JPH08166356A - Method for detecting abnormality of optical fiber - Google Patents

Abstract

PURPOSE: To provide a method for detecting an abnormality inside a naked optical fiber, mainly air bubbles or the like. CONSTITUTION: Parallel light beams 3 are continuously cast sideways to a naked optical fiber 2 not yet coated immediately after being drawn. A forward scattering light 4 is continuously detected, so that an abnormality inside the naked optical fiber 2 is judged from a difference of quantities of light of right and left patterns of the detected scattering light. In this constitution, even when a using detector 5 such as a CCD line sensor or the like generates instable outputs of some degrees, an erroneous detection is not brought about and a highly accurate detection is achieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber abnormality detecting method for detecting an abnormality inside a bare optical fiber, mainly bubbles.

[0002]

2. Description of the Related Art As a method for detecting an abnormality in such an optical fiber, the present applicant has already proposed the method shown in FIG. In this method, the uncoated optical fiber bare wire 2 immediately after being drawn from the optical fiber preform 1 is continuously irradiated with parallel rays 3 from the side, and scattered light 4 scattered in front of the parallel light rays 3 is transferred to a CCD line. The detector 5 represented by a sensor or the like continuously detects. The detected electric signal is processed by the signal processing unit 6, and the scattering pattern 20 is displayed on the monitor 7. On the other hand, the determination processing unit 8 determines the presence or absence of air bubbles and the like, records the same in the recording device 9, and records the abnormality. At the time of detection, an alarm device 10 such as a buzzer issues an alarm.

As the scattering pattern 20, as shown in FIG. 4, a pattern shaped like Mt. Fuji can be obtained. Since the parallel light beam 3 is directly incident on the central portion of the detector 5, the sensor may be charged up. In such a case, as shown in FIG. A mask 11 made of a blocking plate is provided. At this time, a scattering pattern 20 'having no peaks is obtained.

For example, taking the above scattering pattern 20 'as an example, when there is no abnormality inside the bare optical fiber 2,
While a hillside pattern composed of beautiful ridges can be obtained, when an abnormal portion such as a bubble is present, as shown in FIG. 6 (note that the scattering pattern 20 ′ in FIG.
It is displayed rotated. ), An abnormal portion 20a 'consisting of a large uneven portion appears. Therefore, the appearance of this abnormal portion 20a 'reveals that there is an abnormal portion such as a bubble inside the bare optical fiber 2.

[0005]

However, the above C
In the detector 5 such as a CD line sensor, it is inevitable that the output characteristics have some instability (variation) due to the characteristics of the elements. If this is displayed in a slightly exaggerated manner, for example, as shown in FIG. 7, even if there is no abnormality inside the bare optical fiber 2, there is a possibility that a hillside scattering pattern 21 'having large and small uneven portions may occur. .

If there are such large and small irregularity fluctuations, erroneous abnormality detections will occur frequently, and even non-defective parts of the bare optical fiber 2 will be discarded. Therefore, in the detection by the detector 5, it is conceivable to take a time average or form the output through a high-cut filter, but in that case, it becomes difficult to speed up the drawing (spinning). This causes a problem that it is not possible to meet the recent demands such as cost reduction by increasing the spinning speed and further homogenization of the bare optical fiber.

The present invention has been made in view of such a conventional situation, and enables highly accurate detection in an element such as a CCD line sensor even if the output is unstable to some extent. It is intended to provide a method for detecting an abnormality in an optical fiber.

[0008]

According to a first aspect of the present invention, an uncoated optical fiber bare wire immediately after drawing is continuously irradiated with parallel rays from the side, and the forward scattered light is continuously irradiated. The method for detecting an abnormality in an optical fiber is characterized in that the abnormality in the bare optical fiber is determined based on the difference between the light amounts of the right and left patterns of the scattered light detected.

According to the second aspect of the present invention, the uncoated optical fiber bare wire immediately after drawing is continuously irradiated with parallel rays from the side, and the forward scattered light is continuously detected,
There is a method for detecting an abnormality in an optical fiber characterized by performing an abnormality determination inside the bare optical fiber from the difference between the detected pattern light amount of the scattered light and the pattern light amount of the scattered light of a normal bare optical fiber. .

[0010]

With this configuration, in any of the present inventions, even if the detector such as the CCD line sensor used has some output instability, it can be detected with high accuracy without erroneous detection. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, first, a device system similar to the above-described device system of FIG. 3 has no peak portion as shown in FIG. 1 (for preventing charge-up of the sensor as in the case of FIG. 5 above). (When the mask of No. 1 is provided), a scattering pattern 30 'of the forward scattered light 4 is obtained. After that, in the present invention, the signal processing unit 6
As shown in FIG. 1, the total light amount of the left half pattern 30a 'of the scattering pattern 30' is calculated, and the total light amount of the right half pattern 30b 'is also calculated.
Then, these total light amounts are compared, and when the difference exceeds a certain value (threshold value), the judgment processing unit 8 has an abnormal portion such as a bubble in the bare optical fiber 2. Is determined. At this time, if necessary, the alarm device 1
An alarm is triggered by 0. In addition, by the recording device 9,
The presence or absence of abnormality is recorded over the entire length of the bare optical fiber 2.

The above threshold value is set by performing an actual detection test, and when there is an abnormality in the bare optical fiber 2 (a bare bare optical fiber), the left and right half patterns 30a ', 30b. The light amount difference of 'is obtained and set in advance.

In the case of this abnormality detecting method, even if a large number of large and small uneven portions are detected in the actual half patterns 30a 'and 30b', as shown in FIG. Is detected by the same detector 5 such as a CCD line sensor, so that it is considered that substantially the same degree of output instability acts on the left and right half patterns 30a 'and 30b'. Therefore, when there is no abnormality in the bare optical fiber 2, even if a large number of uneven portions appear on the left and right half patterns 30a 'and 30b', they will cancel each other out if the difference between the left and right is taken. Accurate detection is possible regardless of the output instability of the detector 5. Of course, on either pattern side,
If there is an abnormal portion, the difference between the left and right becomes apparently large, so that the abnormality can be easily detected. This method is the invention of claim 1 in the present invention.

Thus, the left and right half patterns 30a ',
Detecting an abnormality from the difference in the amount of light of 30b '
In other words, it means that there is a normal part in any of the left and right halves of the bare optical fiber 2. Therefore, the light intensity of the normal half pattern of the bare optical fiber 2 and all the left and right patterns are detected in advance, and this value (threshold value) is compared with the actually detected half patterns 30a ', 30b'. However, if the difference is taken, the presence or absence of abnormality can be easily detected. This method is the invention of claim 2 in the present invention.

According to the invention of claim 2, the optical fiber happens to be
In the case where there are bubbles of the same size on both the left and right sides of the barbed wire 2, the left and right half patterns 30a ',
Since the difference in the light amount of 30b 'hardly occurs (because they are almost equal to each other), it is difficult to determine the abnormality. However, in the invention of claim 2, since the comparison is made with the normal portion previously detected, the optical fiber It can be determined that the left and right parts of the bare wire 2 are abnormal.

Although each of the above-mentioned embodiments was concerned with the present invention in which the scattering pattern 30 'having no peaks was obtained, the present invention wanted to provide a mask as shown in FIG. The same can be applied to the scattering pattern 30 having a peak in some cases. In this case, the difference between the total amounts of light of the detected left and right half patterns 30a and 30b is taken, or the detected left and right half patterns 30a and 30b are detected.
It is sufficient to compare the total amount of light of a and 30b with the total amount of light of the half pattern and all patterns of the normal bare optical fiber 2.

In each of the above embodiments, the parallel light beam 3 is applied to the bare optical fiber 2 from one direction, but
However, the present invention is not limited to this, and a method in which the irradiation direction of the parallel light beam 3 is different from that of the bare optical fiber 2 traveling in the upper and lower stages, and the irradiation direction is different (preferably, the orthogonal direction). It is also included in the form).
Accordingly, if the irradiation is performed from only one direction, it is difficult to determine the abnormality by the direct incident light before and after the center of the light irradiation line of the bare optical fiber 2, but the same portion is irradiated by the light irradiation from two directions. Since the detection data is obtained, higher detection accuracy can be obtained.

Incidentally, it can be seen that the method of the present invention is superior to the method of the present invention because of the following relationship. When a CCD line sensor is used as a detector,
Letting σ _{1 be} the standard deviation of the output fluctuation of each CCD element, the standard deviation σ of the fluctuation of the area S of the half pattern is σ _1.
2 is σ ₂ = √nσ ₁ where n is the number of elements. Further, the area S of the half pattern can be expressed as S = n · V _AVE , where V _AVE is an average of individual device outputs. on the other hand,
In the method of detecting the uneven portion of the scattering pattern by the conventional method without shaping the output, the difference Δ between the adjacent elements is
You will see V. The standard deviation of the variation of this difference ΔV is
It is equal to the standard deviation σ ₁ above. As a result, σ ₂ / S = σ ₁
The relationship of / (√n · V _AVE ) σ ₁ / ΔV is established. As described above, it is understood that, as described above, comparing the areas of the respective half patterns, that is, the differences in the total amount of light, enables detection with higher accuracy.

[0019]

As described above, according to the optical fiber abnormality detecting method of the present invention, the uncoated bare optical fiber immediately after drawing is continuously irradiated with parallel rays from the side,
The forward scattered light is continuously detected, and the difference between the detected light quantity of the left and right patterns of the scattered light, or the difference between the detected scattered light pattern light quantity and the scattered light pattern light quantity of a normal bare optical fiber Since this is a method for determining an abnormality inside the bare optical fiber, even if there is some output instability in the detector such as the CCD line sensor used, it will not erroneously detect and can be detected with high accuracy. It can be carried out.

As a result, an inexpensive detector can suffice, and of course, it is possible to obtain a high quality bare optical fiber which is free from abnormalities such as bubbles and which is further homogenized. Further, at the time of detection, it is not necessary to take time averaging or output molding through a high cut filter, so that the speed of drawing (spinning) can be increased. In other words, productivity is not impaired by increasing the spinning speed.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a scattering pattern for explaining an embodiment of an optical fiber abnormality detection method according to the present invention.

FIG. 2 is an explanatory diagram showing a scattering pattern for explaining another embodiment of the optical fiber abnormality detection method according to the present invention.

FIG. 3 is a schematic explanatory view showing an example of an apparatus system for carrying out an optical fiber abnormality detection method.

FIG. 4 is a schematic explanatory view showing a relationship between an example of an optical fiber abnormality detection method and a detected scattering pattern.

FIG. 5 is a schematic explanatory view showing the relationship between another example of the optical fiber abnormality detection method and the detected scattering pattern.

FIG. 6 is an explanatory diagram showing a scattering pattern when there is an abnormal portion in a bare optical fiber.

FIG. 7 is an explanatory diagram showing a scattering pattern having large and small uneven portions due to output instability of a detector.

[Explanation of symbols]

 1 Optical fiber base material 2 Optical fiber bare wire 3 Parallel rays 4 Forward scattered light 5 Detector 6 Signal processing unit 20,20 'Scattering pattern 30,30' Scattering pattern

Claims (2)

[Claims] 1. An uncoated optical fiber bare wire immediately after drawing is continuously irradiated with parallel rays from the side, and forward scattered light is continuously detected, and the left and right patterns of the detected scattered light are detected. A method of detecting an abnormality in an optical fiber, which comprises determining an abnormality inside the bare optical fiber based on a difference in light amount. 2. An uncoated optical fiber bare wire immediately after drawing is continuously irradiated with parallel rays from the side, and forward scattered light is continuously detected, and a pattern light amount of the detected scattered light, A method for detecting an abnormality in an optical fiber, wherein an abnormality in the inside of the bare optical fiber is determined based on a difference from a pattern light amount of scattered light of a normal bare optical fiber.