Packaging device and packaging method of fiber grating strain sensor

Abstract

The present invention discloses a packaging device and method for a fiber Bragg grating (FBG) strain sensor. The device includes first and second fiber clamps, a substrate fixture, first and second micro-displacement platforms, a six-axis optical adjustment platform, a fiber Bragg grating (FBG) demodulator, a high-precision force gauge, a visual observation system, a quantitative glue pump, and an adhesive curing device. The first and second fiber clamps clamp the first and second optical fibers; the substrate fixture mounts the strain substrate; the first and second micro-displacement platforms control the movement of the fiber clamps; the six-axis optical adjustment platform supports the substrate fixture; the fiber Bragg grating (FBG) demodulator monitors the central wavelength and waveform of the FBG; the high-precision force gauge applies tension to the FBG; the visual observation system observes the position and posture of the FBG and the strain substrate; the quantitative glue pump dispenses adhesive; and the adhesive curing device accelerates the curing of the adhesive. This invention can effectively control the packaging quality of the fiber Bragg grating (FBG) strain sensor and improve the consistency of strain sensitivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber grating sensing and strain measurement, and in particular relates to a packaging device and a packaging method for a fiber grating strain sensor. Background Art

[0002] Fiber Bragg grating (FBG) strain sensors measure strain based on the fiber Bragg grating (FBG) principle. The FBG is encapsulated with a strain gauge substrate by gluing. This encapsulation process directly affects the consistency of the sensor's strain sensitivity. Since FBG strain sensors cannot be calibrated on-site after being installed on the surface of the structure being measured, strain calculations are typically performed based on the average sensitivity data of a batch of sensors. Inconsistent strain sensitivity across individual sensors can lead to measurement errors. Therefore, improving the sensitivity consistency of FBG strain sensors is key to reducing strain measurement errors.

[0003] The current packaging devices and methods for fiber Bragg grating strain sensors cannot guarantee the consistency of sensor sensitivity. There is a problem of large differences in sensitivity among sensors in the same batch, which leads to large errors in strain measurement results. As a prior art, CN116817783B discloses a pre-tightening packaging structure and method for optical fiber strain sensors. By setting a translation mechanism, it solves the technical problem of low adjustment accuracy of the pre-tightening amount of the sensing optical fiber, thereby improving the strain measurement accuracy under high temperature. However, this patent does not solve the problem of sensitivity consistency of the strain sensor. CN105583484B proposes a packaging device and method for welding packaging of sensors, focusing on improving the packaging efficiency and qualified product rate of optical fiber Bragg grating sensors, but also fails to improve the consistency of strain sensor sensitivity. Summary of the Invention

[0004] The object of the present invention is to provide a packaging device and packaging method for a fiber Bragg grating strain sensor, which can effectively improve the packaging quality of the fiber Bragg grating strain sensor and improve the consistency of the sensor's strain sensitivity.

[0005] To achieve the above objectives, one aspect of the present invention provides a packaging device for a fiber Bragg grating strain sensor, comprising a first fiber holder, a second fiber holder, a substrate fixture, a first micro-displacement platform, a second micro-displacement platform, a six-axis optical adjustment platform, a fiber Bragg grating interrogator, a high-precision tensile gauge, a visual observation system, a quantitative glue pump, and an adhesive curing device;

[0006] The first fiber clamp and the second fiber clamp are used to clamp the first optical fiber and the second optical fiber at both ends of the fiber Bragg grating respectively and temporarily fix them;

[0007] The base fixture has an installation groove that is consistent with the shape of the strain base and is used to install the strain base, limit the strain base, and temporarily fix it;

[0008] The first micro-displacement platform and the second micro-displacement platform are respectively equipped with a first fiber clamp and a second fiber clamp, and are used to control the movement of the first fiber clamp and the second fiber clamp to adjust the position and posture of the fiber Bragg grating;

[0009] The six-axis optical adjustment platform is equipped with a substrate fixture, which is used to control the movement of the substrate fixture to adjust the position and posture of the strained substrate.

[0010] The fiber Bragg grating demodulator is connected to the end of the first optical fiber and is used to monitor the central wavelength and waveform spectrum of the fiber Bragg grating;

[0011] A high-precision tensile force gauge is connected to the end of the second optical fiber and is used to apply tension to the optical fiber Bragg grating;

[0012] The visual observation system is used to observe the position and posture of the fiber Bragg grating and the strain substrate;

[0013] The quantitative glue pump is used to quantitatively and controllably dispense adhesive to bond and package the first optical fiber, the fiber grating, the second optical fiber and the strain substrate;

[0014] The adhesive curing device is used to accelerate the curing of the adhesive.

[0015] Preferably, the packaging device further comprises a base, which is a breadboard having threaded holes distributed at equal intervals, for carrying and installing the first micro-displacement platform, the second micro-displacement platform, the six-axis optical adjustment platform, and the fiber Bragg grating demodulator.

[0016] Preferably, the first optical fiber holder and the second optical fiber holder are respectively provided with V-shaped grooves for non-destructively clamping the first optical fiber and the second optical fiber.

[0017] Preferably, the visual observation system is a multi-axis CCD camera.

[0018] Another aspect of the present invention provides a method for packaging a fiber Bragg grating strain sensor, wherein the fiber Bragg grating strain sensor is packaged using the above-mentioned packaging device, and the method comprises:

[0019] Step S1: connecting the end of the first optical fiber to a fiber Bragg grating (FBG) demodulator to record the initial center wavelength and initial waveform of the fiber Bragg grating (FBG);

[0020] Step S2: Using a first fiber clamp to non-destructively clamp the first optical fiber, using a second fiber clamp to non-destructively clamp the second optical fiber, using a first micro-displacement platform to adjust the first fiber clamp, and using a second micro-displacement platform to adjust the second fiber clamp to adjust the position of the fiber Bragg grating, using a visual observation system to observe and ensure that the fiber Bragg grating is located at the center of the base fixture, using a high-precision tensile gauge to apply tension to the fiber Bragg grating in the horizontal direction, and adjusting the center wavelength of the fiber Bragg grating to the target center wavelength;

[0021] Step S3: Install the strain substrate in the mounting groove of the substrate fixture, limit the strain substrate, use a six-axis optical adjustment platform to adjust the substrate fixture to adjust the position and posture of the strain substrate, and use a visual observation system to observe to ensure that the strain substrate and the fiber Bragg grating are accurately aligned in the horizontal direction, and the strain substrate and the fiber Bragg grating are parallel in the horizontal and vertical directions without any angle, so that the fiber Bragg grating is embedded in the grating groove of the strain substrate to the target depth;

[0022] Step S4: using a quantitative glue pump to dispense adhesive, bonding and encapsulating the first optical fiber, the fiber Bragg grating (FBG), the second optical fiber, and the strain substrate to form a fiber Bragg grating (FBG) strain sensor, and using an adhesive curing device to accelerate the curing of the adhesive;

[0023] Step S5: Open the first fiber clamp, the second fiber clamp, and the substrate clamp, and take out the packaged fiber Bragg grating strain sensor.

[0024] Preferably, in step S2, the tension F applied to the fiber Bragg grating satisfies:

[0025]

[0026] Among them, λ B is the target center wavelength of the fiber Bragg grating; λ0 is the initial center wavelength of the fiber Bragg grating, λ B ≥λ0; A is the circular cross-sectional area of the first and second optical fibers; E is the elastic modulus of the first and second optical fibers; and 0.78 is a constant.

[0027] Preferably, in step S3, the fiber Bragg grating is embedded in the grating groove of the strain substrate to a target depth H B satisfy:

[0028]

[0029] Wherein, K is the strain transfer coefficient; L is the bonding length of the adhesive; and C is a constant related to the materials of the first and second optical fibers, the geometric parameters of the first and second optical fibers, and the properties of the adhesive.

[0030] Preferably, in step S4, the glue supply quantity Q of the quantitative glue supply pump satisfies:

[0031] Q=(D*L*HA*L) / (1-ρ)

[0032] Wherein, D is the width of the adhesive bond; L is the length of the adhesive bond; H is the depth of the grating groove of the strained substrate; A is the circular cross-sectional area of the first and second optical fibers; and ρ is the curing shrinkage of the adhesive.

[0033] The packaging device and packaging method of the fiber Bragg grating strain sensor according to the above aspects of the present invention can effectively improve the packaging quality of the fiber Bragg grating strain sensor and enhance the consistency of the strain sensitivity of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0035] Figure 1 1 is a schematic structural diagram of a packaging device for a fiber Bragg grating strain sensor according to an embodiment of the present invention;

[0036] Figure 2 It is a flow chart of a packaging method of a fiber Bragg grating strain sensor according to an embodiment of the present invention.

[0037] Among them, 1. first optical fiber; 2. fiber Bragg grating; 3. second optical fiber; 4. strain substrate; 5. first optical fiber clamp; 6. second optical fiber clamp; 7. substrate clamp; 8. first micro-displacement platform; 9. second micro-displacement platform; 10. six-axis optical adjustment platform; 11. fiber Bragg grating demodulator; 12. high-precision dynamometer; 13. visual observation system; 14. quantitative glue pump; 15. adhesive curing device; 16. base. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0039] The embodiment of the present invention provides a packaging device for a fiber Bragg grating strain sensor. Figure 1 FIG. 1 is a schematic structural diagram of a packaging device for a fiber Bragg grating strain sensor according to an embodiment of the present invention. Figure 1As shown, the packaging device of the fiber Bragg grating strain sensor according to the embodiment of the present invention includes: a first fiber clamp 5, a second fiber clamp 6, a base clamp 7, a first micro-displacement platform 8, a second micro-displacement platform 9, a six-axis optical adjustment platform 10, a fiber Bragg grating demodulator 11, a high-precision tensile gauge 12, a visual observation system 13, a quantitative glue pump 14, and an adhesive curing device 15.

[0040] The first and second fiber holders 5 and 6 each feature a 150μm-deep V-groove, designed to non-destructively clamp the first and second optical fibers 1 and 3 and temporarily secure them. The first and second optical fibers 1 and 3 are connected to the ends of the fiber Bragg grating 2, respectively. The first and second optical fibers 1 and 3 are made of the same material and parameters. The substrate fixture 7 features a mounting groove that matches the shape of the strain substrate 4 and is 1mm deep. This groove is used to mount the strain substrate 4, limit its position, and temporarily secure it.

[0041] The first micro-displacement platform 8 and the second micro-displacement platform 9 respectively carry and install the first fiber clamp 5 and the second fiber clamp 6, and are used to precisely control the movement of the first fiber clamp 5 and the second fiber clamp 6. The displacement accuracy can reach 0.5μm. By precisely moving the first optical fiber 1 and the second optical fiber 3, the position and posture of the fiber Bragg grating 2 can be precisely adjusted.

[0042] The six-axis optical adjustment platform 10 carries the mounting substrate fixture 7 and is used to precisely control the movement of the substrate fixture 7 with a displacement accuracy of up to 0.5 μm. The angles of the substrate fixture 7 in the X-axis, Y-axis, and Z-axis can be adjusted to achieve precise adjustment of the position and posture of the strain substrate 4. The horizontal direction of the plane where the packaging device is located is the X-axis, the vertical direction is the Y-axis, and the direction perpendicular to the plane formed by the X and Y axes is the Z-axis.

[0043] A fiber Bragg grating (FBG) interrogator 11 is connected to the end of the first optical fiber 1 and is used to monitor the central wavelength and waveform of the fiber Bragg grating 2. A high-precision force gauge 12 is connected to the end of the second optical fiber 3 and is used to apply precise tension to the fiber Bragg grating 2, with an accuracy of up to 0.01 N. A visual observation system 13 utilizes a multi-axis CCD camera for real-time observation of the position and posture of the fiber Bragg grating 2 and strain gauge substrate 4 during adjustment.

[0044] A quantitative adhesive pump 14 is used to controllably dispense adhesive in a quantitative manner, with a minimum dispensing volume of 0.1 μL, to bond and encapsulate the first optical fiber 1, the fiber grating 2, the second optical fiber 3, and the strain substrate 4. An adhesive curing device 15 is used to accelerate the curing of the adhesive. Depending on the type of adhesive used, the curing method can be either heat curing or UV curing.

[0045] The packaging device of the embodiment of the present invention may further include a base 16 , which is a breadboard having threaded holes distributed at equal intervals of 25.4 mm, and is used to carry and install other components and equipment of the packaging device.

[0046] The embodiment of the present invention further provides a packaging method for a fiber Bragg grating strain sensor, which uses the above packaging device to package the fiber Bragg grating strain sensor. Figure 2 As shown, the method according to the embodiment of the present invention includes steps S1 to S5.

[0047] In step S1 , the end of the first optical fiber 1 is connected to the fiber Bragg grating demodulator 11 , and the initial center wavelength value and initial waveform spectrum of the fiber Bragg grating 2 are recorded.

[0048] In step S2 , the optical fiber is clamped, the position and posture of the fiber Bragg grating 2 are adjusted, and tension is applied to the fiber Bragg grating 2 .

[0049] Specifically, the first optical fiber holder 5 is used to non-destructively clamp the first optical fiber 1 , and the second optical fiber holder 6 is used to non-destructively clamp the second optical fiber 3 and temporarily fix them.

[0050] Use the first micro-displacement platform 8 to adjust the first fiber clamp 5, and use the second micro-displacement platform 9 to adjust the second fiber clamp 6 to adjust the position of the fiber Bragg grating 2; use the visual observation system 13 to observe and ensure that the fiber Bragg grating 2 is located at the center of the base fixture 7 and has no obvious angle with the X-axis and Z-axis.

[0051] Use a high-precision tensile force gauge 12 to apply tension to the fiber Bragg grating 2 in the X-axis direction (horizontal direction) to adjust the center wavelength of the fiber Bragg grating 2 to the target center wavelength to ensure that the center wavelengths of the fiber Bragg gratings in the same batch are the same during packaging. The applied tension value F follows the following formula:

[0052]

[0053] Where λ B is the target center wavelength of the fiber Bragg grating, λ B ≥λ0; λ0 is the initial central wavelength of the fiber Bragg grating; A is the circular cross-sectional area of the first and second optical fibers; E is the elastic modulus of the first and second optical fibers; and 0.78 is a constant.

[0054] In one embodiment, the initial center wavelength of the selected fiber Bragg grating 2 is 1549.5 nm, and the target center wavelength is 1550 nm. According to formula (1), the applied tension can be calculated to be 0.36 N.

[0055] In step S3 , the strain substrate 4 is installed and the position and posture of the strain substrate 4 are adjusted.

[0056] Specifically, the strain substrate 4 is installed in the installation groove of the substrate fixture 7 , and the strain substrate 4 is limited and temporarily fixed.

[0057] Use the six-axis optical adjustment platform 10 to adjust the substrate fixture 7 to adjust the position and posture of the strain substrate 4; use the visual observation system 13 to observe and ensure that the strain substrate 4 and the fiber Bragg grating 2 are accurately aligned in the X-axis direction, and the strain substrate 4 and the fiber Bragg grating 2 are parallel and have no angle in the X-axis and Z-axis directions (horizontal and vertical directions). Adjust the relative position of the strain substrate 4 so that the fiber Bragg grating 2 is embedded in the grating groove of the strain substrate 4, ensuring that the fiber Bragg grating 2 of the same batch is embedded in the groove to the same target depth H. B , H B Follow this formula:

[0058]

[0059] Wherein, K is the strain transfer coefficient; L is the adhesive bonding length; and C is a constant related to the materials of the first and second optical fibers, the geometric parameters of the first and second optical fibers, and the properties of the adhesive.

[0060] In one embodiment, if the strain transfer coefficients of the fiber Bragg grating strain sensors of the same batch all reach 0.95, according to formula (2), it can be calculated that the depth of the fiber Bragg grating embedded in the groove is 10 μm.

[0061] In step S4, the first optical fiber 1, the fiber Bragg grating 2, the second optical fiber 3 and the strain substrate 4 are pasted and packaged to form a fiber Bragg grating strain sensor.

[0062] Specifically, a quantitative glue pump 14 is used to dispense UV adhesive to bond and encapsulate the first optical fiber 1, the fiber grating 2, the second optical fiber 3, and the strain substrate 4. An adhesive curing device 15 is used to accelerate the curing of the adhesive. The amount of adhesive dispensed Q follows the following formula:

[0063] Q=(D*L*HA*L) / (1-ρ) (3)

[0064] Where D is the width of the adhesive bond; L is the length of the adhesive bond, which is equivalent to the length of the fiber Bragg grating; H is the depth of the strained substrate grating groove; A is the circular cross-sectional area of the first and second optical fibers; and ρ is the adhesive curing shrinkage rate.

[0065] In one embodiment, the bonding width of the selected UV adhesive is 2 mm, the fiber Bragg grating length is 7 mm, the grating groove depth is 0.5 mm, and the curing shrinkage is 5%. According to formula (3), the glue dosage Q is calculated to be 7.3 μL.

[0066] In step S5, the first fiber holder 5, the second fiber holder 6, and the base fixture 7 are opened to remove the packaged fiber Bragg grating strain sensor. A fiber Bragg grating interrogator 11 is used to record and detect the packaged fiber Bragg grating center wavelength and waveform spectrum, and the sensors are numbered. The packaging is complete.

[0067] In one embodiment, strain sensitivity tests were conducted on fiber Bragg grating strain sensors from the same batch with a central wavelength of 1550 nm. The results are shown in Table 1. Table 2 shows the calculated strain sensitivity dispersion of the sensors from this batch. The dispersion of the sensitivity around its average value is less than 1%, indicating good sensor packaging consistency.

[0068] Table 1 Strain sensitivity test results of sensors from the same batch

[0069]

[0070] Table 2 Calculation results of strain sensitivity dispersion of sensors from the same batch

[0071]

[0072] In summary, the packaging device and packaging method of the fiber Bragg grating strain sensor according to the embodiment of the present invention have the following beneficial effects:

[0073] 1. It can reduce or avoid the strain sensitivity error caused by the packaging process, improve the packaging consistency of the sensor, and thus achieve accurate strain measurement;

[0074] 2. By setting up a second micro-displacement platform, the central wavelength of the fiber Bragg grating can be adjusted so that the fiber Bragg gratings in the same batch have the same central wavelength when packaged;

[0075] 3. By setting up a six-axis optical adjustment platform and a visual observation system, the position and posture of the strain substrate can be precisely adjusted to ensure that the depth of fiber Bragg gratings embedded in the strain substrate is the same for the same batch;

[0076] 4. By setting a quantitative glue pump, the glue amount for each fiber grating strain sensor is the same;

[0077] 5. The dispersion of strain sensitivity to its average value is controlled to within 1%, effectively ensuring the consistency of sensor packaging.

[0078] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A packaging device for a fiber Bragg grating strain sensor, characterized in that: It includes a first optical fiber holder, a second optical fiber holder, a substrate fixture, a first micro-displacement platform, a second micro-displacement platform, a six-axis optical adjustment platform, a fiber Bragg grating demodulator, a high-precision tensile gauge, a visual observation system, a quantitative glue pump and an adhesive curing device; The first fiber clamp and the second fiber clamp are used to clamp the first optical fiber and the second optical fiber at both ends of the fiber Bragg grating respectively and temporarily fix them; The base fixture has an installation groove that is consistent with the shape of the strain base and is used to install the strain base, limit the strain base, and temporarily fix it; The first micro-displacement platform and the second micro-displacement platform are respectively equipped with a first fiber clamp and a second fiber clamp, and are used to control the movement of the first fiber clamp and the second fiber clamp to adjust the position and posture of the fiber Bragg grating; The six-axis optical adjustment platform is equipped with a substrate fixture, which is used to control the movement of the substrate fixture to adjust the position and posture of the strained substrate. The fiber Bragg grating demodulator is connected to the end of the first optical fiber and is used to monitor the central wavelength and waveform spectrum of the fiber Bragg grating; A high-precision tension gauge is connected to the end of the second optical fiber and is used to apply tension to the fiber Bragg grating to adjust the central wavelength of the fiber Bragg grating to a target central wavelength; The visual observation system is used to observe the position and posture of the fiber Bragg grating and the strain substrate; The quantitative glue pump is used to quantitatively and controllably dispense adhesive to bond and package the first optical fiber, the fiber grating, the second optical fiber and the strain substrate; The adhesive curing device is used to accelerate the curing of the adhesive; The tensile force F applied by the high-precision tensile gauge to the fiber Bragg grating satisfies: Among them, λ B is the target center wavelength of the fiber Bragg grating; λ0 is the initial center wavelength of the fiber Bragg grating, λ B ≥λ0; A is the circular cross-sectional area of the first and second optical fibers; E is the elastic modulus of the first and second optical fibers; and 0.78 is a constant.

2. The packaging device according to claim 1, wherein: It also includes a base, which is a breadboard with threaded holes distributed at equal intervals, and is used to carry and install the first micro-displacement platform, the second micro-displacement platform, the six-axis optical adjustment platform, and the fiber Bragg grating demodulator.

3. The packaging device according to claim 1 or 2, characterized in that: The first optical fiber clamp and the second optical fiber clamp are respectively provided with V-shaped grooves for non-destructively clamping the first optical fiber and the second optical fiber.

4. The packaging device according to claim 1 or 2, characterized in that: The visual observation system is a multi-axis CCD camera.

5. A packaging method for a fiber Bragg grating strain sensor, characterized in that: A fiber Bragg grating strain sensor is packaged using the packaging device according to any one of claims 1 to 4, the method comprising: Step S1: connecting the end of the first optical fiber to a fiber Bragg grating (FBG) demodulator to record the initial center wavelength and initial waveform of the fiber Bragg grating (FBG); Step S2: Using a first fiber clamp to non-destructively clamp the first optical fiber, using a second fiber clamp to non-destructively clamp the second optical fiber, using a first micro-displacement platform to adjust the first fiber clamp, and using a second micro-displacement platform to adjust the second fiber clamp to adjust the position of the fiber Bragg grating, using a visual observation system to observe and ensure that the fiber Bragg grating is located at the center of the base fixture, using a high-precision tensile gauge to apply tension to the fiber Bragg grating in the horizontal direction, and adjusting the center wavelength of the fiber Bragg grating to the target center wavelength; Step S3: Install the strain substrate in the mounting groove of the substrate fixture, limit the strain substrate, use a six-axis optical adjustment platform to adjust the substrate fixture to adjust the position and posture of the strain substrate, and use a visual observation system to observe to ensure that the strain substrate and the fiber Bragg grating are accurately aligned in the horizontal direction, and the strain substrate and the fiber Bragg grating are parallel in the horizontal and vertical directions without any angle, so that the fiber Bragg grating is embedded in the grating groove of the strain substrate to the target depth; Step S4: using a quantitative glue pump to dispense adhesive, bonding and encapsulating the first optical fiber, the fiber Bragg grating (FBG), the second optical fiber, and the strain substrate to form a fiber Bragg grating (FBG) strain sensor, and using an adhesive curing device to accelerate the curing of the adhesive; Step S5: Open the first fiber clamp, the second fiber clamp, and the substrate clamp, and take out the packaged fiber Bragg grating strain sensor.

6. The method according to claim 5, wherein In step S3, the fiber Bragg grating is embedded into the grating groove of the strained substrate to a target depth H. B satisfy: Wherein, K is the strain transfer coefficient; L is the bonding length of the adhesive; and C is a constant related to the materials of the first and second optical fibers, the geometric parameters of the first and second optical fibers, and the properties of the adhesive.

7. The method according to claim 5, wherein In step S4, the glue quantity Q supplied by the quantitative glue pump satisfies: Q=(D*L*HA*L) / (1-ρ) Wherein, D is the width of the adhesive bond; L is the length of the adhesive bond; H is the depth of the grating groove of the strained substrate; A is the circular cross-sectional area of the first and second optical fibers; and ρ is the curing shrinkage of the adhesive.

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