JPH10132702A - Method and equipment for measuring flexural rigidity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate flexural rigidity from measurements according to a predetermined theoretical formula by measuring a bending reaction acting on one plane through a reaction measuring means when a wire is held by a wire holding means comprising a positioning means for holding the wire while bending the intermediate part thereof into a U-shape. SOLUTION: The wire holding means 3 comprises the positioning means 2(2a, 2b) mounted on two planes 1 and/or two parallel plans 1(1a, 1b) facing each other and holding a wire T at two intermediate parts thereof while bending into a U-shape. A bending reaction W acting on one plane 1b is measured through a reaction measuring means 4 when the wire T is held by the wire holding means 3. The gap between opposite parallel planes 1(1a, 1b) is decreased by moving an interplane gap setting means 5 downward and the wire T is bent in U-shape thus matching the distance between the centers of the wire T at the opposite ends thereof with a specified value. Finally, flexural rigidity is calculated from the reaction W.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the bending stiffness of a wire such as an optical cable, an optical cord, or an optical fiber, which is an evaluation technique that plays a role in supporting material engineering. The present invention relates to a method for measuring bending stiffness in a type of measuring while maintaining a state in which U is bent in a U-shape, and an improvement of the apparatus.

[0002]

2. Description of the Related Art One of the conventional methods for measuring bending stiffness is applied when the weight of a wire T can be ignored. For example, as shown in FIG. While fixing one end and projecting horizontally with the other end as a free end and holding it in a so-called cantilever state, displacement δ at the end when a load W is applied to the end, or inclination at the end The angle i is measured. For measuring the inclination angle i, a method in which a mirror is attached to an end and an optical lever is used is adopted.

The other is applied when the bending stiffness is relatively small. As shown in FIG. 3B, the structure is the same as that shown in FIG. It measures the weight of itself, that is, the displacement δ at the end or the inclination angle i at the end when the uniformly distributed load w is applied to the entire portion other than the portion where the wire T is fixed. It is.

However, in this type of measuring method, the bending stiffness can be measured only under a condition of small bending deformation, that is, a condition having a small curvature (a large radius of curvature), which is far from the actual use condition in the field. Therefore, there is a problem that a measurement result that does not match the actual condition is derived (for this reason, in the related art, the bending stiffness (easiness of bending or difficulty in bending) is hardly quantitatively evaluated. Only the elongation property due to tension has been an important evaluation item).

In order to make the understanding of this problem clearer, a very common optical cord, that is, an optical cord having a structure in which a core of an optical fiber is wrapped with a tensile fiber and the outside thereof is covered with a plastic coating will be described as a specific example. Then, the tensile fibers according to the optical cord are juxtaposed in the same direction as the optical fiber core wires and are not bonded to each other, so that each of them slides and moves separately by bending deformation. In this case, since the optical cord is measured while being kept almost straight, the static friction generated between the tensile fibers, between the tensile fiber and the optical fiber core, and between the tensile fiber and the jacket is maintained. As a result, However, the bending stiffness is measured to be larger than the actual value, and the result does not conform to the actual condition.

In the optical cord having this type of structure, much of the bending stiffness is borne by the jacket, and the deformation of the jacket is increased by the bending deformation, so that the longitudinal elastic modulus (Young's modulus) of the plastic material is increased. ) Differs depending on the amount of strain, and it is natural that the bending stiffness differs depending on the degree of bending.

Further, this type of measuring method can be applied only to a case where bending deformation is small, and a theoretical formula for calculating bending stiffness from a measured value of displacement or inclination angle originally assumes small displacement. Since the approximation formula is used, even if a large displacement or a large inclination angle is measured, there is a problem that the bending stiffness cannot be accurately calculated because the approximation formula does not conform.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a large bending deformation close to actual use conditions.
It is an object of the present invention to provide a completely new type of bending stiffness measuring method and apparatus capable of obtaining accurate measured values that match actual conditions by measuring the bending stiffness of a wire.

[0009]

That is, as shown in FIG. 1, a bending rigidity measuring method according to the present invention is a U-shaped bending test method in which two opposing parallel planes 1 (1a, 1a,
b) or two opposing parallel planes 1 (1a, 1b) and positioning means 2 (2a, 2a) provided on the two planes 1
According to b), the step of holding the wire T at two locations in the middle of the wire T while bending the wire T into a U-shape, and, when the wire T is held, the axial center distance L in the straight portions at both ends of the wire T A specific length dimension, a step of measuring a measured value of the bending reaction force W acting on one plane 1b when the wire T is held, and a step of determining the bending rigidity from the measured value by a predetermined theoretical formula. And a calculating step.

In this case, in a case where the weight of the wire T can be neglected, from the viewpoint of using the simplest possible mathematical formula, the theoretical formula is preferably set to EI = 0.3483WD2. In this theoretical formula, the reason why 0.3483 is used as the coefficient and the upper four digits of the actual numerical value is used is that the upper four digits are considered sufficient for practical use of the wire rod in terms of accuracy. Therefore, for example, 0.348 may be used as a coefficient without any problem.

As shown in FIG. 1, the apparatus for embodying such a method for measuring bending stiffness holds two portions of a portion located in the middle of a wire T while bending the wire T into a U-shape. Two opposing parallel planes 1 (1a, 1b) or two opposing parallel planes 1 (1a, 1b) and the two planes 1
A wire holding means 3 comprising positioning means 2 (2a, 2b) provided thereon, and a bending reaction force W acting on one flat surface 1b when the wire T is held by the wire holding means 3.
And a bending reaction force measuring means 4 for measuring the bending reaction force W
Is characterized by calculating the bending stiffness by a predetermined theoretical formula from the measured values of.

In such technical means, the wire T to be measured does not matter whether the shape is circular or square, and the length of the wire is not limited. , The wire T
Is short enough to accept all of
It does not matter whether or not the wire T is long enough to receive all of the wire T by the bending reaction force measuring means 4.

However, regarding the weight of the wire T, the weight of the wire T cannot be ignored with respect to the bending reaction force W, or the weight of the wire T
When the bending stiffness is small with respect to the weight of the wire rod or when a highly accurate measurement value is required, from the viewpoint of increasing the measurement accuracy, the weight of the lower portion from the vertex of the bent portion of the wire T is determined from the bending reaction force W. It is required to subtract.

The wire holding means 3 may be any two parallel flat surfaces 1 facing each other, or two parallel flat surfaces 1 facing each other and a positioning means 2 provided on the two flat surfaces 1. The positional relationship between the two opposing flat surfaces 1a and 1b is not limited to the vertical direction as long as they are parallel to each other, but the axial center distance L in the linear portions at both ends of the wire T can be maintained at a specific length, and At least at the time of measurement, it is necessary that the wire T be held along the two planes 1 so as not to be shifted laterally.

In this case, the wire holding means 3
In the case where the cross-sectional dimension of the wire T is determined and the value of the axial center distance L may be one, the space between the two planes 1a and 1b may be fixed, but the wire T can be more quickly and easily. From the viewpoint of setting the two planes 1a, 1b
It is preferable to include a plane spacing setting means 5 for arbitrarily setting the spacing of.

The plane interval setting means 5 includes not only means for vertically sliding both or any one of the two planes 1a and 1b but also means for measuring the distance between the two planes 1a and 1b, for example, , And a means for directly performing manual measurement using a tool such as a caliper.

Further, in this case, the positioning means 2 can maintain the axial distance L at a specific length by using the two planes 1, and can displace laterally along the two planes 1. The holding form is not limited as long as it can be fixed so that it is not fixed, but from the viewpoint of more reliably preventing lateral displacement, a rod-shaped member that regulates the lateral movement of the wire T when bending and holding in a U shape is used. In addition to forming a groove corresponding to the cross section of the wire T by being fixed to the two planes 1 or providing V-shaped grooves corresponding to the cross section of the wire T in upper and lower members forming the two planes 1, for example, It is preferable to use an adhesive tape, a rubber band, a clip, or the like.

The form of the V-shaped groove does not matter whether a member having the V-shaped groove is attached or whether the upper and lower members forming the two planes 1 are directly processed.

The bending reaction force measuring means 4 may be of any type such as a spring type or a load cell type. From the viewpoint of automating a series of operations, the measured value recording unit 6 that records the change over time of the measured value of the bending reaction force W, and the bending rigidity is automatically calculated based on the measured value recorded by the unit. It is preferable to include bending stiffness calculating means 7.

In the case where the plane 1b of the two planes 1 moves up and down with a load, the two planes 1a, 1a
From the viewpoint of maintaining the interval of b at a constant value, it is necessary to have a height adjustment function and the like. That is,
In order to avoid such inconvenience, for example, a balance (for example, a load cell type) that does not cause displacement of the upper surface due to a load can be used.

Here, in the case where the wire T is measured using a long sample that cannot be entirely received by the bending reaction force measuring means 4, two opposed parallel flat surfaces 1 are used.
a and 1b are required to be held in close contact with each other, but from the viewpoint of preventing the weight of the portion where the wire T protrudes long from being applied to the bending reaction force measuring means 4, the above-described 2 It is possible to provide a support that supports the protruding wire T having substantially the same height as the plane 1 b of the plane 1.

The support in this case is also provided on the flat surface 1.
The portion of the wire T that cannot be received by the reaction force measuring means 4 bends due to the vertical movement of b, and the wire T rises and the two planes 1
a, from the viewpoint of preventing inconvenience such as release of the close contact state with 1b, which hinders accurate measurement, a height adjusting function for adjusting the height following the vertical movement of the plane 1b is provided. Need to be.

In the case of the apparatus invention as described above, in a case where the weight of the wire T can be neglected, from the viewpoint of using the simplest mathematical expression, the theoretical expression is preferably set to EI = 0.3483WD2. In this theoretical formula, as described above, the reason why 0.3483 is used as the coefficient and the upper four digits of the actual numerical value is used is that the upper four digits are sufficient for practical use of the wire rod in terms of accuracy. For this reason, it is possible to use 0.348 as a coefficient corresponding to the required accuracy.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings.

First Embodiment FIG. 2 shows a first embodiment of a bending rigidity measuring apparatus to which the present invention is applied. FIG. 2A is a front view, and FIG.
Is a side view.

The bending rigidity measuring apparatus according to the present embodiment
As shown in FIG.
2 is erected and fixed, and a balance 13 is placed on the base 11, while a support plate 12 is integrally mounted on the support 12 with a slider 15 that slides up and down along the support 12. The measurement surface 13a on which the measurement target positioned on the upper surface of the balance 13 is to be placed, and the pressing surface 14a of the pressing plate 14 are parallel to each other regardless of the vertical movement of the slider 15. It constitutes a plane.

In this embodiment, since the wire T to be measured has a circular cross section and a relatively short length, the balance 13 can receive all of its weight. A guide member 16 is provided on each of the measuring surface 13a of the balance 13 and the pressing surface 14a of the pressing plate 14, and is formed by the measuring surface 13a and the guiding member 16 or the pressing surface 14a and the guiding member 16. It is positioned by being fitted in the groove, so that it does not shift laterally during measurement.

Further, as a method of measuring the distance between the pressing surface 14a and the measuring surface 13a, a method of directly performing manual measurement using a tool such as a caliper may be used. A method of reading a scale processed on the support column 12 is adopted.
Adopts a load cell type in which the measurement surface is not displaced by the load. For this reason, it is only necessary to read the scale of the column 12 at the time of measurement, and there is no need to provide a height adjustment function and the like. Has become.

By the way, U-shaped bending of a wire (2 in overseas)
-Point bend, that is, called two-point bending), an exceptionally accurate theoretical formula has been obtained despite the fact that it belongs to a geometric nonlinear problem that is generally difficult to analyze. Are frequently used for bending strength tests of optical fibers.

That is, the bending stiffness EI is related between the bending reaction force W and the axial center distance D, and a theoretical formula is shown in the following literature.

"Analysis of bending strength of optical fiber, Proceedings of IEICE Spring National Convention 1988, 1-33
5, Lecture number B-584] According to the above document, the following equation is given.

[0032]

(Equation 1)

Here, E (ψ, k) and F (ψ, k) are a first kind elliptic integral and a second kind elliptic integral, respectively. These are defined as follows:

[0034]

(Equation 2)

[0035]

(Equation 3)

Since the term expressed by the elliptic integral in the equation (1) is a constant, if it is digitized, the following simple equation can be obtained.

[0037]

(Equation 4)

That is, this is the theoretical formula that forms the basis of the present invention. By substituting the actual measured values (bending reaction force W and axial center distance D) in the present embodiment into Equation (4), the bending The rigidity EI can be easily calculated.

In this embodiment, the upper four digits of the actual numerical value are used as the coefficients of the equation (4).

The result of equation (4) can be derived also from the following document. Although the expression of the calculation result is different from the above document, the same calculation result can be obtained because the calculation model is the same. .

"MJ Matthewson et al." Strength measu
rement of optical fibers by bending ", Journal of Am
erican Ceramic Society, Vol. 69, No. 11, pp. 815-821 (19
86) ''

Further, in the present embodiment, the weight of the wire T with respect to the bending reaction force W is extremely small, so the weight of the wire T is ignored. When the own weight of the wire T cannot be ignored, when the bending stiffness is small relative to the weight of the wire T, or when a high-precision measurement value is required, the bending reaction force W is used to calculate the bending portion of the wire T. It is necessary to subtract the weight of the lower part from the apex, and this
Measurement accuracy can be improved.

Next, the process of measuring the bending stiffness of the wire T using the bending stiffness measuring apparatus according to this embodiment will be described.

First, the pressing plate 14 is slid upward to increase the distance between the pressing surface 14a and the measuring surface 13a.

One of the two portions located in the middle of the wire T to be measured is connected to the measuring surface 13 of the balance 13.
a and the guide member 16, and the other is held between the pressing surface 14 a of the pressing plate 14 and the guide member 16.

Next, by moving the slider 15 downward, the distance between the pressing surface 14a and the measurement surface 13a is reduced to bend the wire T into a U-shape, and the axial center distance D at both ends of the wire T is specified. Set to match the value.

The bending rigidity is calculated by substituting the measured values (the bending reaction force W and the axial center distance D) into the above equation (4) from the measured values of the bending reaction force of the wire T by the balance 13 at that time.

In this case, the axial center distance D can be easily obtained by subtracting the outer dimension of the wire T from the distance between the pressing surface 14a and the measuring surface 13a.

In this embodiment, the pressing surface 14a
Can be set arbitrarily, so that the wire T can be set quickly and easily. However, such a means has a fixed cross-sectional dimension of the wire T and a value of the axial center distance D. Not required if only one is needed.

Even when it is necessary to measure wires T having different cross-sectional dimensions or different intervals D between the center axes, the holding plate 14 can be replaced, for example, the holding plate can be attached to the support 12 without the slider 15. 14 can be easily removed, by replacing it as appropriate,
I can deal with it.

The bending rigidity measuring device according to the present embodiment,
Using both the conventional bending rigidity measuring device shown in FIG.
When the bending stiffness of a commercially available optical cord having an outer diameter of 2 mm was measured, the measured value according to the present invention was a result of 1/3 to 1/4 as compared with the conventional one, and the result was as follows. While showing the inadequacy of the conventional measurement method,
This demonstrates the usefulness of the present invention.

The bending stiffness of a wire made of a plastic material changes with time due to creep characteristics. According to the present invention, it is also necessary to record the time change of reading of a balance according to the present invention. Thus, the automation of recording and the automatic calculation of bending stiffness can be easily realized by connecting an electronic balance having an output terminal to a personal computer.

In this case, a commercially available balance is not used as it is, but it is possible to reduce the size of the apparatus by incorporating a measuring mechanism based on the same principle.

Embodiment 2 FIG. 3 shows Embodiment 2 of a bending rigidity measuring apparatus to which the present invention is applied. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted here.

The basic configuration of the bending stiffness measuring apparatus according to the second embodiment is substantially the same as that of the first embodiment, but is different from the first embodiment in that a guide member is provided as means for preventing the wire T from laterally shifting. A rubber band 26 is used in place of the wire rod 16, and a wire support T31 is provided because the length of the wire T is long and the balance 13 cannot receive all of its weight. 31
The rubber band 3 is used as a means for preventing the wire T from shifting laterally.
2 is provided.

In the figure, a rubber band 26 is provided at the free end of the holding plate 14, and the holding plate 14 and the wire T
To hold the shape of the wire T on the free end side (the right side in the figure) from the point of action 27 of the bending reaction force W on the holding surface 14a in a straight line, and reduce the weight of the wire T by the holding plate 14. By supporting, no extra load acts on the balance 13.

The height of the upper surface of the wire support table 31 is set to be the same as the height of the measuring surface 13 a of the balance 13, so that the weight of the wire T protruding from the balance 13 is not added to the balance 13. Further, a rubber band 32 is fixed to the wire support 31, and the wire support 31
And the wire T to function as a unit so that the shape of the wire T on the free end side (the right side in the figure) of the bending reaction force W on the measurement surface 13 a of the balance 13 is maintained straight.

Therefore, according to the second embodiment,
Even if the length of the wire T is long and the balance 13 cannot receive all of its weight, the same operation and effect as those of the first embodiment can be obtained.

[0059]

As described above, according to the present invention, the two portions of the wire located at the middle of the wire are
When the wire is held by two opposing parallel planes or two opposing parallel planes and a positioning means provided on the two planes, and the wire is held by the wire holding means while being bent in the shape of a letter. And a bending reaction force measuring means for measuring the bending reaction force acting on one of the planes, so that the bending stiffness is calculated by a predetermined theoretical formula from the measured value of the bending reaction force. It is possible to measure the bending stiffness of the wire rod at the time of near large bending deformation, and thus it is possible to obtain an accurate bending stiffness (measured value) that matches the actual condition. That is, according to the present invention, it is possible to greatly contribute to the practical use of various wires such as various cables such as an optical cable, an optical cord, and an optical fiber.

[Brief description of the drawings]

FIG. 1 is a schematic view of a bending rigidity measuring method and apparatus according to the present invention.

FIG. 2 is a schematic diagram of a bending rigidity measuring device according to Embodiment 1 of the present invention.

FIG. 3 is a schematic diagram of a bending rigidity measuring device according to a second embodiment of the present invention.

FIG. 4 is a schematic view of a bending rigidity measuring device as a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 2 planes 1a ... plane 1b ... plane 2 ... Positioning means 2a ... Positioning means 2b ... Positioning means 3 ... Wire rod holding means 4 ... Bending reaction force measuring means 5 ... Plane interval setting means 6 ... Measured value recording means 7 ... Bending rigidity Calculating means 11 ... Surface plate 12 ... Column 13 ... Balance 13a ... Measurement surface 14 ... Pressing plate 14a ... Pressing surface 15 ... Slider 16 ... Guide member 26 ... Rubber band 27 ... Working point 28 ... Working point 31 ... Wire rod support 32 ... Rubber band W: Bending reaction force D: Shaft center distance P: Load w: Uniformly distributed load δ: Displacement i: Incline angle T: Wire rod

Claims (6)

[Claims] 1. In a U-shaped bending test method, two opposing parallel planes (1: 1a, 1b) or two opposing parallel planes (1: 1a, 1b) and two opposing parallel planes (1). Positioning means provided (2: 2a, 2b)
A step of holding the wire (T) at two locations in the middle of the wire (T) while bending the wire (T) into a U-shape; and a straight line at both ends of the wire (T) when the wire (T) is held. A step of setting the axial center distance (L) in the portion to a specific length, and one plane (1b) when the wire (T) is held
A step of measuring a measured value of a bending reaction force (W) acting on the object, and a step of calculating bending stiffness from the measured value by a predetermined theoretical formula. 2. The bending rigidity measuring method according to claim 1, wherein the theoretical equation is EI = 0.3483WD2. 3. Two opposing parallel planes (1: 1a, 1b) or two opposing parts which hold two portions of a portion located in the middle of the wire (T) while bending the wire (T) into a U-shape. Parallel planes (1: 1a, 1b) and the two planes (1)
A wire rod holding means (3) comprising positioning means (2: 2a, 2b) provided above, and a bend acting on one plane (1b) when the wire rod (T) is held by the wire rod holding means (3). A bending reaction force measuring means (4) for measuring the reaction force (W), wherein the bending rigidity is calculated from the measured value of the bending reaction force (W) by a predetermined theoretical formula. apparatus. 4. The wire holding means (3) according to claim 3, wherein said wire holding means (3) includes a plane interval setting means (5) for arbitrarily setting an interval between said two planes (1: 1a, 1b). Characteristic bending stiffness measuring device. 5. A measurement value recording means (6) according to claim 3, wherein said bending reaction force measuring means (4) records a change over time of a measurement value of the bending reaction force (W). )
And a bending stiffness calculating means (7) for automatically calculating bending stiffness based on the measured values recorded by the means. 6. The bending rigidity measuring apparatus according to claim 3, wherein the theoretical formula is EI = 0.3483WD2.