JP7439808B2 - Disconnection detection method and disconnection detection device - Google Patents

Description

The present invention relates to a disconnection detection method and a disconnection detection device for detecting disconnection of a conductor in a U-shaped cable.

Patent Document 1 discloses a method for detecting signs of conductor breakage due to bending in a wire cable having a conductor made of a stranded conductor made of a plurality of wires twisted together. Specifically, in this method, a wire cable is periodically bent and extended in one direction while a current is flowing therethrough, and a current component that changes in synchronization with the bending period is detected. That is, in this method, a state in which a part of the wire breakage repeatedly contacts and separates in synchronization with the bending cycle is detected.

JP2007-139488A

The occurrence of a disconnection in a conductor of a cable that is bent in a U-shape is generally detected by measuring the electrical resistance of the conductor within the cable. If a break occurs in some of the wires included in the conductor, the resistance value of the conductor increases. The occurrence of wire breakage can be detected based on the rate of increase in the resistance value from the initial state.

However, when disconnection occurs in only a small portion of the wires included in the conductor, that is, when the number of wire breaks is small, the rate of increase in the resistance value becomes extremely small. For this reason, in practice, it may be difficult to clearly detect a wire breakage based on the rate of increase in resistance value unless the ratio of the number of broken wires in the conductor reaches a level of at least 50% or more. As a result, it is not easy to detect a wire breakage at an early stage immediately after the wire breakage occurs, and there is a possibility that the occurrence of a wire breakage cannot be detected with high sensitivity.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a disconnection detection method and a disconnection detection device that can detect with high sensitivity the occurrence of a disconnection in a conductor.

In order to solve the above-mentioned problems, the present invention provides a method for detecting a disconnection of a wire in a cable having a conductor made of a stranded conductor made by twisting a plurality of wires, the method comprising: A U-shaped bending operation is performed in which one end of the cable is periodically slid at a predetermined stroke along the longitudinal direction of the cable, and the U-shaped bending operation is performed in a time-series manner. Measure the changing resistance value of the conductor, set the frequency corresponding to the cycle of the U-shaped bending operation as the operating frequency, and calculate the resistance value fluctuation component of the operating frequency included in the time-series change in the resistance value of the conductor. A wire breakage detection method is provided, which detects a wire breakage in the strand based on the magnitude of the extracted resistance value fluctuation component of the operating frequency.

Further, in order to solve the above-mentioned problems, the present invention provides a device for detecting disconnection of the strands of a cable having a conductor made of a stranded conductor made of a plurality of strands twisted together. a U-shaped bending mechanism that performs a U-shaped bending operation of periodically sliding one end of the cable at a predetermined stroke along the longitudinal direction of the cable while the cable is bent in a U-shape; Measure the resistance value of the conductor that changes over time due to the bending operation, and set the frequency corresponding to the cycle of the U-shaped bending operation as the operating frequency, and measure the operation included in the time-series change in the resistance value of the conductor. A measuring device for extracting a resistance value fluctuation component of a frequency, and a wire breakage detection device that detects a wire breakage of the strand based on the magnitude of the extracted resistance value fluctuation component of the operating frequency.

According to the present invention, it is possible to provide a disconnection detection method and a disconnection detection device that can detect with high sensitivity the occurrence of a disconnection in a conductor.

(a) is a schematic diagram showing a disconnection detection device according to an embodiment of the present invention, and (b) is a schematic diagram illustrating an example of the operation of the U-shaped bending mechanism in (a). FIG. 2 is a cross-sectional view showing a schematic configuration example of a cable. FIG. 3 is a schematic diagram for explaining the resistance value when a cable breaks. It is a schematic diagram explaining the measurement principle of a cable resistance value. FIG. 2 is a diagram illustrating a schematic configuration example and an operation example of a measuring instrument. 5 is a diagram illustrating an example of an effect obtained by using the measurement principle of FIG. 4. FIG. It is a figure which shows an example of the result of performing disconnection detection of a cable. FIG. 2 is a flow diagram showing an example of processing contents in a disconnection detection method according to an embodiment of the present invention. (a) is a graph in which the maximum value, minimum value, and average value of the resistance value are calculated for each measurement section separated by a predetermined time interval in the time-series change in the resistance value of the conductor; b) is a graph of the normalized resistance value obtained from (a).

[Embodiment]
Embodiments of the present invention will be described below with reference to the accompanying drawings.

(Disconnection detection device)
FIG. 1(a) is a schematic diagram showing a configuration example of a disconnection detection device according to the present embodiment, and FIG. 1(b) is an operational example of the U-shaped bending mechanism in FIG. 1(a). FIG. FIG. 2 is a cross-sectional view illustrating a schematic configuration example of a cable to be detected for disconnection.

In the cable 10 shown in FIG. 2, a pressure-wrapping tape 14 is spirally wound around a cable core 13 in which five electric wires 11 and a thread-like interposition 12 are twisted together, and the pressure-wrapping tape 14 is wrapped around the cable core 13 so as to cover the periphery of the pressure-wrapping tape 14. A sheath 15 is provided. The electric wire 11 includes a conductor 11a made of a stranded conductor obtained by twisting a plurality of wires together, and an insulator 11b provided so as to cover the periphery of the conductor 11a. The conductor 11a is constructed by, for example, twisting together 19 strands of annealed copper wire with an outer diameter of 0.08 mm. The interposition 12 is made of jute or cotton, for example. The insulator 11b is made of, for example, a fluororesin such as ETFE (tetrafluoroethylene-ethylene copolymer). Note that the number of electric wires 11 used in the cable 10 is not limited to five. The pressing tape 14 is made of a tape member made of, for example, nonwoven 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 wire conductor. That is, the number of electric wires 11 may be one, several, or several dozen or more. Note that when there is only one electric wire 11, the interposer 12, the pressing tape 14, and the sheath 15 are often eliminated. In this case, the cable 10 and the electric wire 11 are the same.

The disconnection detection device 1 shown in FIG. Be prepared.

The U-shaped bending mechanism 20 performs a U-shaped bending operation in which the cable 10 is bent into a U-shape and one end of the cable 10 is periodically slid at a predetermined stroke along the longitudinal direction of the cable. conduct. In the U-shaped bent state, the cable 10 has two straight portions 10a and 10b arranged in parallel, and a semicircular curved portion 10c connecting the straight portions 10a and 10b. The U-shaped bending mechanism 20 includes a fixed part 21 to which one end of the cable 10 (one straight part 10a) is fixed, and a sliding part to which the other end of the cable 10 (the other straight part 10b) is fixed. 22. The sliding part 22 is provided to face the fixed part 21 in the same direction as the opposing direction of both the linear parts 10a and 10b, and can be slid relative to the fixed part 21 by a drive part (not shown). It is composed of The sliding direction of the sliding portion 22 is a direction along the longitudinal direction of the straight portion 10b fixed to the sliding portion 22.

As shown in FIG. 1(b), the U-shaped bending mechanism 20 causes the cable 10 to be bent at regular intervals so that the cable 10 reciprocates between the first U-shaped bent state 40a and the second U-shaped bent state 40b. Perform a curving motion. The first U-shaped bent state 40a is a state in which the sliding part 22 is slid furthest toward the curved part 10c, and the length of the straight part 10a fixed to the fixed part 21 along the longitudinal direction of the cable is the longest, The length of the straight portion 10b fixed to the slide portion 22 along the longitudinal direction of the cable is the shortest. That is, in the first U-shaped bent state 40a, the curved part 10c approaches the cable end closest to the straight part 10b in the longitudinal direction of the cable, and the linear distance from the curved part 10c to the cable end of the straight part 10b (slide distance along the direction of movement) is the shortest. The second U-shaped bent state 40b is a state in which the sliding portion 22 is slid to a position farthest from the curved portion 10c, and the length of the straight portion 10a fixed to the fixed portion 21 along the cable longitudinal direction is the longest. The straight portion 10b fixed to the slide portion 22 has the longest length along the longitudinal direction of the cable. That is, in the second U-shaped bent state 40b, the curved part 10c comes closest to the cable end on the straight part 10a side in the cable longitudinal direction, and the linear distance from the curved part 10c to the cable end of the straight part 10a (slide distance along the direction of movement) is the shortest.

One reciprocation between the first U-shaped bending state 40a and the second U-shaped bending state 40b corresponds to one cycle of the U-shaped bending operation. Hereinafter, the frequency corresponding to the cycle of the U-shaped bending operation, that is, the frequency of one round trip between the first U-shaped bending state 40a and the second U-shaped bending state 40b, will be referred to as the operating frequency. For example, when one cycle (one round trip) of the U-shaped bending motion shown in FIG. 1(b) is 1 second, the operating frequency f is 1 Hz. In this case, the U-shaped bending mechanism 20 takes 0.5 seconds to transition from the first U-shaped bent state 40a to the second U-shaped bent state 40b, and then changes from the second U-shaped bent state 40b to the first U-shaped bent state 40b in 0.5 seconds. The U-shaped bending operation of returning to the bent state 40a is repeated. The number of operations, which is the number of times this U-shaped bending operation is performed, is once in one cycle of the U-shaped bending operation. Note that the operating frequency f may be determined to an appropriate value by taking into consideration the usage conditions of the cable 10 in actual use. Further, the radius of curvature of the curved portion 10c may also be determined to an appropriate value by taking into consideration the usage conditions of the cable 10 in actual use.

The measuring device 30 measures the resistance value of the conductor 11a of the cable 10 that changes over time according to the U-shaped bending operation of the U-shaped bending mechanism 20, and measures the resistance value included in the time-series change in the resistance value of the cable 10. The resistance value fluctuation component of the operating frequency f is extracted. Then, the wire breakage detection device 1 detects a wire breakage of the conductor 11a based on the magnitude of the resistance value fluctuation component of the operating frequency f extracted by the measuring device 30.

Specifically, the measuring device 30 includes a resistance measuring section 35 and a frequency analyzing section 36. For example, the resistance measurement unit 35 applies a constant voltage between both ends of the cable 10 (conductor 11a) and measures the current flowing in time series, or applies a constant current to the cable 10 (conductor 11a) and then measures the current flowing over time. By measuring the voltage generated between both ends over time, changes in the resistance value of the cable 10 (conductor 11a) are measured. The frequency analysis unit 36 extracts the resistance value fluctuation component at the operating frequency f from the time-series change in the resistance value of the conductor 11a. Further details of the measuring device 30 will be described later.

(Issues with disconnection detection as a premise)
FIG. 3 is a schematic diagram for explaining the resistance value when a disconnection occurs in the conductor 11a. When a disconnection occurs in the conductor 11a, the resistance value R [Ω] of the conductor 11a is theoretically expressed by equation (1). In formula (1), ρ [Ω・m] is the resistivity of the strand, La [m] is the conductor length at the non-broken point, and the entire length of the conductor 11a shown in FIG. 3 (cable length) It is expressed by equation (2) using L[m] and the length Lb[m] of the conductor 11a at the disconnection point. Further, Sa [m ² ] is the conductor cross-sectional area at the non-broken point, and Sb [m ² ] is the conductor cross-sectional area at the broken line.
R=ρ×(La/Sa)+ρ×(Lb/Sb)…(1)
La=L−Lb…(2)

As shown in equation (1), the resistance value R of the conductor 11a has a characteristic that is inversely proportional to the cross-sectional area Sb of the disconnection location. In this case, when the cross-sectional area Sb is large to some extent, the resistance value R does not change much, but when the cross-sectional area Sb becomes sufficiently small, the resistance value R increases rapidly. That is, when the ratio of the number of broken wires in the conductor 11a is small, the cross-sectional area Sb is sufficiently large, so the resistance value R does not change much. As an example, when the ratio of the number of broken wires reaches about 70% to 80%, the cross-sectional area Sb becomes sufficiently small, and the resistance value R can increase by about 20% from the initial resistance value.

Here, a case is assumed in which a general detection method is used to detect wire breakage simply based on the rate of increase from the initial resistance value. In this case, as mentioned above, in addition to the fact that the resistance value R does not change noticeably until the proportion of the number of broken wires in the conductor 11a becomes sufficiently large, the resistance value R also depends on the environmental temperature and the resistance measurement. It is difficult to determine at what stage the initial disconnection occurs because it may vary depending on the contact potential at the time. For example, if the temperature characteristic of the resistance value R is about 0.4%/℃, if the environmental temperature increases by 20℃, the resistance value R will increase by about 8%. , may be larger than the change in resistance value R due to wire breakage.

Therefore, with a general detection method, it is difficult to detect an initial disconnection, or in other words, it is difficult to detect a disconnection with high sensitivity. Therefore, it is advantageous to use the disconnection detection device 1 shown in FIGS. 1(a) and 1(b).

(Principle of disconnection detection)
FIG. 4 is a schematic diagram illustrating the principle of wire breakage detection when the wire breakage detection device 1 of FIGS. 1(a) and 1(b) is used. In the example of FIG. 4, a disconnection has occurred at some locations of a plurality of wires included in the conductor 11a of the cable 10. In FIG. 4, this disconnection location is indicated by reference numeral 16. FIG. 4 shows a change in the resistance value R of the cable 10 when performing a U-shaped bending operation. In this example, the operation cycle of the U-shaped bending operation is 1 second, and the operation frequency f is 1 Hz. In addition, in this example, a state in which the slide portion 22 is moved to an intermediate position between the first U-shaped bent state 40a and the second U-shaped bent state 40b shown in FIG. 1(b) is defined as a reference state 40c, and the reference state 40c ( from the first U-shaped bending state 40a (time 0.25 seconds), the reference state 40c (time 0.50 seconds), and the second U-shaped bending state 40b (time 0.75 seconds) to the reference state 40c. Perform a U-shaped bending motion to return to (time 1.00 seconds).

As shown in FIG. 5, in the reference state 40c (time 0 seconds), the disconnection point 16 is located on the outside of the bend from the center of the cable at the bending part 10c, and the conductor length Lb of the disconnection point 16 becomes longer. . Accordingly, the resistance value R in the above formula (1) increases. Thereafter, when the first U-shaped bending state 40a (time 0.25 seconds) is reached, the disconnection point 16 shifts to the straight part 10a, so the conductor length Lb of the disconnection point 16 becomes shorter than the reference state 40c, and the resistance value R decreases.

Thereafter, when returning to the reference state 40c (time 0.50 seconds), the conductor length Lb at the disconnection point 16 becomes longer and the resistance value R increases again. Thereafter, when the second U-shaped bending state 40b (time 0.75 seconds) is reached, the disconnection point 16 moves to the straight part 10b, so the conductor length Lb of the disconnection point 16 becomes shorter than the reference state 40c, and the resistance value R decreases. Thereafter, when returning to the reference state 40c (time 1.00 seconds), the conductor length Lb at the disconnection point 16 becomes longer and the resistance value R increases again.

In this way, as a result of the conductor length Lb at the disconnection point 16 periodically expanding and contracting in the length direction of the cable 10 in synchronization with the U-shaped bending operation, the resistance value R of the conductor 11a is modulated at the operating frequency f. It turns out. On the other hand, if no wire breakage occurs, ideally the change in resistance value R does not include a resistance value fluctuation component that changes at the operating frequency f.

Therefore, the measuring device 30 measures the resistance value of the cable 10 that changes over time according to the U-shaped bending operation by the U-shaped bending mechanism 20, and determines the operating frequency based on the time-series change in the resistance value of the cable 10. Extract the resistance value fluctuation component of f. Thereby, the time point at which the resistance value fluctuation component of the operating frequency f occurs can be regarded as the time point at which the initial disconnection occurs. In other words, looking at it from a different perspective, the initial disconnection can be detected based on whether or not a resistance value fluctuation component of the operating frequency f occurs at each point in time (for example, whether the magnitude of the component is greater than or equal to a threshold value). Including this, it becomes possible to detect that a disconnection has occurred in at least the strands of the conductor 11a.

(Details of measuring device 30)
FIG. 5 is a diagram showing a schematic configuration example and an operation example of the measuring device 30 in FIG. 1(a). The measuring instrument 30 shown in FIG. 5 has a configuration example including a lock-in amplifier that detects a specific frequency component from a measurement signal. As shown in FIG. 5, the measuring device 30 includes a resistance measuring section 35 and a frequency analyzing section 36.

The resistance measurement unit 35 includes, for example, a DC signal source (for example, a DC constant voltage source) 35a, an input resistor 35b, a resistance value detector 35c, and the like. Note that when a DC constant current source is used as the DC signal source 35a, the input resistor 35b is not necessary. The DC signal source 35a applies a DC signal (DC voltage here) to the cable 10 (conductor 11a) via the input resistor 35b. In response, the cable 10 (conductor 11a) outputs a modulated signal (for example, a voltage signal) including a component of the operating frequency f (=1 Hz) as shown in FIG. 4 through the U-shaped bending operation. . The resistance value detector 35c detects a time-series change in the resistance value R of the conductor 11a, for example, by amplifying this modulation signal with a predetermined gain.

The frequency analysis section 36 includes, for example, a carrier signal generator 36a, a mixer 36b, a low pass filter (LPF) 36c, and the like. The carrier signal generator 36a generates a carrier signal having the same carrier frequency (ωc, 1 Hz in FIG. 4) as the operating frequency f, that is, the resistance value fluctuation frequency due to wire breakage, and the same phase as the resistance value fluctuation frequency. The mixer 36b multiplies this carrier signal by the output signal from the resistance value detector 35c (in other words, performs synchronous detection), thereby producing a signal in which a DC component signal and a "2×ωc" component signal are superimposed. Output. In the carrier signal generator 36a shown in FIG. 5, sin(ωct) can extract the resistance value fluctuation component of the operating frequency f when ωc=2πf.

The low-pass filter 36c receives the output signal from the mixer 36b, cuts off the "2×ωc" component signal, and passes the DC component signal. This DC component signal represents the magnitude of the resistance value fluctuation component at the operating frequency f (=ωc). The basic configuration of a lock-in amplifier is thus configured to detect a component of a predetermined frequency (here, the operating frequency f) using the carrier signal generator 36a, mixer 36b, and low-pass filter 36c. The signal from the low-pass filter 36c is converted into a digital signal by the A/D converter 37, and output to an arithmetic device such as a personal computer (not shown). The arithmetic device detects the occurrence of wire breakage, for example, by comparing the input signal with a threshold value.

FIG. 6 is a diagram illustrating an example of the effect obtained by using the principle of FIG. 4. In FIG. 6, for example, when the general detection method described above is used, an increased component of the resistance value R due to the disconnection occurs at the DC frequency (=0 Hz). However, normally, as the frequency decreases, noise components (for example, variation components depending on temperature and contact potential during measurement, 1/f noise due to amplification by semiconductor elements, etc.) increase. For this reason, with general detection methods, it may be difficult to distinguish between the increasing component of the resistance value R and the noise component unless the increasing component of the resistance value R becomes large (for example, unless the degree of wire breakage progresses). . In other words, the measurement results can be greatly influenced by the measurement environment that causes noise components.

On the other hand, if the method shown in FIG. 4 is used, the component of change in the resistance value R due to the disconnection will occur at the operating frequency f (1 Hz in FIG. 4). At the operating frequency f (1 Hz in FIG. 4), the noise component is smaller than at the DC frequency (=0 Hz). Therefore, even if the change component of the resistance value R is small to some extent (that is, even in an initial disconnection state), it is possible to distinguish between the change component of the resistance value R and the noise component. In other words, the measurement results are less affected by the measurement environment.

In addition, the configuration using a lock-in amplifier as shown in FIG. This is equivalent to a configuration in which the signal is passed through a band pass filter (BPF) whose center frequency is the operating frequency f. At this time, if a certain amount of measurement time is secured, the bandwidth of this bandpass filter (BPF) can be effectively narrowed. This means that the time constant of the low-pass filter 36c in FIG. 5 can be designed to be large. The narrower the bandwidth of the bandpass filter (BPF), the more the influence of noise components can be reduced (in other words, the SN ratio can be improved).

In addition, although the configuration example of FIG. 5 applies a DC signal to the cable 10 (conductor 11a), it is not limited to DC signals, but can also apply an AC signal of a predetermined frequency (for example, about 10 kHz) using an AC signal source. It may be applied. In this case, the cable 10 outputs a signal obtained by amplitude modulating this AC signal with a modulation signal having an operating frequency f. Therefore, by multiplying this output signal by a carrier signal having the same frequency as the alternating current signal of the alternating current signal source using a mixer, a modulated signal having the operating frequency f can be demodulated. When such a method is used, measurement can be performed at a higher frequency (for example, about 10 kHz), and as a result, the influence of noise components becomes less likely to occur.

Note that the configuration of the measuring instrument 30 in FIG. 1(a) is not limited to the configuration using a lock-in amplifier as shown in FIG. The configuration may be such that the information is extracted. Furthermore, the configuration of the measuring device 30 is such that, for example, the output signal from the resistance value detector 35c in FIG. It may be configured to extract the components of

(Using higher-order frequencies of operating frequency)
As shown in FIG. 4, the change in resistance value R obtained when the U-shaped bending operation is repeated has a waveform similar to a pulse wave with a predetermined duty ratio. Therefore, the time-series change in the resistance value R includes not only a resistance value fluctuation component at the operating frequency f, but also a resistance value fluctuation component at a higher frequency n times the operating frequency (n is a natural number of 2 or more). It will be done.

Therefore, the frequency analysis unit 36 analyzes the resistance value fluctuation component of the operating frequency f included in the time-series change in the resistance value R of the conductor 11a and the frequency n times the operating frequency f (n is a natural number of 2 or more). The resistance value fluctuation component of the extracted operating frequency f and the magnitude of the resistance value fluctuation component of the higher-order frequency (that is, the resistance value fluctuation component of FIG. 7 described later) are extracted. It is possible to detect a break in a strand based on the amplitude of the strand. As mentioned above, when the frequency is low, it is easily affected by external noise, and there is a risk of false detection depending on the surrounding environment, but it is necessary to consider not only the operating frequency but also the resistance value fluctuation component at higher frequencies (For example, by comparing the magnitude of the resistance value fluctuation component of the extracted operating frequency or high-order frequency with a preset threshold value), it is possible to suppress false detections and detect the occurrence of wire breakage with higher accuracy. It becomes possible.

As can be seen from FIG. 4, the waveform of the resistance value R changes depending on the position of the breakage point 16 in the longitudinal direction of the cable and whether it is located on the inside or outside of the bend in the curved portion 10c. Therefore, by analyzing the waveform of the resistance value R measured by the resistance measuring section 35, it is also possible to estimate at which position in the longitudinal direction of the cable the disconnection point 16 has occurred.

(Actual measurement results)
FIG. 7 is a diagram showing an example of the results of detecting a disconnection of the cable 10 using the disconnection detection device 1 shown in FIGS. 1(a) and 1(b). The vertical axis in FIG. 7 indicates the strength of the DC component signal (amplitude of resistance value fluctuation) output from the low-pass filter 36c. The bending radius of the curved portion 10c was 8 mm, and the operating frequency f was 1.16 Hz (70 rpm).

As shown in FIG. 7, in the region after the number of U-shaped bends reaches approximately 63,700 times, the operating frequency f (=1.16 Hz) and higher-order frequencies n times higher than the operating frequency f (=1.16 Hz) (secondary: 2.32 Hz, 3rd order: 3.48Hz, 4th order: 4.64Hz...) components are clearly detected. Therefore, the time when the number of U-shaped bends reaches about 63,700 can be estimated as the time when the initial wire breakage occurs.

(Disconnection detection method)
FIG. 8 is a flowchart showing an example of processing contents in the disconnection detection method according to the present embodiment. First, in step S10, the cable 10 to be inspected is mounted on the disconnection detection device 1 shown in FIG. 1(a). Subsequently, in step S11, the operations of the U-shaped bending mechanism 20 and the measuring device 30 shown in FIG. 1(a) are started. In response, the U-shaped bending mechanism 20 slides the slide portion 22 to reciprocate between the first U-shaped bent state 40a and the second U-shaped bent state 40b, as shown in FIG. 1(b). Then, a U-shaped bending motion is performed. Also, during that time, the measuring device 30 measures the resistance value of the cable 10 (conductor 11a) that changes over time, and extracts the resistance value fluctuation components of the operating frequency f and its higher-order frequencies included in the change. do.

Next, in step S12, such operations of the U-shaped bending mechanism 20 and the measuring device 30 are continued for a predetermined period. The predetermined period is, for example, in the configuration of a lock-in amplifier as shown in FIG. , is the period required to reliably detect the resistance value fluctuation component at the operating frequency f via the low-pass filter 36c. In other words, it is the period required to detect when the period modulated by the operating frequency f occurs not once, but continuously to some extent. This predetermined period can be changed as appropriate depending on the configuration of the measuring device 30, the measurement environment (that is, the magnitude of the noise component), and the like.

Subsequently, in step S13, the operations of the U-shaped bending mechanism 20 and the measuring device 30 are stopped. Thereafter, in step S14, the measurement result of the measuring device 30 is referred to, and in step S15, it is determined whether the magnitude of the resistance value fluctuation component of the operating frequency f extracted by the measuring device 30 is greater than or equal to a predetermined first threshold value. It will be judged. If the determination in step S15 is YES, the process advances to step S16. If it is determined NO in step S15, it is determined in step S18 that there is no disconnection, and the process ends.

In step S16, it is determined whether the magnitude of the resistance value fluctuation component at a higher frequency n times the operating frequency f is equal to or greater than a predetermined second threshold value. The order of high frequency components to be used in step S16 can be set as appropriate. Further, it may be determined whether each of a plurality of high-order frequency resistance fluctuation components with different n values is equal to or greater than a threshold value. If YES is determined in step S16, it is determined in step S17 that there is a disconnection, and the process ends. If it is determined NO in step S16, it is determined in step S18 that there is no disconnection, and the process ends.

With such a flow, it becomes possible to detect a break in the conductor 11a of the cable 10, including an initial break, using the predetermined period in step S12 as the inspection time. That is, it becomes possible to detect a disconnection of the conductor 11a in a sufficiently short inspection time. Note that in step S17, the administrator or the like may be notified of the fact that it is determined that there is a disconnection using an alarm system such as sound or light.

(Actions and effects of embodiments)
As described above, in the disconnection detection method according to the present embodiment, the cable 10 is bent into a U-shape, and one end of the cable 10 is periodically moved along the longitudinal direction of the cable at a predetermined stroke. A U-shaped bending operation is performed in which the conductor 11a is slid in a fixed manner, and the resistance value of the conductor 11a that changes over time due to the U-shaped bending operation is measured. The resistance value fluctuation component at the operating frequency f included in the time-series change in the resistance value of is extracted, and a break in the wire is detected based on the magnitude of the resistance value fluctuation component at the extracted operating frequency f. .

This makes it possible to detect wire breaks in the conductor 11a of the cable 10, including initial wire breaks, and as a result, it becomes possible to detect wire breaks with high sensitivity. Specifically, it becomes possible to detect an initial disconnection that is difficult to detect using a general detection method that uses the rate of increase in resistance value. As a result, in various systems to which the cable 10 is attached, countermeasures can be taken before a serious failure (for example, almost complete disconnection) occurs, and system reliability can be improved.

Further, in the conventional general detection method using the rate of increase in resistance value, the resistance value of the conductor 11a before disconnection, that is, the initial resistance value, is required, but in this embodiment, the absolute value of the resistance value is required. Instead, since the occurrence of wire breakage is detected using the amount of variation (relative amount) in the resistance value during the U-shaped bending operation, the initial resistance value is not necessary. Therefore, according to the present embodiment, even if the initial resistance value of the conductor 11a is unknown, it is possible to detect with high sensitivity that a disconnection has occurred in the strands of the conductor 11a.

(Other embodiments)
In the above embodiment, a method of detecting the occurrence of a disconnection in the conductor 11a has been described, but after the occurrence of a disconnection, it is also possible to estimate the progress state of the disconnection (=estimation of the progress state of the disconnection).

Fig. 9(a) shows the graph of the time-series change in resistance R by calculating the maximum value, minimum value, and average value of resistance value R for each measurement section separated by a predetermined time interval. This is what I did. It is desirable that the time interval used as the measurement section is longer than the cycle of the U-shaped bending motion, and can be, for example, about 100 cycles.

As shown in FIG. 9A, it can be seen that as the number of U-shaped bending operations increases and the wire breakage progresses, the difference between the maximum value and the minimum value of the resistance value R becomes larger. Therefore, based on the difference between the maximum value and the minimum value of the resistance value R, it is possible to estimate the progress state of the disconnection of the conductor 11a. For example, by setting a plurality of threshold values in stages and comparing each threshold value with the difference between the maximum value and the minimum value of the resistance value R, it is possible to estimate the progress state of the disconnection of the conductor 11a. Note that the progress state of wire breakage of the conductor 11a is the ratio of how many wires are broken out of all the wires that constitute the conductor 11a. When the progress state of the disconnection reaches a predetermined rate (for example, 80% or more), it is determined that the life of the cable 10 (=cable life) has been reached. Then, it is predicted whether the estimated progress state of the disconnection has reached the end of the cable life (=cable life prediction). Based on the cable life prediction result, it can be determined whether to replace the cable 10 or perform predictive maintenance of the cable 10.

Furthermore, calculate the average value of the resistance value R for each of the above measurement sections, and calculate multiple normalized resistance value fluctuation widths obtained using the following formula: Normalized resistance value fluctuation width = (maximum value - minimum value) / average value and find their average value. The progress state of the disconnection of the conductor 11a may be estimated based on the average value of this normalized resistance value fluctuation width. A graph of the normalized resistance value fluctuation range obtained from FIG. 9(a) is shown in FIG. 9(b). Since the difference between the maximum and minimum values of resistance value R and the average value are affected by the surrounding environmental temperature in the same way, the difference between the maximum and minimum values of resistance value R is normalized by the average value. This makes it possible to cancel the influence of changes in environmental temperature and estimate the progress state of wire breakage with higher accuracy. Then, based on the estimated progress state of disconnection, the cable life is predicted in the same way as above, and based on the cable life prediction result, it is determined whether to replace the cable 10 or perform predictive maintenance of the cable 10. can be judged.

Further, the cable 10 may be applied to any device such as an industrial robot as long as it performs a U-shaped bending motion. In this case, for example, if a severe disconnection occurs in the cable 10 (for example, almost a complete disconnection), it may cause a stoppage of equipment such as an industrial robot and, by extension, a stoppage of the production process at the factory. Therefore, it is desirable to detect a minor wire breakage (initial wire breakage) that is a sign of a serious wire breakage at an early stage before it occurs. Therefore, for example, during periodic maintenance of equipment such as industrial robots, it is useful to detect initial disconnections using the above embodiments.

Specifically, if a device similar to that in FIG. 1(a) is constructed and the U-shaped bending mechanism 20 in FIG. 1(a) is configured using a U-shaped bending part in a device such as an industrial robot. good. Then, the U-shaped bending motion of the cable 10 may be performed using a control unit of a device such as an industrial robot, or by using an external device that can apply an external force to the device such as an industrial robot. Note that the measuring device 30 may be added from outside each time, or may be built in a device such as an industrial robot in advance. Note that the procedure for detecting disconnection when such a configuration is used is the same as in the case of FIG. 8. However, the process of step S10 in FIG. 8 is unnecessary because the cable 10 is already attached. In this way, even if the cable 10 is already attached to a predetermined device and is in actual use, it is possible to detect an initial disconnection with high sensitivity without removing the cable 10.

In addition to such application examples, the life characteristics of a cable similar to the cable 10 used in devices such as industrial robots can be obtained at the manufacturing stage by using a disconnection detection device 1 as shown in Fig. 1(a). It is also beneficial to reflect the results in the maintenance of equipment such as industrial robots. Specifically, by using the device shown in FIG. 1(a), it is possible to determine the number of bends in the cable 10 that can cause an initial disconnection. information can be provided. In this case, by comparing the provided number of bends with the operating history of devices such as industrial robots, the administrator can take various measures before a severe disconnection occurs in the cable 10 (i.e., the cable reaches the end of its service life). It becomes possible to take the following steps.

(Summary of embodiments)
Next, technical ideas understood from the embodiments described above will be described using reference numerals and the like in the embodiments. However, each reference numeral in the following description does not limit the constituent elements in the claims to those specifically shown in the embodiments.

[1] A method for detecting disconnection of the strands of a cable (10) having a conductor (11a) made of a stranded conductor made by twisting a plurality of strands, the cable (10) being arranged in a U-shape. In the bent state, a U-shaped bending operation is performed in which one end of the cable (10) is periodically slid along the longitudinal direction of the cable at a predetermined stroke, and the U-shaped bending operation causes the cable (10) to move in a time-series manner. Measure the resistance value of the conductor (11a) that changes, and set the frequency corresponding to the cycle of the U-shaped bending operation as the operating frequency, and measure the operation included in the time-series change in the resistance value of the conductor (11a). A wire breakage detection method that extracts a resistance value fluctuation component of a frequency and detects a wire breakage of the strand based on the magnitude of the extracted resistance value fluctuation component of the operating frequency.

[2] Extract the resistance value fluctuation component at the operating frequency and the resistance value fluctuation component at higher-order frequencies included in the time-series change in the resistance value of the conductor (11a), and extract the extracted resistance value at the operating frequency. The disconnection detection method according to [1], wherein disconnection of the strand is detected based on the magnitude of the fluctuation component and the resistance value fluctuation component of its higher-order frequency.

[3] Determine the maximum and minimum values of the resistance value of the conductor (11a) in a time-series change in resistance value for each measurement period separated by a time interval equal to or longer than the cycle of the U-shaped bending operation, The disconnection detection method according to [1] or [2], wherein the progress state of the disconnection of the conductor (11) is estimated based on the difference between the maximum value and the minimum value of the resistance value.

[4] For each measurement section, find the average value of the time-series changes in the resistance value of the conductor (11a), and calculate the average value using the following formula: Normalized resistance value variation width = (maximum value - minimum value) / average value. The disconnection detection method according to [3], wherein the progress state of the disconnection of the conductor (11a) is estimated based on the normalized resistance value fluctuation range.

[5] A device for detecting disconnection of the strands of a cable (10) having a conductor (11a) made of a stranded conductor made by twisting a plurality of strands, the cable (10) being arranged in a U-shape. a U-shaped bending mechanism (20) that performs a U-shaped bending operation of periodically sliding one end of the cable (10) at a predetermined stroke along the longitudinal direction of the cable in the bent state; The resistance value of the conductor (11a) that changes over time due to the U-shaped bending operation is measured, and the time series of the resistance value of the conductor (11a) is determined by setting the frequency corresponding to the cycle of the U-shaped bending operation as the operating frequency. a measuring device (30) for extracting a resistance value fluctuation component of the operating frequency included in a change in the operating frequency, and detecting a break in the wire based on the magnitude of the extracted resistance value fluctuation component of the operating frequency Disconnection detection device (1).

Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. Furthermore, it should be noted that not all combinations of features described in the embodiments are essential for solving the problems of the invention. Moreover, the present invention can be implemented with appropriate modifications within a range that does not depart from the spirit thereof.

1... Disconnection detection device 10... Cables 10a, 10b... Straight section 10c... Curved section 11... Electric wire 11a... Conductor 16... Disconnection point 20... U-shaped bending mechanism 21... Fixed section 22... Slide section 30... Measuring device 35... Resistance measurement Section 36...Frequency analysis section 40a...First U-shaped bending state 40b...Second U-shaped bending state 40c...Reference state

Claims (4)

A method for detecting disconnection of the strands of a cable having a conductor made of a stranded conductor made by twisting a plurality of strands, the method comprising:
performing a U-shaped bending operation in which the cable is bent into a U-shape, and one end of the cable is periodically slid at a predetermined stroke along the longitudinal direction of the cable;
A resistance value of the conductor that changes over time due to the U-shaped bending action is measured, and a frequency corresponding to the cycle of the U-shaped bending action is set as an operating frequency and is included in the time-series change in the resistance value of the conductor. extracting a resistance value fluctuation component at the operating frequency and a resistance value fluctuation component at its higher-order frequency ;
Detecting a break in the wire based on the magnitude of the extracted resistance value fluctuation component at the operating frequency and the resistance value fluctuation component at its higher-order frequency ;
Disconnection detection method. For each measurement period separated by a time interval equal to or longer than the cycle of the U-shaped bending operation, the maximum value and minimum value of the resistance value in the time-series change in the resistance value of the conductor are determined, and the maximum value and the minimum value of the resistance value are determined. estimating the progress state of disconnection of the conductor based on the difference from the minimum value;
The disconnection detection method according to claim 1 . For each measurement section, find the average value of the time-series changes in the resistance value of the conductor, and calculate the normalized resistance value obtained from the following formula: Normalized resistance value variation width = (maximum value - minimum value) / average value estimating the progress state of disconnection of the conductor based on the fluctuation range;
The disconnection detection method according to claim 2 . A device for detecting disconnection of the strands of a cable having a conductor made of a stranded conductor made by twisting a plurality of strands,
a U-shaped bending mechanism that performs a U-shaped bending operation in which the cable is bent into a U-shape, and one end of the cable is periodically slid at a predetermined stroke along the longitudinal direction of the cable;
A resistance value of the conductor that changes over time due to the U-shaped bending action is measured, and a frequency corresponding to the cycle of the U-shaped bending action is set as an operating frequency and is included in the time-series change in the resistance value of the conductor. a measuring device that extracts a resistance value fluctuation component at the operating frequency and a resistance value fluctuation component at a higher-order frequency thereof ,
Detecting a break in the wire based on the magnitude of the extracted resistance value fluctuation component at the operating frequency and the resistance value fluctuation component at its higher-order frequency ;
Disconnection detection device.

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