Method for inspecting electric contact point

Abstract

To provide a method for inspection which can inspect an electric contact point for soundness.SOLUTION: A vibration operation of applying periodic vibrations to an electric contact point is performed and the resistance value of the electric contact point which is changed temporally by the vibration operation is measured, the measured resistance value of the electric contact point which is changed temporally is frequency-analyzed, and a resistance value variable component at the vibration frequency corresponding to the operation frequency of the vibration operation is extracted from the result of the frequency analysis. On the basis of the size of the extracted resistance value variable component, whether a part with a large contact resistance is being generated in the electric contact point is detected.SELECTED DRAWING: Figure 7

Description

Technical Field

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

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] Although the occurrence of disconnection in the conductor of the cable has been detected, the inspection of the soundness (presence or absence of poor connection) of the electrical contact has not been performed.

[0005] Therefore, an object of the present invention is to provide an inspection method capable of inspecting the soundness of electrical contacts.

Means for Solving the Problems

[0006] The present invention aims to solve the above problems, and provides a method for inspecting the soundness of an electrical contact, comprising: performing a vibration application operation of applying periodic vibration to the electrical contact; measuring a resistance value of the electrical contact that changes in a time series by the vibration application operation; performing a frequency analysis on the measured resistance value of the electrical contact that changes in the time series; extracting a resistance value fluctuation component at a vibration frequency corresponding to an operation period of the vibration application operation from an analysis result of the frequency analysis; and detecting whether or not a portion having a large contact resistance exists in the electrical contact based on a magnitude of the extracted resistance value fluctuation component.

Effect of the Invention

[0007] According to the present invention, an inspection method capable of inspecting the soundness of an electrical contact can be provided.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0009] [Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0010] 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.

[0011] As shown in FIG. 2, the cable 10 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 by, for example, collectively twisting 19 strands made of soft copper wires having an outer diameter of 0.08 mm. The insulator 11b is made of, for example, a fluororesin such as ETFE (tetrafluoroethylene-ethylene copolymer). 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, for example, a tape member made of 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.

[0012] The cable 10 to be detected for disconnection may already be 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.

[0013] 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.

[0014] The vibration applying mechanism 2 is a mechanism that performs a vibration applying operation for 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.

[0015] The vibration applying mechanism 2 has 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.

[0016] 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.

[0017] Also, the vibration applying mechanism 2 is preferably configured to apply vibrations so that displacement occurs in the cable 10 in a direction perpendicular to the longitudinal direction of the cable 10 in a state where a certain tension is applied 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, and in a state where a certain tension is 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 is preferably provided so as to vibrate (reciprocate) in a direction perpendicular to the longitudinal direction of the cable. Here, the "certain 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. Note that the cable 10 between the pair of gripping portions 21 is preferably gripped by the gripping portions 21 so that there is no looseness (that is, no play) such that the tension does not vary due to the movement of the vibration head 22. Furthermore, the gripping portion 21 should not only hold down the sheath of the cable 10, but also grip it 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 resulting reduction in tension fluctuations, as well as to suppress a decrease in sensitivity due to small resistance value fluctuations caused by vibration and an increase in resistance value fluctuations and deterioration of locality due to disconnection outside the gripping portion 21. Also, 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. Note that the vibration operation 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 to the cable 10.

[0018] In the present embodiment, a portable vibration operation mechanism 2 having the 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 operation 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 operation mechanism 2 for inspection. Also, 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.

[0019] The resistance measuring device 3 measures the resistance value of the conductor 11a that changes in time series by the vibration excitation operation. In the present embodiment, the resistance measuring device 3 measures the resistance value of the conductor 11a during the vibration excitation 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 is not limited thereto, and 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 preferably measures the resistance value at a sampling rate sufficiently fast with respect to the operation cycle of the vibration excitation operation. Details of the resistance measuring device 3 will be described later.

[0020] The arithmetic unit 4 includes 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 is configured to be able to display various data such as the 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. Further, the display 43 and the input device 44 do not necessarily have to be connected to the arithmetic unit 4 by wire, and may be connected wirelessly. 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.

[0021] (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 wire break occurs in the strands in the conductor 11a, the length of the broken wire portion 11c (the distance between the ends of the strands facing each other across the broken wire portion 11c) periodically varies, and accordingly, the resistance value of the conductor 11a periodically (with the same period as the vibration period) varies.

[0022] Since this variation in resistance value is small, simply measuring the resistance value alone will be buried in noise and it will be difficult to detect. However, the variation in resistance value due to the broken wire portion 11c becomes a resistance value variation signal modulated at the vibration frequency corresponding to the operation period of the vibration operation. Therefore, by extracting the resistance value variation component at the vibration frequency from the result of measuring the resistance value of the conductor 11a over a continuous time, it is possible to suppress noise and extract only the variation in resistance value due to the broken wire portion 11c with high sensitivity. By narrowing the bandwidth through long-time measurement of the variation in resistance value by the resistance measuring device 3, it is possible to further suppress the influence of noise. Then, by detecting a wire break in the strand based on the magnitude of the extracted resistance value variation component, it becomes possible to detect a wire break in the strand with high sensitivity. Note that in FIG. 3, for simplicity of the drawing, the case where the cable 10 has only one conductor 11a is shown.

[0023] 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 periodically (with the same period as the vibration period) varies. As a result, the variation in the resistance value of the conductor 11a becomes larger, and it becomes possible to improve the detection accuracy of a wire break in the strand.

[0024] Furthermore, in the present embodiment, any position in the longitudinal direction of the cable 10 is set as an inspection site, and by performing a vibration excitation operation on the inspection site, even if the conductor 11a is actually in a broken state, due to the contact of the broken portion of the conductor 11a, it is possible to highly sensitively detect whether a disconnection has occurred even in a case where it is considered that there is no fluctuation in the resistance value and the cable is not disconnected. Therefore, in the present embodiment, a plurality of positions in the longitudinal direction of the cable 10 are set as inspection sites, and by performing the above-described inspection at each inspection site, it is possible to specify the position where the disconnection has occurred in the longitudinal direction of the cable 10. Further, 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 magnitude of the resistance value fluctuation component extracted at each of the plurality of inspection sites in the longitudinal direction of the cable 10.

[0025] If the vibration excitation frequency is too low, the influence of noise increases. Therefore, the vibration excitation frequency is preferably at least 0.5 Hz or more, and more preferably 1.0 Hz or more. Also, if the vibration excitation frequency is too high, the cable 10 will not follow the vibration. Therefore, the vibration excitation frequency is preferably set to a frequency at which the cable 10 can follow. Further, in order to avoid the influence of power supply noise, the vibration excitation frequency is preferably set so as to avoid the same frequency band as the power supply frequency. Furthermore, as the outer diameter of the cable 10 increases, the rigidity increases and displacement due to the vibration excitation operation is 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 is preferably set according to the outer diameter of the cable 10 (the rigidity of the cable 10).

[0026] (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) by 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.

[0027] 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.

[0028] 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 to output a signal in which a signal of the DC component and a signal of the "2×ωc" component are superimposed. In the carrier signal generator 36a shown in FIG. 4(b), when sin(ωct) is assumed to have ωc = 2πf, the resistance value fluctuation component of the excitation frequency f can be extracted.

[0029] The low-pass filter 36c receives the output signal from the mixer 36b, blocks the signal of the "2×ωc" component, and allows the signal of the DC component to pass through. 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, it is possible to detect a component of a predetermined frequency (for example, a component of a predetermined high-order frequency described later). 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.

[0030] Note that 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 the 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 such as an amplitude-modulated signal of this AC signal with the modulation signal of the excitation frequency f is output from the cable 10. Therefore, if a carrier signal of 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 can be performed at a higher frequency (for example, about 10 kHz), and as a result, the influence of noise components is less likely to occur.

[0031] (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 RAM and ROM, software, interfaces, storage devices, and the like.

[0032] 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.

[0033] FIG. 5 is a diagram showing an example of the frequency analysis data 51 obtained by the frequency analysis unit 411 when non-disconnected parts and disconnected parts in the longitudinal direction of the cable 10 with an outer diameter of about 6 mm are used as inspection parts 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-disconnected part of the cable 10, as shown in the region indicated as "vibrating the non-disconnected part" in the figure, at the excitation frequency of about 1 Hz and its higher-order frequencies that are n times that (n is a natural number of 2 or more), it can be seen that the intensity hardly increases (that is, there is hardly any change in intensity). On the other hand, when vibrations are applied to the disconnected part of the cable 10, as shown in the region indicated as "vibrating the disconnected part" in the figure, it can be seen that the intensity at the excitation frequency of about 1 Hz and each of its higher-order frequencies that are n times that (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.

[0034] The extraction unit 412 extracts a resistance value fluctuation component (= intensity) at the excitation frequency f corresponding to the operation period of the vibration operation based on the frequency analysis data 51, which is the analysis result of the frequency analysis. Further, the extraction unit 412 may extract a resistance value fluctuation 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 a resistance value fluctuation occurs in the conductor 11a due to the vibration operation.

[0035] The disconnection detection unit 413 detects the disconnection of a conductor (i.e., the disconnection of the strands constituting the conductor) based on the magnitude of the resistance value fluctuation component at the vibration frequency f extracted by the extraction unit 412. More specifically, the magnitude of the resistance value fluctuation component at the vibration frequency f extracted by the extraction unit 412 (in the example of FIG. 5, the magnitude of the resistance value fluctuation component at a frequency of about 1 Hz) is compared with a preset threshold value. If the magnitude of the resistance value fluctuation component at the vibration 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 fluctuation component at the vibration frequency f with each of the plurality of threshold values, the degree of strand disconnection (such as the number of strands that have disconnected) can be detected step by step.

[0036] Further, the disconnection detection unit 413 may detect the disconnection of the strands by comparing the magnitude of the resistance value fluctuation component at a higher-order frequency f×n (n is a natural number of 2 or more) based on the vibration frequency f with a preset threshold value. That is, the disconnection detection unit 413 may detect the disconnection of the strands based on the magnitude of the resistance value fluctuation component at the vibration frequency f and its higher-order frequencies. The determination result is stored in the storage unit 42 as disconnection detection data 52.

[0037] When the disconnection detection unit 413 detects a disconnection, the alarm unit 414 issues an alarm. 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.

[0038] 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, it may be configured to share the result of disconnection detection (that is, disconnection detection data 52) with device users such as robot users and device manufacturers such as robot manufacturers. 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 can be downloaded by the control unit 41 mounted on another server device, a personal computer, or the like, and disconnection detection can be performed.

[0039] (Disconnection Detection Method) FIG. 6 is a flowchart showing the procedure of the disconnection detection method according to the present embodiment. Disconnection detection may be performed, for example, during regular inspection of a device or the like in which the cable 10 is wired. Further, the flow in FIG. 6 may be repeated while changing the inspection site of the cable 10 (the position where the vibration head 22 of the vibration operation mechanism 2 is applied).

[0040] 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 resistance measuring device 3 starts measuring the resistance value of the conductor 11a.

[0041] 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). As a result, 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.

[0042] Subsequently, in step S13, the vibration excitation 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.

[0043] 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 excitation operation and the measurement of the resistance value. For example, in a state where the vibration excitation 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 inspection time can be shortened.

[0044] Thereafter, in step S15, the extraction unit 412 extracts the resistance value variation component at the vibration excitation frequency f from the frequency analysis data 51. At this time, the resistance value variation components of predetermined higher-order frequencies included in a preset frequency range may be extracted.

[0045] 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.

[0046] (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 vibrations 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 application 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.

[0047] As a result, it becomes possible to accurately detect only the resistance value fluctuation component due to the disconnection of the strands while suppressing the influence of noise, 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 the disconnection of the strands in the conductor 11a of the cable 10, including the initial disconnection that was difficult to detect by a general detection method using the resistance increase rate, and it becomes possible to detect the disconnection 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.

[0048] Further, in a general detection method using the conventional resistance increase rate, 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.

[0049] 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 of the resistance value due to the temperature is independent of the operation period of the vibration application operation, according to the present embodiment, it is possible to detect the disconnection of the conductor 11a without being affected by the temperature change.

[0050] Furthermore, by using the portable vibration mechanism 2, it becomes possible to inspect whether there is a disconnection in the already wired and laid cable 10 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 disconnection detection can be easily performed. Also, by moving the inspection site along the longitudinal direction of the cable 10 and repeating 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.

[0051] (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 occurrence of the disconnection.

[0052] 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, as the number of broken strands of the conductor increases and the disconnection progresses, the difference between the maximum value and the minimum value of the resistance value of the conductor 11a increases. 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 broken. Also, the estimated disconnection progress state is stored in the storage unit 42 shown in FIG. 1 as disconnection progress state data.

[0053] 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 or not 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.

[0054] (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 a connection failure). A 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 as shown in FIG. 7. 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.

[0055] For example, on the surfaces of the electrodes 100a and 101a, an oxide film or a corroded portion may occur 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 (with 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.

[0056] That is, in the section including the contact portions of the two electrodes 100a and 101a (electrical contacts to be inspected), if the resistance value that changes in time series due to the vibration operation is measured by the resistance measuring device 3, similar to the above-described embodiment, it becomes 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. 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.

[0057] In the example of FIG. 7, the vibration head 22 is pressed against the connector 100 to apply vibration, but this is not the only case. As long as it is the position where the electrical contact to be inspected is vibrated, vibration can be applied anywhere. For example, vibration can 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, but this is not the only case. For example, connectors connecting cables to each other can be inspected in the same manner.

[0058] (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 that specifically show the components in the claims in the embodiment.

[0059] [1] A method for detecting a break in the conductor (11a) of a cable (10) having the conductor (11a), the method comprising: performing a vibration application operation of 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 a time series due to the vibration application operation; performing a frequency analysis on the measured resistance value of the conductor (11a) that changes in a time series; extracting a resistance value variation component at a vibration frequency corresponding to the operation period in the vibration application operation from the analysis result of the frequency analysis; and detecting a break in the conductor (11a) at the inspection site based on the magnitude of the extracted resistance value variation component.

[0060] [2] In the vibration application operation according to [1], vibrations are applied so that displacement occurs in the cable (10) in a direction perpendicular to the longitudinal direction of the cable (10) while a constant tension is applied to the cable (10).

[0061] [3] Extracting a resistance value variation component at a high-order frequency based on the vibration frequency from the analysis result of the frequency analysis, and detecting a break in the conductor (11a) based on the magnitude of the resistance value variation component at the vibration frequency and its high-order frequencies according to [1] or [2].

[0062] [4] A device for detecting a break in the conductor (11a) of a cable (10) having the conductor (11a), the device comprising: a vibration application mechanism (2) that performs a vibration application operation of applying periodic vibrations to an arbitrary inspection site in the longitudinal direction of the cable (10); a resistance measuring device (3) that measures the resistance value of the conductor (11a) that changes in a time series due to the vibration application operation; a frequency analysis unit (411) that performs a frequency analysis on the measured resistance value of the conductor (11a) that changes in a time series; an extraction unit (412) that extracts a resistance value variation component at a vibration frequency corresponding to the operation period of the vibration application operation from the analysis result of the frequency analysis; and a break detection unit (413) that detects a break in the conductor (11a) at the inspection site based on the magnitude of the extracted resistance value variation component.

[0063] The embodiments of the present invention have been described above. However, the embodiments described above do not limit the invention according to the claims. It should also 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 implemented with appropriate modifications without departing from its gist.

[0064] 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, and the conductor to be subjected to disconnection detection may be any one composed of a plurality of strands, and may 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 horizontally wound shield (horizontally wound conductor) in which a plurality of strands are spirally wound.

Explanation of Reference Numerals

[0065] 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. 1. A method for inspecting the integrity of an electrical contact, comprising the steps of: A vibration operation is performed to apply periodic vibration to the electrical contacts, measuring a resistance value of the electrical contact that changes over time due to the vibration operation; performing a frequency analysis on the measured resistance value of the electrical contact that changes over time; A resistance value fluctuation component at a vibration frequency corresponding to an operating period of the vibration operation is extracted from a result of the frequency analysis, detecting whether or not a portion having a high contact resistance is present in the electrical contact based on the magnitude of the extracted resistance value variation component; How to inspect electrical contacts.

2. The electrical contact is a connector that connects a cable to a device, The vibration motion is performed on either the cable or the connector. The method for inspecting electrical contacts according to claim 1 .

3. the electrical contact is a connector for connecting cables together, The vibration motion is performed on either the cable or the connector. The method for inspecting electrical contacts according to claim 1 .

4. The electrodes provided on the connector are plated on their surfaces, The vibration motion is performed on the connector.

4. The method for inspecting electrical contacts according to claim 2 or 3.

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