Loosening detection sensor, loosening detection device, and loosening detection method

Abstract

A loosening detection sensor (5) which has an opening portion (51) and which detects loosening of a bolt (4) that is inserted through the opening portion (51) or a nut (6) that engages with the bolt (4) is provided with: an insulating layer (5c); a first electrically conductive layer (5b) having a first surface in contact with one surface of the insulating layer (5c); a second electrically conductive layer (5d) having a first surface in contact with the other surface of the insulating layer (5c); and a resistance portion formed on a second surface of at least one of the first electrically conductive layer (5b) and the second electrically conductive layer (5d).

Description

Looseness detection sensor, looseness detection device, and looseness detection method

[0001] The present disclosure relates to a loosening detection sensor, a loosening detection device, and a loosening detection method for detecting loosening of bolts and nuts that fasten components.

[0002] Bolts and nuts are used to fasten parts in infrastructure structures such as bridges, plant facilities, playground equipment, etc. When parts are fastened together with bolts and nuts, the fastening can become loose due to factors such as vibration, plastic deformation caused by excessive stress, and fatigue over time.Furthermore, the bolt and nut may come off, making it impossible to maintain the fastening.

[0003] Non-Patent Document 1 discloses that a bolt is provided with a match mark and the position of the match mark is monitored to detect looseness of the bolt.

[0004] Non-Patent Document 2 discloses that loose bolts are detected by applying paint containing a fluorescent pigment to the bolts and irradiating them with ultraviolet light.

[0005] Anti-loosening bolts and nuts, available online (https: / / www.euroke.co.jp / linecap1 / ) Gladys method, available online (http: / / www.planus.jp / pdf / bort-0001.pdf)

[0006] However, with the method of attaching match marks disclosed in Non-Patent Document 1 and the method of applying paint containing a fluorescent pigment disclosed in Non-Patent Document 2, if the bolt to be inspected is installed in a location that is difficult for an operator to see, such as being attached to the bottom surface of a part, it may be difficult to inspect the bolt for looseness, and a lot of effort may be required.

[0007] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a loosening detection sensor, a loosening detection device, and a loosening detection method that can easily inspect bolts and nuts for looseness.

[0008] A loosening detection sensor according to one embodiment of the present disclosure has an opening and detects loosening of a bolt inserted into the opening or a nut engaged with the bolt, and comprises an insulating layer, a first conductive layer having a first surface in contact with one surface of the insulating layer, a second conductive layer having a first surface in contact with the other surface of the insulating layer, and a resistor portion formed on the second surface of at least one of the first conductive layer and the second conductive layer.

[0009] A loosening detection device according to one aspect of the present disclosure comprises a loosening detection sensor and a loosening detection unit, and is configured to detect loosening of a bolt or a nut engaged with the bolt. The loosening detection sensor comprises an insulating layer, a first conductive layer arranged with its first surface in contact with one surface of the insulating layer, a second conductive layer arranged with its first surface in contact with the other surface of the insulating layer, and a resistive layer formed on a second surface of at least one of the first conductive layer and the second conductive layer. The loosening detection unit comprises an application unit that applies a high-frequency signal to the first conductive layer or the second conductive layer, a sweep unit that sweeps the high-frequency signal, a frequency detection unit that detects the resonant frequency of the high-frequency signal, a recording unit that records the resonant frequency when no loosening has occurred in the bolt or nut, and a determination unit that determines that loosening has occurred in the bolt or nut when the difference between the resonant frequency recorded in the recording unit and the resonant frequency detected by the frequency detection unit is greater than a threshold value.

[0010] A loosening detection method according to one aspect of the present disclosure is a loosening detection method for detecting loosening of a bolt or a nut engaged with the bolt using a loosening detection sensor having an opening and including an insulating layer, a first conductive layer having a first surface in contact with one surface of the insulating layer, a second conductive layer having a first surface in contact with the other surface of the insulating layer, and a resistor portion formed on a second surface of at least one of the first conductive layer and the second conductive layer, wherein an application unit applies a high-frequency signal to the first conductive layer or the second conductive layer, a sweeping unit sweeps the high-frequency signal, a frequency detection unit detects the resonant frequency of the loosening detection sensor, and a determination unit determines that loosening has occurred in the bolt or nut when the difference between the resonant frequency when no loosening has occurred in the bolt or nut and the resonant frequency detected by the detection unit is greater than a predetermined threshold value.

[0011] According to the present disclosure, it is possible to easily inspect bolts and nuts for looseness.

[0012] FIG. 1 is a perspective view showing a loosening detection sensor according to the first embodiment installed in a fastening portion of a bolt. FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1. FIG. 3 is an explanatory diagram showing the configuration of a loosening detection device according to the first embodiment and its peripheral components. FIG. 4 is a schematic plan view of the loosening detection sensor. FIG. 5 is an explanatory diagram showing the connection between the loosening detection sensor and a loosening detection unit. FIG. 6 is a graph showing changes in resonant frequency when the conductivity between the head of the bolt and the first conductive layer is changed. FIG. 7 is a graph showing changes in resonant frequency of the loosening detection sensor. FIG. 8 is a flowchart showing the procedure for detecting bolt loosening in the loosening detection device according to the first embodiment. FIG. 9 is a cross-sectional view showing a loosening detection sensor mounted in a loosening detection device according to a modified example of the first embodiment installed in a fastening portion of a nut. FIG. 10 is an explanatory diagram showing the cross-sectional shape of a loosening detection sensor according to a second embodiment. FIG. 11 is a plan view of a sensor according to the second embodiment, showing an example in which a convex portion is formed concentrically around the opening, extending twice around the opening. Fig. 12 is a plan view of a sensor according to a second embodiment, showing an example in which the protrusions are formed in a mesh pattern. Fig. 13 is a block diagram showing the hardware configuration of a loosening detection unit according to the embodiment.

[0013] [Description of First Embodiment] Hereinafter, an embodiment will be described with reference to the drawings. Fig. 1 is a perspective view showing a state in which a loosening detection sensor 5 according to the first embodiment is installed in a fastening portion of a bolt 4. Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1. Fig. 3 is an explanatory diagram showing the configuration of a loosening detection device 100 according to the first embodiment and its peripheral components. Fig. 4 is a diagram schematically showing a plan view of the loosening detection sensor 5. Fig. 5 is an explanatory diagram showing the connection between the loosening detection sensor 5 and the loosening detection unit 3.

[0014] As shown in Fig. 3, the loosening detection device 100 according to this embodiment includes a loosening detection unit 3 and a loosening detection sensor 5 (hereinafter abbreviated as "sensor 5"). First, the relationship between the bolt 4, nut 6, and sensor 5 will be described with reference to Figs. 1 and 2. In the following, the component 1 side (upper side in the drawings) shown in Figs. 1 to 3 will be defined as the upper side, and the component 2 side (lower side in the drawings) will be defined as the lower side.

[0015] As shown in FIGS. 1 and 2, when two plate-like parts 1 and 2 are overlapped and joined together, the positions of bolt holes 1a and 2a drilled in the parts 1 and 2, respectively, are aligned.

[0016] Then, a flat sensor 5 (details will be described later) is inserted onto the shaft 4b of the bolt 4 and passed through the bolt holes 1a and 2a. A nut 6 is screwed onto the threaded portion 4c protruding downward from the part 2 to fasten the two parts 1 and 2 together firmly.

[0017] As shown in FIG. 4 , the sensor 5 has a circular shape in a plan view, with a circular opening 51 formed in the center. The outer periphery of the sensor 5 and the opening 51 are not limited to being circular, and may have other shapes. The sensor 5 also has a five-layer structure, as shown in FIGS. 1 and 2 . Specifically, the sensor 5 has an insulating layer 5c formed in the middle, and a first conductive layer 5b and a second conductive layer 5d formed on the upper and lower surfaces of the insulating layer 5c, respectively. Furthermore, a first resistive layer 5a is formed on the upper surface of the first conductive layer 5b, and a second resistive layer 5e is formed on the lower surface of the second conductive layer 5d.

[0018] That is, the sensor 5 includes an insulating layer 5c, and the upper surface (one surface) of the insulating layer 5c is in contact with the lower surface (first surface) of the first conductive layer 5b. The lower surface (other surface) of the insulating layer 5c is in contact with the upper surface (first surface) of the second conductive layer 5d. The upper surface (second surface) of the first conductive layer 5b is in contact with the first resistance layer 5a (resistance portion). The lower surface (second surface) of the second conductive layer 5d is in contact with the second resistance layer 5e (resistance portion).

[0019] Although the present embodiment describes an example in which the first resistance layer 5 a and the second resistance layer 5 e are formed, a configuration in which either the first resistance layer 5 a or the second resistance layer 5 e is formed may be used. That is, the resistance portion is formed on the second surface of at least one of the first conductive layer 5 b and the second conductive layer 5 d.

[0020] The insulating layer 5c is formed of an insulating material. Examples of the insulating material include resins such as Fr4 (Flame Retardant Type 4), polyimide, and ceramics such as zirconium oxide. Materials other than resin and ceramics, such as glass, may also be used. The first conductive layer 5b and the second conductive layer 5d are formed of a conductive material. The conductive material is the same material as that used for general washers. Examples of the conductive material include stainless steel materials such as SUS304, SUS310, and SUS316, or vapor depositions of these metals.

[0021] 1 to 3, the thickness of each layer 5a to 5e forming the sensor 5 is exaggerated to facilitate understanding. That is, the length in the planar direction and the length in the vertical direction of each layer 5a to 5e do not correspond to the same scale.

[0022] The diameter of the opening 51 (see FIG. 4) formed in the center of the sensor 5 is slightly larger than the diameter of the shank 4b and threaded portion 4c of the bolt 4. Because the diameter of the opening 51 is larger than the diameters of the shank 4b and threaded portion 4c, when the sensor 5 is attached, the sensor 5 does not come into contact with the shank 4b and threaded portion 4c, or even if they do come into contact, the resistance at this point is high enough to prevent AC signals from passing through. In addition, the head 4a of the bolt 4 and the first resistance layer 5a are in surface contact. The top surface of the component 1 and the second resistance layer 5e are in surface contact.

[0023] As shown in Figure 2, when a bolt 4 is inserted into the bolt holes 1a, 2a of two parts 1, 2 and a nut 6 is screwed and fastened, the sensor 5 is sandwiched between the head 4a of the bolt 4 and the top surface of the part 1 and firmly connected.

[0024] Next, a description will be given of the configuration of the looseness detection unit 3 shown in Fig. 3. The looseness detection unit 3 includes an application unit 31, a sweep unit 32, a frequency detection unit 33, a recording unit 34, and a determination unit 35.

[0025] The application unit 31 generates a high-frequency signal of several GHz to several tens of GHz and applies it to the first conductive layer 5b. Specifically, as shown in FIG. 5, the application unit 31 of the looseness detection unit 3 is connected to the first conductive layer 5b by a signal line Q1. The frequency detection unit 33 of the looseness detection unit 3 is connected to the second resistance layer 5e by a ground line Q2. The application unit 31 applies the high-frequency signal to the first conductive layer 5b via the signal line Q1.

[0026] The sweep unit 32 sweeps the frequency of the high frequency signal output by the application unit 31 within a desired frequency band.

[0027] The frequency detection unit 33 detects the resonant frequency of the high-frequency signal applied to the sensor 5. The resonant frequency can be determined by performing a fast Fourier transform (FFT) on the characteristics of the current input to the first conductive layer 5 b. That is, the sweep unit 32 sweeps the frequency of the high-frequency signal output by the application unit 31, and detects the frequency at which the current flowing through the first conductive layer 5 b reaches a peak value as the resonant frequency.

[0028] The recording unit 34 records the peak value of the current detected by the frequency detection unit 33 and the frequency at which the current reaches the peak value. The recording unit 34 records the peak value of the current and the frequency at that time when the bolt 4 is firmly fastened, i.e., when no loosening has occurred.

[0029] The determination unit 35 compares the peak value recorded in the recording unit 34 with the peak value detected by the frequency detection unit 33, and determines whether or not loosening has occurred in the bolt 4 based on the amount of change in the peak value. That is, the determination unit 35 determines that loosening has occurred in the bolt 4 or the nut 6 when the difference between the resonance frequency recorded in the recording unit 34 and the resonance frequency detected by the frequency detection unit 33 is greater than a threshold value.

[0030] Next, the resonant frequency f1 of the sensor 5 will be described. As is well known, when the propagation speed of a high-frequency signal is v, the equation (resonant frequency f1) = v / (resonant wavelength λ1) holds. The resonant wavelength λ1 is the wavelength of the primary natural frequency. Therefore, if the length of half the circumference of a circle passing through the center of the ring width W of the sensor 5 is L as shown in Figure 4, L and λ1 have the relationship shown in equation (1) below.

[0031] L=(λ1 / 2)*n (1) where n is an integer equal to or greater than 1. The resonance wavelength λ1 is the wavelength of the high frequency signal confined in the insulating layer 5c, and differs depending on the material of the insulating layer 5c.

[0032] The resonance frequency f1 changes depending on the tightening state of the bolt 4. When the bolt 4 is loose, the resonance frequency f1 is the same as the resonance frequency of the sensor 5 alone. On the other hand, when the bolt 4 is tightened, the inner peripheral portion of the sensor 5 is short-circuited by the bolt 4, and the electric field strength at the inner peripheral portion decreases. As a result, the propagation mode of the high-frequency signal changes, and the resonance wavelength λ1 shown in the above equation (1) becomes shorter. In other words, the resonance frequency f1 becomes higher.

[0033] From the above, by measuring the resonant frequency f1 of the sensor 5, it is possible to detect the loosening state of the bolt 4 based on changes in this resonant frequency f1. Furthermore, in this embodiment, as shown in FIGS. 1 to 3, the first resistive layer 5a is formed on the upper surface of the first conductive layer 5b, and the resistive layer 5e is formed on the lower surface of the conductive layer 5d. This reduces the conductivity between the head 4a of the bolt 4 and the first conductive layer 5b, and generates a capacitance between them. Similarly, the conductivity between the component 1 and the second conductive layer 5d reduces, and generates a capacitance between them.

[0034] As a result, when the bolt 4 loosens, the amount of change in the resonant frequency f1 increases, and furthermore, the loss of electromagnetic waves within the sensor 5 can be reduced, thereby increasing the detection sensitivity of the resonant frequency f1. In other words, when the bolt 4 loosens and the axial force of the bolt 4 decreases, a change in the resonant frequency f1 occurs at an early stage, making it possible to detect the loosening of the bolt 4 at an early stage without overlooking any signs of loosening.

[0035] Figure 6 is a graph showing the change in resonant frequency when the conductivity between the head 4a of the bolt 4 and the first conductive layer 5b is changed. In Figure 6, the horizontal axis represents frequency [GHz], and the vertical axis represents arbitrary units [dB]. Curve s1 (solid line) represents the case where the conductivity is 10 [S / m], curve s2 (dashed line) represents the case where the conductivity is 50 [S / m], and curve s3 (dash-dotted line) represents the case where the conductivity is 100 [S / m]. From each of curves s1 to s3, it can be seen that the resonant frequency shifts to a lower frequency as the conductivity between the head 4a of the bolt 4 and the first conductive layer 5b decreases (contact resistance increases).

[0036] FIG. 7 is a graph showing changes in the resonant frequency of sensor 5, with curve s11 (dashed line) showing data when the five-layer sensor 5 according to this embodiment is used and the bolt 4 is fastened, i.e., when no loosening has occurred in the bolt, curve s12 (straight line) showing data when the five-layer sensor 5 according to this embodiment is used and the bolt 4 has loosened and the axial force has dropped by 20%, and curve s13 (dashed line) showing data when the three-layer sensor (conventional sensor) not having the first and second resistance layers 5a, 5e is used and the bolt 4 has loosened and the axial force has dropped by 90%.

[0037] 7, when the conventional three-layered sensor is used, the resonant frequency does not change significantly even though the bolt 4 loosens and the axial force drops by 90%. On the other hand, when the five-layered sensor 5 according to this embodiment is used, the resonant frequency changes significantly when the bolt 4 loosens and the axial force drops by 20%. This means that the onset of loosening of the bolt 4 can be detected with high accuracy even if the bolt 4 loosens only slightly.

[0038] Next, the operation of the loosening detection device 100 according to this embodiment will be described with reference to the flowchart shown in Figure 8. It is assumed that the bolt 4 is initially firmly fastened. First, in step S1 of Figure 8, the application unit 31 applies a high-frequency signal to the first conductive layer 5b. Furthermore, the sweep unit 32 sweeps the frequency of the high-frequency signal output by the application unit 31.

[0039] In step S2, the frequency detection unit 33 detects the frequency at which the current value of the sensor 5 reaches its peak.

[0040] In step S3, the frequency detection unit 33 records the frequency at which the current value reaches its peak and the peak value in the recording unit 34.

[0041] In step S4, the determination unit 35 compares the peak value and resonance frequency at the previous detection recorded in the recording unit 34 with the peak value and resonance frequency detected by the frequency detection unit 33 at the current detection.

[0042] In step S5, the determination unit 35 calculates the difference between the previously detected resonance frequency and the currently detected resonance frequency, and determines whether the amount of change is less than a predetermined threshold value. If it is less than the threshold value (S5; YES), the process proceeds to step S6, and if not (S5; NO), the process proceeds to step S7.

[0043] In step S6, the determination unit 35 determines that no loosening has occurred in the bolt 4. In other words, the fact that the amount of change is less than the threshold value means that no large fluctuations have occurred in the resonant frequency of the sensor 5, and it is determined that the bolt 4 has not loosened.

[0044] In step S7, the determination unit 35 determines that loosening has occurred in the bolt 4. That is, if the amount of change is equal to or greater than the threshold value, it means that the resonant frequency of the sensor 5 has fluctuated significantly, and it is determined that the bolt 4 has loosened. In this way, if loosening occurs in the bolt 4, it can be detected immediately.

[0045] As described above, the bolt loosening detection device 100 according to this embodiment includes the loosening detection sensor 5 and the loosening detection unit 3, and detects loosening of the bolt 4 or the nut 6 engaged with the bolt 4. The loosening detection sensor 5 includes an insulating layer 5c, a first conductive layer 5b disposed with its first surface in contact with one surface of the insulating layer 5c, a second conductive layer 5d disposed with its first surface in contact with the other surface of the insulating layer 5c, and a resistive layer formed on the second surface of at least one of the first conductive layer 5b and the second conductive layer 5d. The loosening detection unit 3 includes an application unit 31 that applies a high-frequency signal to the first conductive layer 5b or the second conductive layer 5d, a sweep unit 32 that sweeps the high-frequency signal, a frequency detection unit 33 that detects the resonant frequency of the high-frequency signal, a recording unit 34 that records the resonant frequency when no loosening has occurred in the bolt 4 or the nut 6, and a determination unit 35 that determines that loosening has occurred in the bolt 4 or the nut 6 when the difference between the resonant frequency recorded in the recording unit 34 and the resonant frequency detected by the frequency detection unit 33 is greater than a threshold value.

[0046] In this embodiment, the loosening detection sensor 5 has a five-layer structure consisting of an insulating layer 5c, first and second conductive layers 5b and 5d, and first and second resistive layers 5a and 5e. A high-frequency signal is applied to the first conductive layer 5b to detect the resonant frequency. Whether or not the bolt 4 has loosened is detected based on changes in this resonant frequency. This allows the operator to easily detect the looseness of the bolt 4 without requiring much effort. Furthermore, the looseness of the bolt 4 can be easily inspected even if the bolt 4 is installed in a location that is difficult to see.

[0047] Furthermore, by forming the first and second resistance layers 5a, 5e, if the bolt 4 becomes loose, the amount of change in the resonant frequency can be increased even if the axial force of the bolt 4 decreases by, for example, about 20%. Therefore, if the bolt 4 becomes loose, the occurrence of loosening can be recognized at an early stage, and work such as replacing the bolt can be carried out.

[0048] In the first embodiment described above, an example is shown in which the first resistance layer 5a is formed on the upper surface of the first conductive layer 5b and the second resistance layer 5e is formed on the lower surface of the second conductive layer 5d, but this is not limited to this, and the effects of the above embodiment can be achieved as long as at least one of the first conductive layer 5b and the second conductive layer 5d is formed.

[0049] [Description of Modification of First Embodiment] Next, a description will be given of a modification of the first embodiment. Fig. 9 is a cross-sectional view showing a state in which a loosening detection sensor 5A mounted on a loosening detection device according to the modification is disposed between a nut 6 and a component 2, and the bolt 4 and the nut 6 are fastened together.

[0050] As shown in Fig. 9, the loosening detection sensor 5A has a four-layer structure in which, from bottom to top, a first resistive layer 5a, a first conductive layer 5b, an insulating layer 5c, and a second conductive layer 5d are laminated. As in the first embodiment, applying a high-frequency signal to the first conductive layer 5b makes it possible to detect loosening of the nut 6. Also, as in the first embodiment, in Fig. 9, a second resistive layer 5e may be disposed between the upper surface of the second conductive layer 5d and the lower surface of the component 2.

[0051] [Description of Second Embodiment] Next, a second embodiment will be described. In the first embodiment described above, an example was described in which the first resistance layer 5a is formed on the upper surface of the first conductive layer 5b, and the second resistance layer 5e is formed on the lower surface of the second conductive layer 5d. In the second embodiment, convex portions are formed on the upper surface of the first conductive layer 5b and the lower surface of the second conductive layer 5d, replacing the first and second resistance layers 5a, 5e.

[0052] 10 is an explanatory diagram showing the cross-sectional shape of a loosening detection sensor 5B (hereinafter abbreviated as "sensor 5B") according to the second embodiment. As shown in FIG. 10, sensor 5B has a three-layer structure consisting of an insulating layer 5c, a first conductive layer 5b, and a second conductive layer 5d. Furthermore, a plurality of protrusions 52 are formed on the upper surface of first conductive layer 5b, and a plurality of protrusions 53 are formed on the lower surface of second conductive layer 5d.

[0053] 11 and 12 are plan views of the sensor 5B. FIG. 11 shows an example in which the protrusions 52 and 53 are formed concentrically around the opening 51 in two circles. FIG. 12 shows an example in which the protrusions 52 and 53 are formed in a mesh pattern. That is, the protrusions 52 and 53 are formed in a mesh pattern on at least one of the upper (second surface) of the first conductive layer 5b and the lower (second surface) of the second conductive layer 5d. The protrusions 52 and 53 are an example of a resistor portion formed on the second surface of at least one of the first conductive layer 5b and the second conductive layer 5d.

[0054] With this configuration, it is possible to reduce the conductivity at the contact portion between the first conductive layer 5b and the bolt 4 and at the contact portion between the second conductive layer 5d and the component 1 (see FIG. 2), and it is possible to obtain the same effect as providing the first and second resistance layers 5a and 5e shown in FIG. 2. Therefore, similar to the first embodiment described above, it is possible to detect the occurrence of loosening of the bolt 4 or the nut 6 at an early stage.

[0055] Furthermore, by forming the protrusions 52, 53 in a concentric circle shape or a mesh shape, it is possible to firmly fix the sensor 5B to the bolt 4, and also to firmly fix the sensor 5B to the part 1.

[0056] 10, the upper surface of the first conductive layer 5b is machined to form the convex portion 52, and the lower surface of the second conductive layer 5d is machined to form the convex portion 53. However, the convex portions 52 and 53 may be formed of a different resistive material from the first and second conductive layers 5b and 5d. With this configuration, as with the first embodiment, it is possible to detect loosening of the bolt 4 or nut 6 early and without requiring much effort.

[0057] The looseness detection unit 3 of the present embodiment described above can be, for example, a general-purpose computer system including a CPU (Central Processing Unit, processor) 901, a memory 902, a storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device 904, an input device 905, and an output device 906, as shown in Fig. 13. The memory 902 and the storage 903 are storage devices. In this computer system, the CPU 901 executes a predetermined program loaded on the memory 902, thereby realizing each function of the looseness detection unit 3.

[0058] The slack detection unit 3 may be implemented in one computer or in multiple computers. Also, the slack detection unit 3 may be a virtual machine implemented in a computer.

[0059] The program for the loosening detection unit 3 can be stored in a computer-readable recording medium such as an HDD, SSD, USB (Universal Serial Bus) memory, CD (Compact Disc), or DVD (Digital Versatile Disc), or can be distributed via a network. The computer-readable recording medium is, for example, a non-transitory recording medium.

[0060] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0061] REFERENCE SIGNS LIST 1, 2 Component 3 Loosening detection section 4 Bolt 5, 5A, 5B Loosening detection sensor 5a First resistance layer (resistance section) 5b First conductive layer 5c Insulation layer 5d Second conductive layer 5e Second resistance layer (resistance section) 6 Nut 31 Application section 32 Sweep section 33 Frequency detection section 34 Recording section 35 Determination section 51 Opening 52, 53 Convex section (resistance section) 100 Loosening detection device

Claims

1. A loosening detection sensor having an opening for detecting loosening of a bolt inserted into said opening or a nut engaged with said bolt, comprising: an insulating layer; a first conductive layer having a first surface in contact with one surface of said insulating layer; a second conductive layer having a first surface in contact with the other surface of said insulating layer; and a resistor portion formed on the second surface of at least one of said first conductive layer and said second conductive layer.

2. The loosening detection sensor according to claim 1, wherein the resistance portion is a resistance layer.

3. The looseness detection sensor according to claim 1, wherein the resistance portion is a convex portion machined on at least one of the second surface of the first conductive layer and the second surface of the second conductive layer.

4. The looseness detection sensor according to claim 1, wherein the resistance portion is a protrusion formed of a resistance material on at least one of the second surface of the first conductive layer and the second surface of the second conductive layer.

5. The loosening detection sensor according to claim 3 or 4, wherein the opening is circular, and the protrusion is formed concentrically with the opening.

6. A looseness detection sensor according to claim 3 or 4, wherein the protrusions are formed in a mesh pattern.

7. A loosening detection device comprising a loosening detection sensor and a loosening detection unit, for detecting loosening of a bolt or a nut engaged with the bolt, wherein the loosening detection sensor comprises: an insulating layer; a first conductive layer arranged with its first surface in contact with one surface of the insulating layer; a second conductive layer arranged with its first surface in contact with the other surface of the insulating layer; and a resistive layer formed on a second surface of at least one of the first conductive layer and the second conductive layer, and the loosening detection unit comprises: an application unit that applies a high-frequency signal to the first conductive layer or the second conductive layer; a sweep unit that sweeps the high-frequency signal; a frequency detection unit that detects the resonant frequency of the high-frequency signal; a recording unit that records the resonant frequency when no loosening has occurred in the bolt or nut; and a determination unit that determines that loosening has occurred in the bolt or nut when the difference between the resonant frequency recorded in the recording unit and the resonant frequency detected by the frequency detection unit is greater than a threshold value.

8. A loosening detection method for detecting loosening of a bolt or a nut engaging with the bolt using a loosening detection sensor having an opening, the loosening detection sensor comprising: an insulating layer; a first conductive layer having a first surface in contact with one surface of the insulating layer; a second conductive layer having a first surface in contact with the other surface of the insulating layer; and a resistor portion formed on a second surface of at least one of the first conductive layer and the second conductive layer, wherein an application portion applies a high-frequency signal to the first conductive layer or the second conductive layer; a sweep portion sweeps the high-frequency signal; a frequency detection portion detects the resonant frequency of the loosening detection sensor; and a determination portion determines that the bolt or nut has loosened when the difference between the resonant frequency when the bolt or nut is not loosened and the resonant frequency detected by the detection portion is greater than a predetermined threshold value.

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