Intelligent bolt based on grating strain gauge

Abstract

The utility model provides a kind of smart bolt based on grating strain gauge, including bolt and grating strain gauge, the inside of the bolt is opened with hole, grating strain gauge is provided with quick-drying adhesive, grating strain gauge is pasted in the hole by the quick-drying adhesive.By quick-drying adhesive, grating strain gauge is directly pasted in bolt hole, and this directly pasting mode in bolt hole makes grating quickly and sensitively "feel" the axial strain inside bolt, so that its sensitivity is at least increased by 5 times relative to traditional scheme using capillary steel tube, greatly improves the sensitivity of grating strain gauge in monitoring the bolt tightness state online, and its manufacturing cost is low, so a kind of high-sensitivity, low-cost optical fiber type smart bolt is realized.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing, and in particular to a smart bolt based on a grating strain gauge. Background Technology

[0002] Bolts are considered the preferred fastener in practical applications due to their ability to connect and fasten detachable parts and their ease of disassembly. However, this ease of disassembly also makes bolts prone to loosening and loss of preload. Depending on the application, the consequences of bolt loosening vary: from minor economic losses to serious personal injury or death. To avoid safety accidents and economic losses caused by bolt loosening, real-time online monitoring of bolt tightness is essential. Fiber optic smart bolts are devices that utilize optical fibers as both sensing elements and light transmission media to detect bolt tightness in real time.

[0003] The typical manufacturing method for fiber optic smart bolts involves creating a square or round hole of a certain depth inside the bolt, then encapsulating a grating (a structure in optical fiber that exhibits periodic refractive index changes after being exposed to ultraviolet light, capable of reflecting a specific center wavelength, the wavelength of which is proportional to the grating pitch) within a capillary tube. The capillary tube is then sealed within the square or round hole inside the bolt using epoxy resin. Its working principle is as follows: when torque or axial tension is applied to the bolt, axial strain is generated inside the bolt. This strain is transmitted to the capillary tube, which "senses" this strain and causes the grating (its grating pitch) to elongate or shorten, thereby changing the center wavelength of the grating. However, the sensitivity (the slope of the curve showing the relationship between center wavelength and force) of this type of fiber optic smart bolt is not high, typically around 10-15 pm / kN. This is because the capillary tube is positioned between the bolt and the grating, resulting in low transmission efficiency when the axial strain generated inside the bolt is transmitted to the grating, leading to low sensitivity of the smart bolt.

[0004] CN202010421567.1 discloses a high-temperature smart bolt that uses a femtosecond laser to inscribe a grating, which is then metallized and encapsulated. A grating sensor is then implanted into the bolt hole using a "threaded structure + high-temperature adhesive" approach. Its function is to achieve intelligent monitoring of bolts in high-temperature environments. While this solution eliminates the use of capillary steel tubes, the metallized grating encapsulation is costly and unsuitable for large-scale applications, and its sensitivity is also quite limited.

[0005] In conclusion, how to construct a highly sensitive, low-cost fiber optic smart bolt is a problem that needs to be solved.

[0006] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] The main objective of this invention is to overcome the shortcomings of the aforementioned background technology and provide a high-sensitivity, low-cost smart bolt based on a grating strain gauge.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A smart bolt based on a grating strain gauge includes a bolt and a grating strain gauge. The bolt has a hole inside, and the grating strain gauge is coated with quick-drying adhesive. The grating strain gauge is adhered to the hole by the quick-drying adhesive.

[0010] Furthermore:

[0011] The grating strain gauge is mounted in the hole by a removable or fixed spring-loaded mechanism, and the quick-drying adhesive is adhered to the hole by applying elastic pressure to the grating strain gauge.

[0012] The grating strain gauge includes an optical fiber with a grating, a substrate, a fixing film, and a protective layer. The fixing film fixes the optical fiber with the grating on the substrate, and the protective layer is disposed on the fixing film. Preferably, the fixing film is a polyimide film.

[0013] The grating strain gauge also includes limiting blocks located on both sides of the optical fiber with the grating. The lower surface of the limiting block is fixed to the substrate by adhesive. The fixing film is solidified and formed by liquid material and attached to the substrate by the limiting block.

[0014] The limiting block includes a left limiting block and a right limiting block, the left limiting block and the right limiting block having L-shaped front ends arranged opposite to each other, and a gap is formed between the two L-shaped front ends to allow optical fibers to pass freely.

[0015] It also includes an optical fiber connector, an optical fiber sleeve, a sheath, and a parallel optical fiber, wherein the optical fiber of the grating strain gauge is connected to the optical fiber connector in sequence through the parallel optical fiber, the sheath, and the optical fiber sleeve.

[0016] The removable spring-loaded mechanism constitutes a feeding fixture, including fastening screws, upper and lower clamping plates, and a pressure spring disposed between the upper and lower clamping plates. The fastening screws are mounted on the upper and lower clamping plates to adjust the tightness between them. When the fastening screws are tightened, the upper and lower clamping plates are brought together. The grating strain gauge is mounted on the feeding fixture with the side with the quick-drying adhesive facing away from the upper and lower clamping plates and is fed into the hole. When the fastening screws are loosened, the pressure spring applies a separating force to the upper and lower clamping plates, pressing the quick-drying adhesive along with the grating strain gauge into the hole. Preferably, before pressing the grating strain gauge into the hole, high-temperature adhesive tape is used to temporarily fix the grating strain gauge on the feeding fixture.

[0017] The fixed spring-loaded mechanism includes a mounting auxiliary block and a bow-shaped spring. The grating strain gauge is disposed on the mounting auxiliary block, with the side of the grating strain gauge containing the quick-drying adhesive facing away from the mounting auxiliary block. The bow-shaped spring is disposed on the opposite side of the mounting auxiliary block. Optionally, the hole is a deformable square hole, and the fixed spring-loaded mechanism further includes a mounting auxiliary rod for engaging the deformable square hole to compress the bow-shaped spring.

[0018] The grating strain gauge also includes a locking sleeve, an optical fiber flange, and a sleeve. The locking sleeve is used to connect and lock the optical fiber flange and the mounting auxiliary block. The sleeve passes through the optical fiber flange. The locking sleeve has a ferrule for mounting the optical fiber embedded in it. The sleeve is used to mate the ferrule with the optical fiber connector.

[0019] The hole contains a filler, preferably a waterproof silicone.

[0020] The present invention has the following beneficial effects:

[0021] The smart bolt based on a grating strain gauge of this invention eliminates the need for a capillary steel tube as an intermediate transmission medium. Instead, the grating strain gauge is directly adhered to the bolt hole using quick-drying adhesive. This direct adhesion method allows the grating to quickly and sensitively "sense" the axial strain inside the bolt, increasing its sensitivity by at least five times compared to the traditional method using a capillary steel tube. This significantly improves the sensitivity of the grating strain gauge in online monitoring of bolt tightness, and its manufacturing cost is low. Thus, a high-sensitivity, low-cost fiber optic smart bolt is achieved. In a preferred embodiment, the grating strain gauge is mounted using an in-hole removable or in-hole fixed spring-loaded mechanism. Elastic pressure is applied to the grating strain gauge inserted into the bolt hole, thereby firmly adhering the quick-drying adhesive to the bolt hole. This achieves a reliable and convenient method of adhering the grating strain gauge to the bolt hole using quick-drying adhesive.

[0022] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the discrete grating strain gauge in an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the integrated grating strain gauge in an embodiment of the present invention.

[0025] Figure 3 This is a schematic diagram of attaching a discrete grating strain gauge to the inside of a bolt using a feeding fixture in an embodiment of the present invention.

[0026] Figure 4 This is a schematic diagram of attaching an integrated grating strain gauge to the inside of a bolt using an installation auxiliary rod in an embodiment of the present invention.

[0027] Figure 5 This is a front cross-sectional view of a discrete grating strain gauge pasted inside a bolt in an embodiment of the present invention.

[0028] Figure 6 This is a side cross-sectional view of an integrated grating strain gauge being attached inside a bolt in an embodiment of the present invention.

[0029] Figure 7 This is a schematic diagram of applying torque to the smart bolt in an embodiment of the present invention;

[0030] Figure 8a This is a curve showing the relationship between the applied torque and the center wavelength in an embodiment of the present invention;

[0031] Figure 8b This is the curve showing the relationship between axial force and center wavelength in an embodiment of the present invention.

[0032] The attached figures are labeled as follows:

[0033] 1. Discrete grating strain gauge

[0034] 1.1 Fiber Optic Connector

[0035] 1.2 Fiber Optic Sleeve

[0036] 1.3 Sheath

[0037] 1.4 with optical fiber

[0038] 1.5 Optical fiber etched with a grating

[0039] 1.5.1 Grating

[0040] 1.6 Substrate

[0041] 1.7 Limit Block

[0042] 1.8 Polyimide film

[0043] 1.9 Protective Layer

[0044] 2 Integrated grating strain gauge

[0045] 2.1 Install auxiliary blocks

[0046] 2.2 Bow-shaped shrapnel

[0047] 2.3 Locking sleeve

[0048] 2.4 Square Fiber Optic Flange

[0049] 2.5 Ceramic Sleeve

[0050] 3 bolts

[0051] 3.1 Square Hole

[0052] 3.2 Deformation Hole

[0053] 3.3 Fiber Optic Flange Mounting Holes

[0054] 4. Quick-drying adhesive

[0055] 5. Feed the tooling

[0056] 5.1 Springs

[0057] 5.2 Fastening screws

[0058] 5.3 Plywood

[0059] 6. Install the auxiliary stick

[0060] 7. Filler material in the hole

[0061] 8 Bolt fixing blocks

[0062] 9. Test bench

[0063] 10 nuts

[0064] 11. Digital torque wrench. Detailed Implementation

[0065] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0066] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for fixing, coupling, or communication.

[0067] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0068] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0069] See Figures 1 to 7 This invention provides a smart bolt based on a grating strain gauge, including a bolt 3 and grating strain gauges 1 and 2. The bolt 3 has holes 3.1 and 3.2 inside. The grating strain gauges 1 and 2 are provided with quick-drying adhesive 4, and the grating strain gauges 1 and 2 are attached to the holes 3.1 and 3.2 by the quick-drying adhesive 4.

[0070] The smart bolt can be either a fiber-optic-coated or fiber-free type. In both types, a grating strain gauge is directly adhered to the inside of the bolt using quick-drying adhesive. When the smart bolt is subjected to torque or axial tension, axial strain occurs inside the bolt, causing the grating in the strain gauge to elongate or shorten axially, thereby changing the center wavelength of the grating. By monitoring this change in center wavelength, the bolt's tightness can be monitored in real time. The smart bolt with a fiber optic coaxial cable can use a discrete grating strain gauge (see [reference]). Figure 1 , Figure 3 and Figure 5 ). A fiber-retaining smart bolt can utilize an integrated optical grating strain gauge 2 (see...) Figure 2 , Figure 4 and Figure 6 ).

[0071] The quick-drying adhesive 4 can be 502 glue, 401 glue, 406 glue, etc. After applying a force of about 10N to the grating strain gauge for 1-2 minutes, the grating strain gauge can be firmly bonded to the inside of the bolt.

[0072] The bolt hole can be a square hole 3.1 (see [reference]). Figure 3 ) or deformed hole 3.2 (see Figure 4Square or deformed holes can be created inside the bolt using electrical discharge machining (EDM). To facilitate the adhesion of the grating strain gauge, the surface of the hole where the strain gauge is to be attached should be flat, smooth, free of oil and debris.

[0073] Gratings can be fabricated using ultraviolet lasers and phase masks. This fabrication method is characterized by low cost and the ability to fabricate gratings in batches. Grating types can include Bragg gratings, long-period gratings, tilted gratings, chirped gratings, etc.

[0074] In a preferred embodiment, a removable spring-loaded mechanism (see [reference]) Figure 1 , Figure 3 and Figure 5 ) or fixed spring-loaded mechanism (see Figure 2 , Figure 4 and Figure 6 The grating strain gauges 1 and 2 are mounted in the holes 3.1 and 3.2, and elastic pressure is applied to the grating strain gauges 1 and 2 to firmly adhere the quick-drying adhesive 4 to the holes 3.1 and 3.2. The grating strain gauges are mounted using a removable or fixed spring-loaded mechanism within the holes, and elastic pressure is applied to the grating strain gauges inserted into the bolt holes, thereby firmly adhering the quick-drying adhesive to the bolt holes. This achieves a reliable and convenient method of firmly adhering the grating strain gauges to the bolt holes using quick-drying adhesive.

[0075] See Figure 1 and Figure 2 In a preferred embodiment, the grating strain gauge includes an optical fiber 1.5 having a grating 1.5.1, a substrate 1.6, a fixing film (such as a polyimide film 1.8), and a protective layer 1.9. The fixing film fixes the optical fiber 1.5 having the grating 1.5.1 onto the substrate 1.6, and the protective layer 1.9 is disposed on the fixing film. More preferably, the fixing film is a polyimide film 1.8.

[0076] See Figure 1 and Figure 2 In a preferred embodiment, the grating strain gauge further includes limiting blocks 1.7 located on both sides of the optical fiber 1.5 having the grating 1.5.1. The lower surface of the limiting blocks 1.7 is fixed to the substrate by adhesive. The fixing film (such as a polyimide film 1.8) is cured from liquid material and attached to the substrate 1.6 by means of the limiting blocks 1.7. In a more preferred embodiment, the thermosetting process of the polyimide film 1.8 will be further described in detail below.

[0077] See Figure 1 and Figure 2In a preferred embodiment, the limiting block 1.7 includes a left limiting block and a right limiting block, the left limiting block and the right limiting block having L-shaped front ends arranged opposite to each other, and a gap is formed between the two L-shaped front ends to allow the optical fiber to pass through freely.

[0078] See Figure 1 and Figure 2 In a preferred embodiment, the device further includes an optical fiber connector 1.1, an optical fiber sleeve 1.2, a sheath 1.3, and a parallel optical fiber 1.4. The optical fiber of the grating strain gauge is connected to the optical fiber connector 1.1 in sequence through the parallel optical fiber 1.4, the sheath 1.3, and the optical fiber sleeve 1.2.

[0079] See Figure 3 In a preferred embodiment, the removable spring-loaded mechanism constitutes a feeding fixture 5, which includes a fastening screw 5.2, upper and lower clamping plates 5.3, and a pressure spring 5.1 disposed between the upper and lower clamping plates 5.3. The fastening screw 5.2 is mounted on the upper and lower clamping plates 5.3 to adjust the tightness between them. When the fastening screw 5.2 is tightened, the upper and lower clamping plates 5.3 are pressed together. The grating strain gauge is mounted on the feeding fixture 5 with the side with the quick-drying adhesive 4 facing away from the upper and lower clamping plates 5.3 and fed into the bolt hole. When the fastening screw 5.2 is loosened, the pressure spring 5.1 applies a force to the upper and lower clamping plates 5.3, pressing the quick-drying adhesive 4 together with the grating strain gauge into the bolt hole. Before pressing the grating strain gauge into the bolt hole, high-temperature adhesive tape can be used to temporarily fix the grating strain gauge on the feeding fixture 5. After the grating strain gauge is attached to the bolt hole, it can be removed and sent to tooling 5.

[0080] See Figure 2 and Figure 4 In a preferred embodiment, the fixed spring-loaded mechanism includes a mounting auxiliary block 2.1 and a bow-shaped spring 2.2. The grating strain gauge is disposed on the mounting auxiliary block 2.1, with the side of the grating strain gauge containing the quick-drying adhesive 4 facing away from the mounting auxiliary block 2.1. The bow-shaped spring 2.2 is disposed on the opposite side of the mounting auxiliary block 2.1. Optionally, the bolt hole is a deformation hole 3.2, and the fixed spring-loaded mechanism further includes a mounting auxiliary rod 6 for engaging the deformation hole 3.2 to compress the bow-shaped spring 2.2.

[0081] See Figure 2 and Figure 4In a preferred embodiment, the grating strain gauge further includes a locking sleeve 2.3, an optical fiber flange 2.4, and a sleeve 2.5. The locking sleeve 2.3 is used to connect and lock the optical fiber flange 2.4 and the mounting auxiliary block 2.1. The sleeve 2.5 passes through the optical fiber flange 2.4. The locking sleeve 2.3 has an embedded ferrule for mounting the optical fiber. The sleeve 2.5 is used to mate the ferrule with the optical fiber connector 1.1.

[0082] See Figure 5 and Figure 6 In a preferred embodiment, the hole contains a filler 7. More preferably, the filler 7 comprises waterproof silicone.

[0083] The smart bolt based on grating strain gauges in this invention eliminates the need for capillary steel tubes as an intermediate transmission medium. Instead, the grating strain gauges are directly adhered to the bolt hole using quick-drying adhesive. This direct adhesion method allows the grating to quickly and sensitively "sense" the axial strain inside the bolt, increasing its sensitivity by at least 5 times compared to the traditional method using capillary steel tubes. This significantly improves the sensitivity of the grating strain gauges in online monitoring of bolt tightness, and its manufacturing cost is low. Thus, a highly sensitive and low-cost fiber optic smart bolt is realized.

[0084] The following describes specific embodiments of the present invention.

[0085] A schematic diagram of the discrete grating strain gauge in an embodiment of the present invention is shown below. Figure 1As shown, it includes an optical fiber connector 1.1, an optical fiber sleeve 1.2, a sheath 1.3, an optical fiber with a grating 1.4, an optical fiber with a grating 1.5, a substrate 1.6, a limiting block 1.7, a polyimide film 1.8, and a protective layer 1.9. Among them, fiber optic connector 1.1 is used to connect the grating strain gauge to the grating demodulation instrument; fiber optic sleeve 1.2 is used to protect the optical fiber between fiber optic connector 1.1 and sheath 1.3; sheath 1.3 is used to connect the parallel fiber 1.4 to fiber optic sleeve 1.2; parallel fiber 1.4 is used to strengthen the mechanical strength of the optical fiber between sheath 1.3 and substrate 1.6; the grating-etched optical fiber 1.5 is divided into two segments: a grating segment and an optical fiber segment. The grating segment contains grating 1.5.1, which serves as the sensitive element for strain sensing and has the characteristics of low cost and mass production capability. The optical fiber segment only serves as the medium for transmitting light; the substrate 1.6 is made of metal material, such as stainless steel or aluminum alloy, with a thickness of only 40-80 micrometers, and both upper and lower surfaces are flat, smooth, and free of oil stains. No debris; the limiting block 1.7 is composed of a left limiting block and a right limiting block, and the lower surface of both the left and right limiting blocks has a layer of pressure-sensitive adhesive, which is adhesive and can be directly adhered to the substrate. The left and right limiting blocks are used to limit the length, width, and height dimensions of the polyimide film 1.8; the polyimide film 1.8 is used to firmly fix the grating segment to the substrate 1.6. The polyimide film 1.8 is obtained by thermosetting a polyimide solution. Preferably, the temperature control process of the thermosetting process of the polyimide film 1.8 is as follows: raising the temperature from room temperature to 80℃-100℃ and maintaining it for 1-2 hours, raising the temperature to 150℃-160℃ and maintaining it for 1-2 hours, raising the temperature to 220℃-230℃ and maintaining it for 2-3 hours, and then allowing the temperature to cool naturally to room temperature. The lower surface of the protective layer 1.9 also has a layer of pressure-sensitive adhesive, which is adhesive and can be directly adhered to the upper surface of the limiting block.

[0086] Figure 2 This is a schematic diagram of the integrated grating strain gauge in an embodiment of the present invention, comprising an optical fiber sleeve 1.2, a sheath 1.3, an optical fiber 1.4, an optical fiber 1.5 with a grating, a substrate 1.6, a limiting block 1.7, a polyimide film 1.8, a protective layer 1.9, an installation auxiliary block 2.1, a bow-shaped spring 2.2, a locking sleeve 2.3, a square optical fiber flange 2.4, and a ceramic sleeve 2.5. The installation auxiliary block 2.1 is used to fix the grating strain gauge and assist in its adhesion; the bow-shaped spring 2.2 generates pressure on the installation auxiliary block 2.1, which is transmitted to the grating strain gauge through the installation auxiliary block 2.1; the locking sleeve 2.3 (with an embedded ceramic ferrule) connects and locks the square optical fiber flange 2.4 to the installation auxiliary block 2.1, wherein the square optical fiber flange 2.4 and the locking sleeve 2.3 are further connected by the ceramic sleeve 2.5, which is used for the mating of the external optical fiber connector with the ceramic ferrule in the locking sleeve 2.3.

[0087] Figure 3 This is a schematic diagram illustrating the process of attaching a discrete grating strain gauge 1 to the inside of a bolt using a feeding fixture in an embodiment of the present invention. The process is described as follows: 1) Place the discrete grating strain gauge 1 on the feeding fixture 5 with the lower surface of the substrate 1.6 facing upwards and temporarily fix it with high-temperature adhesive tape; 2) Tighten the fastening screws 5.2 to minimize the distance between the upper and lower clamping plates 5.3; 3) Apply an appropriate amount of quick-drying adhesive 4 to the lower surface of the substrate 1.6; 4) Place the feeding fixture with the discrete grating strain gauge 1 on it. 5. Quickly insert the bolt 3 into the bottom of the square hole 3.1 inside the bolt 3; 5) Loosen the fastening screw 5.2. Due to the presence of the spring 5.1, it will provide an elastic force to the upper and lower clamps 5.3, causing them to push upwards onto the base 1.6, which is coated with an appropriate amount of quick-drying adhesive 4. After 1-2 minutes, due to the strong adhesive effect of the quick-drying adhesive 4, the base 1.6 will be firmly adhered to the inner wall of the square hole 3.1 inside the bolt 3; 6) Take out the tooling 5 and the high-temperature adhesive paper to complete the pasting of the discrete grating strain gauge 1.

[0088] Figure 4 This is a schematic diagram of attaching an integrated grating strain gauge to the inside of a bolt using an installation auxiliary rod in an embodiment of the present invention. The process is described as follows: 1) Apply an appropriate amount of quick-drying adhesive 4 to the lower surface of the substrate 1.6 of the integrated grating strain gauge 2; 2) Simultaneously and quickly insert the installation auxiliary rod 6 (used to compress the bow-shaped spring 2.2, so that it exerts pressure on the installation auxiliary block 2.1) and the integrated grating strain gauge 2 into the bottom of the deformable square hole 3.2 inside the bolt 3; 3) Due to the pressure exerted by the installation auxiliary rod 6 on the bow-shaped spring 2.2... The pressure exerted by the arc-shaped spring 2.2 on the mounting auxiliary block 2.1 is transmitted to the grating strain gauge through the mounting auxiliary block 2.1; 4) An appropriate amount of quick-drying adhesive 4 is applied to the substrate 1.6. After being squeezed for 1-2 minutes, the substrate 1.6 is firmly adhered to the inner wall of the deformable square hole 3.3 inside the bolt 3 due to the strong adhesive effect of the quick-drying adhesive 4; 5) The integral grating strain gauge 2 is attached by connecting the square fiber optic flange 2.4 and the fiber optic flange mounting hole 3.3 with screws.

[0089] Figure 5 This is a front cross-sectional view of the discrete grating strain gauges pasted inside the bolt in an embodiment of the present invention. The discrete grating strain gauge 1 is located at the bottom of the square hole 3.1 inside the bolt 3. In addition to the discrete grating strain gauge 1, the square hole 3.1 also contains a hole filler 7, which can be waterproof silicone or the like.

[0090] Figure 6 This is a side cross-sectional view of the integrated grating strain gauge being pasted inside the bolt in an embodiment of the present invention. The integrated grating strain gauge 2 is located at the bottom of the deformable square hole 3.2 inside the bolt 3. In addition to the integrated grating strain gauge 2, the deformable square hole 3.2 also contains a hole filler 7, which can be waterproof silicone or the like.

[0091] Figure 7 This is a schematic diagram illustrating the application of torque to the smart bolt in an embodiment of the present invention. It is worth noting that, to avoid repetition, the following embodiment uses a smart bolt with a pigtail as an example (this also applies to smart bolts without pigtails). Bolt 3 is fixed to the test bench 9 by bolt fixing block 8 using screws. The discrete grating strain gauge 1 in the smart bolt with a pigtail is connected to a grating demodulator via fiber optic connector 1.1. One function of the grating demodulator is to demodulate the center wavelength of the grating 1.5.1. Additionally, a matching nut 10 needs to be screwed onto bolt 3. A digital torque wrench 11 is used to apply a torque of 0-500 N·m to the nut 10. It is important to note that before starting the measurement, the digital torque wrench 11 must be zeroed, and the nut 10 should be in a quasi-pre-tightened state (the axial force along the bolt axis is zero; once torque is applied, the axial force is not zero).

[0092] Figure 8a shows the relationship curve between the applied torque and the center wavelength in this embodiment of the invention. Based on actual measurements, when the applied torque is 0 N·m (i.e., the bolt is in a "loose" state), the center wavelength of the discrete grating strain gauge 1 is approximately 1536.3 nm; when the applied torque is approximately 450 N·m (i.e., the bolt is in a "tight" state), the center wavelength of the discrete grating strain gauge 1 is approximately 1537.1 nm. It can be seen that the center wavelength (y) of the discrete grating strain gauge 1 and the applied torque (x) satisfy a good linear relationship: y = 0.0016x + 1536.4117, with a linearity (R0) of [missing value]. 2 The value is 0.9718. Based on this linear relationship, the tightness of bolt 3 can be obtained by monitoring the change in the center wavelength of discrete grating strain gauge 1 in real time online.

[0093] According to the current industry standard HB / Z 251-1993 "Relationship between bolt tightening torque and axial force", it can be seen that the bolt torque and axial force satisfy a linear relationship, that is, M=k·d·F (1).

[0094] In the formula, M is the tightening torque of the bolt, in N·m; F is the axial force of the bolt, in N; k is the bolt tightening torque coefficient; and d is the bolt diameter, in m.

[0095] In this embodiment, an M24 alloy steel bolt is selected, i.e., d is 24×10. -3 m, when the thread is unlubricated, the value of k is generally taken as 0.2. Therefore, according to the above equation (1), we can obtain the axial force under the applied torque.

[0096] Figure 8b This is the relationship curve between axial force and center wavelength in the embodiments of the present invention, derived from formula (1) and Figure 8aIt can be seen that the center wavelength (y) of discrete grating strain gauge 1 satisfies a good linear relationship with the axial force (i): y = 0.0773i + 1536.4117, and the linearity (R) is good. 2 The sensitivity is 0.9718. In other words, the sensitivity of the smart bolt in this invention is 0.0773 nm / kN, or 77.3 pm / kN. This sensitivity is 5.15-7.73 times that of existing smart bolts (10-15 pm / kN), meaning that the sensitivity of the smart bolt in this invention is at least 5 times higher.

[0097] The working principle of this invention is as follows:

[0098] Because the quick-drying adhesive firmly bonds the grating strain gauge to the inside of the bolt, when the smart bolt is subjected to torque or axial tension, axial strain will occur inside the bolt. Since the grating strain gauge in this invention is bonded and assembled inside the bolt, the strain inside the bolt can very sensitively drive the grating in the grating strain gauge to elongate or shorten axially, thereby changing the center wavelength of the grating. By monitoring the change in the center wavelength, the tightness of the bolt can be monitored online in real time and reliably.

[0099] The background section of this invention may include background information about the problems or environment in which the invention is being developed, and is not necessarily a description of prior art. Therefore, the content included in the background section does not constitute an admission of prior art by the applicant.

[0100] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A smart bolt based on a grating strain gauge, characterized in that, The device includes a bolt and a grating strain gauge. The bolt has an internal hole. The grating strain gauge includes an optical fiber with a grating, a substrate, a fixing film, and a protective layer. The fixing film fixes the optical fiber with the grating to the substrate. The protective layer is disposed on the fixing film. The lower surface of the substrate is adhered to the inner wall of the hole inside the bolt using quick-drying adhesive, thereby adhering the entire grating strain gauge to the hole using the quick-drying adhesive. The grating strain gauge also includes limiting blocks located on both sides of the optical fiber with the grating. The lower surface of the limiting blocks is fixed to the substrate using adhesive. The fixing film is formed by curing a liquid material and adhering to the substrate using the limiting blocks. The limiting blocks include a left limiting block and a right limiting block, which are arranged opposite to each other. The L-shaped front end forms a gap between the two L-shaped front ends, allowing the optical fiber to pass freely. A fixed spring-loaded mechanism mounts the grating strain gauge within the hole and applies elastic pressure to the grating strain gauge to firmly adhere the quick-drying adhesive within the hole. The fixed spring-loaded mechanism includes an installation auxiliary block and a bow-shaped spring. The grating strain gauge is mounted on the installation auxiliary block, with the side of the grating strain gauge containing the quick-drying adhesive facing away from the installation auxiliary block. The bow-shaped spring is located on the opposite side of the installation auxiliary block. The grating strain gauge also includes a locking sleeve, an optical fiber flange, and a sleeve. The locking sleeve connects and locks the optical fiber flange to the installation auxiliary block. The sleeve passes through the optical fiber flange and has an embedded ferrule for mounting the optical fiber. The sleeve mates the ferrule with the optical fiber connector.

2. The smart bolt as described in claim 1, characterized in that, The fixing film is a polyimide film.

3. The smart bolt as described in claim 1, characterized in that, It also includes an optical fiber connector, an optical fiber sleeve, a sheath, and a parallel optical fiber, wherein the optical fiber of the grating strain gauge is connected to the optical fiber connector in sequence through the parallel optical fiber, the sheath, and the optical fiber sleeve.

4. The smart bolt as described in claim 1, characterized in that, The hole is a deformable square hole, and the fixed spring-loaded mechanism also includes an auxiliary mounting rod for engaging the deformable square hole to compress the bow-shaped spring.

5. The smart bolt as described in any one of claims 1 to 3, characterized in that, The hole contains a filling material.

6. The smart bolt as described in claim 5, characterized in that, The filler includes waterproof silicone.

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