JP3186613B2 - Synthetic quartz stretching apparatus and stretching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic quartz stretching apparatus and a stretching method capable of detecting defects caused by bubbles at the same time as stretching an ingot made of synthetic quartz in an electric furnace.
About the law .

[0002]

2. Description of the Related Art In the production of an optical fiber preform made of synthetic quartz, a soot synthesized by a VAD method or the like is dehydrated and sintered to produce a preform base material ingot. Although the diameter of this ingot is φ100 to 150 mm, the diameter of the preform when it is actually drawn into an optical fiber is φ30 to 80 mm, so that the preform of the desired diameter is drawn by stretching the ingot in an electric furnace. To manufacture. Electric furnace (drawing device) for drawing ingots
Is designed to send an ingot from the upper part of the furnace, and to heat the preform reduced in diameter from below the furnace while being heated to about 2000 ° C. Such a stretching apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-2539, but only describes an example of stretching a preform having a maximum diameter of 52 mm to a diameter of 4 mm. Therefore, the diameters of ingots and preforms targeted in the present invention are completely different and cannot be simply compared. As a problem due to an increase in the diameter of the ingot, the size of the electric furnace may be increased, so that the air flow in the furnace may be disturbed or the temperature distribution may be disturbed by the movement of the ingot. As a result, special measures are required for controlling the diameter. Also,
In a large electric furnace, it is difficult to completely shut off oxygen mixed in from the upper and lower parts of the furnace, so carbon and the like used as a heater and a heat insulating material are oxidized, and an oxide adheres to the preform, and In some cases, the carbon material adhered when the surface of the reform is soiled or softened remains as a scratch.

[0003]

Further, when the size of the ingot is increased, air bubbles easily enter the inside of the preform due to inadequate manufacturing conditions and the like. Bubbles remaining inside the preform may cause defects such as breakage of the fiber during drawing or an increase in light loss at the location of the bubbles. In order to remove air bubbles from the preform of the product, the presence or absence of air bubbles can be visually inspected after stretching, and if there are air bubbles, it can be dealt with by cutting at this position. However, depending on the cutting position, the preform becomes short and cannot be used as a product, so the cut portion is discarded, which causes a reduction in yield.

[0004] In order not to lower the yield even if there are bubbles, it is desirable to determine the cutting position of the preform in accordance with the location of the bubbles. For this purpose, it is conceivable that an operator inspects the preform while the preform is being stretched in an electric furnace, marks a place where air bubbles are present, and cuts at this position. However, in this operation, during the stretching operation, the operator needs to constantly stick to the stretching device and search for air bubbles, and thus there is a problem that labor saving and automation of the stretching process cannot be performed. Also, when detecting bubbles during the stretching step, the light emitted from the electric furnace,
Since it is scattered at the position of the bubble, there is an advantage that the bubble is relatively easily detected. In a case where bubbles are to be detected in a place other than the stretching step, a method of irradiating the preform with strong light and detecting light scattered by the bubbles while rotating the preform is used. In this case, a lighting device for irradiating light and a mechanism for rotating the preform are newly required.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a heating apparatus for drawing an ingot and an electric furnace for drawing an ingot in an apparatus for drawing an optical fiber preform member made of synthetic quartz.
Immediately below the furnace , attached to the stretching device, radiated from the electric furnace
A device for detecting bubbles remaining inside the preform by light is provided. Detect bubbles
The devices to be released are CCD camera, image processing device and control
Computer, the CCD camera is extended
Install two or more units around the preform
Preferably, a filter is mounted. In addition, the present invention
The synthetic quartz stretching method heats an ingot made of synthetic quartz
When producing preforms for optical fiber by stretching
And one or more CCD cameras are installed just below the electric furnace.
And captures at least two image data with the CCD camera.
Image data processed by the image processing device.
By measuring the change in the position of the bright spot
Features to detect bubbles remaining inside the preform
And

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
FIG. 1 shows a stretching apparatus of the present invention. The stretching apparatus of the present invention
It comprises a rotary chuck 3, a pull-down driving device 4, an electric furnace 5, a preform stretching driving device 6, and a bubble detection device for detecting bubbles remaining inside the preform.
The bubble detecting device includes a CCD camera 7 installed immediately below an electric furnace , an image processing device 8, and a computer 9 for recording and controlling image data. Diameter 100 synthesized by VAD method etc. and manufactured through dehydration sintering process
The preform base material ingot 1 having a diameter of about 150 mm and a length of 1000 to 1300 mm is attached to a rotary chuck 3 at the upper part of the apparatus. Is inserted into the electric furnace 5. The ingot 1 heated to about 2000 ° C. in the electric furnace 5 partially softens. The heated ingot 1 is drawn to a preset preform diameter (30 to 80 mmφ) and reduced in diameter by a preform drawing drive device 6 installed in the lower part of the electric furnace . The preform stretching driving device 6 was read by an outer diameter measuring device 10 installed in the middle and immediately below the electric furnace 5,
Based on the data of the preform diameter, the stretching speed is constantly changed to control the preform diameter to be constant. Preform 2 immediately after coming out of the furnace is completely solidified at a temperature lower than the softening point, but its surface temperature is 10
It is around 00 ° C. In the present invention, the ingot before being stretched and the stretched preform member are stretched while being synchronously rotated at a constant rotation speed. In the stretching device of the present invention,
Installed CCD camera 7 directly below the electric furnace 5, the preform 2 in the middle drawing is captured thereby, wherein the image
Data is collected. Since the surface of the preform 2 and the area immediately below the electric furnace are extremely hot, a filter for preventing heat rays is provided at the front of the CCD camera 7 to protect the camera from heat. Have been.

The place where the CCD camera 7 is installed is desirably as close to the exit of the electric furnace 5 as possible. When away from the electric furnace , dust flies due to the temperature distribution around the preform, and the dust is attracted by the influence of static electricity generated on the preform, and a large amount of dust may adhere to the surface of the preform. In addition, the preform stretching driving device 6
In this case, since a stretching force is applied by directly adhering to the preform 2, dirt adheres to the surface of the preform. Dust and dirt adhering to the surface of the preform in this way hinder the detection of air bubbles. Therefore, it is easier to detect the dust immediately below the electric furnace where the preform surface is as clean as possible.

[0008] Bubbles in the preform are light emitted from an electric furnace and appear as bright spots. In addition, the light radiated from the furnace is reflected around the preform and at a position immediately after leaving the electric furnace , so that they appear as a large group of light. Further, at this time, since the surface of the ordinary preform has scratches and stains, these are also observed as bright spots at the same time. Thus, the bubbles in the preform,
Scratches, dirt, and reflected light are detected in the same manner in one screen and become image data by the CCD camera 7, so it is necessary to extract only data of bright spots due to bubbles from among them. The collected image data is sent to the image processing device 8 and subjected to filtering processing such as image sharpening, binarization, and detection of the outer peripheral portion. Only those are extracted.

[0009] The bright spot data includes not only bubbles remaining inside the preform but also data resulting from dirt and scratches on the front and back surfaces. The bright spot data is composed of the position, size, and shape of the center of gravity of the bright spot, and is sent to the computing computer 9 in order to extract only the data of the bubbles. When the preform is stretched while rotating around the center of the cylinder, image data is captured at regular intervals by at least one CCD camera, and the image-processed bright spot data is transferred to a computer. It is captured. The computer can measure the change in the position of the bright spot by comparing the data of the bright spot captured at least twice. Thereby, it can be distinguished whether it is inside the preform or on the surface. That is, the scratches and dirt on the front surface of the preform are observed while moving at the same speed as the rotation speed of the preform, and the scratches on the back surface have the refractive index (n = 1.458) of the preform and the air (n = 1). ) Larger, the light is refracted inside the preform and appears to move faster than it actually is. Since air bubbles inside the preform may appear to move at a speed intermediate between these, bright spots (scratch and dirt) on the preform surface and bright spots (bubbles) inside the preform can be distinguished. Will be possible. In this way, when the preform is stretched while rotating, in principle, one CCD
The camera can also extract bubbles and determine the position. However, if the stretching speed is higher than the rotation, the luminescent spot may deviate from the viewing angle of the camera before one bright spot is detected twice or more in one rotation. In this case, by capturing images almost simultaneously from two or more cameras from different locations, it becomes possible to observe the entire preform in the circumferential direction.

However, in the case where the preform is stretched without being rotated, two or more cameras are inevitably installed to view the entire preform. In this case, since the refractive index of the preform is large, it is not possible to observe the entire inside of the preform unless at least six cameras, preferably at least four cameras, are installed. However, as the number of cameras increases, the installation location increases, and the work space may be limited. Therefore, the number of cameras is limited to about eight. As a method of reducing the number of cameras, it is conceivable to collect image data at regular intervals while moving the cameras around the preform in the circumferential direction. However, in that case, a drive mechanism of the camera is required, and the installation becomes complicated, and there is a problem that the installation place becomes large.

As a method for utilizing the position information of the bubbles collected as described above, there are the following methods. The simplest method is to alert the worker that an air bubble has been detected by alerting the worker, visually checking the air bubble based on it, marking the location where the air bubble is located,
It is to cut at this position later. With this method, the stretching process cannot be completely automated, but it is not necessary for the operator to stick to the stretching device during the stretching operation, and the labor can be greatly reduced as compared with the related art. Another method is to automatically mark the surface of the preform in accordance with the information on the position of the detected foam, and the operator can later cut at this position, and based on this position information, It is also possible to add a device for automatically cutting at that position and a device for transporting and stocking the cut preform. In this case, the stretching step can be completely automated.

[0012]

The present invention will be described below with reference to examples and comparative examples. Embodiment 1 FIG. 1 shows an example of a stretching apparatus of the present invention. Here, the ingot 1 is stretched while rotating, and two CCD cameras 7
This shows an apparatus for taking in a stretched preform image by using (NEC, trade name TI-324A). The base material ingot 1 used here had a diameter obtained by dehydrating and sintering a soot ingot synthesized by the VAD method.
It is 140mm long and 1250mm long. This ingot was stretched to be processed into a preform having a diameter of 45 mm. The ingot 1 fixed to the rotary chuck 3 at the upper part of the electric furnace is inserted into the electric furnace 5 set at 2000 ° C. at a speed of 20 mm / min, and the preform stretching driving device 6 is installed below the electric furnace. At a controlled speed to give a preform having a constant diameter. The stretching speed of the preform-driven stretching device 6 is set to a value calculated based on the preform diameter measured during and after melting by an outer diameter measuring device 10 set in the middle of and immediately below the electric furnace. And
The drawing speed is constantly changed, and as a result, the diameter of the preform 2 is controlled to be constant. The image data captured by the CCD camera 7 installed immediately below the electric furnace is detected through an image processing device 8 and an arithmetic computer 9 to detect the position of the air bubble and alert the operator. In response to the alarm, the worker marked the position of the bubble on the preform, and cut the preform at the position of the bubble after the completion of stretching. As a result,
The worker does not need to constantly stick to the stretching device to search for the presence or absence of air bubbles, which facilitates the work.

Embodiment 2 FIG. 2 shows another example of the stretching apparatus of the present invention. This device stretches the ingot 1 without rotating the chuck 14 without rotating the ingot 1. By installing four CCD cameras 7 around the preform 2 immediately below the electric furnace 5, almost all images of the entire preform are obtained. Can be captured at the same time. In addition, a marker 11 for automatically marking a position where a bubble was detected with a carbide tool was added. Using this apparatus, an ingot was drawn in the same manner as in Example 1. This time, the worker was away from the apparatus during the stretching, and cut the preform at the marked position after the completion of the stretching. Therefore, the preform stretching operation can be performed semi-automatically.

Embodiment 3 FIG. 3 shows still another example of the stretching apparatus of the present invention. In this apparatus, as in Embodiment 1, the apparatus is extended while being rotated by a rotary chuck and detects bubbles with two CCD cameras 7, and a cutting apparatus that automatically cuts a preform at a position where bubbles are detected. 12 and transport the cut preform,
Stocking device 13 was added. Therefore, it is possible to automatically detect bubbles and cut the preform at the positions of the bubbles without any trouble of the operator.

[0015]

According to the present invention, labor saving and automation of the stretching process can be achieved by adding a device for automatically detecting the position of the bubble. In addition, there is no variation among operators, which is effective in quality control of bubble detection. Also, when installing the detection device of the bubble just under the electric furnace, electric
The light emitted from the furnace is located at the location of the bubbles inside the preform.
Since air bubbles can be detected by being scattered, there is no need to install special illumination for detection, and the installation location of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a view showing one example of a synthetic quartz stretching apparatus of the present invention.

FIG. 2 is a view showing another example of the synthetic quartz stretching apparatus of the present invention.

FIG. 3 is a view showing still another example of the synthetic quartz stretching apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ingot 2 ... Preform 3 ... Rotary chuck 4 ... Pull-down drive 5 ... Electric furnace 6 ... Preform extension drive 7 ... CCD camera 8 ... Image processing device 9 ... Computer for calculation 10 ... Outer diameter measuring device 11 ... Marker 12 ... Preform cutting device 13 ... Preform transport and stock device 14 ... Non-rotating chuck

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Research Laboratories (56) References JP-A-59-207849 (JP) , A) JP-A-7-187723 (JP, A) JP-A-7-229813 (JP, A) JP-A-61-290344 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB (Name) C03B 37/012

Claims (6)

(57) [Claims] 1. An apparatus for drawing an optical fiber preform member made of synthetic quartz for drawing an ingot.
A synthetic quartz drawing apparatus, further comprising a heating electric furnace and a device attached directly to the electric furnace and attached to the drawing device for detecting bubbles remaining inside the preform by light emitted from the electric furnace. . 2. The synthetic quartz stretching apparatus according to claim 1, wherein the ingot before being stretched and the stretched preform member are stretched while being rotated synchronously at a constant rotation speed. 3. The synthetic quartz stretching apparatus according to claim 1, wherein the apparatus for detecting bubbles includes a CCD camera, an image processing apparatus, and a control computer. 4. The synthetic quartz stretching apparatus according to claim 3, wherein two or more CCD cameras are provided around the stretched preform. 5. The synthetic quartz stretching apparatus according to claim 3, wherein the CCD camera is provided with a filter for preventing heat rays. 6. Heat drawing of an ingot made of synthetic quartz
To manufacture optical fiber preforms
One or more CCD cameras are installed immediately below the furnace,
Capture at least two image data with CCD camera
The bright spot data processed by the image processing device
By processing and measuring the change in the position of the bright spot,
Detecting bubbles remaining inside the foam
Synthetic quartz stretching method.