10 via the sliding support 7. The hollow sleeve rod 8 and the sliding support 7 are fixedly connected, and the diameter of the central through hole of the hollow sleeve rod 8 and the sliding support 7 is larger than the outer diameter of the cylindrical guide rail 10. One end of the cylindrical guide rail 10 is connected to one end of the fixed support fixing rod 12 via the fixed support 6, and the other end of the fixed support fixing rod 12 is fixed to the inner surface of the long side plate of the sensor housing 1. After installation, the hollow sleeve rod 8, the cylindrical guide rail 10, and the fixed support fixing rod 12 are arranged parallel to the wide side direction of the sensor housing 1. The sliding support 7 has a through hole 71 at its center and is mounted on the cylindrical guide rail 10, allowing it to move back and forth along the guide rail 10, which is also the direction of displacement measurement. The fixed support 6 has blind holes on both sides of its center, for mounting the ends of the fixed support rod 12 and the cylindrical guide rail 10 respectively. The other end of the cylindrical guide rail 10 is connected to the hollow sleeve rod 8. The short rotating rod 5 has holes at both ends and is hinged to the sliding support 7 and the long rotating rod 4 via pins. The long rotating rod 4 has a hole at one end, which is hinged to the fixed support 6 via a pin, and this end can rotate around the pin. The other end of the long rotating rod 4 is fixedly connected to one side of the arc-shaped toothed rod 3. A groove is left in the middle of the long rotating rod 4 as a space for hinged connection with the short rotating rod 5. A series of parallel and equidistant pin holes 42 are provided on both sides of the groove. The short rotating rod 5 changes its range by connecting different pin holes 42.

[0061] The guiding device is used to limit the sliding support 7 to displacement only along the cylindrical guide rail 10, so that the movement direction of the sliding support 7 is consistent with the measurement direction, which refers to the axial direction of the cylindrical guide rail 10. The measuring device includes an arc-shaped toothed rod 3, a strip-shaped toothed plate 9, a beam of equal strength 2, an optical fiber 21, and a first grating 22 and a second grating 23 on the optical fiber, that is, the present invention includes two fiber optic grating sensors. When the sliding support 7 moves, it drives the long and short rotating rods to rotate. The arc-shaped toothed rod 3 connected to the end of the long rotating rod 4 rotates around the fixed support 6, amplifying the displacement of the sliding support 7 into the rotation distance of the arc-shaped toothed rod 3. This, in turn, converts the small external displacement to be measured into the displacement of the sliding support 7 through the hollow pressure rod 8. The sliding support 7, long rotating rod 4, short rotating rod 5, and arc-shaped toothed rod 3 constitute a sliding body. The top of the strip-shaped toothed plate 9 is tightly engaged with the other side of the arc-shaped toothed rod 3, and the bottom of the strip-shaped toothed plate 9 is fixedly connected to the equal-strength beam 2. The first grating 22 and the second grating 23 are located on the tension and compression surfaces of the equal-strength beam 2, respectively. The first grating 22 and the second grating 23 are connected to an external optical signal demodulation device through optical fiber 21 passing through optical fiber through-holes 14 and 15, respectively, and convert the optical signal into an electrical signal. The two gratings have equal strain sensitivities but opposite signs, and different temperature and strain sensitivities. Therefore, temperature and strain can be separated using an external temperature compensation method. After the arc-shaped toothed rod 3 is displaced, the strip toothed plate 9 drives the equal-strength beam 2 to bend. The amplified displacement change is then measured by a fiber optic grating attached to the equal-strength beam 2.

[0062] The fixed support 6 is a cylindrical structure with a fixed support blind hole 62 at the center and a fixed support pin hole 61 on the side wall. The fixed support blind hole 62 is used to install the end of the cylindrical guide rail 10.

[0063] The hollow sleeve rod 8 includes a top circular protrusion and a hollow sleeve rod post 82. The outer diameter of the circular protrusion is larger than the diameter of the through hole 13 at the rear end of the side plate of the box. The hollow sleeve rod post 81 is sleeved with the cylindrical guide rail 10.

[0064] The pin holes reserved in the middle of the long rotating rod 4 for connecting with the short rotating rod 5 are a series of equally spaced through holes on both sides, which are the pin holes 42 of the long rotating rod. By connecting with different pin holes, the length of the lever arm can be adjusted, thereby changing the efficiency of the displacement from the sliding support 7 to the rotational linear displacement of the arc-shaped toothed rod 3, thus achieving the purpose of changing the range.

[0065] The sliding support 7 is a rotating structure with a central circular through hole 71. The diameter of the through hole 71 is slightly larger than the diameter of the cylindrical guide rail 10, and the two are lubricatedly fitted together. The bottom of the sliding support 7 is fixedly connected to the hollow sleeve rod 8. That is, the cylindrical guide rail 10 is fitted onto the hollow sleeve rod 8, and the bottom of the sliding support 7 is fixedly connected to the hollow sleeve rod 8, and the two move synchronously.

[0066] The arc-shaped toothed rod 3 and the strip-shaped toothed plate 9 are tightly meshed by teeth, simplifying the geometric model to the tangency between the arc and the straight line. A fixed blind hole 31 is provided on one side of the arc-shaped toothed rod 3 for mounting the end of the long rotating rod 4.

[0067] The method of using a sensitivity-enhanced, adjustable-precision fiber Bragg grating micro-displacement sensor is as follows:

[0068] The displacement transmitted from the outside is applied to the solid base of the hollow sleeve rod 8, thereby pushing the sliding support 7 to slide along the cylindrical guide rail 10, driving the short rotating rod 5 and the long rotating rod 4 to rotate. The short rotating rod 5 rotates around the sliding support 7, and the long rotating rod 4 rotates around the fixed support 6. The arc-shaped toothed curved rod 3 and the long rotating rod 4 are fixedly connected, converting the displacement of the far end of the long rotating rod 4 into the rotational linear displacement of the arc-shaped toothed curved rod 3. The strip-shaped toothed plate 9, which meshes with the arc-shaped toothed curved rod 3, is displaced along the circumferential tangential direction, causing the equal strength beam 2 to bend and produce deflection. The first and second fiber optic gratings attached to the compression and tension sides of the equal strength beam 2 sense strain and temperature changes, causing the center wavelength of the grating to drift according to the following formulas:

[0069]

[0070]

[0071] Since the center wavelengths of the two gratings have different sensitivities to temperature and strain, the effect of temperature can be eliminated by applying tensile and compressive strains with the same value but opposite signs.

[0072] Taking the measurement of displacement under pressure by a sensor as an example, after the hollow sleeve rod 8 is compressed by external displacement, it moves 2mm into the sensor along the cylindrical guide rail 10, i.e., Δl = 2mm; assuming the length R of the long rotating rod 4 is 30mm, the length a of the short rotating rod 5 is 15mm, the distance b from the connection point of the short rotating rod 5 and the long rotating rod 4 to the fixed support 6 is 10mm, and the initial distance l0 between the sliding support 7 and the fixed support 6 is 18mm, then according to the formula described in the invention content section, the expanded displacement calculation process is as follows:

[0073]

[0074] The displacement then becomes 4.92 / 2 = 2.46 times.

[0075] According to the invention, the displacement amplification factor can also be adjusted by adjusting the short rotating rod 5 to fix it at different pin hole positions in the pin hole 42 of the long rotating rod.

[0076] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A sensitivity-enhanced, adjustable-precision fiber Bragg grating micro-displacement sensor, characterized in that, The fiber optic grating micro-displacement sensor includes a sensor housing (1), a movable lever mechanism inside the housing, and a measuring device; wherein: The sensor housing (1) is a rectangular box: a through hole (13) for installing a hollow sleeve rod (8) is opened at the rear end of a long side plate of the box; an equal strength beam fixing plate (11) is fixed in the middle of the inner surface of the front short side plate of the box. The equal strength beam fixing plate (11) is arranged along the length of the box, and its top is fixed to the bottom of the equal strength beam (2). The movable lever mechanism includes: a cylindrical guide rail (10), a fixed support (6), a sliding support (7), a hollow sleeve rod (8), a long rotating rod (4), a short rotating rod (5), and a fixed support fixing rod (12); the hollow sleeve rod (8) is inserted into the sensor housing (1) through the through hole (13) and then sleeved on the cylindrical guide rail (10) through the sliding support (7), wherein the hollow sleeve rod (8) and the sliding support (7) are fixedly connected; the other end of the cylindrical guide rail (10) is connected to one end of the fixed support fixing rod (12) through the fixed support (6), and the other end of the fixed support fixing rod (12) is fixed inside the long side plate of the sensor housing (1). Surface; the short rotating rod (5) is drilled at both ends and connected to the sliding support (7) and the long rotating rod (4); the long rotating rod (4) is drilled at one end and connected to the fixed support (6), and the end can rotate; the other end of the long rotating rod (4) is fixedly connected to one side of the arc-shaped toothed rod (3); a groove is left in the middle of the long rotating rod (4) as the space for it to hinge with the short rotating rod (5); a series of pin holes (42) are provided on both sides of the groove; the short rotating rod (5) can change the range by connecting different pin holes (42); the movement direction of the sliding support (7) is consistent with the measurement direction; the measurement direction refers to the axial direction of the cylindrical guide rail (10); The measuring device includes an arc-shaped toothed rod (3), a strip-shaped toothed plate (9), a beam of equal strength (2), an optical fiber (21), and a first grating (22) and a second grating (23) on the optical fiber; the top of the strip-shaped toothed plate (9) is tightly engaged with the other side of the arc-shaped toothed rod (3), and the bottom of the strip-shaped toothed plate (9) is fixedly connected to the beam of equal strength (2); when the sliding support (7) moves, it drives the long and short rotating rods to rotate, and the arc-shaped toothed rod (3) connected to the end of the long rotating rod (4) rotates around the fixed support (6) as the center, amplifying the displacement of the sliding support (7) into the rotation distance of the arc-shaped toothed rod (3). The small external displacement to be measured is then converted into the displacement of the sliding support (7) through the hollow pressure bar 8. The sliding support (7), the long rotating bar (4), the short rotating bar (5), and the arc-shaped toothed rod (3) constitute the sliding body. The first grating (22) and the second grating (23) are located on the tension and compression surfaces of the equal strength beam (2) respectively, and are connected to the external optical signal demodulation device through the optical fiber (21) respectively. After the arc-shaped toothed rod (3) generates displacement, the strip toothed plate (9) drives the equal strength beam (2) to bend, and then the amplified displacement change is measured by the fiber optic grating pasted on the equal strength beam (2).

2. The enhanced-sensitivity, adjustable-precision fiber Bragg grating micro-displacement sensor according to claim 1, characterized in that, The connections between the long rotating rod (4) and the fixed support (6), the short rotating rod (5) and the sliding support (7), and the short rotating rod (5) and the long rotating rod (4) are all pin connections, ensuring free rotation between components.

3. The enhanced-sensitivity, adjustable-precision fiber Bragg grating micro-displacement sensor according to claim 1, characterized in that, The hollow sleeve rod (8) includes a top circular protrusion and a hollow sleeve rod column (82). The outer diameter of the circular protrusion is larger than the diameter of the through hole (13) at the rear end of the side plate of the box. The hollow sleeve rod column (81) is sleeved with the cylindrical guide rail (10).

4. The enhanced-sensitivity, adjustable-precision fiber Bragg grating micro-displacement sensor according to claim 1, characterized in that, The sliding support (7) is a rotating body structure with a circular through hole (71) in the center. The diameter of the through hole (71) is larger than the diameter of the cylindrical guide rail (10), and the two are lubricated and sleeved together.

5. The enhanced-sensitivity, adjustable-precision fiber Bragg grating micro-displacement sensor according to claim 1, characterized in that, The arc-shaped toothed rod (3) and the strip-shaped toothed plate (9) are tightly meshed by teeth, which simplifies to the tangency between the arc and the straight line corresponding to the geometric model.

6. A sensing method for a fiber optic grating micro-displacement sensor with adjustable precision according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1, Installation and Fixing: First, make the annular protrusion of the hollow sleeve rod (8) press tightly against the surface being monitored to ensure that the external micro-displacement can be completely converted into the displacement of the sliding body; The second step is temperature compensation: the first fiber grating (22) is pasted on the tension surface of the equal strength beam (2), and the second fiber grating (23) is pasted on the compression surface of the equal strength beam (2), ensuring that it is parallel to the axial direction of the equal strength beam (2); The third step is displacement measurement: by measuring the center wavelength drift of the first fiber grating (22) and the second fiber grating (23), the axial strain of the first grating caused only by the bending of the equal strength beam (2) is calculated. For the first fiber grating (22), the calculation is performed according to the following formula: Where, Δλ B1 λ is the change in the center wavelength of the fiber grating. B1 P is the center wavelength of the grating; e1 α1, ζ1, and ζ1 are the effective photoelastic coefficient, thermal expansion coefficient, and thermo-optic coefficient of the grating, respectively. They are all constants related to the grating material. When selecting gratings, it should be ensured that the material constants of the first and second gratings are different. ε1 and ΔT1 are the axial displacement and temperature change of the grating, respectively. For the second fiber grating (23), the axial strain and temperature variables are obtained using the same formula: The meanings of each letter are explained in the same way as in formula (1); Combining the measurement data of the two gratings above, and according to the external temperature compensation method, ε represents the axial strain of the grating. Since they have the same value but opposite signs, the temperature and strain can be separated using the following equation: Among them, K B1,T K B2,T These are the temperature sensitivities of the two gratings, K. B1,s K B2,s The sensitivities of the two gratings to strain are calculated using the following formulas: K B,T =a+z K B,s =1-P e Fourth step, displacement amplification: The displacement transmitted to the sliding support (7) through the hollow sleeve rod (8) is as follows: In the initial state, the initial distance between the sliding support (7) and the fixed support (6) is l0, and the initial installation angle between the long rotating rod and the cylindrical guide rail (10) is θ0. One of the series of pin holes in the pin hole 42 of the long rotating rod is selected as the initial installation position, so that the installation position of the short rotating rod (5) on the long rotating rod (4) is b from the fixed support (6); in addition, the lengths of the long rotating rod (5) and the short rotating rod (4) remain constant as R and a respectively. Taking the displacement under pressure as an example, the hollow sleeve rod (8) moves into the sensor, and the displacement generated by the sliding support (7) after being compressed is Δl; the movable lever mechanism drives the short rotating rod (5) and the long rotating rod (4) to rotate, and the angle between the long rotating rod (4) and the cylindrical guide rail (10) after rotation is θ1; a, b, R, l0, and θ0 represent the short rotating rod, Δl represents the sliding support, and θ1 represents the long rotating rod. According to the cosine theorem, the initial installation angle θ0 can be determined by the lengths of the three sides: After the sliding support (7) transmits the external displacement, it moves a distance Δl along the direction of the cylindrical guide rail (10), and the position of the sliding support (7) becomes (l0-Δl). Similarly, the angle θ1 of the long rotating rod (4) can be determined as follows: At this time, the rotational linear displacement of the arc-shaped toothed crank (3) connected to the far end of the long rotating rod (4) can be determined as: By using the above method, the short rotating rod (5) can be connected to different pin hole positions on the long rotating rod (4) to adjust the connection length b of the long rotating rod (4) during installation, thereby achieving the purpose of changing the displacement amplification efficiency.

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