JP7439814B2 - Conductor strain evaluation method and device, cable life prediction method - Google Patents

Description

The present invention relates to a conductor strain evaluation method and device, and a cable life prediction method.

For example, cables that are repeatedly bent and/or twisted are known, such as cables that are wired to movable parts of industrial robots. For example, in the case of cables used in industrial robots, there is a risk that a sudden break in the cable may cause a production line to stop, causing major inconvenience. Therefore, it is desirable to replace the cable before many of the plurality of conductors arranged in the cable become disconnected (that is, before the cable reaches the end of its life). In order to determine when it is time to replace the cable, it is necessary to accurately evaluate the disconnection of the conductor included in the cable.

Conventionally, in order to evaluate the lifespan of a cable, tests were conducted in which the cable was repeatedly bent and twisted, and the conductor resistance rose above a predetermined percentage due to breakage of the multiple strands that make up the conductor. The number of operations was set as the cable life.

Note that prior art document information related to the invention of this application includes Patent Document 1.

JP2007-139488A

Regarding the conventional method of evaluating cable life, the evaluation time may be extremely long, for example, several months, for cables in recent years whose durability against bending and twisting has greatly improved. , there was a problem that evaluation took too much time. Therefore, there has been a need for a method that can predict the lifespan of cables in a shorter time.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method and apparatus for evaluating conductor strain, and a method for predicting cable life, which can predict the life of a cable in a short time.

In order to solve the above-mentioned problems, the present invention has been made to solve the above-mentioned problem. A method for evaluating the strain of the conductor, which measures the resistance value of the conductor that changes over time when the operation is periodically applied to the cable, and A method for evaluating conductor strain is provided, in which the strain is evaluated based on the range of variation in resistance value.

Further, in order to solve the above-mentioned problems, the present invention provides a cable having a conductor made of a stranded conductor made by twisting a plurality of wires together, when a bending and/or twisting operation is applied to the conductor. A device for evaluating applied strain, comprising: a resistance value measuring unit that measures a resistance value of the conductor that changes over time when the operation is periodically applied to the cable; and the resistance value measuring unit. Provided is a conductor strain evaluation device, comprising: a strain evaluation unit that evaluates the strain based on the variation width of the resistance value of the conductor that changes over time measured in the above.

Further, in order to solve the above-mentioned problems, the present invention calculates the fluctuation range of the resistance value using a conductor strain evaluation method, and calculates the fluctuation range of the resistance value and the number of operations of the cable until the cable reaches the end of its service life. A cable life prediction method is provided, in which the relationship is determined in advance, and the number of operations of the cable until the cable reaches the end of its life is predicted based on the determined variation range of the resistance value and the relationship.

According to the present invention, it is possible to provide a method and apparatus for evaluating conductor strain, and a method for predicting cable life, which can predict life in a short time.

FIG. 1 is a schematic diagram of a cable life prediction device using a conductor strain evaluation device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of the cable. It is a figure explaining the resistance value of the conductor measured when operating an operating part. It is a figure explaining estimation of an operating frequency. It is a figure explaining the setting of the starting point of a cycle. FIG. 3 is a diagram illustrating how to obtain a strain equivalent amount. FIG. 2 is a graph diagram showing the relationship between the strain equivalent amount and the number of operations until the cable reaches the end of its life. FIG. 3 is a flow diagram of a conductor strain evaluation method according to an embodiment of the present invention.

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

In predicting the life of a cable when repeatedly bending and/or twisting is applied to the cable, the inventors considered the strain imparted to the conductor by one operation, and based on this strain. The idea was to predict the number of operations a cable will take until it reaches its end of life. That is, the cable life prediction method according to the present embodiment calculates the number of operations until the cable reaches its lifespan (cable lifespan) based on the strain imparted to the conductor when the cable is repeatedly subjected to bending and/or twisting motions. ) is a method of predicting Cable life is defined as, for example, the percentage of wires that break out of all the wires that make up the conductor when the cable is repeatedly bent and/or twisted. When the ratio exceeds a predetermined percentage (for example, 80% or more), it is determined that the cable life has reached its end.

Note that the bending action applied to the cable includes, for example, bending a cable having a conductor made of a stranded conductor made by twisting a plurality of strands into a U-shape, and then bending one end of the cable into a U-shape. A U-shaped bending operation in which the cable is periodically slid with a predetermined stroke along the longitudinal direction, and a state in which the cable is bent in either a clockwise or counterclockwise direction as shown in Figure 3, which will be described later. There is a left-right bending operation in which a constant force is applied to the cable at a constant cycle so as to reciprocate between a bent state in the clockwise direction or the counterclockwise direction. Furthermore, as a twisting motion applied to a cable, for example, one end of a cable having a conductor made of a stranded conductor made by twisting a plurality of wires is fixed, and a predetermined twisting motion is applied to the cable from the fixed part along the longitudinal direction of the cable. Twisting in which the cable is repeatedly twisted at a constant cycle in the circumferential direction of the cable at a predetermined twisting angle (for example, ±180° to ±360°) using a twisting section provided at a position with a twisting length (for example, 10 mm or more). There is movement.

In order to accurately predict the cable life using this method, it is necessary to accurately measure the strain imparted to the conductor when bending and/or twisting is applied to the cable. However, strain measurement using conventionally commonly used strain gauges is difficult to obtain sufficient accuracy and takes time and effort. Therefore, the present inventors considered measuring the change in the resistance value of the conductor itself, which is the subject of strain measurement. However, the change in resistance value when strain is applied to a conductor is minute, and it is difficult to measure accurately because it is buried in noise. Therefore, the present inventors conducted intensive studies to accurately measure minute changes in resistance value when strain is applied to a conductor, and as a result, they arrived at the present invention.

(Conductor strain evaluation device 1 and cable life prediction device 100)
FIG. 1 is a schematic diagram of a cable life prediction device 10 using a conductor strain evaluation device 1 according to the present embodiment. Further, FIG. 2 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of the cable 10. As shown in FIG.

In the cable 10 shown in FIG. 2, a pressure-wrapping tape 14 is spirally wound around a cable core 13 in which six 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 made of, for example, a set of stranded wires formed by twisting together 26 strands of annealed copper wire with an outer diameter of 0.16 mm. Note that the number of wires used for the conductor 11a is not limited to 26. The interposer 12 is a filament made of jute or cotton, for example. The insulator 11b is made of, for example, a fluororesin such as ETFE (tetrafluoroethylene-ethylene copolymer). Although not shown in FIG. 2, a central interposition made of a linear body made of polyethylene or the like may be arranged at the center of the cable. The outer diameter of each electric wire 11 is, for example, 1.74 mm, and the outer diameter of the cable 10 is, for example, 6.8 mm.

Note that the number of electric wires 11 used in the cable 10 is not limited to six. 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 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 the conductor 11a composed of at least a plurality of wires.

As shown in FIG. 1, the conductor strain evaluation device 1 measures the conductor 11a when bending and/or twisting is applied to a cable 10 having a conductor 11a made of a stranded conductor made by twisting a plurality of wires. This is a device for evaluating applied strain, and includes an operating section 20, a resistance value measuring section 30, and an arithmetic device 31.

The operating unit 20 repeatedly applies bending and/or twisting motion to the cable 10 at a constant cycle. Here, a case will be described in which the operating section 20 imparts a left-right bending motion to the cable 10, but is not limited to this, and may also impart a U-shaped bending motion or a twisting motion to the cable 10. Alternatively, a combination of bending and twisting motions may be applied. Moreover, when evaluating the cable 10 already mounted on a device such as an industrial robot, the device such as the industrial robot can also be used as the operating unit 20.

In the example of FIG. 1, the operating unit 20 includes a disc-shaped pedestal 21 rotatably provided on a base (not shown), and a disc-shaped pedestal 21 that is provided oppositely on the pedestal 21 with the center axis of the pedestal 21 in between. It has a pair of cylindrical mandrels 22 and a fixing part 23 for fixing the cable 10 on the pedestal 21. When the base 21 is rotated left and right around the central axis, the cable 10 arranged to pass between the mandrels 22 is bent left and right along the mandrels 22. Note that the operating unit 20 shown in FIG. 1 is just an example, and can be modified as appropriate.

The resistance value measuring section 30 measures the resistance value of the conductor 11a that changes over time when the operating section 20 periodically applies an operation such as bending to the cable 10. The resistance value measuring section 30 measures the resistance value between both ends of the conductor 11a in the cable 10 set in the operating section 20 over time. Data on the resistance value of the conductor 11a that changes over time (=resistance value data 50) measured by the resistance value measuring section 30 is input to the arithmetic device 31 and stored in the storage section 31b. Note that although a case is shown in which the resistance value measuring section 30 is provided separately from the arithmetic device 31, the resistance value measuring section 30 may be built in the arithmetic device 31. Further, when a device such as an industrial robot is used as the operating section 20, the resistance value measuring section 30 may be installed in the control device of the device such as the industrial robot.

Here, the resistance value of the conductor 11a measured when the cable 10 is bent left and right in the operating section 20 will be explained. As shown in FIG. 3, from a state in which the cable 10 is straight (referred to as a basic state C), the pedestal 21 is rotated 90 degrees clockwise to bend the cable 10 by 90 degrees (referred to as a first state A). 21 counterclockwise by 90° to return the cable 10 to a straight line (basic state C). Thereafter, the pedestal 21 is rotated 90 degrees counterclockwise to bend the cable 10 by -90 degrees (referred to as the second state B), and the pedestal 21 is rotated 90 degrees clockwise to return the cable 10 to a straight line (basically Condition C). In this way, by sequentially moving the pedestal 21 from the basic state C to the first state A, the basic state C, the second state B, and the basic state C, the operation is performed once (one cycle). . The time required for one operation, that is, the operation cycle, was 2 seconds (the frequency when performing one operation (=operation frequency) was 0.5 Hz).

In the cable 10, since the plurality of electric wires 11 are twisted together, the strain applied to the conductor 11a changes depending on the state of the twist. In the example of FIG. 3, in the first state A in which the cable 10 is bent at 90 degrees, the conductor 11a passes on the outside of the bend, so the conductor 11a is stretched compared to the basic state C, and the resistance value increases. However, in the second state B where the cable 10 is bent by -90°, the conductor 11a does not stretch because it passes through the inside of the bend, and the resistance value of the conductor 11a remains almost unchanged from the basic state C. state. Therefore, as shown in the lower part of Figure 3, the change in resistance value within one cycle of operation becomes an asymmetrical waveform that contains many high-order frequency components n times the operating frequency (n is a natural number of 2 or more). It becomes a waveform.

The arithmetic device 31 includes a control section 31a and a storage section 31b. The control unit 31a includes an operating frequency estimation unit 32, a period start point setting unit 33, and a distortion evaluation unit 34. The operating frequency estimation section 32, period start point setting section 33, and distortion evaluation section 34 are realized by appropriately combining an arithmetic element such as a CPU, a memory such as a RAM or ROM, software, an interface, a storage device, and the like. A display 60 is connected to the arithmetic unit 31, and can display various data stored in the storage unit 31b, such as strain equivalent data 55 and predicted life data 57, which will be described later. . Further, although not shown, the arithmetic device 31 is provided with an input device such as a keyboard, and various settings and display contents of the display 60 can be operated by inputting from the input device. Note that the display device 60 may be configured with a touch panel display so that the display device 60 also serves as an input device. Furthermore, the display device 60 does not need to be connected to the arithmetic device 31 by wire, and may be connected wirelessly. In this case, the display 60 may be, for example, a display of a smartphone or a tablet.

The arithmetic device 31 is composed of, for example, a personal computer. Note that the present invention is not limited to this, and the calculation device 31 may be, for example, a server device. In this case, the resistance value data 50 measured by the resistance value measuring section 30 will be transmitted to the arithmetic device 31, which is a server device, via the network. When the arithmetic device 31 is configured as a server device, it may be configured so that strain evaluation results and cable life prediction results, which will be described later, can be shared with users of devices such as industrial robots and device manufacturers, for example. . Further, the control section 31a and the storage section 31b may be configured as separate devices. For example, the configuration is such that the resistance value data 50 stored in the storage unit 31a of the server device is downloaded by the control unit 31a installed in another server device, a personal computer, etc., and strain evaluation and cable life prediction are performed. You can also do that.

The operating frequency estimating section 32 is for estimating the operating frequency based on the resistance value data 50 measured by the resistance value measuring section 30 when the operating frequency is unknown. Therefore, if the operating frequency (or operating cycle) is known or can be obtained from the position information of the pedestal 21 or information such as time linked to the position information of the pedestal 21, the operating frequency estimator 32 is omitted. It is possible.

The operating frequency estimating unit 32 performs frequency analysis of the resistance value data 50 measured by the resistance value measuring unit 30, that is, the resistance value data of the conductor 11a that changes over time, and calculates the operating frequency based on the result of the frequency analysis. Estimate. Specifically, as shown in FIG. 4, frequency analysis is performed on the resistance value data 50 measured by the resistance value measuring section 30, and the signal magnitude (i.e., the amplitude of resistance value fluctuation or resistance value fluctuation) is analyzed for each frequency component. Find the value fluctuation range). In this embodiment, since a load is applied to the cable 10 at a constant period (operating frequency), in the analysis result 51 of frequency analysis, the operating frequency component and its n-times higher-order frequency component are different from other frequency components. becomes larger compared to Therefore, it is preferable to extract frequencies whose signal magnitude is relatively large from the analysis result 51 of the frequency analysis, and estimate the smallest (lowest order) frequency among the extracted frequencies as the operating frequency. Note that it is preferable to exclude frequency components near 0 Hz (for example, 0.2 Hz or less) where the influence of noise is large. Furthermore, even if the signal size is large at a frequency, if the signal size at a frequency n times the frequency is small and no high-order frequency components occur, the frequency may be excluded as noise. . In the example of FIG. 4, when frequency components near 0 Hz are excluded, the frequency components of 0.5 Hz and 1.0 Hz surrounded by broken lines become large, and it can be estimated that the smallest frequency component, 0.5 Hz, is the operating frequency. The operating frequency estimated by the operating frequency estimation section 32 is stored in the storage section 31b as operating frequency data 50a.

The cycle start point setting section 33 is for setting the start point of a motion cycle in motions such as bending. Therefore, when the starting point of the cycle is known (for example, when the position information of the pedestal 21 or information such as time linked to the position information of the pedestal 21 is obtained in association with the resistance value data 50). In this case, the cycle start point setting section 33 can be omitted.

As shown in FIG. 5, in the present embodiment, in order to eliminate the influence of noise, the period start point setting unit 33 uses the operating frequency estimation unit 32 to estimate the resistance value from the resistance value data 50 of the conductor 11a that changes over time. The operating frequency component (in this case, 0.5 Hz) is extracted, and the starting point of the cycle is set based on the time-series change 52 of the extracted operating frequency component. For example, the cycle start point setting unit 33 determines the point in time when the resistance value of the conductor 11a becomes equal to the resistance value (indicated by a broken line in FIG. 5) of the conductor 11a under no load (basic state C), and The starting point of the cycle can be set at the point in time when the resistance value increases from 1 to 3 and reaches a maximum (first state A in FIG. 3). The period from the starting point set here to the point in time when an operation cycle corresponding to the operation frequency has elapsed is an interval corresponding to one operation. Note that the specific method for setting the starting point of the period is not particularly limited, and the basic state C may not be the starting point of the period. In other words, any time point can be set as the start point of the cycle as long as it is possible to specify that the same state is in each operation cycle. For example, the time point when the resistance value reaches its maximum (first state A) Alternatively, the starting point of the cycle may be set at the point in time when the value becomes minimum (second state). The start point of the cycle set by the cycle start point setting unit 33 is stored in the storage unit 31b as cycle start point data 50b.

The strain evaluation section 34 evaluates the strain based on the fluctuation width of the resistance value of the conductor 11a that changes over time, which is measured by the resistance value measurement section 30. However, if the variation width of the resistance value is used only in an interval corresponding to one operation, the influence of noise becomes large and sufficient evaluation accuracy may not be obtained. Therefore, in the present embodiment, the strain evaluation unit 34 divides the resistance value of the conductor 11a, which changes over time, into each operating cycle, and calculates the change in the resistance value of each divided cycle from the starting point of the cycle. The resistance values were averaged for each elapsed time to determine the averaged change in resistance value for one period, and the strain was evaluated based on the variation width of the resistance value in the averaged change in resistance value for one period.

More specifically, as shown in FIG. 6, the distortion evaluation section 34 first calculates the resistance based on the operating frequency estimated by the operating frequency estimation section 32 and the period start point set by the period start point setting section 33. The value data 50 is divided into sections corresponding to one operation (that is, the resistance value data 50 is divided into every operation cycle). Hereinafter, the divided resistance value data 50 will be referred to as divided resistance value data 53. The obtained divided resistance value data 53 are stored in the storage section 31b.

Here, in order to further suppress the influence of noise and perform evaluation with higher accuracy, it is desirable to use as many pieces of divided resistance value data 53 as possible. Therefore, when measuring the resistance value data 50, it can be said that it is desirable to carry out the measurement for a relatively long time. Specifically, it is more desirable to set the period during which the resistance value is measured so as to include 300 operating cycles or more.

Then, the strain evaluation unit 34 superimposes and averages the plurality of divided resistance value data 53, and obtains the averaged resistance value data for one section (one period). Hereinafter, this averaged resistance value data for one section (one period) will be referred to as averaged resistance value data 54. When averaging, it is preferable to add up all the resistance values at the same time in each section (the elapsed time from the start point of the cycle) and divide by the number of the added sections. The obtained averaged resistance value data 54 is stored in the storage section 31b.

Then, the strain evaluation unit 34 uses the fluctuation range of the resistance value in the obtained averaged resistance value data 54, that is, the value obtained by subtracting the minimum value from the maximum value of the resistance value in the averaged resistance value data 54, as the strain equivalent amount. demand. This strain equivalent amount is an amount proportional to the strain applied to the conductor 11a. Although it is possible to calculate the strain applied to the conductor 11a from the strain equivalent amount, in this embodiment, this strain equivalent amount is used as it is as a parameter representing the degree of strain applied to the conductor 11a. The obtained strain equivalent amount is stored in the storage section 31b as strain equivalent amount data 55.

The cable life prediction device 100 calculates the cable 10 based on the conductor strain evaluation device 1 according to the present embodiment and the strain equivalent amount (variation range of resistance value in the averaged resistance value data 54) determined by the conductor strain evaluation device 1. has a life prediction unit 35 that predicts the number of operations of the cable 10 until the end of its life. The life prediction section 35 is installed in the control section 31a of the arithmetic device 31, and is realized by appropriately combining arithmetic elements such as a CPU, memories such as RAM and ROM, software, interfaces, storage devices, and the like.

The life prediction unit 35 determines in advance the relationship between the strain equivalent amount (the fluctuation range of the resistance value in the averaged resistance value data 54) and the number of operations of the cable 10 until the cable 10 reaches the end of its life, and calculates the relationship. Based on this, the number of operations of the cable 10 until the cable 10 reaches the end of its life is predicted. FIG. 7 is a graph showing the relationship between the measured strain equivalent amount and the number of operations until the cable 10 reaches the end of its life (lifetime operation number). As shown in FIG. 7, the strain equivalent amount and the number of operations until the cable 10 reaches its lifetime have a substantially proportional relationship. A relationship such as that shown in FIG. 7 is obtained in advance through an experiment or the like, and is stored in the storage unit 31b as relationship data 56 for life prediction. The life prediction unit 35 uses the relationship data 56 for life prediction stored in the storage unit 31b to determine the number of operations until the cable 10 reaches its life, which corresponds to the strain equivalent amount determined by the conductor strain evaluation device 1. The obtained number of operations until the cable 10 reaches the end of its life is stored in the storage section 31b as predicted life data 57.

(Conductor strain evaluation method and cable life prediction method)
FIG. 8 is a flow diagram of the conductor strain evaluation method according to the present embodiment. As shown in FIG. 8, in the conductor strain evaluation method according to the present embodiment, first, in step S10, the cable 10 to be measured is mounted on the operating section 20, and the cable 10 to be measured is mounted on both ends of the conductor 11a to be measured. Connect the resistance value measuring section 30. Thereafter, in step S11, the operation section 20 starts operating, and the resistance value measuring section 30 starts measuring the resistance value of the conductor 11a. Then, the operation of the operating section 20 and the measurement of the resistance value measuring section 30 are continued for a predetermined period (step S12). Thereafter, in step S13, the operation of the operating section 20 and the measurement of the resistance value measuring section 30 are stopped, and the obtained resistance value data 50 is stored in the storage section 31b. The resistance value data 50 obtained here corresponds to the "resistance value of the conductor 11a that changes over time when motion is periodically applied to the cable 10" in the present invention.

Thereafter, in step S14, the operating frequency is estimated from the resistance value data 50. Specifically, as explained in FIG. 4, the resistance value data 50 is subjected to frequency analysis, and based on the analysis result 51 of the frequency analysis, the lowest frequency (however, The operating frequency corresponding to the operating cycle is estimated from (appropriately excluding frequencies with large noise such as frequencies near 0 Hz). The operating frequency estimated by the operating frequency estimation section 32 is stored in the storage section 31b as operating frequency data 50a. Note that if the operating frequency is known or can be obtained from the position information of the pedestal 21 or information such as time linked to the position information of the pedestal 21, step S14 can be omitted.

Thereafter, in step S15, the starting point of the cycle is set. Specifically, as explained in FIG. 5, the operating frequency component stored as the operating frequency data 50a is extracted from the resistance value data 50, and the operating frequency component is calculated based on the time-series change 52 of the extracted operating frequency component. Set the starting point of the operating cycle to . The start point of the cycle set by the cycle start point setting unit 33 is stored in the storage unit 31b as cycle start point data 50b. Note that if the starting point of the cycle is known, step S15 can be omitted.

Thereafter, in step S16, the resistance value data 50 is divided to obtain divided resistance value data 53. Specifically, as explained with reference to FIG. ), the resistance value data 50 is divided into a plurality of divided resistance value data 53. The obtained divided resistance value data 53 is stored in the storage section 31b.

Thereafter, in step S17, the plurality of divided resistance value data 53 obtained in step S16 are superimposed and averaged to obtain averaged resistance value data 54. Specifically, as explained in FIG. 6, the plurality of divided resistance value data 53 are averaged for each elapsed time from the start point of the cycle, and the averaged resistance is calculated as the change in resistance value for one cycle. Value data 54 is obtained. The obtained averaged resistance value data 54 is stored in the storage section 31b.

Thereafter, in step S18, a strain equivalent amount is determined from the fluctuation range of the resistance value in the averaged resistance value data 54 obtained in step S17. The obtained strain equivalent amount is an amount proportional to the strain applied to the conductor 11a in one operation, and the strain applied to the conductor 11a can be evaluated using this strain equivalent amount. In this way, in the conductor strain evaluation method according to the present embodiment, strain is evaluated based on the averaged variation range of the resistance value of the conductor 11a per operation. The obtained strain equivalent amount is stored in the storage section 31b as strain equivalent amount data 55.

In the cable life prediction method according to the present embodiment, a test is conducted in advance and the relationship shown in FIG. The relationship with the number of times is calculated and stored in the storage unit 31b as relationship data 56 for life prediction. The operating conditions of the cable 10 (e.g., number of bends, bending radius, bending angle, number of twists, length of twist, twisting angle, twisting speed, etc.), structural conditions (e.g., conductor dimensions, twisting speed, etc.), (wire conductor configuration, insulator dimensions, number of wires, wire twist pitch, etc.) or material conditions (e.g. conductor material, insulator material, pressure wrapping tape material, sheath material, etc.) have been updated. At times, the cable 10 is evaluated for strain using the conductor strain evaluation method described above, and the amount of strain equivalent to updating the operating conditions of the cable 10 (=the amount of strain equivalent after updating) is determined. The updated strain equivalent amount obtained here is stored in the storage unit 31b as strain equivalent amount data (=updated strain equivalent amount data) 55 due to updating of the operating conditions of the cable 10, etc. The life prediction unit 35 calculates a cable whose operating condition has been updated based on the relationship data 56 for life prediction and the updated strain equivalent amount (variation range of resistance value) stored as the updated strain equivalent amount data 55. 10 predicts the number of operations until the end of its life. The predicted number of operations until the cable 10 reaches the end of its life is stored in the storage unit 31b as predicted life data 57. Further, the operating conditions, structural conditions, and material conditions of the cable 10 are stored in the storage section 31b as condition data when the strain equivalent amount data 55 and the predicted life data 57 stored in the storage section 31b are calculated.

Note that the predicted lifespan data 57 stored in the storage unit 31b can also be used as the relationship data 56 for lifespan prediction. For example, the predicted life data 57 that has existed for a predetermined period (for example, several days, months, or years) from the time it was stored in the storage unit 31b is left as the predicted life data 57, and the predetermined The predicted lifespan data 57 whose period has passed may be configured to be transferred to the relationship data 56 for lifespan prediction. Further, the predicted life data 57 stored in the storage unit 31b is configured to be transferred to the relationship data 56 for life prediction when the updated strain equivalent amount data 55 is stored in the storage unit 31b. It's okay. The condition data may include information on the date and time when strain was evaluated.

(Actions and effects of embodiments)
As explained above, the conductor strain evaluation method according to the present embodiment measures the resistance value of the conductor 11a that changes over time when motion is periodically applied to the cable 10, and The strain is evaluated based on the range of variation in the resistance value of the conductor 11a.

This makes it possible to easily evaluate the strain of the conductor 11a, and based on the evaluated strain, it becomes possible to quickly evaluate the number of operations at which the cable 10 reaches its lifetime. Conventionally, it was necessary to perform the test until a disconnection occurred in the conductor 11a (the resistance value of the conductor 11a increased above a predetermined percentage), which required a very long test time, for example, several months. According to the embodiment, it is possible to predict the lifespan of the cable 10 in a short period of time, for example, about several tens of minutes, although it depends on the operating cycle applied to the cable 10. Furthermore, although the change in the resistance value of the conductor 11a due to strain is minute, divided resistance value data 53 obtained by dividing the measured resistance value data 50 into sections are averaged to obtain averaged resistance value data 54, and this average By determining the fluctuation range of the resistance value in the resistance value data 54 as the strain equivalent amount, it is possible to suppress the influence of noise and accurately evaluate the strain (that is, measure the strain equivalent amount).

For example, it is possible to predict the lifespan of the cable 10 by simulation, but in order to accurately predict the lifespan, it is necessary to prevent friction between the electric wire 11 and surrounding members, movement of the electric wire 11 due to bending, etc. It is necessary to perform the simulation in consideration of various behaviors such as changes in the twisted state of the electric wires 11 due to bending or the like. Therefore, it is very difficult to accurately predict the lifespan of the cable 10 by simulation. According to the present invention, the lifespan of the cable 10 can be predicted using the strain that occurs when the cable 10 is actually operated, so that highly accurate lifespan prediction is possible.

Furthermore, according to the present embodiment, it is possible to predict the lifespan in a short time, so the strain evaluation and the lifespan of the cable 10 can be performed under various operating conditions, structural conditions, material conditions, etc. (hereinafter referred to as operating conditions, etc.) of the cable 10. By repeating the prediction, it becomes easy to obtain the operating conditions that place the least burden on the conductor 11a and the longest life of the cable 10, that is, to optimize the operating conditions. For example, changes in the lifespan of the cable 10 when the radius of curvature when bending the cable 10 is changed, changes in the lifespan when the extra length of the cable 10 in the movable part that applies bending etc. are changed, etc. It becomes easy to easily predict the life of the cable 10 based on the conditions, etc., and to optimize the structure of the cable 10, the material conditions used for the cable 10, etc.

(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] Strain imparted to the conductor (11a) when bending and/or twisting is applied to the cable (10) having the conductor (11a) made of a stranded wire conductor made by twisting a plurality of wires together A method for evaluating the resistance value of the conductor (11a) that changes over time when the operation is periodically applied to the cable (10), and the measured resistance value changes over time. A method for evaluating conductor strain, in which the strain is evaluated based on a range of variation in the resistance value of the conductor (11a).

[2] The resistance value of the conductor (11a), which changes over time, is divided into each operation cycle, which is the cycle of the operation, and the change in the resistance value of each divided cycle is calculated over the course of time from the start point of the cycle. The distortion is evaluated based on the variation width of the resistance value in the averaged change in the resistance value for one cycle, which is averaged for each period to find the change in the resistance value for one cycle. 1], the conductor strain evaluation method described in [1].

[3] The method according to [2], wherein the resistance value of the conductor (11a) that changes over time is subjected to frequency analysis, and an operating frequency corresponding to the operating cycle is estimated based on the result of the frequency analysis. Conductor strain evaluation method.

[4] Extract the estimated operating frequency component from the time-series changing resistance value of the conductor (11a), and calculate the period based on the time-series change in the extracted operating frequency component. The conductor strain evaluation method described in [3], which sets a starting point of the conductor strain.

[5] Strain imparted to the conductor (11a) when bending and/or twisting is applied to the cable (10) having the conductor (11a) made of a stranded conductor made of a plurality of wires twisted together a resistance value measuring unit (30) that measures a resistance value of the conductor (11a) that changes over time when the operation is periodically applied to the cable (10); a strain evaluation unit (34) that evaluates the strain based on the variation width of the resistance value of the conductor (11a) that changes over time measured by the resistance value measurement unit (30); Conductor strain evaluation device (1).

[6] The variation range of the resistance value is determined by the conductor strain evaluation method according to any one of [1] to [3], and the range of variation of the resistance value and the range of variation of the resistance value are determined by the conductor strain evaluation method according to any one of [1] to [3]. A relationship with the number of operations of the cable (10) is determined in advance, and based on the obtained variation width of the resistance value and the relationship, the number of operations of the cable (10) until the cable (10) reaches the end of its life is determined. A method for predicting cable life.

(Additional note)
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.

The present invention can be modified and implemented as appropriate without departing from the spirit thereof. For example, in the above embodiment, the cable 10 is given motion at a constant cycle, but the motion cycle does not have to be strictly constant, and there may be some deviation (for example, 10% or less with respect to the reference motion cycle). deviation) is allowed.

Furthermore, in the above embodiment, a case has been described in which the strain of one conductor 11a in the cable 10 is evaluated. may be evaluated.

Furthermore, by frequency analysis, a frequency band with particularly large noise, such as a frequency near 0 Hz, is extracted, and resistance value data is created by removing the extracted frequency band with large noise. The strain equivalent amount may be derived using This makes it possible to further suppress the influence of noise and obtain the strain equivalent amount with higher accuracy.

1...Conductor strain evaluation device 10...Cable 11...Wire 11a...Conductor 11b...Insulator 20...Operating section 30...Resistance value measuring section 32...Operating frequency estimation section 33...Period start point setting section 34...Strain evaluation section

Claims (5)

A method for evaluating the strain imparted to a cable when bending and/or twisting is applied to a cable having a conductor made of a stranded conductor made of a plurality of wires twisted together, the method comprising:
Measuring the resistance value of the conductor that changes over time when the operation is periodically applied to the cable,
Divide the measured resistance value of the conductor that changes over time into each operation cycle, which is the cycle of the operation, and average the change in resistance value of each divided cycle for each elapsed time from the start point of the cycle. and calculating the value obtained by subtracting the minimum value from the maximum value of the resistance value in one period of averaged changes in resistance value as a strain equivalent amount, and evaluating the strain using the strain equivalent amount.
Conductor strain evaluation method. frequency-analyzing the resistance value of the conductor that changes over time, and estimating an operating frequency corresponding to the operating cycle based on the result of the frequency analysis;
The conductor strain evaluation method according to claim 1 . extracting the estimated operating frequency component from the time-series changing resistance value of the conductor, and setting a starting point of the period based on the time-series change in the extracted operating frequency component;
The conductor strain evaluation method according to claim 2 . An apparatus for evaluating strain imparted to a cable when a bending and/or twisting operation is applied to a cable having a conductor made of a stranded wire conductor made by twisting a plurality of strands, the device comprising:
a resistance value measuring unit that measures a resistance value of the conductor that changes over time when the operation is periodically applied to the cable;
The time-series changing resistance value of the conductor measured by the resistance value measurement unit is divided into each operation cycle, which is the operation cycle, and the change in resistance value of each divided cycle is measured from the starting point of the cycle. The value obtained by subtracting the minimum value from the maximum value of the resistance value in the averaged change in resistance value for one cycle is calculated as the strain equivalent amount, and the strain is evaluated using the strain equivalent amount. comprising an evaluation section;
Conductor strain evaluation device. Determining the strain equivalent amount by the conductor strain evaluation method according to any one of claims 1 to 3,
determining in advance the relationship between the strain equivalent amount and the number of operations of the cable until the cable reaches its lifespan;
predicting the number of operations of the cable until the cable reaches the end of its life based on the obtained strain equivalent amount and the relationship;
Cable life prediction method.

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