JPH10281929A - Method and device for testing bending fatigue of optical communication cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a repeat bending test method and evaluation method capable of precisely measuring the progress of setting of an optical communication cable to be repeatedly bent, or the easiness of curling and easiness of correcting it. SOLUTION: In this method, the rocking angle of a rocking arm A is successively measured by a measuring device, the lower end of a test piece S is engagingly locked from both lateral side through tension gauges L, and the bending force added to the test piece S is successively measured by the tension gauges L. One lateral bending is taken as one cycle, the hysteresis graph every bending cycle is determined with the tension measured value by the tension gauge L as the vertical axis every cycle, and the measured value of rocking angle of the rocking arm as horizontal axis, and the area or cut piece of the hysteresis graph is calculated and measured every bending cycle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bending fatigue test method for an optical communication cable, which can accurately measure a change in set due to repeated bending of an optical communication cable, and is subjected to repeated bending. It can accurately test the deterioration speed and durability of an optical communication cable.

[0002]

2. Description of the Related Art When an optical communication cable is too flexible, it is inconvenient to maintain the optical communication cable in a predetermined state such as buckling of the optical communication cable in a laid state. If the distance is too small, the optical communication cable cannot be laid as designed, and there is a problem in that the actual laying work is hindered. For this reason, it is required that the optical communication cable has flexibility conforming to the laying conditions and the like, and the specific optical communication cable has specifications (a range of flexibility required when bending at a specific radius). It is necessary to confirm in advance that it has the same flexibility. On the other hand, the flexibility of an optical communication cable that is repeatedly bent after being laid gradually increases. If this set-off increases, the protection ability for the internal optical fiber decreases, causing damage or disconnection of the optical fiber. Even if the optical fiber is not damaged or disconnected, the residual strain accumulated in the optical fiber increases. Transmission loss increases. For this reason, it is necessary to measure in advance the progress of sag due to repeated bending, the ease of bending, and the ease of bending for each optical communication cable, and the degradation rate and durability of the transmission characteristics of the optical communication cable. Is extremely important to accurately predict Incidentally, as a test method for the repeated bending of the optical communication cable, there is a repetition bending test method of IEC794-1-E6 in the United States (hereinafter, this is referred to as a conventional "repetition bending test method"). A conventional repetitive bending test apparatus is as shown in FIG. 3, and the outline thereof is as follows. That is, the mandrel M includes a pair of left and right circular mandrels M having a circular cross section and a swing arm A swinging left and right about the axis P.
A test piece S of an optical communication cable is passed between the test pieces, an upper end thereof is fixed to the swing arm A, a weight W having a predetermined weight is fixed to a lower end of the test piece S, and a predetermined tension is applied. When the swing arm A is swung 90 degrees to the left and right in this state, the test piece S is bent 90 degrees left and right along the mandrels M, M. After swinging the swing arm A right and left a predetermined number of times (the number of repetitions is arbitrary, for example, 100 times), the transmission characteristics of the test piece are tested, and the degree of damage is visually inspected. The degree of deterioration of the transmission characteristics after a given optical communication cable is repeatedly bent a predetermined number of times by the conventional repetitive bending test method, the degree of settling of the optical communication cable,
Although it is possible to confirm the degree of damage in appearance, it is not possible to test the transition of the degree of deterioration of transmission characteristics and the progress of damage to the optical fiber. That is, an optical communication cable is a cable in which a large number of optical fibers are twisted and covered around a tension member, a large number of optical fibers are accommodated in a slot, and a large number of slots are centered on the tension member. There are various types such as those coated in a twisted state, and the cross-sectional structure is complicated and not uniform. For this reason, the residual strain that occurs internally due to repeated bending also varies depending on the internal structure of the optical communication cable. Due to the residual distortion, the transmission characteristics of the optical fiber deteriorate, and in some cases, the optical fiber is locally damaged, and in extreme cases, the optical fiber may be disconnected. Therefore, by measuring the magnitude of the flexibility (bending force) after being repeatedly bent, it is possible to confirm the progress of the deterioration of the transmission characteristics of the optical fiber and the progress of the damage of the optical fiber. Can not.

[0003]

SUMMARY OF THE INVENTION The present invention provides a repetitive bending test method and an evaluation method capable of accurately measuring the progress of settling of an optical communication cable subjected to repeated bending, and the ease with which the optical communication cable is bent and easily removed. The idea is to devise it.

[0004]

The means taken to solve the above problems are constituted by the following elements on the premise of the above-mentioned conventional repetitive bending test method. (B) Measuring the swing angle of the swing arm sequentially with a measuring device. (B) Locking the lower end of the test piece from the left and right via a tensiometer, and successively measuring the force applied to the test piece. (C) One cycle of bending to the left and right is defined as one cycle, and the value measured by the tension meter is set on the vertical axis for each cycle, and the measured value of the swing angle of the swing arm is set on the horizontal axis. (D) calculating and measuring the area and intercept of the hysteresis graph for each cycle. Note that the axis P of the swing arm is arranged on a line connecting the centers of the left and right mandrels so that the position of the test piece wrapped around the mandrel when it is bent right and left is not changed, or the test piece is moved with respect to the swing arm. It is necessary to take measures to prevent the axial force (force in the compression direction) from acting on the test piece such as holding it vertically movably.
Further, since the swing arm has a function of repeatedly winding the test piece around the right and left mandrels M, 90 degrees, the swing arm is not necessarily a literal "swing arm" as long as it has this function.

[0005]

[Operation] The operation will be described with reference to FIGS. The radius of the left and right mandrels M is 6 times the wire diameter of the optical communication cable
It is 10 times (for example, 250 mm). When the test piece S of the optical communication cable is wound around the mandrel M, a force acts on the tension meter (load cell) L at the lower end of the test piece S in the direction opposite to the bending direction, and this is sequentially measured by the tension meter (this is the optical communication cable). Is equivalent to a bending force when bent at 90 degrees along the mandrel M). At this time, since the swing angle of the swing arm A is also sequentially measured, the area of the hysteresis graph G shown in FIG. 2 drawn by the two measured values is calculated every cycle of bending, and this is taken as measurement data. . Note that the hysteresis shown in the hysteresis graph G is due to the residual strain generated when the optical communication cable is bent to one side, and the sag of the optical communication cable proceeds as the residual strain decreases. As the bending is repeated, the test piece is sagged and the flexibility is increased (easy to bend), so that the maximum measured value of the tensiometer L is reduced. In addition, the residual strain is reduced as the bending is repeated.
The area of the hysteresis graph becomes smaller. Therefore, a change in the area of the hysteresis graph G indicates a change in the degree of progress of the set. On the other hand, for each optical communication cable of various specifications, the correlation between the progress of sag and the rate of deterioration of the transmission characteristics of the optical fiber, the correlation between the progress of sag and the degree of damage to the optical fiber, the progress of sag The correlation between the situation and the degree of damage in appearance of the optical communication cable is obtained in advance. Then, the change of the calculation result of the area of the hysteresis graph G of the test piece and the above-mentioned correlation show the deterioration of the transmission efficiency due to the repeated bending of each optical communication cable, the degree of damage to the optical fiber, and the appearance of the optical communication cable. Can be accurately predicted. Also, by tracking the change in the maximum tension for each cycle of bending, the change in the flexibility of the test piece can be confirmed. Further, in FIG. 2, the point at which the curve intersects the θ axis (θ intercept)
Means the amount of bending when the bending force is released. That is, it is the amount of bending remaining after bending the cable to a predetermined angle, and from this value, it is possible to quantitatively know how easily the cable is bent. On the other hand, the point where the curve intersects the F-axis (f-intercept) is the bending force required to hold the cable in a straight line, and indicates the degree of bending of the cable bent to a predetermined angle. From these amounts, it is possible to quantitatively know the ease of taking the curve in the step of taking the curve of the cable and the force applied to the fixture when fixing the cable having the curve in a straight line.

[0006]

[Effect] When the laid optical communication cable is repeatedly bent, the progress of the sag of the cable, the progress of the deterioration of the transmission characteristics of the optical fiber due to the progress of the sag, and the tendency of the cable to bend easily Since the ease of taking a sloping bend can be accurately evaluated by the test method of the present invention,
It can be inspected before installation to see if it is suitable for use. It is also possible to provide important data for the laying design and maintenance management of the optical communication cable based on the test result by this test method. Furthermore, by using the evaluation result by this test method, it is possible to obtain a cable suitable for the laying work and the laying place.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of the present invention.

FIG. 2 is a hysteresis graph according to the test method of the present invention.

FIG. 3 is a conceptual diagram of a conventional repeated bending test method.

[Explanation of symbols]

 A: swing arm M: mandrel P: swing axis L: tension meter (load cell) S: test piece of optical communication cable G: hysteresis graph W: weight

Claims (3)

[Claims] 1. A test piece of an optical communication cable is passed between left and right mandrels, its lower end is fixed, and its upper part is held by a swing arm, and the swing arm moves left and right along the outer peripheral surface of the mandrel. A bending fatigue test method for an optical communication cable that is bent by 90 degrees, wherein a swing angle of the swing arm is sequentially measured by a measuring device, and a lower end of the test piece is locked from right and left via a tension meter. The bending force applied to the test piece is sequentially measured by the tensiometer. One bending to the left and right is defined as one cycle, and the tension measured by the tensiometer is set as the vertical axis for each cycle, and the swing arm swings. Take the hysteresis graph for each bending cycle with the measured value of the dynamic angle as the horizontal axis, calculate the area and intercept of the hysteresis graph for each bending cycle and measure the bending of the optical communication cable. Fatigue test method. 2. The method according to claim 1, wherein the radius of the mandrel is 6 to 10 times the diameter of the optical communication cable. 3. A test piece of an optical communication cable is passed between the left and right mandrels, the lower end thereof is fixed, and the upper portion is held by a swing arm. The swing arm allows the test piece to move right and left along the outer peripheral surface of the mandrel. A bending fatigue testing device for an optical communication cable that bends by 90 degrees, wherein the swing angle of the swing arm is sequentially measured by a measuring device, and the lower ends of the test pieces are locked from right and left via a tensiometer, respectively. An optical communication cable bending fatigue tester for sequentially measuring a bending force applied to a test piece by the tensiometer.