JP7567833B2 - Disconnection detection method and device - Google Patents

Description

The present invention relates to a method and device for detecting breaks in a conductor in a twisted cable.

Patent Document 1 shows a method for detecting signs of conductor breakage due to bending in a wire cable having a conductor made of a stranded conductor in which multiple strands are twisted together. Specifically, in this method, the wire cable is periodically bent and stretched in one direction while a current is flowing through it, and the current component that changes in synchronization with the bending period is detected. In other words, this method detects a state in which some broken points are repeatedly coming into contact and separating in synchronization with the bending period.

JP 2007-139488 A

The occurrence of a break in the conductor of a twisted cable is generally detected by measuring the electrical resistance of the conductor inside the cable. When a break occurs in one of the wires contained in the conductor, the resistance value of the conductor increases. Therefore, for example, by measuring the resistance value of the conductor in advance in an initial state where no breaks have occurred, it is possible to detect the occurrence of a break based on the rate of increase in the resistance value from the initial state.

However, if a break occurs in only a small portion of the wires contained in the conductor, i.e., if the number of broken wires is small, the rate of increase in resistance value will be extremely small. For this reason, in practice, it may be difficult to clearly detect a break based on the rate of increase in resistance value unless the proportion 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 break in the early stages immediately after it occurs, and there is a risk that the occurrence of a break cannot be detected with high sensitivity.

Therefore, the present invention aims to provide a wire break detection method and a wire break detection device that can detect the occurrence of a wire break in a conductor with high sensitivity.

The present invention aims to solve the above problems, and provides a method for detecting a break in a wire of a cable having a conductor made of a stranded conductor formed by twisting a plurality of strands together, which comprises performing a twisting operation to periodically twist the cable in the circumferential direction, measuring the resistance of the conductor that changes over time due to the twisting operation, performing a frequency analysis of the measured resistance of the conductor that changes over time, extracting from the results of the frequency analysis a resistance value fluctuation component of a predetermined high-order frequency that is included in a preset frequency range among high-order frequencies based on an operating frequency that corresponds to the operating period of the twisting operation, and detecting a break in the wire based on the magnitude of the extracted resistance value fluctuation component of the high-order frequency.

In addition, in order to solve the above problems, the present invention provides a wire breakage detection device that detects a break in a wire of a cable having a conductor made of a stranded conductor formed by twisting a plurality of strands together, the wire breakage detection device comprising: a twisting mechanism that performs a twisting operation to periodically twist the cable in the circumferential direction; a resistance measuring device that measures the resistance value of the conductor that changes over time due to the twisting operation; a frequency analysis unit that performs frequency analysis of the resistance value of the conductor that changes over time measured by the resistance measuring device; an extraction unit that extracts, from the results of the frequency analysis, resistance value fluctuation components of a predetermined high-order frequency that is included in a preset frequency range from high-order frequencies based on an operating frequency that corresponds to the operating period of the twisting operation; and a wire breakage detection unit that detects a break in the wire based on the magnitude of the resistance value fluctuation components of the high-order frequency extracted by the extraction unit.

The present invention provides a disconnection detection method and device that can detect the occurrence of a disconnection in a conductor with high sensitivity.

1 is a schematic diagram showing a wire break detection device according to an embodiment of the present invention; 1 is a cross-sectional view showing a schematic configuration example of a cable that is a target for disconnection detection; 10A and 10B are diagrams illustrating a change in resistance value when a conductor is twisted in the case where no break occurs in the wires of the conductor. 10A and 10B are diagrams illustrating a change in resistance value when a conductor is twisted in a case where a break occurs in a wire of the conductor. 1A and 1B are diagrams illustrating a schematic configuration example of a resistance measuring device. 5A and 5B are diagrams illustrating an example of frequency analysis data obtained by a frequency analysis unit. FIG. 4 is a flowchart showing the steps of a disconnection detection method.

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

(General configuration of disconnection detection device 1)
Fig. 1 is a schematic diagram showing a wire breakage detection device 1 according to the present embodiment. Fig. 2 is a cross-sectional view showing a schematic configuration example of a cable 10 that is an object of wire breakage detection.

The cable 10 shown in FIG. 2 is configured by winding a pressure winding tape 14 in a spiral shape around a cable core 13 in which five electric wires 11 and thread-like intervening members 12 are twisted together, and providing a sheath 15 to cover the periphery of the pressure winding tape 14. Each electric wire 11 has a conductor 11a made of a stranded conductor made of multiple strands twisted together, and an insulator 11b provided to cover the periphery of the conductor 11a. The conductor 11a is configured by, for example, twisting together 19 strands of soft copper wire with 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 members 12 are made of, for example, jute or staple fiber. The number of electric wires 11 used in the cable 10 is not limited to five. The pressure winding tape 14 is made of, for example, a tape member made of nonwoven fabric, paper, resin, etc. The sheath 15 is made of, for example, PE (polyethylene), PP (polypropylene), PVC (polyvinyl chloride), etc. 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 twisted conductor. That is, the electric wire 11 may be one, several, or several tens or more. When there is only one electric wire 11, the insert 12, the holding winding tape 14, and the sheath 15 are often omitted. In this case, the cable 10 and the electric wire 11 refer to the same thing.

As shown in FIG. 1, the wire breakage detection device 1 is a device that detects a break in a wire of a cable 10 having a conductor 11a made of a stranded conductor formed by twisting together multiple wires, and includes a twisting mechanism 2, a resistance measuring device 3, and a computing device 4.

The twisting mechanism 2 is a mechanism that performs a twisting operation to periodically twist the cable 10 in its circumferential direction (the direction along the outer circumference of the cable 10 shown in FIG. 2). In this embodiment, the cable 10 is mounted on an industrial robot 2a, and the industrial robot 2a on which the cable 10 is mounted is used as a twisting device having the twisting mechanism 2. However, the twisting mechanism 2 is not limited to this and may be any mechanism that can periodically twist the cable 10, and may be realized, for example, by a twisting test device for performing a twisting test. Furthermore, the twisting mechanism 2 is not limited to a mechanism that performs only a twisting operation, and may be a mechanism that performs a bending operation to periodically bend the cable 10 in addition to the twisting operation.

The industrial robot 2a having the twisting mechanism 2 is provided with a robot control device 2b for controlling the operation of the industrial robot 2a. The robot control device 2b is equipped with a test operation control unit 2c that controls the twisting mechanism 2 to perform a test operation (hereinafter referred to as test operation control) in order to perform a test to detect a break in the conductor 11a in the cable 10. In this embodiment, the test operation control unit 2c applies a periodic twisting operation to the cable 10 by performing a test operation control that periodically twists the twisting mechanism 2 of the industrial robot 2a, i.e., the moving part to be inspected (for example, the joint of the industrial robot 2a, etc.) during a test to detect a break in the conductor 11a. Note that the test to detect a break in the conductor 11a may be performed, for example, during a regular inspection of the industrial robot 2a, or may be performed every time the industrial robot 2a starts operating. The test operation control unit 2c may also be configured to control the test operation at a fixed time, such as when the industrial robot 2a is started or when the factory starts work, and to perform a test to detect a break in the conductor 11a.

The resistance measuring device 3 measures the resistance value of the conductor 11a, which changes over time due to the twisting operation. In this embodiment, the resistance measuring device 3 measures the resistance value of the conductor 11a over time from the start to the end of the test operation control by the test operation control unit 2c. The data on the resistance value of the conductor 11a, which changes over time (=resistance value data 50), measured by the resistance measuring device 3 is input to the calculation device 4 and stored in the memory unit 42.

In this embodiment, the resistance measuring device 3 is mounted on the robot control device 2b of the industrial robot 2a. However, this is not limited to the above, and the resistance measuring device 3 may be configured separately from the robot control device 2b, and some of its functions may be mounted on the computing device 4. Details of the resistance measuring device 3 will be described later.

The arithmetic device 4 has a control unit 41 and a storage unit 42. The details of the control unit 41 and the storage unit 42 will be described later. The arithmetic device 4 is connected to a display unit 43, and is configured to be able to display various data such as resistance value data 50 and the results of disconnection detection on the display unit 43. Although not shown, the arithmetic device 4 is provided with an input device such as a keyboard, and various settings and the display contents of the display unit 43 can be operated by inputting from the input device. The display unit 43 may be configured as a touch panel display so that the display unit 43 also serves as an input device. Furthermore, the display unit 43 does not have to be connected to the arithmetic device 4 by wire, and may be connected wirelessly. In this case, the display unit 43 may be, for example, a display of a smartphone or tablet.

(Principle of disconnection detection)
First, a change in resistance value when the conductor 11a is twisted (i.e., a change in resistance value of the conductor 11a due to twisting strain) will be described in the case where no break occurs in the wire of the conductor 11a. As shown in FIG. 3, the conductor 11a is twisted by a predetermined angle (for example, +180 degrees) in a direction in which the twist of the conductor 11a is tightened (here, the positive direction) from a basic state C where no twist is applied in the circumferential direction to a first state A. Then, the conductor 11a is twisted by a predetermined angle in the opposite direction (a direction in which the twist of the conductor 11a is loosened, here, the negative direction) to return to the basic state C, and is further twisted by a predetermined angle (for example, -180 degrees) in the negative direction to a second state B. Then, the conductor 11a is twisted by a predetermined angle in the positive direction to return to the basic state C. In this way, the conductor 11a is twisted in the circumferential direction from the basic state C to the first state A, the basic state C, the second state B, and the basic state C, thereby completing one twisting operation (one period). Here, the time required for one twisting operation, that is, the operation cycle, is set to 1 second, and the operation frequency, which is the frequency when one twisting operation is performed, is set to 1.0 Hz.

Since the conductor 11a is composed of multiple strands 111 twisted together, when the conductor 11a is twisted in the positive direction (i.e., transitioning from the basic state C to the first state A), the strain of each strand 111 increases, and each strand 111 is stretched and its cross-sectional area decreases, so that the resistance value of the conductor 11a increases. When the conductor 11a is returned from the first state A to the basic state C without twist, the strain of each strand 111 decreases, and the cross-sectional area of each strand 111 that was stretched is restored, so that the resistance value of the conductor 11a decreases. Next, when the conductor 11a is twisted in the negative direction (i.e., transitioning from the basic state C to the second state B), the strands are loosened and each strand 111 tries to spread outward. However, because the insulator 11b is formed around the conductor 11a, each of the strands 111 that try to expand outward is pressed down by the insulator 11b, increasing the strain of each strand 111 and increasing the resistance of the conductor 11a. When the conductor 11a is returned from the second state B to the basic state C without twisting, the strain of each strand 111 decreases and the resistance decreases.

In this way, when the conductor 11a is subjected to a twisting motion, the resistance value increases twice in one operating cycle. In other words, when the conductor 11a is subjected to a twisting motion, the resistance value fluctuation component at a frequency twice the operating frequency increases. Note that, in order to simplify the drawing, only five wires 111 of the conductor 11a are shown in FIG. 3, but in reality, the number of wires 111 that make up the conductor 11a is more than five.

Next, we will explain the change in resistance value when the conductor 11a is twisted when a break occurs in the wire 111. As shown in Figure 4, when the conductor 11a is twisted in the positive direction in which the twist is tightened (i.e., when the conductor 11a is transitioned from the basic state C to the first state A), the broken part gradually expands as the conductor 11a is stretched, and the resistance value of the conductor 11a increases. Then, when the conductor is returned from the first state A to the basic state C without twisting, the broken part gradually shrinks and the resistance value decreases.

Next, the conductor 11a is twisted in the negative direction, which untwists the wires. When the twisting direction changes from the positive to the negative direction, the wires 111 are pushed in for a very short time, shortening the broken part (or the wires 111 sandwiching the broken part come into contact with each other), and the resistance value decreases significantly for a very short time. Then, when the conductor 11a is twisted in the negative direction, which untwists the wires 111 (i.e., transitioning from basic state C to second state B), the twist untwists and each wire 111 tries to spread outward, expanding the broken part and increasing the resistance value of the conductor 11a. Then, when returning from second state B to the basic state C without twists, the broken part gradually shrinks and the resistance value decreases.

In this way, the fluctuation in resistance value due to breakage of the wire 111 basically occurs in sync with the fluctuation in resistance value due to strain. However, it can be seen that the short-term decrease in resistance value when the direction of twisting applied to the conductor 11a changes occurs only when a break occurs in the wire 111. And since this "decrease in resistance value when the direction of twisting applied to the conductor 11a changes" is an event in which the resistance value changes over a short period of time, it appears as a high-order frequency component based on the operating frequency. Therefore, in this embodiment, a break in the wire 111 is detected by detecting the "decrease in resistance value when the direction of twisting applied to the conductor 11a changes" by focusing on the high-order frequency component of the operating frequency.

(Details of Resistance Meter 3)
FIG. 5(a) is a diagram showing a schematic configuration example of the resistance measuring device 3. As shown in FIG. 5(a), the resistance measuring device 3 includes a resistance measuring unit 35 having a DC signal source (e.g., a DC constant voltage source) 35a, an input resistor 35b, and a resistance value detector 35c. 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 (here, a DC voltage) to the cable 10 (conductor 11a) via the input resistor 35b. In response to this, a modulated signal (e.g., a voltage signal) including a component of the operating frequency f (=1 Hz) as shown in FIGS. 3 and 4 is output from the cable 10 (conductor 11a) by a twisting operation. The resistance value detector 35c detects a time-series change in the resistance value of the conductor 11a, for example, by amplifying this modulated signal with a predetermined gain. The signal from the resistance detector 35 c is converted into a digital signal by the A/D converter 37 and output to the calculation device 4 as resistance data 50 .

The configuration of the resistance measuring device 3 shown in FIG. 5(a) is merely an example and can be modified as appropriate. For example, as shown in FIG. 5(b), the resistance measuring device 3 may have an integrated frequency analysis unit 36. In this case, the frequency analysis unit 411 (see FIG. 1) of the calculation device 4 described later can be omitted.

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, 1 Hz in the case of Figs. 3 and 4) as the operating frequency f, i.e., the resistance value fluctuation frequency due to a break, and the same phase as the resistance value fluctuation frequency. The mixer 36b multiplies (in other words, synchronously detects) this carrier signal by the output signal from the resistance value detector 35c, thereby outputting a signal in which a DC component signal and a "2 x ωc" component signal are superimposed. In the carrier signal generator 36a shown in Fig. 5(b), 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, blocks the "2×ωc" component signal, and passes the DC component signal. This DC component signal represents the magnitude of the resistance value fluctuation component of the operating 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 specific frequency (for example, a component of a specific higher-order frequency, which will be described later). The signal from the low-pass filter 36c is converted into a digital signal by the A/D converter 37 and is output to the calculation device 4.

In the configuration examples of Figures 5(a) and (b), a DC signal is applied to the cable 10 (conductor 11a), but it is not limited to a DC signal, and an AC signal of a predetermined frequency (e.g., about 10 kHz) may be applied using an AC signal source. In this case, a signal is output from the cable 10 that is an amplitude-modulated AC signal with a modulation signal of operating frequency f. If a mixer is used to multiply this output signal by a carrier signal of the same frequency as the AC signal from the AC signal source, the modulation signal of operating frequency f can be demodulated. Using such a method allows measurements to be performed at a higher frequency (e.g., about 10 kHz), making it less susceptible to the effects of noise components.

(Calculation device 4)
The control unit 41 of the calculation device 4 is equipped with a frequency analysis unit 411, an extraction unit 412, a disconnection detection unit 413, and an alarm unit 414. The frequency analysis unit 411, the extraction unit 412, the disconnection detection unit 413, and the alarm unit 414 are realized by appropriately combining a calculation element such as a CPU, a memory such as a RAM or a ROM, software, an interface, a storage device, and the like.

The frequency analysis unit 411 performs frequency analysis on the resistance value data 50 measured by the resistance measuring device 3 (i.e., data on the resistance value of the conductor 11a that changes over time). The results of the frequency analysis are stored in the storage unit 42 as frequency analysis data 51. Note that frequency analysis refers to analyzing the magnitude of each frequency component contained 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.

Figures 6(a) and (b) are diagrams showing an example of frequency analysis data 51 obtained by the frequency analysis unit 411. Figure 6(a) shows a frequency range of 1 Hz to 10 Hz, and Figure 6(b) shows a frequency range of 30 Hz to 50 Hz. Figures 6(a) and (b) also show frequency analysis results for a cable 10 using five 28 AWG electric wires 11, with a twist length of 50 mm and a twist angle of ±180 degrees.

As shown in FIG. 6(a), in the low frequency range, the effects of distortion and noise caused by twisting are large, and the magnitude of the component hardly changes whether or not there is a break in the wire 111. In contrast, as shown in FIG. 6(b), in the high frequency range of 30 Hz to 50 Hz, the component becomes larger after the break occurs. This is thought to be a reflection of the "decrease in resistance value when the direction of twisting applied to the conductor 11a changes" described in FIG. 4.

Based on the frequency analysis data 51, which is the result of the frequency analysis, the extraction unit 412 extracts resistance value fluctuation components of a predetermined high-order frequency included in a preset frequency range from among high-order frequencies f×n (n is a natural number of 2 or more) based on the operating frequency f corresponding to the operating period of the twisting operation. Here, the "preset frequency range" may be set to a frequency range greater than the frequency at which resistance value fluctuation occurs due to the strain applied to the conductor 11a by the twisting operation (in the example of Figs. 6(a) and (b), a frequency of 10 Hz or less), and more specifically, may be set to a frequency range of 10 times or more of the operating frequency f. For example, in the example of Figs. 6(a) and (b), the frequency range may be set to 30 Hz or more and 50 Hz or less, and resistance value fluctuation components of three high-order frequencies of about 33 Hz, about 36 Hz, and about 40 Hz included in this frequency range may be extracted. The frequency range and the frequencies of the high-order frequencies to be extracted within the frequency range may be set appropriately based on the results of an experiment conducted in advance.

The disconnection detection unit 413 detects a disconnection of the wire 111 based on the magnitude of the resistance value fluctuation components of the high-order frequencies extracted by the extraction unit 412. More specifically, the magnitude of each of the resistance value fluctuation components of the high-order frequencies extracted by the extraction unit 412 (in the example of Figs. 6(a) and (b), the resistance value fluctuation components of three high-order frequencies of about 33 Hz, about 36 Hz, and about 40 Hz) is compared with a preset threshold value, and if any of the resistance value fluctuation components is equal to or greater than the threshold value, it is determined that a disconnection has occurred. Note that this is not limited to the above, and for example, it may be determined that a disconnection has occurred when a predetermined number (e.g., half) of the extracted resistance value fluctuation components are equal to or greater than the threshold value. The determination result is stored in the storage unit 42 as disconnection detection data 52.

The alarm unit 414 issues an alarm when the disconnection detection unit 413 detects a disconnection. The alarm unit 414 issues an alarm, for example, by sounding an alarm, displaying an alarm on the display 43, or issuing an alarm signal to an external device such as a management device, and notifies the administrator that a disconnection has been detected.

The calculation device 4 is configured as, for example, a personal computer. However, this is not limited to this, and the calculation device 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 calculation device 4, which is a server device, via a network. When the calculation device 4 is configured as a server device, it may be configured so that the results of the disconnection detection (i.e., the disconnection detection data 52) and the like can be shared with, for example, a user who uses the industrial robot 2a or a robot manufacturer. In addition, the control unit 41 and the storage unit 42 may be configured as 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 or personal computer, etc., to perform disconnection detection.

(Disconnection detection method)
7 is a flow chart showing the procedure of the disconnection detection method according to the present embodiment. First, in step S10, the test operation control unit 2c mounted on the robot control device 2b starts controlling the test operation of the industrial robot 2a. This starts a twisting operation that periodically twists the cable 10 to be inspected in the circumferential direction. Then, in step S11, the resistance measuring device 3 starts measuring the resistance value of the conductor 11a.

Next, in step S12, the test operation control 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 to detect a break. This predetermined period can be changed as appropriate depending on the configuration of the resistance measuring device 3 and the measurement environment (i.e., the magnitude of the noise component). In this way, the resistance value of the conductor 11a, which changes over time due to the twisting operation, is measured by the resistance measuring device 3.

Next, in step S13, the test operation control and the measurement of the resistance value of the conductor 11a are stopped. The measured resistance value data of the conductor 11a is sent to the calculation device 4 as resistance value data 50 and stored in the memory unit 42 of the calculation device 4. Note that in this embodiment, the detection of a disconnection is performed only during the test operation control, but this is not limited to this, and it is also possible to configure the detection of a disconnection to be performed constantly while the industrial robot 2a is being driven. In this case, instead of the above-mentioned steps S10 to S13, the measurement of the resistance value of the conductor 11a by the resistance measuring device 3 is continuously performed while the industrial robot 2a is being driven.

Then, in step S14, the frequency analysis unit 411 performs frequency analysis on the resistance value data 50. The results of the frequency analysis are stored in the memory unit 42 as frequency analysis data 51.

After that, in step S15, the extraction unit 412 extracts resistance value fluctuation components of a predetermined high-order frequency included in a preset frequency range from the frequency analysis data 51. Then, in step S16, the break detection unit 413 determines whether the magnitude of the resistance value fluctuation components of the high-order frequency extracted by the extraction unit 412 is equal to or greater than a preset threshold value. If the determination is YES in step S16, the break detection unit 413 determines that there is a break in the conductor 11a in step S17, and the alarm unit 414 issues an alarm in step S18, and then the process ends. If the determination is NO in step S16, the break detection unit 413 determines that there is no break in the conductor 11a, and the process ends.

(Functions and Effects of the Embodiments)
As described above, in the wire break detection method according to the present embodiment, a twisting operation is performed in which the cable 10 is periodically twisted in the circumferential direction, the resistance value of the conductor 11a which changes over time due to the twisting operation is measured, the measured resistance value of the conductor 11a which changes over time is frequency analyzed, and from the results of the frequency analysis, resistance value fluctuation components of a predetermined high-order frequency included in a preset frequency range are extracted from among high-order frequencies based on an operating frequency corresponding to the operating period of the twisting operation, and a wire break in the wire 111 is detected based on the magnitude of the resistance value fluctuation components of the extracted high-order frequency.

This makes it possible to detect the "reduction in resistance when the direction of twist applied to the conductor 11a changes" described in FIG. 4, and accurately detects breaks in the wires 111 in the conductor 11a of the cable 10. The "reduction in resistance when the direction of twist applied to the conductor 11a changes" is a very short and small change, but by performing frequency analysis, it is possible to remove the effects of noise and other factors and accurately detect it. In other words, according to this embodiment, it is possible to detect breaks in the wires 111 in the conductor 11a of the cable 10, including early breaks that are difficult to detect using a general detection method using the rate of increase in resistance, and it is possible to detect breaks with high sensitivity. As a result, measures can be taken before a serious failure (for example, almost complete break) occurs in various devices to which the cable 10 is attached, and the reliability of the device can be improved.

In addition, in the conventional detection method using the rate of increase in resistance, the resistance value of the conductor 11a before the break, i.e., the initial resistance value, was required. However, in this embodiment, the occurrence of a break is detected using the amount of change (relative amount) in the resistance value during the twisting operation, rather than the absolute value of the resistance value, so the initial resistance value is not required. Therefore, according to this embodiment, even if the initial resistance value of the conductor 11a is unknown, it is possible to detect with high sensitivity that a break has occurred in the wire 111 of the conductor 11a.

Furthermore, the resistance value of the conductor 11a and the contact resistance between the conductor 11a and the resistance measuring device 3 vary greatly with temperature, but the variation in resistance value due to temperature is unrelated to the operating period of the twisting operation, so according to this embodiment, it is possible to detect a break in the conductor 11a without being affected by temperature changes.

(Modification)
In the above embodiment, a method for detecting the occurrence of a break in the conductor 11a has been described, but it is also possible to estimate the progression of the break after the break occurs (= estimation of the break progression state).

As a result of the study by the inventors, it has been found that in the time series change of the resistance value of the conductor 11a, the difference between the maximum and minimum values of the resistance value of the conductor 11a increases as the number of broken wires 111 increases and the breakage progresses. Therefore, it is possible to estimate the progress of the breakage of the conductor 11a based on the difference between the maximum and minimum values of the resistance value. For example, by setting multiple threshold values in stages and comparing each threshold value with the difference between the maximum and minimum values of the resistance value, the progress of the breakage of the conductor 11a can be estimated. The progress of the breakage of the conductor 11a is the proportion of the number of wires 111 that are broken among all the wires 111 that make up the conductor 11a. The estimated progress of the breakage is stored as breakage progress data in the memory unit 42 shown in FIG. 4.

If the cable 10 is set to have reached its lifespan (=cable lifespan) when the breakage progression state reaches a predetermined percentage (e.g., 80% or more), it becomes possible to predict the lifespan of the cable 10 by predicting whether the estimated breakage progression state has reached the cable lifespan. Based on the lifespan prediction result of the cable 10, it can be determined whether to replace the cable 10 or perform predictive maintenance of the cable 10. The lifespan prediction result of the cable 10 obtained based on the breakage progression state is stored as cable lifespan prediction data in the storage unit 42 shown in FIG. 4. The calculation device 4 may also be configured to display the obtained breakage progression state data and cable lifespan prediction data on the display 43.

In addition, in this embodiment, the case of detecting a break in the cable 10 mounted on the industrial robot 2a has been described, but it is also useful to obtain the life characteristics of a cable of the same type as the cable 10 used in the industrial robot 2a or other device in advance during the manufacturing stage using a twisting test device or the like as the twisting mechanism 2, and to reflect the results in the maintenance of the industrial robot 2a or other device. This makes it possible to determine the number of bends that may cause an initial break in the cable 10, and to provide information on this number of bends to, for example, the manager of the industrial robot 2a or other device. In this case, the manager can compare the provided number of bends with the operation history of the industrial robot 2a or other device, and take various measures before a serious break occurs in the cable 10 (i.e., before the cable reaches its end of life).

(Summary of the embodiment)
Next, the technical ideas grasped from the above-described embodiment will be described by using the reference numerals and the like in the embodiment. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiment.

[1] A method for detecting a break in a wire (111) of a cable (10) having a conductor (11a) made of a stranded conductor formed by twisting a plurality of wires (111), comprising: performing a twisting operation to periodically twist the cable (10) in the circumferential direction; measuring the resistance of the conductor (11a) that changes over time due to the twisting operation; performing frequency analysis on the measured resistance of the conductor (11a) that changes over time; extracting, from the results of the frequency analysis, a resistance value fluctuation component of a predetermined high-order frequency included in a preset frequency range among high-order frequencies based on an operating frequency that corresponds to the operating period of the twisting operation; and detecting a break in the wire (111) based on the magnitude of the extracted resistance value fluctuation component of the high-order frequency.

[2] The disconnection detection method described in [1], in which the preset frequency range is set to a frequency range greater than the frequency at which a resistance value fluctuation occurs due to the strain applied to the conductor (11a) by the twisting operation.

[3] The disconnection detection method described in [1] or [2], in which the preset frequency range is set to a frequency range that is 10 times or more the operating frequency.

[4] A device for detecting a break in a wire (111) of a cable (10) having a conductor (11a) made of a stranded conductor formed by twisting together a plurality of wires (111), the device comprising: a twisting mechanism (2) for performing a twisting operation to periodically twist the cable (10) in the circumferential direction; a resistance measuring device (3) for measuring the resistance value of the conductor (11a) that changes over time due to the twisting operation; and a resistance measuring device (4) for measuring the resistance value of the conductor (11a) that changes over time measured by the resistance measuring device (3) in the circumferential direction. A wire breakage detection device (1) including a frequency analysis unit (411) that performs wave number analysis, an extraction unit (412) that extracts, from the results of the frequency analysis, resistance value fluctuation components of a predetermined high-order frequency included in a preset frequency range from among high-order frequencies based on an operating frequency that corresponds to the operating period of the twisting operation, and a wire breakage detection unit (413) that detects a wire breakage in the wire (111) based on the magnitude of the resistance value fluctuation components of the high-order frequency extracted by the extraction unit (412).

Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the embodiments described above. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. The present invention can be modified as appropriate without departing from the spirit of the invention.

Reference Signs List 1... Disconnection detection device 2... Twisting operation mechanism 2a... Industrial robot 2b... Robot control device 2c... Test operation control unit 3... Resistance measuring device 4... Calculation device 41... Control unit 411... Frequency analysis unit 412... Extraction unit 413... Disconnection detection unit 414... Alarm unit 10... Cable 11... Electric wire 11a... Conductor 111... Strand

Claims (4)

A method for detecting a break in a wire of a cable having a conductor made of a stranded conductor formed by twisting together a plurality of wires, comprising the steps of:
A twisting operation is performed to periodically twist the cable in a circumferential direction,
measuring a resistance value of the conductor that changes over time due to the twisting operation;
performing a frequency analysis on the measured resistance value of the conductor that changes over time;
extracting, from a result of the frequency analysis, a resistance value fluctuation component of a predetermined high-order frequency included in a preset frequency range among high-order frequencies based on an operating frequency corresponding to an operating period of the twisting operation;
a decrease in resistance value when a direction of twist applied to the conductor is changed by the twisting operation is detected based on the magnitude of the extracted resistance value fluctuation component of the high-harmonic frequency, thereby detecting a break in the wire.
Disconnection detection method. The preset frequency range is set to a frequency range higher than a frequency at which a resistance value variation occurs due to a strain applied to the conductor by the twisting operation.
The method for detecting a disconnection according to claim 1 . The preset frequency range is set to a frequency range of 10 times or more of the operating frequency.
The disconnection detection method according to claim 1 or 2. A device for detecting a break in a wire of a cable having a conductor made of a stranded conductor formed by twisting together a plurality of wires, comprising:
a twisting mechanism that performs a twisting operation to periodically twist the cable in a circumferential direction;
a resistance measuring device for measuring a resistance value of the conductor that changes over time due to the twisting operation; and
a frequency analysis unit that performs frequency analysis on the resistance value of the conductor that changes over time and is measured by the resistance measuring device;
an extracting unit that extracts, from a result of the frequency analysis, a resistance value fluctuation component of a predetermined high-order frequency included in a preset frequency range from high-order frequencies based on an operation frequency corresponding to an operation period of the twisting operation;
A disconnection detection unit that detects a disconnection of the wire by detecting a decrease in resistance when a direction of twist applied to the conductor changes due to the twisting operation based on the magnitude of the resistance value fluctuation component of the high-order frequency extracted by the extraction unit.
Disconnection detection device.

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