JP7401817B2 - Looseness detection sensor and looseness detection method using it - Google Patents

Description

The present invention relates to a loosening detection sensor that detects loosening of bolts or nuts that fix parts, and a loosening detection method using the same.

Bolts are used to tighten and fix parts, and are used in a variety of applications, from large equipment such as infrastructure structures and plant equipment to familiar products such as vehicles, play equipment, and furniture. Bolt joints may loosen or fall off due to deterioration such as vibration, compositional deformation due to excessive force, and fatigue.

These causes, for example, bridge collapse accidents, gas and liquid leaks from joints, damage to play equipment, and personal accidents caused by falling objects from high places. In order to prevent these accidents, for example, Non-Patent Document 1 proposes a method of marking bolts and monitoring the misalignment of the alignment marks. Furthermore, Non-Patent Documents 2 and 3 disclose methods of detecting abnormalities using waveguide sensors.

Measures against loosening of structures, [searched on April 13, 2020], Internet (https://www.euroke.co.jp/linecap1/) E. Matsunaga ; M. Nakamura ; T. Minotani ; M. Tsuda, “Paintable Wireless Passive Sensor based on Electromagnetic Waveguide to Detect Loose Bolts for Remote Infrastructure Inspection.” Proc. IEEE SENSORS 2019, Montreal, QC, Canada, Canada,2019 . E. Matsunaga, T. Minotani, S. Oka, and M. Tsuda, “Fundamental study of coating-type sensor for detection of infrastructure deterioration.” Proceedings of the 65th Japan Conference on Materials and Environments, Japan, pp. 178-181 , 2019 (in Japanese).

However, methods such as monitoring the misalignment of alignment marks are not suitable when the inspection target is located in a place that is difficult to see, or when inspecting a part that is difficult to visually inspect, such as at a distance. In addition, the method of detecting abnormalities using waveguide sensors requires the sensor to be painted on the structure, so if paint is painted on the bolt, there are problems with construction, such as having to repaint it after detecting looseness. There are challenges. Another problem is that it is difficult to install sensors in existing equipment that has already been constructed.

The present invention has been made in view of this problem, and an object thereof is to provide a looseness detection sensor that causes fewer problems in construction and is easy to install in installed equipment, and a looseness detection method using the same. do.

A loosening detection sensor according to one aspect of the present invention is a loosening detection sensor that detects loosening of a bolt or nut that fixes a component, and the loosening detection sensor includes an insulating layer and a first insulating layer sandwiching the insulating layer from above and below. The gist is that it is provided with a conductive layer and a second conductive layer, and has a washer shape that is sandwiched between the component and the bolt or the component and the nut without directly contacting the shaft of the bolt.

Further, a looseness detection method according to one aspect of the present invention is a looseness detection method performed by the above-mentioned looseness detection apparatus, and includes an insulating layer, and a first conductive layer and a second conductive layer sandwiching the insulating layer from above and below. A high-frequency signal having a frequency in a predetermined range is swept and applied to a looseness detection sensor having a washer shape that is sandwiched between the component and the bolt or the component and the nut without making direct contact with the shaft of the bolt. , a reflected wave receiving step of receiving a reflected wave of the high frequency signal, a peak value recording step of recording a peak value of the reflected wave, and a comparing step of comparing the peak value and the past peak value to determine the amount of change. and a determination step of determining that there is no slack when the amount of change is less than a threshold, and determining that there is slack when the amount of change is greater than or equal to the threshold.

According to the present invention, it is possible to provide a looseness detection sensor and a looseness detection method using the same, which have few problems in construction and are easy to install in installed equipment.

FIG. 2 is a perspective view showing an example of a bolt fixing portion using a loosening detection sensor according to an embodiment of the present invention. 2 is a structural cross-sectional view taken along line AA shown in FIG. 1. FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a loosening detection sensor and a loosening detection device according to a first embodiment of the present invention. FIG. 2 is a diagram showing an example of the planar shape of the looseness detection sensor shown in FIG. 1; 4 is a diagram showing a resonance frequency spectrum measured using the looseness detection sensor and the looseness detection device shown in FIG. 3. FIG. FIG. 4 is a block diagram showing an example of the functional configuration of the looseness detection device shown in FIG. 3. FIG. 4 is a flowchart showing a processing procedure of the looseness detection device shown in FIG. 3. FIG. It is a schematic diagram showing the loosening detection sensor concerning a 2nd embodiment of the present invention. FIG. 9 is a diagram showing a resonance frequency spectrum measured using the looseness detection sensor and the looseness detection device shown in FIG. 8; It is a schematic diagram showing the loosening detection sensor concerning a 2nd embodiment of the present invention. FIG. 11 is a diagram showing a resonance frequency spectrum measured using the looseness detection sensor and the looseness detection device shown in FIG. 10. 11 is a schematic diagram showing a modification of the looseness detection sensor shown in FIG. 10. FIG. 13 is a diagram showing a resonance frequency spectrum measured using the looseness detection sensor and the looseness detection device shown in FIG. 12. FIG.

Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are given to the same parts in the plurality of drawings, and description thereof will not be repeated.

[First embodiment]
FIG. 1 is a perspective view showing an example of a looseness detection sensor according to a first embodiment of the present invention. The loosening detection sensor 5 shown in FIG. 1 is used to detect loosening of a bolt 4 and a nut that fix two parts 1 and 2.

In the example shown in FIG. 1, parts 1 and 2 are made of steel. The structure for fixing the two parts 1 and 2 is not limited to this example. There may be a plurality of bolts 4. The looseness detection sensor 5 has a washer shape and is arranged between the component 1 and the bolt 4 or between the component 2 and the nut.

FIG. 2 is a structural cross-sectional view taken along line AA shown in FIG. In FIG. 2, a bolt 4, a nut 6, and a typical washer 9 are shown in their appearance.

As shown in FIG. 2, the looseness detection sensor 5 is arranged, for example, on the neck 4a side of the bolt 4. Alternatively, it may be placed on the nut 6 side. Further, it may be arranged on both the neck 4a side and the nut 6 side.

The looseness detection sensor 5 has a three-layer structure in which an insulating layer 5b is sandwiched between a first conductive layer 5a and a second conductive layer 5c. Moreover, the looseness detection sensor 5 has a washer shape that is sandwiched between the component 1 and the bolt 4 or the component 2 and the nut 6 without directly contacting the shaft 4b of the bolt 4.

The size of the hole in the center of the washer shape is larger than the diameter of the shaft 4b of the bolt 4 whose loosening is to be detected. are electrically connected to each other. On the other hand, the shape does not directly contact the shaft 4b of the bolt 4 and the threaded portion 4c.

The first and second conductive layers 5a and 5c are made of the same material as a general washer. For example, stainless steel materials such as SUS304, 310, and 316 and vapor deposits of these metals are used.

The insulating layer 5b is made of elastic resin such as PTFE or PTE, for example. Alternatively, materials other than resins such as oxides and glass may be used.

FIG. 3 is a schematic diagram showing the looseness detection device 200 of the looseness detection sensor 5 according to the present embodiment. FIG. 4 is a diagram showing an example of the planar shape of the looseness detection sensor 5. As shown in FIG.

The looseness detection device 200 sweeps and applies a high frequency signal having a frequency in a predetermined range to the first conductive layer 5a, and detects the resonance frequency (natural frequency) of the looseness detection sensor 5. The resonance wavelength λ ₁ of the looseness detection sensor 5 can be expressed by the following equation. The resonance wavelength λ ₁ is the wavelength of the first-order natural frequency.

The resonance wavelength λ ₁ is the wavelength of the high frequency signal confined in the insulating layer 5b of the looseness detection sensor 5. Therefore, the resonant wavelength λ ₁ differs depending on the material of the insulation layer 5b. Here, L is the length of the half circumference of a circle passing through the center of the washer-shaped ring width W. n is an integer of 1 or more.

The resonant frequency f changes depending on how the bolt 4 is tightened. When the bolt 4 is loose, the resonance frequency is the same as the resonance frequency of the loosening detection sensor 5 alone (Formula (1)). On the other hand, when the bolt 4 is tightened, the inner circumferential portion of the loosening detection sensor 5 is short-circuited by the head of the bolt 4, so that the electric field strength at the inner circumferential portion decreases. Therefore, the propagation mode of the high-frequency signal changes, and the resonant wavelength λ ₁ expressed by equation (1) becomes shorter. In this way, loosening of the bolt 4 can be detected based on changes in the resonance frequency. Furthermore, the loosening of the bolt 4 can also be detected based on the presence or absence of the resonance frequency.

FIG. 5 shows an example of a change in the resonance frequency detected using the looseness detection sensor 5 manufactured for the M30 bolt 4. The horizontal axis in FIG. 3 is frequency (GHz), and the vertical axis is arbitrary units (dB).

In FIG. 5, the solid line indicates the resonance frequency when the bolt 4 is tightened, and the broken line indicates the resonance frequency when the bolt 4 is loosened. The resonant frequency of about 2.1 GHz changes to about 1.4 GHZ by loosening the bolt 4. Further, the resonance frequency of about 2.9 GHZ changes to about 2.5 GHZ by loosening the bolt 4.

In this way, loosening of the bolt 4 can be detected based on a change in the resonance frequency. The looseness detection sensor 5 according to this embodiment has a washer shape that is sandwiched between the bolt 4 or the nut 6, and therefore has excellent workability. In addition, since the shape is annular, the risk of injury to workers is low and safety is high.

Next, a loosening detection device according to an embodiment of the present invention will be described.

(Looseness detection device)
FIG. 6 is a block diagram showing an example of the functional configuration of the looseness detection device 200 according to the embodiment of the present invention. A flowchart showing the processing procedure is shown in FIG.

The looseness detection device 200 includes a frequency sweep section 20, a high frequency application section 21, a vibration mode detection section 22, a vibration mode recording section 23, a determination section 24, and a control section 25. The control unit 25 is a functional configuration unit that controls the operation of each functional configuration unit, and can be configured by, for example, a computer including ROM, RAM, CPU, and the like. When the control unit 25 is implemented by a computer, a part of the vibration mode detection unit 22, the vibration mode recording unit 23, and the determination unit 24 can also be configured by the computer.

The looseness detection device 200 inputs a high frequency signal to the first conductive layer 5a of the looseness detection sensor 5. The frequency sweep section 20 sweeps frequencies within a predetermined range. The high frequency application section 21 generates a high frequency signal of the frequency swept by the frequency sweep section 20, and applies it to the first conductive layer 5a of the looseness detection sensor 5 (step S1).

The vibration mode detection unit 22 detects the vibration mode of the looseness detection sensor 5 (step S2). The vibration mode can be determined, for example, by fast Fourier (FFT) transforming the characteristics of the current input to the first conductive layer 5a.

Alternatively, the vibration mode may be detected by fast Fourier transforming the reflected wave reflected from the first conductive layer 5a. When detecting from reflected waves, the vibration mode detection section 22 is connected in series between the conductive film 7 and the vibration mode recording section 23 (not shown). Specific examples of vibration modes will be described later.

The vibration mode recording section 23 records the peak value of the vibration detected by the vibration mode detection section 22 (step S3). The peak value of vibration can be determined, for example, from the maximum value of the current input from the first conductive layer 5a. The peak value can be expressed, for example, by a current value and a frequency at which the current flows.

The determination unit 24 first compares the obtained peak value with the peak value obtained in the past to determine the amount of change (step S4). The amount of change may be, for example, a current value and a frequency, or may be only a frequency.

Then, the determination unit 24 determines that there is no slack when the amount of change is less than the threshold value (step S6), and determines that there is slack when the amount of change is greater than or equal to the threshold value (step S7). A specific example of determining looseness will be described later.

As explained above, the looseness detection method executed by the looseness detection apparatus 200 according to the present embodiment is the looseness detection method executed by the above-mentioned looseness detection apparatus 200, and includes the insulating layer 5b and the insulating layer 5b from above and below. Looseness detection sensor 5 is provided with a first conductive layer 5a and a second conductive layer 5c that are sandwiched, and is in the shape of a washer that is sandwiched between the component 1 and the bolt 4 or the component 2 and the nut 6 without making direct contact with the shaft 4b of the bolt 4. a reflected wave receiving step (step S2) of sweeping and applying a high frequency signal with a frequency in a predetermined range (step S1) and receiving a reflected wave of the high frequency signal;
a peak value recording step (step S3) of recording the peak value of the reflected wave;
a comparison step (step S4) of comparing the peak value and the past peak value to determine the amount of change;
If the amount of change is less than a threshold, it is determined that there is no slack (step S6), and if the amount of change is greater than or equal to the threshold, it is determined that there is slack (step S7). . Thereby, it is possible to detect loosening of the portion where the two parts 1 and 2 are fastened by the bolt 4.

Note that looseness may be detected based on the manner in which a peak value occurs. The mode refers to, for example, a change in the frequency interval showing the peak value from a non-uniform state to a uniform state.

[Second embodiment]
FIG. 8 is a diagram showing a loosening detection sensor according to a second embodiment of the present invention. FIG. 8(a) is a plan view, and FIG. 8(a) is a schematic cross-sectional view.

As shown in FIG. 8, the first conductive layer 52a, the insulating layer 52b, and the second conductive layer 52c have an annular shape, and a feeding point for feeding a high frequency signal to the first conductive layer 52a or the second conductive layer 52c; One point of the first conductive layer 52a and the second conductive layer 52c on the side opposite to the power feeding point is short-circuited by the conductive member 7.

The relationship between the resonant wavelength λ ₂ of the looseness detection sensor 52 according to this embodiment and the length L of the half circumference of a circle passing through the center of the washer-shaped ring width W can be expressed by the following equation.

Here, m is an odd number. The lowest resonance condition when the bolt 4 is tightened is m=1. Further, since the first conductive layer 52a and the second conductive layer 52c are short-circuited by the length of the half circumference of the ring, the resonance wavelength λ resonates on the shorter wavelength side according to the following formula, unlike in the first embodiment. I can do it.

Here m=2n+1. n is an integer of 1 or more, and m is an odd number of 3 or more. Therefore, the relationship between the resonant wavelength λ ₂ and the resonant frequency wavelength λ ₁ can be expressed by the following equation.

As shown in equation (4), resonance can be achieved on the shorter wavelength side compared to the first embodiment. Therefore, this embodiment can improve the degree of freedom in design.

FIG. 9 shows an example of a change in the resonance frequency detected using the loosening detection sensor 52 manufactured for M30 bolt 4. The horizontal axis in FIG. 9 is frequency (GHz), and the vertical axis is arbitrary units (dB).

A ring-shaped sensor resonates along the length of the half circumference of the ring, but if a short circuit is made at a position opposite to the power feeding point with respect to the center of the sensor, when the bolt 4 is loosened, the result will be as shown in equation (2). There is a resonant wavelength. Furthermore, since the ends of the half circumference of the ring are forcibly short-circuited, the wavelength of each resonance is shifted to the shorter wavelength side according to equation (4).

If the resonant frequency shown in equation (2) is used to detect looseness, the resonant frequency can be lowered. Further, by utilizing the feature shown in equation (3), detection at a higher frequency than that of the looseness detection sensor 5 becomes possible.

Note that the position where the first conductive layer 52a and the second conductive layer 52c are short-circuited by the conductive member 7 may be any position in the annular shape. In other words, it is only necessary that the first conductive layer 52a and the second conductive layer 52c are short-circuited by the conductive member 7 at a point different from the power supply point that supplies the high-frequency signal to the first conductive layer 52a or the second conductive layer 52c. . Thereby, the degree of freedom in designing the looseness detection sensor can be increased.

{Third embodiment}
FIG. 10 is a diagram showing a loosening detection sensor according to a third embodiment of the present invention. The looseness detection sensor 53 shown in FIG. 10 has an insulating layer 53b (not shown) and a first conductive layer 53a and a second conductive layer 53c (not shown), like the looseness detection sensors 5 and 52 described above. It has a three-layer structure that is sandwiched between the two.

In the loosening detection sensor 53 according to this embodiment, when the bolt 4 is loosened, the resonance wavelength λ appears according to the following equation.

Here n is an integer.

On the other hand, when the bolt 4 is tightened, the electric field strength at the inner peripheral portion of the looseness detection sensor 5 decreases, so the propagation mode of the high frequency signal changes, and the resonant wavelength λ expressed by equation (5) becomes shorter. In this way, loosening of the bolt 4 can be detected based on the wavelength of the resonant frequency. Furthermore, the loosening of the bolt 4 can also be detected based on the presence or absence of the resonance frequency.

FIG. 11 is a diagram showing changes in the resonance frequency when loosening of the bolt 4 is detected by the loosening detection sensor 53. The horizontal axis in FIG. 11 is frequency (GHz), and the vertical axis is arbitrary units (dB).

If the bolt 4 is loose, the resonant wavelength λ of the sensor appears depending on the length L according to equation (5). On the other hand, when the sensor is tight, a resonance mode is formed in which the electric field strength at the inner circumference of the sensor is reduced, and the resonance frequency shifts to the high frequency side.

Note that the looseness detection sensor 53 of the third embodiment is not limited to the planar shape shown in FIG. 10. For example, it may be semicircular as shown in FIG. 12.

FIG. 13 is a diagram showing changes in the resonance frequency when loosening of the bolt 4 is detected by the loosening detection sensor 53. The relationship between the horizontal axis and the vertical axis is the same as in FIG. 11, etc.

As shown in FIG. 13, when the bolt 4 is loosened (dashed line), the resonance frequency changes at approximately equal intervals (Equation (5)).

The looseness detection sensor 53 according to this embodiment may have a planar shape that can be inserted under the bolt 4 or nut 6. In short, each of the insulating layer 53b, the first conductive layer 53a, and the second conductive layer 53c has a planar shape that can be inserted under the bolt 4 or nut 6 from a direction perpendicular to the axis 4b of the bolt 4. Thereby, the loosening detection sensor 53 can be placed without removing the bolt 4 that has already been installed.

As described above, according to the looseness detection sensor 5, 52, 53 and the looseness detection method using the looseness detection sensor 5 and the looseness detection device 200 according to the present embodiment, the Based on changes in the natural frequencies of the loosening detection sensors 5, 52, and 53, loosening of the bolt 4 or nut 6 that fixes the part is detected. Therefore, it is suitable for inspecting places where it is difficult to see the inspection target or areas where visual inspection is difficult at a distance.

Moreover, if the loosening detection sensors 5, 52, 53 and the loosening detecting device 200 are placed apart from each other, loosening of bolts can be detected remotely. The looseness detection sensor 5 and the looseness detection device 200 may be connected by a high frequency signal line such as a micro split line. Alternatively, the connection may be made using a waveguide or the like.

Alternatively, the looseness detection device 200 may be placed near the bolt 4, which is a structurally important part, and the detection results may be transmitted wirelessly. By doing so, the risks associated with testing can be eliminated. It is also possible to reduce inspection costs.

Note that the looseness detection sensors 5, 52, and 53 of the present invention are not limited to the first to third embodiments described above. It can be widely applied to structures in which two parts 1 and 2 are fixed with bolts 4. Further, if the surface of the component 1 is conductive, the second conductive layer 5c may be omitted.

As described above, the present invention is not limited to the above-described embodiments, and can be modified within the scope of the invention.

1, 2: Part 4: Bolt 4a: Neck 4b: Shaft 4c: Screw 5: Looseness detection sensor 5a: First conductive layer 5b: Insulating layer 5c: Second conductive layer 6: Nut 7: Conductive member 9: Washer 200: Looseness detection device 20: Frequency sweep section 21: High frequency application section 22: Vibration mode detection section 23: Vibration mode recording section 24: Judgment section 25: Control section

Claims (4)

A loosening detection sensor that detects loosening of bolts or nuts that fix parts,
The looseness detection sensor is
A washer comprising an insulating layer, and a first conductive layer and a second conductive layer sandwiching the insulating layer from above and below, and is sandwiched between the component and the bolt or the component and the nut without directly contacting the shaft of the bolt. shape ,
A high frequency signal having a frequency swept in a predetermined range is applied to the first conductive layer.
Looseness detection sensor. A loosening detection sensor that detects loosening of bolts or nuts that fix parts,
The looseness detection sensor is
A washer comprising an insulating layer, and a first conductive layer and a second conductive layer sandwiching the insulating layer from above and below, and is sandwiched between the component and the bolt or the component and the nut without directly contacting the shaft of the bolt. shape,
The first conductive layer, the insulating layer, and the second conductive layer are
The first conductive layer has an annular shape, and one point of the first conductive layer and the second conductive layer, which are located at a different position from a power feeding point that feeds a high frequency signal to the first conductive layer or the second conductive layer, are short-circuited by a conductive member. There is
Looseness detection sensor. Each of the insulating layer, the first conductive layer, and the second conductive layer has a planar shape that can be inserted between the component and the bolt or between the component and the nut from a direction perpendicular to the axis. The looseness detection sensor according to claim 1. A loosening detection method performed by a loosening detection device that detects loosening of bolts or nuts that fix parts, the method comprising:
A washer comprising an insulating layer, and a first conductive layer and a second conductive layer sandwiching the insulating layer from above and below, and is sandwiched between the component and the bolt or the component and the nut without directly contacting the shaft of the bolt. a reflected wave receiving step of sweeping and applying a high frequency signal with a frequency in a predetermined range to the looseness detection sensor having a shape, and receiving a reflected wave of the high frequency signal;
a peak value recording step of recording the peak value of the reflected wave;
a comparison step of comparing the peak value and the past peak value to determine the amount of change;
A method for detecting looseness, comprising: determining that there is no slack when the amount of change is less than a threshold, and determining that there is slack when the amount of change is greater than or equal to a threshold.

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