Inspection method

Abstract

To provide an inspection method capable of detecting with high sensitivity the occurrence of disconnection in a conductor.SOLUTION: In a method for inspecting disconnection of a conductor 11a of a cable 10, vibration operation for displacement in a direction vertical to a longitudinal direction of the cable 10 is performed on an arbitrary detection portion in the longitudinal direction of the cable 10 by using a portable vibration operation mechanism 2, so that a resistance value of the conductor 11a, which changes on a time series basis, is measured. A resistance value variation component at a vibration frequency corresponding to an operation period of the vibration operation is extracted by performing frequency analysis on the measured resistance value so that the disconnection of the conductor 11a at the detection portion is detected on the basis of the magnitude of the extracted resistance value variation component.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for inspecting a cable.

Background Art

[0002] Patent Document 1 discloses a method for detecting a sign of conductor disconnection caused by bending, targeting a wire cable having a conductor composed of a stranded conductor in which a plurality of strands are twisted together. Specifically, in this method, the wire cable is periodically bent and extended in one direction while a current is flowing, and a current component that changes in synchronization with this bending period is detected. That is, in this method, a state in which some disconnection points repeatedly make contact and separation in synchronization with the bending period is detected.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The occurrence of disconnection in the conductor of a cable is generally detected by measuring the electrical resistance of the conductor in the cable. When a disconnection occurs in a part of the strands included in the conductor, the resistance value of the conductor increases. Therefore, for example, by measuring in advance the resistance value of the conductor in the initial state where no disconnection has occurred, the occurrence of disconnection can be detected based on the increase rate of the resistance value from the initial state of the resistance value.

[0005] However, when a break occurs in a very small part of the strands included in the conductor, that is, in the initial stage of breakage where the number of broken strands is small (= initial breakage), the increase rate of the resistance value of the conductor is extremely small and difficult to distinguish from noise (for example, fluctuations in the resistance value due to temperature changes in the surrounding environment or electrical external noise). Therefore, in practice, it can be difficult to determine whether a break has occurred based on the increase rate of the resistance value of the conductor unless the ratio of the number of broken strands to the total number of strands constituting the conductor reaches a predetermined ratio (for example, a level of at least 50% or more). As a result, it is not easy to detect the occurrence of a break based on the increase rate of the resistance value of the conductor in the initial stage from the initial state where no break has occurred to immediately after the initial breakage occurs. In devices such as industrial robots, a malfunction of the device may occur due to a break in the conductor of the cable wired to the device. From the perspective of reducing such concerns, it is desired to be able to detect that a break has occurred even in the initial stage (that is, to be able to detect the occurrence of a break with high sensitivity).

[0006] Therefore, an object of the present invention is to provide an inspection method capable of highly sensitively detecting the occurrence of a break in a conductor and the like.

Means for Solving the Problems

[0007] The present invention is a method for inspecting a break in a conductor of a cable for the purpose of solving the above problems. By using a portable vibration mechanism, a vibration operation is performed in a direction perpendicular to the longitudinal direction of the cable on an arbitrary inspection site in the longitudinal direction of the cable, thereby measuring the resistance value of the conductor that changes over time. By performing frequency analysis on the measured resistance value, a resistance value fluctuation component at a vibration frequency corresponding to the operation period of the vibration operation is extracted, and based on the magnitude of the extracted resistance value fluctuation component, the break in the conductor at the inspection site is detected. An inspection method is provided.

[0008] The present invention also provides a method for inspecting a break in a conductor of a cable. The method uses a portable vibration mechanism to perform a vibration operation that displaces the cable in a direction perpendicular to the longitudinal direction of the cable at an arbitrary inspection site in the longitudinal direction of the cable. By measuring the resistance value of the conductor that changes over time and performing frequency analysis on the measured resistance value, a resistance value fluctuation component at a vibration frequency corresponding to the operation period of the vibration operation is extracted. Based on the magnitude of the extracted resistance value fluctuation component, the progress state of the break in the conductor at the inspection site is estimated.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide an inspection method capable of highly sensitively detecting the occurrence of a break in a conductor.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0011] [Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0012] FIG. 1 is a schematic configuration diagram showing a disconnection detection device 1 according to the present embodiment. FIG. 2 is a cross-sectional view showing a schematic configuration example of a cable 10 to be detected for disconnection.

[0013] The cable 10 shown in FIG. 2 is configured by spirally winding a holding tape 14 around a cable core 13 formed by twisting five electric wires 11 and a filamentous intervening member 12, and providing a sheath 15 so as to cover the periphery of the holding tape 14. Each electric wire 11 has a conductor 11a made of a stranded conductor formed by twisting a plurality of strands and an insulator 11b provided so as to cover the periphery of the conductor 11a. The conductor 11a is configured, for example, by collectively twisting 19 strands made of soft copper wires having an outer diameter of 0.08 mm. The insulator 11b is made of a fluororesin such as ETFE (tetrafluoroethylene-ethylene copolymer), for example. The intervening member 12 is made of, for example, jute or sphagnum. Note that the number of electric wires 11 used in the cable 10 is not limited to five. The holding tape 14 is made of a tape member made of, for example, non-woven fabric, paper, resin, or the like. The sheath 15 is made of, for example, PE (polyethylene), PP (polypropylene), PVC (polyvinyl chloride), or the like. Note that the cable 10 is not limited to the illustrated configuration, and may have various configurations as long as it includes at least the conductor 11a made of a stranded conductor. That is, the number of electric wires 11 may be one, several, or dozens or more. When there is one electric wire 11, the intervening member 12, the holding tape 14, and the sheath 15 are often eliminated. In this case, the cable 10 and the electric wire 11 indicate the same thing.

[0014] The cable 10 to be detected for disconnection may be one that has already been wired and laid in a device or the like. For example, the cable 10 to be detected for disconnection may be a cable wired to an industrial robot or a cable wired to an automobile.

[0015] As shown in FIG. 1, the disconnection detection device 1 is a device that detects a disconnection of the conductor 11a of a cable 10 having a conductor 11a made of a stranded conductor formed by twisting a plurality of strands, and includes a vibration generating mechanism 2, a resistance measuring device 3, and an arithmetic device 4.

[0016] The vibration applying mechanism 2 is a mechanism that performs a vibration applying operation of applying periodic vibrations to an arbitrary inspection site in the longitudinal direction of the cable 10, and is configured to be able to locally apply vibrations to an arbitrary position in the longitudinal direction of the cable 10 that becomes the inspection site. In the present embodiment, a case where the cable 10 to be detected for disconnection is mounted on the industrial robot 110 will be described.

[0017] The vibration applying mechanism 2 includes a probe 2a that vibrates the inspection site of the cable 10 and a vibration applying operation control device 2b that controls the vibration applying operation of the probe 2a. The test for detecting the disconnection of the conductor 11a may be performed, for example, during a regular inspection of the industrial robot 110.

[0018] The probe 2a of the vibration applying mechanism 2 has a vibrating vibration head 22, and is configured to apply vibrations of a certain period to the inspection site by pressing the vibration head 22 against an arbitrary inspection site of the cable 10.

[0019] Further, the vibration mechanism 2 may be configured to apply vibration to cause displacement in the cable 10 in a direction perpendicular to the longitudinal direction of the cable 10 while applying a constant tension to the cable 10. More specifically, the probe 2a has a pair of gripping portions 21 that grip the cable 10 at two locations sandwiching the inspection site of the cable 10. With a constant tension applied to the cable 10 by these pair of gripping portions 21, the vibration head 22 can be applied to the inspection site of the cable 10 located between the pair of gripping portions 21. The vibration head 22 may be provided so as to vibrate (reciprocate) in a direction perpendicular to the longitudinal direction of the cable. Here, the "constant tension" means, for example, a tension such that the tension of the cable (specifically, the conductor 11a in the cable 10) between the pair of gripping portions 21 varies due to the movement of the vibration head 22. The cable 10 between the pair of gripping portions 21 may be gripped by the gripping portions 21 so that there is no looseness to the extent that the tension does not vary due to the movement of the vibration head 22 (that is, there is no play). Further, the gripping portion 21 may grip not only the sheath of the cable 10 but also with a pressure such that the cable core inside the cable 10 does not move. By doing so, it is possible to suppress the cable core from moving due to vibration and the tension variation from becoming small, and to suppress the resistance value variation due to vibration from becoming small and the sensitivity from decreasing, and the resistance value variation due to disconnection outside the gripping portion 21 from becoming large and the locality from deteriorating. Further, when the vibration applied to the cable 10 acts in a direction along the longitudinal direction of the cable 10, it may cause noise. Therefore, it is desirable that the vibration applied to the cable 10 does not have a component along the longitudinal direction of the cable 10. The vibration mechanism 2 may have an auxiliary member for assisting the cable 10 to vibrate due to the movement of the vibration head 22. As the auxiliary member, for example, it is arranged at a position facing the vibration head 22 so as to contact the surface of the cable 10. The auxiliary member causes the cable 10 to be displaced toward the vibration head 22 when the vibration head 22 moves away from the cable 10 (that is, the cable 10 returns to the position when no vibration is applied to the cable 10).This makes it easier to apply vibrations that cause displacement in the cable 10.

[0020] In the present embodiment, a portable vibration mechanism 2 having a probe 2a is used. Therefore, it is possible to detect whether a disconnection has occurred in the conductor 11a constituting the cable 10 without removing the already wired and laid cable 10. However, it is not limited to this, and a fixed vibration mechanism 2 may be used. In this case, when inspecting the already wired and laid cable 10, the cable 10 is removed from the wiring location or the laying location, and the cable 10 is set in the vibration mechanism 2 for inspection. Further, if localization of the disconnection location is not required, the gripping portion 21 is not essential and can be omitted, for example, when inspecting a cable 10 that is already wired with a certain tension.

[0021] The resistance measuring device 3 measures the resistance value of the conductor 11a that changes in time series due to the vibration operation. In the present embodiment, the resistance measuring device 3 measures the resistance value of the conductor 11a during the vibration operation over time. The data of the resistance value of the conductor 11a that changes in time series measured by the resistance measuring device 3 is input to the arithmetic unit 4 and stored in the storage unit 42 as resistance value data 50. In the present embodiment, the resistance measuring device 3 is configured separately from the arithmetic unit 4, but it is not limited to this, and it may be configured integrally with the arithmetic unit 4, or a part of its function may be mounted on the arithmetic unit 4. Further, the resistance measuring device 3 may be mounted on a control device (not shown) of the industrial robot 110. The resistance measuring device 3 is preferably configured to measure the resistance value at a sampling rate that is sufficiently fast with respect to the operation cycle of the vibration operation. Details of the resistance measuring device 3 will be described later.

[0022] The arithmetic unit 4 has a control unit 41 and a storage unit 42. Details of these control unit 41 and storage unit 42 will be described later. A display 43 is connected to the arithmetic unit 4, and it is configured to be able to display various data such as resistance value data 50 and the result of disconnection detection on the display 43. Further, an input device 44 such as a keyboard or a mouse is provided in the arithmetic unit 4, and various settings and operations of the display content of the display 43 can be performed by the input of the input device 44. Note that the display 43 may be configured as a touch panel display so that the display 43 also serves as the input device 44. Furthermore, the display 43 and the input device 44 do not necessarily have to be wired-connected to the arithmetic unit 4 and may be wirelessly connected. In this case, the display 43 and the input device 44 may be a mobile terminal such as a smartphone or a tablet, for example.

[0023] (Principle of disconnection detection) When the vibration head 22 of the vibration mechanism 2 is brought into contact with a desired inspection site of the cable 10 and vibrated, the inspection site of the cable 10 is vibrated in accordance with the vibration of the vibration head 22. As a result, as shown in FIG. 3, the inspection site of the cable 10 is periodically displaced in accordance with the periodic displacement of the vibration head 22, and a reciprocating motion perpendicular to the longitudinal direction of the cable 10 occurs at the inspection site of the cable 10. At this time, if a break occurs in the strands in the conductor 11a, the length of the broken portion 11c (the distance between the ends of the strands facing each other across the broken portion 11c) periodically varies, and accordingly, the resistance value of the conductor 11a periodically varies (with the same period as the vibration period).

[0024] Since the variation in this resistance value is slight, simply measuring the resistance value alone will be buried in noise and it will be difficult to detect. However, the variation in the resistance value due to the disconnection point 11c becomes a resistance value variation signal modulated at the excitation frequency corresponding to the operation period of the excitation operation. Therefore, by extracting the resistance value variation component at the excitation frequency from the result of measuring the resistance value of the conductor 11a over a continuous time, it becomes possible to suppress noise and extract only the variation in the resistance value due to the disconnection point 11c with high sensitivity. By narrowing the bandwidth through long-time measurement of the variation in the resistance value by the resistance measuring device 3, it is possible to further suppress the influence of noise. And by detecting the disconnection of the wire strand based on the magnitude of the extracted resistance value variation component, it becomes possible to detect the disconnection of the wire strand with high sensitivity. Note that in FIG. 3, for the sake of simplification of the figure, a case where the cable 10 has only one conductor 11a is shown.

[0025] Furthermore, in the present embodiment, since the cable 10 is gripped by a pair of gripping portions 21, as the position of the inspection site of the cable 10 is periodically displaced, the tension acting on the conductor 11a also varies periodically (with the same period as the period of vibration). Thereby, the variation in the resistance value of the conductor 11a becomes larger, and it becomes possible to improve the detection accuracy of the disconnection of the wire strand.

[0026] Furthermore, in the present embodiment, by setting an arbitrary position in the longitudinal direction of the cable 10 as the inspection site and performing an excitation operation on the inspection site, even in a case where the conductor 11a is actually in a disconnected state but the disconnection point of the conductor 11a is in contact and it is regarded as not having a resistance value variation and not being disconnected, it is possible to detect with high sensitivity whether a disconnection has occurred. Therefore, in the present embodiment, by setting a plurality of positions in the longitudinal direction of the cable 10 as inspection sites and performing the above-described inspection at each inspection site, it is possible to specify the occurrence position of the disconnection in the longitudinal direction of the cable 10. Also, in the present embodiment, it is also possible to estimate the progress state of the disconnection in the longitudinal direction of the cable 10 based on the magnitudes of the resistance value variation components extracted at each of the plurality of inspection sites in the longitudinal direction of the cable 10.

[0027] If the excitation frequency is too low, the influence of noise becomes significant. Therefore, the excitation frequency is preferably at least 0.5 Hz or higher, and more preferably 1.0 Hz or higher. Also, if the excitation frequency is too high, the cable 10 will not follow the vibration. Thus, the excitation frequency should be such that the cable 10 can follow. Furthermore, to avoid the influence of power supply noise, the excitation frequency may be set to avoid the same frequency band as the power supply frequency. Additionally, as the outer diameter of the cable 10 increases, its rigidity increases and displacement due to the excitation operation becomes less likely to occur. Therefore, it is desirable to increase the distance between the pair of gripping portions 21 as the outer diameter of the cable 10 increases. That is, the distance between the pair of gripping portions 21 may be set according to the outer diameter of the cable 10 (the rigidity of the cable 10).

[0028] (Details of the Resistance Measuring Device 3) FIG. 4(a) is a diagram showing a schematic configuration example of the resistance measuring device 3. As shown in FIG. 4(a), the resistance measuring device 3 includes a resistance measuring unit 35 having a DC signal source (for example, a DC constant voltage source) 35a, an input resistance 35b, and a resistance value detector 35c. When a DC constant current source is used as the DC signal source 35a, the input resistance 35b is unnecessary. The DC signal source 35a applies a DC signal (here, a DC voltage) to the cable 10 (conductor 11a) via the input resistance 35b. In response to this, a modulation signal (for example, a voltage signal) including a component of the excitation frequency f is output from the cable 10 (conductor 11a) due to the excitation operation. The resistance value detector 35c detects, for example, the time-series change in the resistance value of the conductor 11a by amplifying this modulation signal with a predetermined gain. The signal from the resistance value detector 35c is converted into a digital signal by the A / D converter 37 and output to the arithmetic unit 4 as resistance value data 50.

[0029] Note that the configuration of the resistance measuring device 3 shown in FIG. 4(a) is merely an example and can be changed as appropriate. For example, as shown in FIG. 4(b), the resistance measuring device 3 may integrally include a frequency analysis unit 36. In this case, the frequency analysis unit 411 (see FIG. 1) of the arithmetic unit 4 described later can be omitted.

[0030] The frequency analysis unit 36 includes, for example, a carrier signal generator 36a, a mixer 36b, and a low-pass filter (LPF) 36c. The carrier signal generator 36a generates a carrier signal having the same carrier frequency (ωc) as the excitation frequency f, that is, the resistance value fluctuation frequency due to disconnection, and having the same phase as the resistance value fluctuation frequency. The mixer 36b multiplies (in other words, synchronously detects) this carrier signal and the output signal from the resistance value detector 35c, and outputs a signal in which a signal of a DC component and a signal of a "2×ωc" component are superimposed. In the carrier signal generator 36a shown in FIG. 4(b), sin(ωct) can extract the resistance value fluctuation component of the excitation frequency f when ωc = 2πf.

[0031] The low-pass filter 36c receives the output signal from the mixer 36b, blocks the signal of the "2×ωc" component, and passes the signal of the DC component. This signal of the DC component represents the magnitude of the resistance value fluctuation component of the excitation frequency f (=ωc). In this way, by using the carrier signal generator 36a, the mixer 36b, and the low-pass filter 36c, a component of a predetermined frequency (for example, a component of a predetermined high-order frequency described later) can be detected. The signal from the low-pass filter 36c is converted into a digital signal by the A / D converter 37 and output to the arithmetic unit 4.

[0032] In the configuration examples of FIGS. 4(a) and 4(b), a DC signal was applied to the cable 10 (conductor 11a), but not limited to a DC signal, an AC signal of a predetermined frequency (for example, about 10 kHz) may be applied using an AC signal source. In this case, a signal obtained by amplitude-modulating this AC signal with a modulation signal of the excitation frequency f is output from the cable 10. Therefore, if a carrier signal having the same frequency as the AC signal of the AC signal source is multiplied by this output signal using a mixer, the modulation signal of the excitation frequency f can be demodulated. By using such a method, measurement at a higher frequency (for example, about 10 kHz) can be performed, and as a result, the influence of noise components is less likely to occur.

[0033] (Arithmetic unit 4) The control unit 41 of the arithmetic unit 4 is equipped with a frequency analysis unit 411, an extraction unit 412, a disconnection detection unit 413, and an alarm unit 414. These frequency analysis unit 411, extraction unit 412, disconnection detection unit 413, and alarm unit 414 are realized by appropriately combining arithmetic elements such as a CPU, memories such as a RAM and a ROM, software, an interface, a storage device, and the like.

[0034] The frequency analysis unit 411 performs frequency analysis on the resistance value data 50 measured by the resistance measuring device 3 (that is, the data of the resistance value of the conductor 11a that changes in time series). The result of the frequency analysis is stored in the storage unit 42 as frequency analysis data 51. Note that frequency analysis means analyzing the magnitude of each frequency component included in the resistance value data 50 and obtaining frequency analysis data 51, which is data obtained by extracting the magnitude of the component for each frequency.

[0035] FIG. 5 is a diagram showing an example of the frequency analysis data 51 obtained by the frequency analysis unit 411 when each of the non-disconnection part and the disconnection part in the longitudinal direction of the cable 10 having an outer diameter of about 6 mm is used as an inspection part and vibrations of about 60 rpm (about 1 Hz) are applied to these inspection parts. As shown in FIG. 5, when vibrations are applied to the non-disconnection part of the cable 10, as shown in the region indicated as "vibrating the non-disconnection part" in the figure, at the excitation frequency of about 1 Hz and its higher-order frequencies that are n times (n is a natural number of 2 or more), it can be seen that the intensity hardly increases (that is, there is almost no change in intensity). On the other hand, when vibrations are applied to the disconnection part of the cable 10, as shown in the region indicated as "vibrating the disconnection part" in the figure, it can be seen that the intensity at each of the excitation frequency of about 1 Hz and its higher-order frequencies that are n times (n is a natural number of 2 or more) increases. Note that when the vibration is stopped, as shown in the region indicated as "stopping vibration" in the figure, the intensity at these frequencies almost disappears.

[0036] The extraction unit 412 extracts a resistance value variation component (= intensity) at the excitation frequency f corresponding to the operation period of the excitation operation based on the frequency analysis data 51 which is the analysis result of the frequency analysis. Further, the extraction unit 412 may further extract a resistance value variation component (= intensity) at a higher-order frequency f×n (n is a natural number of 2 or more) based on the excitation frequency f. At this time, the higher-order frequency to be extracted may be appropriately set to a frequency at which the resistance value of the conductor 11a varies due to the excitation operation.

[0037] The disconnection detection unit 413 detects the disconnection of the conductor (that is, the disconnection of the strands constituting the conductor) based on the magnitude of the resistance value variation component at the excitation frequency f extracted by the extraction unit 412. More specifically, the magnitude of the resistance value variation component at the excitation frequency f extracted by the extraction unit 412 (in the example of FIG. 5, the magnitude of the resistance value variation component at a frequency of about 1 Hz) is compared with a preset threshold value, and if the magnitude of the resistance value variation component at the excitation frequency f is equal to or greater than the threshold value, it is determined that a disconnection has occurred. Note that a plurality of threshold values may be set, and by comparing the magnitude of the resistance value variation component at the excitation frequency f with each of the plurality of threshold values, the degree of strand disconnection (the number of strands that are disconnected, etc.) may be detected step by step.

[0038] Further, the disconnection detection unit 413 may detect the disconnection of the strands by comparing the magnitude of the resistance value variation component at a higher-order frequency f×n (n is a natural number of 2 or more) based on the excitation frequency f with a preset threshold value. That is, the disconnection detection unit 413 may detect the disconnection of the strands based on the excitation frequency f and the magnitude of the resistance value variation component at its higher-order frequency. The determination result is stored in the storage unit 42 as disconnection detection data 52.

[0039] The alarm unit 414 issues an alarm when the disconnection detection unit 413 detects a disconnection. The alarm unit 414 issues an alarm, for example, by sounding an alarm tone, displaying an alarm on the display 43, transmitting an alarm signal to an external device such as a management device, etc., to notify the administrator that a disconnection has been detected.

[0040] The arithmetic unit 4 is configured by, for example, a personal computer. However, it is not limited to this, and the arithmetic unit 4 may be, for example, a server device. In this case, the resistance value data 50 measured by the resistance measuring device 3 is transmitted to the arithmetic unit 4 which is a server device via a network. When the arithmetic unit 4 is configured by a server device, the result of disconnection detection (that is, disconnection detection data 52) etc. may be configured to be shared with a device user such as a robot user or a device manufacturer such as a robot manufacturer. Further, the control unit 41 and the storage unit 42 may be configured by separate devices. For example, the resistance value data 50 stored in the storage unit 42 of the server device may be downloaded by the control unit 41 mounted on another server device or a personal computer etc., and configured to perform disconnection detection.

[0041] (Disconnection Detection Method) FIG. 6 is a flowchart showing the procedure of the disconnection detection method according to the present embodiment. The disconnection detection may be performed, for example, at the time of regular inspection of a device etc. where the cable 10 is wired. Further, the flow in FIG. 6 may be repeatedly performed while changing the inspection site of the cable 10 (the position where the vibration head 22 of the vibration operation mechanism 2 is applied).

[0042] First, in step S10, the vibration operation mechanism 2 starts a vibration operation of applying periodic vibration to the inspection site of the cable 10 to be inspected. Then, in step S11, the measurement of the resistance value of the conductor 11a by the resistance measuring device 3 is started.

[0043] Next, in step S12, the vibration operation and the measurement of the resistance value of the conductor 11a are continued for a predetermined period. The predetermined period is the period required to obtain sufficient resistance value data for disconnection detection. This predetermined period may vary appropriately depending on the configuration of the resistance measuring device 3 and the measurement environment (that is, the magnitude of the noise component) etc. Thereby, the resistance value of the conductor 11a that changes in time series due to the vibration operation is measured by the resistance measuring device 3.

[0044] Subsequently, in step S13, the vibration application operation and the measurement of the resistance value of the conductor 11a are stopped. The measured resistance value data of the conductor 11a is transmitted to the arithmetic unit 4 and stored in the storage unit 42 as resistance value data 50.

[0045] Thereafter, in step S14, the frequency analysis unit 411 performs a frequency analysis of the resistance value data 50. The result of the frequency analysis is stored in the storage unit 42 as frequency analysis data 51. Note that the frequency analysis in step S14 may also be performed without stopping the vibration application operation and the measurement of the resistance value. For example, in a state where the vibration application operation and the measurement of the resistance value of the conductor 11a are continued, the frequency analysis unit 411 performs a frequency analysis when a predetermined period has elapsed. Thereby, the presence or absence of a disconnection in the conductor 11a can be grasped in a timely manner, and the time required for the inspection can be shortened.

[0046] Thereafter, in step S15, the extraction unit 412 extracts the resistance value variation component at the vibration application frequency f from the frequency analysis data 51. At this time, the resistance value variation component of a predetermined high-order frequency included in a preset frequency range may be extracted.

[0047] Thereafter, in step S16, the disconnection detection unit 413 determines whether the magnitude of the resistance value variation component extracted by the extraction unit 412 is equal to or greater than a preset threshold value. If it is determined YES in step S16, in step S17, the disconnection detection unit 413 determines that there is a disconnection in the conductor 11a at the inspection site, and in step S18, after the alarm unit 414 issues an alarm, the process ends. If it is determined NO in step S16, the disconnection detection unit 413 determines that there is no disconnection in the conductor 11a at the inspection site, and the process ends.

[0048] (Operations and Effects of the Embodiment) As described above, in the disconnection detection method according to the present embodiment, a vibration application operation is performed to apply periodic vibration to an arbitrary inspection site in the longitudinal direction of the cable 10, the resistance value of the conductor 11a that changes in time series due to the vibration application operation is measured, the measured resistance value of the conductor 11a that changes in time series is subjected to frequency analysis, and from the analysis result of the frequency analysis, a resistance value fluctuation component at a vibration frequency corresponding to the operation period of the vibration application operation is extracted, and based on the magnitude of the extracted resistance value fluctuation component, disconnection of the strands at the inspection site is detected.

[0049] As a result, it is possible to suppress the influence of noise and accurately detect only the resistance value fluctuation component due to the disconnection of the strands, and it becomes possible to accurately detect the disconnection of the strands in the conductor 11a of the cable 10. That is, according to the present embodiment, it becomes possible to detect disconnection of the strands in the conductor 11a of the cable 10, including initial disconnections that were difficult to detect by a general detection method using the rate of increase in resistance value, and it becomes possible to detect disconnections with high sensitivity. As a result, in various devices to which the cable 10 is attached, it is possible to take measures before a serious failure (for example, almost complete disconnection) occurs, and it becomes possible to improve the reliability of the device.

[0050] Further, in a general detection method using the conventional rate of increase in resistance value, the resistance value of the conductor 11a before disconnection, that is, the initial resistance value was required, but in the present embodiment, since the occurrence of disconnection is detected using the amount of change (relative amount) of the resistance value during the vibration application operation instead of the absolute value of the resistance value, the initial resistance value is not required. Therefore, according to the present embodiment, even when the initial resistance value of the conductor 11a is unknown, it is possible to highly sensitively detect that a disconnection has occurred in the strands of the conductor 11a.

[0051] Furthermore, although the resistance value of the conductor 11a and the contact resistance between the conductor 11a and the resistance measuring device 3 vary greatly depending on the temperature, since the variation in the resistance value due to temperature is independent of the operation period of the vibration application operation, according to the present embodiment, it is possible to detect disconnection of the conductor 11a without being affected by temperature changes.

[0052] Furthermore, by using the portable vibration mechanism 2, it becomes possible to inspect whether or not a cable 10 that has already been wired and laid has a disconnection without removing it from the device or the like, and it becomes possible to significantly shorten the time required for the inspection. Also, in the present embodiment, since it is possible to perform disconnection detection simply by applying vibration to the cable 10 by bringing the vibration head 22 into contact with the cable 10 without bending or twisting the cable 10, it has high versatility and can easily perform disconnection detection. Also, by moving the inspection site along the longitudinal direction of the cable 10 and repeating the disconnection detection, it becomes possible to detect at which position in the longitudinal direction of the cable 10 a disconnection has occurred. Also, in the present embodiment, it is also possible to estimate the progress state of the disconnection in the longitudinal direction of the cable 10 by comparing the magnitudes of the resistance value fluctuation components extracted at each of a plurality of inspection sites in the longitudinal direction of the cable 10.

[0053] (Modification 1) In the above-described embodiment, a method for detecting that a disconnection has occurred in the conductor 11a has been described, but it is also possible to estimate the progress state of the disconnection (=disconnection progress state estimation) after the disconnection has occurred.

[0054] As a result of the study by the present inventors, it has been found that in the time-series change of the resistance value of the conductor 11a, the difference between the maximum value and the minimum value of the resistance value of the conductor 11a increases as the number of broken strands increases and the disconnection progresses. Therefore, it is possible to estimate the progress state of the disconnection of the conductor 11a based on the difference between the maximum value and the minimum value of this resistance value. For example, by setting a plurality of threshold values stepwise and comparing each threshold value with the difference between the maximum value and the minimum value of the resistance value, it is possible to estimate the progress state of the disconnection of the conductor 11a. Note that the disconnection progress state of the conductor 11a is the ratio of how many of all the strands constituting the conductor 11a are disconnected. Also, the estimated disconnection progress state is stored in the storage unit 42 shown in FIG. 1 as disconnection progress state data.

[0055] When the progress state of this disconnection reaches a predetermined ratio (for example, 80% or more), if it is set that the cable 10 has reached its lifespan (= cable lifespan), it becomes possible to predict the lifespan of the cable 10 by predicting whether the estimated disconnection progress state has reached the cable lifespan. Based on the lifespan prediction result of the cable 10, it is possible to determine whether to replace the cable 10 or perform predictive maintenance of the cable 10. Note that the lifespan prediction result of the cable 10 obtained based on the disconnection progress state is stored in the storage unit 42 shown in FIG. 1 as cable lifespan prediction data. Further, the arithmetic unit 4 may be configured to be able to display the obtained disconnection progress state data and cable lifespan prediction data on the display 43.

[0056] (Modification Example 2) Further, the present invention can be applied to the inspection of the soundness of the connector or the soundness of the electrical contact (presence or absence of poor connection). As shown in FIG. 7, the case where the connector 100 provided at the end of the cable 10 is connected to the device-side connector 101 provided in an arbitrary device will be described. In the example of FIG. 7, by connecting both connectors 100 and 101, the electrode (connector-side electrode) 100a provided in the connector 100 and the electrode (device-side electrode) 101a provided in the device-side connector 101 are electrically connected.

[0057] For example, on the surfaces of the electrodes 100a and 101a, an oxide film or a corroded portion may be generated due to the influence of water adhesion, or the plating provided on the surfaces of the electrodes 100a and 101a may peel off, and the contact resistance increases at the corresponding portion. Then, when a periodic vibration is applied to the connector 100 and a periodic vibration is applied to the contact portion between the two electrodes 100a and 101a, the contact resistance between the two electrodes 100a and 101a fluctuates periodically (at the same period as the vibration) due to the influence of the portion with a large contact resistance. Therefore, it is possible to detect whether there is a portion with a large contact resistance (whether an oxide film or a corroded portion has occurred, or whether the plating has peeled off) based on the magnitude of the fluctuating component at the excitation frequency in the contact resistance.

[0058] That is, if the resistance value that changes in time series due to the vibration operation is measured by the resistance measuring device 3 in the section including the contact portions of the two electrodes 100a and 101a (the electrical contacts to be inspected), it is possible to inspect the soundness of the connectors 100 and 101 or the soundness element wire of the electrical contact between the two electrodes 100a and 101a, similar to the above-described embodiment. More specifically, the resistance value that changes in time series measured by the resistance measuring device 3 is subjected to frequency analysis, and from the analysis result in the frequency analysis, the resistance value fluctuation component of the vibration frequency corresponding to the operation period of the vibration operation is extracted. Based on the magnitude of the extracted resistance value fluctuation component, it is possible to detect whether there is a portion with a large contact resistance such as an oxide film in the electrical contact, and to inspect the soundness of the connectors 100 and 101 or the soundness element wire of the electrical contact between the two electrodes 100a and 101a. Note that the arithmetic unit 4 in FIG. 7 is the same as the arithmetic unit 4 shown in FIG. 1.

[0059] In the example of FIG. 7, the vibration head 22 is pressed against the connector 100 to apply vibration. However, the present invention is not limited to this, and vibration may be applied anywhere as long as it is at a position where the electrical contact to be inspected is vibrated. For example, vibration may be applied to the cable 10 or the device-side connector 101. Further, in the example of FIG. 7, the connectors 100 and 101 connecting the cable 10 and the device are described. However, the present invention is not limited to this, and for example, connectors connecting cables to each other can be inspected in the same manner.

[0060] (Summary of the embodiment) Next, the technical idea grasped from the above-described embodiment will be described by referring to the reference numerals and the like in the embodiment. However, each reference numeral and the like in the following description are not limited to the members specifically shown in the embodiment for the components in the claims.

[0061] [1] A method for detecting a disconnection of the conductor (11a) of a cable (10) having the conductor (11a), the method comprising: performing a vibration application operation for applying periodic vibrations to an arbitrary inspection site in the longitudinal direction of the cable (10); measuring the resistance value of the conductor (11a) that changes in time series due to the vibration application operation; performing frequency analysis on the measured resistance value of the conductor (11a) that changes in time series; extracting a resistance value variation component at a vibration application frequency corresponding to the operation period in the vibration application operation from the analysis result of the frequency analysis; and detecting a disconnection of the conductor (11a) at the inspection site based on the magnitude of the extracted resistance value variation component.

[0062] [2] In the vibration application operation according to [1], vibrations are applied in a direction perpendicular to the longitudinal direction of the cable (10) so that displacement occurs in the cable (10) while a constant tension is applied to the cable (10).

[0063] [3] Extracting a resistance value variation component at a high-order frequency based on the vibration application frequency from the analysis result of the frequency analysis, and detecting a disconnection of the conductor (11a) based on the magnitudes of the resistance value variation components at the vibration application frequency and its high-order frequencies, according to the disconnection detection method described in [1] or [2].

[0064] [4] A device for detecting a disconnection of the conductor (11a) of a cable (10) having the conductor (11a), the device comprising: a vibration application mechanism (2) for performing a vibration application operation for applying periodic vibrations to an arbitrary inspection site in the longitudinal direction of the cable (10); a resistance measuring device (3) for measuring the resistance value of the conductor (11a) that changes in time series due to the vibration application operation; a frequency analysis unit (411) for performing frequency analysis on the measured resistance value of the conductor (11a) that changes in time series; an extraction unit (412) for extracting a resistance value variation component at a vibration application frequency corresponding to the operation period of the vibration application operation from the analysis result of the frequency analysis; and a disconnection detection unit (413) for detecting a disconnection of the conductor (11a) at the inspection site based on the magnitude of the extracted resistance value variation component.

[0065] The embodiments of the present invention have been described above. However, the embodiments described above do not limit the invention according to the claims. Also, it should be noted that not all combinations of features described in the embodiments are essential means for solving the problems of the invention. Further, the present invention can be appropriately modified and implemented without departing from its gist.

[0066] For example, in the above embodiment, the case where the conductor 11a to be subjected to disconnection detection is a stranded conductor has been described. However, the present invention is not limited to this. The conductor to be subjected to disconnection detection may be composed of a plurality of strands, and may also be an external conductor (shield layer) provided so as to collectively cover the periphery of the cable core. More specifically, the conductor to be subjected to disconnection detection may be a braided shield (braided conductor) in which a plurality of strands are braided, or may be a spiral shield (spiral conductor) in which a plurality of strands are spirally wound.

Explanation of Reference Numerals

[0067] 1... Disconnection detection device 2... Vibration generating mechanism 21... Gripping portion 22... Vibration head 3... Resistance measuring device 4... Arithmetic unit 41... Control unit 411... Frequency analysis unit 412... Extraction unit 413... Disconnection detection unit 10... Cable 11... Electric wire 11a... Conductor

Claims

1. A portable vibration mechanism is used to perform a vibration operation on an arbitrary inspection portion in the longitudinal direction of a cable, displacing the portion in the longitudinal direction of the cable perpendicular to the longitudinal direction of the cable, thereby measuring the resistance of the conductor of the cable, which changes over time; The measured resistance value is subjected to frequency analysis to extract a resistance value fluctuation component at a vibration frequency corresponding to an operating period of the vibration operation, detecting a break in the conductor at the inspection portion based on the magnitude of the extracted resistance value variation component; A method for inspecting the cable, comprising the steps of: The inspection portion is moved along a longitudinal direction of the cable, and a break in the conductor is detected at each of the inspection portions. Testing method.

2. A portable vibration mechanism is used to perform a vibration operation that displaces an arbitrary test portion in the longitudinal direction of a cable in a direction perpendicular to the longitudinal direction of the cable, thereby measuring the resistance value of the conductor of the cable that changes over time; The measured resistance value is subjected to frequency analysis to extract a resistance value fluctuation component at a vibration frequency corresponding to an operating period of the vibration operation, estimating a progression state of the disconnection of the conductor at the inspection portion based on the magnitude of the extracted resistance value variation component. A method for inspecting the cable, comprising the steps of: the inspection portion is moved along the longitudinal direction of the cable, and the magnitudes of the resistance value variation components extracted at each of the plurality of inspection portions are compared to estimate a progress state of the disconnection of the conductor in the longitudinal direction of the cable. Testing method.

3. The vibration operation has a vibration frequency of 0.5 Hz or more. The inspection method according to claim 1 or 2.

4. The vibration operation includes gripping two points of the cable along the longitudinal direction of the cable, and periodically applying vibration to the cable such that an inspection site located between the two points is displaced in a direction perpendicular to the longitudinal direction of the cable. The inspection method according to claim 1 or 2.

5. The vibration operation includes gripping two points of the cable that sandwich the inspection part, thereby applying a constant tension to the cable at the inspection part, and periodically applying vibrations that displace the inspection part in a direction perpendicular to the longitudinal direction of the cable, thereby periodically changing the tension acting on the conductor in the cable. The inspection method according to claim 4.

6. A detection result of the breakage of the conductor is displayed on a display unit. The inspection method according to claim 1 .

7. Inspecting the conductor of the cable that is being laid or installed for breaks; The inspection method according to claim 1 or 2.

8. the vibration mechanism has a probe integrally including a vibration head and a pair of gripping parts that grip the cable at two points sandwiching the inspection area; and performing the vibration operation by applying tension to the cable by gripping the cable with the pair of gripping parts and vibrating the vibration head against the inspection site between the pair of gripping parts. The inspection method according to claim 1 or 2.

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