JP2003226542A - Method and apparatus for grinding optical fiber preform ingot to cylinder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for grinding optical fiber preform ingot to a cylinder with excellent size precision. <P>SOLUTION: Soot is deposited around a starting core member and is sintered to be converted to transparent glass. In a method for grinding an obtained optical fiber preform ingot to a cylinder, a distance between a grinding stone and a core center is determined based on variation of a target diameter in a longitudinal direction of the preform ingot. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical grinding method and a cylindrical grinding apparatus for an optical fiber preform ingot (hereinafter, simply referred to as preform ingot) having excellent dimensional accuracy.

[0002]

2. Description of the Related Art In a manufacturing process of a base material ingot, for example, after a clad portion is deposited on the surface of a starting core member by an OVD (external attachment) method, the base material ingot is processed into a base material ingot through processes such as dehydration and sintering. Become. In the OVD method, in the step of depositing soot (glass fine particles) on the surface of the starting core member, a generally known method for improving the production rate is to supply a raw material gas and perform hydrolysis in an oxyhydrogen flame. The method of increasing the diameter of the burner that causes soot in (1) and the method of increasing the number of burners can be mentioned.

As a technique for increasing the productivity by the OVD method, there is known a method of increasing the length of the core to increase the ratio of the straight body portion to be the product of the base material ingot.

[0004]

When the method of increasing the diameter of the burner for supplying the raw material gas to improve the production rate is adopted, the adhesion of the soot is extremely large at the initial stage of depositing the soot on the surface of the starting core member. There is a problem of being bad. Further, when a plurality of burners having a large diameter are used, there is a problem in that the flames interfere with each other and the deposition efficiency does not improve as expected.

When the method of increasing the number of burners is adopted, since there are a plurality of burners, irregularities are formed on the surface of the deposited soot. In particular, when the amount of raw material gas is increased and high-rate deposition is performed, there is a problem in that irregularities become prominent.
As a result, the resulting optical fiber does not have good optical properties, especially the desired cutoff wavelength and dispersion wavelength in a single mode optical fiber.

On the other hand, the method of increasing the length of the core has a problem that the length of the core is increased, so that the bending is increased in the deposition process performed at a high temperature and the shape is often nonuniform. It was

As a method of bringing the unevenness of the base material ingot and the bent core portion thus generated to the center of the base material ingot, a method of aligning the rotation axis of the core and the rotation axis of the base material ingot (Japanese Patent Laid-Open No. 2000- No. 47039) is known. However, the grindstone used in the cylindrical grinding machine can be used in the longitudinal direction even if the target diameter of the grinding point is adjusted to match the target diameter of the grinding point at the center of the rotating grindstone surface. When the diameter changes, there is a problem that it is overcut depending on the amount of change.

As a means for solving the above-mentioned problem, a method of reducing the width of the contact portion between the grindstone and the base material ingot can be considered, but this is not a practical method because it lowers the grinding ability.

The present invention has been made in view of the above problems, and an object thereof is to provide a cylindrical grinding method and a cylindrical grinding apparatus for a base material ingot having excellent dimensional accuracy.

[0010]

DISCLOSURE OF THE INVENTION The present invention has solved the above problems, and a method of cylindrical grinding of a base material ingot according to the present invention is characterized in that soot is deposited around a starting core member and sintered to form a transparent glass. In the cylindrical grinding method of the optical fiber base material ingot, based on the change amount of the target diameter with respect to the longitudinal direction of the base material ingot, characterized by determining the distance between the grindstone and the core center, the grindstone and the core center When determining the distance, the position of the center of the grindstone is set to a value larger than the target diameter and grinding is performed. For example, there is a method in which an amount corresponding to the amount of change in the target diameter is manually added to the target diameter, or a program is performed to automatically add the amount to the target diameter for grinding.

The amount corresponding to the change amount of the target diameter with respect to the longitudinal direction of the base material ingot is the amount of excessive cutting that occurs when grinding the grinding stone at the center of the grinding stone to match the target diameter. The amount changes according to the amount of change in the target diameter in the longitudinal direction of the base material ingot. Therefore, in order to add the amount corresponding to the change amount of the target diameter to the target diameter, the overcut amount c corresponding to the change amount a of the target diameter
Should be added to the target diameter, and the position of the center of the grindstone should be adjusted to this position.

A cylindrical grinding apparatus for a base material ingot according to the present invention is a cylindrical grinding apparatus for an optical fiber base material ingot which is obtained by depositing soot around a starting core member and sintering the soot into a transparent vitreous material. An amount corresponding to the change amount of the target diameter in the longitudinal direction can be added to the target diameter. That is, the cylindrical grinding apparatus of the present invention is configured to be manually implemented or programmed and automatically implemented so that the value becomes larger than the target diameter in accordance with the change amount of the target diameter.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

FIG. 1 is a schematic cross-sectional view for schematically explaining a cylindrical grinding method of a base material ingot in which a target diameter has a large variation amount, that is, a diameter changes rapidly along the longitudinal direction. Base material ingot 1 whose diameter changes rapidly
On the other hand, when the grindstone 2a is adjusted to the target diameter at the grindstone center C, and the grindstone 2a is moved along the target diameter line 3 to the position of the grindstone 2b while the grindstone is moving, the grindstone shows "actual grinding range" in the figure. As indicated by "," the width of the base material ingot is in contact with the base material ingot, and thus excessive cutting occurs according to the target diameter change amount of the base material ingot and the contact width of the grindstone. Therefore, as for the actual finish, the dimension line 5 before grinding is finished along the finish line 4.

At this time, assuming that the change amount of the target diameter per unit length in the longitudinal direction is a and the contact width between the base material ingot and the grindstone is b, the overcut amount c is obtained by the following equation (1). To be c = a ・ b / 2 (mm) …………………… (1) Then, along the longitudinal direction of the base metal ingot, the overcut amount c obtained by the above formula is calculated as the target diameter at the grinding position. The position of the grindstone is added to the position of the grindstone, and the grindstone center is aligned with this position for grinding. In this way, the position of the grindstone is controlled in accordance with the change amount a of the target diameter that changes along the longitudinal direction of the base material ingot, and the position of the grindstone is moved while grinding so that the difference between the finished diameter and the target diameter can be reduced over the entire length. Can be made smaller.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. (Example 1) The diameter before grinding was 146 from one end to the other end.
A 1,500 mm long base metal ingot changing from mmφ to 168 mmφ is set and ground so that the target diameter changes from 145 mmφ to 163 mmφ (see curve A in FIG. 2 described later). The contact width b between the grindstone and the base material ingot is 30 m.
set to m.

A target diameter that changes along the longitudinal direction of the base material ingot is input to the control device, and this target diameter is
The whole length of the base metal ingot was programmed so that the grinding wheel center of the grinding wheel was aligned with the position obtained by adding the overcutting amount c calculated by the above equation (1) in correspondence with the change amount a.

Grinding is carried out by rough grinding with a surface roughness of # 12 as a grindstone.
Using a diamond wheel of 0, the maximum depth of cut 0.75
It was ground 4 times in mm. For finish grinding, a diamond wheel with a surface roughness of # 200 was used, and grinding was performed once with a depth of cut of 0.1 mm. The roughness of the finished surface was 0.02 mm.

The diameter of the ground base material ingot was measured with an outer diameter measuring instrument, and the results shown in the graph of FIG. 2 were obtained. In the figure, a curve A is a target diameter (vertical axis: left side) in the longitudinal direction (horizontal axis) of the base material ingot, and a curve B
Indicates the difference between the target diameter and the finished diameter (vertical axis: right side). As a result, good results were obtained with a maximum difference of 0.1 mm between the target diameter and the finished diameter.

(Comparative Example 1) The diameter before grinding was 142 in the longitudinal direction.
A 1,500 mm long base metal ingot changing from mmφ to 166 mmφ was ground in the longitudinal direction along a target diameter changing from 141 mmφ to 160 mmφ. Grinding was performed by a conventional grinding method in which the distance between the center of the grindstone and the center of rotation of the base material ingot was adjusted to match the target diameter. That is, grinding was performed under the same conditions as in Example 1 except that the amount of overcut was not added to the target diameter. The roughness of the finished surface was 0.02 mm. The result of grinding is as shown in the graph of FIG. 3, and as the amount of change in the target diameter increased, the difference in the finished diameter with respect to the target diameter increased in proportion to this.

[0021]

The present invention has the above-mentioned structure,
Even when a base material ingot whose target diameter changes rapidly in the longitudinal direction is ground, a base material ingot having excellent dimensional accuracy can be obtained as compared with the conventional grinding method.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view explaining a grinding state by a cylindrical grindstone with respect to a base material ingot in which a target diameter rapidly changes in a longitudinal direction.

FIG. 2 is a graph showing a difference between a target diameter and a finish diameter by the grinding method of the present invention, a curve A shows a target diameter, and a curve B shows a difference between the target diameter and a finish diameter.

FIG. 3 is a graph showing a difference between a finish diameter and a target diameter by a conventional grinding method.

[Explanation of symbols]

1 ... Base material ingot, 2a, 2b ... Whetstone, 3 ... Target diameter line, 4 ... Finishing line, 5: Dimension line before grinding, C: The center of the whetstone.

Claims (5)

[Claims] 1. A soot is deposited around the starting core member,
In a cylindrical grinding method of an optical fiber base material ingot that is sintered and made into a transparent glass, the distance between the grindstone and the core center is determined based on the amount of change in the target diameter with respect to the longitudinal direction of the base material ingot. Cylindrical grinding method for optical fiber base material ingot. 2. The cylindrical grinding method for an optical fiber preform ingot according to claim 1, wherein, when determining the distance between the grindstone and the core center, the position of the grindstone center is set to a value larger than the target diameter. 3. The cylindrical grinding method for an optical fiber preform ingot according to claim 2, wherein the position of the center of the grindstone is a position in which an overcut amount c corresponding to a target diameter change amount a is added to the target diameter. 4. Depositing soot around the starting core member,
In a cylindrical grinding device for an optical fiber base material ingot that has been sintered and made into a transparent glass, it is configured so that an amount corresponding to a change amount of the target diameter in the longitudinal direction of the base material ingot can be added to the target diameter. Cylindrical grinding device for optical fiber base material ingot. 5. The optical fiber preform ingot according to claim 4, wherein the amount corresponding to the amount of change in the target diameter is an excessive amount of shaving that occurs when the grindstone is ground at the wheel center according to the target diameter. Cylindrical grinding machine.