Method for measuring bending amount of rod-like body

Abstract

To provide a method for measuring the bending amount of a rod-like body with which measurement of the bending amount of a rod-like body gasped by a terminal part can be carried out without being affected by a deflection due to the deadweight.SOLUTION: Regarding a rod-like body at least one end of which is supported by a support body capable of rotating around the horizontal direction as an axis, the coordinate of a radical center position of the rod-like body at longitudinal distance 0, n, L from a measurement start end, with L denoting the bending amount measurement range of the rod-like body, is determined, and measurement is taken of the radial center position at each distance and a line connecting the measured center positions is determined for each rotation angle in a rod state. A line connected by a prescribed expression 1 using the coordinate of the center position of the rod-like body at a distance n of each line from the measurement start end is taken as the bending amount in a direction V of the rod-like body at each position, a line connected by a prescribed expression 2 is taken as the bending amount in a direction H of the rod-like body at each position, and further the square root of the sum of square of the bending amount in the direction V and square of the bending amount in the direction H, of which distances from a longitudinal measurement end of the rod-like body are at the same point, is taken as the bending amount at the point of the rod-like body.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for measuring the amount of bending of a rod-shaped body, particularly a glass preform for an optical fiber.

Background Art

[0002] A glass lathe for processing a glass preform for an optical fiber generally includes a heat source that heats and softens the glass preform and is movable along the glass preform, a chuck that holds the glass preform or a dummy glass connected to the glass preform, and a mechanism that deforms the softened glass preform by moving the heat source or the chuck. When the glass preform is directly held by the chuck for processing, many parts of the held portion cannot be heated and become wasted. Therefore, a dummy glass is often connected to the glass preform and the dummy glass portion is held for processing.

[0003] When processing a glass preform for an optical fiber with the above glass lathe, it is important to check whether the shape after processing satisfies the standard and then remove it from the glass lathe. If it is found in the inspection process after glass lathe processing that the standard is not met, it is necessary to reprocess it with the glass lathe. For this purpose, the product part of the glass preform needs to be re-welded with the dummy glass held by the chuck of the glass lathe and reprocessed such as stretching and bending correction. This not only greatly reduces the yield but also consumes resources such as labor and materials.

[0004] As an example of the standard for the shape of a glass preform for an optical fiber, it is not difficult to check the outer diameter even with a glass lathe. By installing a laser outer diameter measuring device that can move in the longitudinal direction along the glass preform on the glass lathe, the outer diameter in the longitudinal direction of the glass preform for an optical fiber can be easily measured.

[0005] On the other hand, it is difficult to check the amount of bending of the glass base material. Conventionally, as a method for measuring the amount of bending of a rod-shaped body such as a glass base material for an optical fiber, the distances from the reference positions of each point at both ends and the middle part of the material to be measured in a stationary state or a state of being transferred in a direction perpendicular to the longitudinal direction of the rod-shaped body are detected by an optical method, and the amount of bending is measured from these distances. A method has been proposed in Patent Document 1 and the like.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the method of Patent Document 1, since a plurality of optical detectors are required, there are large cost and design constraints. In particular, in a glass lathe, since the influence of the heating source is large, it is difficult to adopt. Further, as described above, a glass lathe is a device for connecting and processing a glass base material to a dummy glass whose end portion is gripped by a chuck. Therefore, the glass base material is deflected to some extent by its own weight. In measuring the bending, the amount of bending corrected for the influence of the deflection must be calculated. In addition, there are often differences in shape between the dummy glass gripped by the chuck and the glass base material after processing connected thereto, and they often do not have a uniform beam shape. Therefore, with correction by calculating the amount of deflection based on the formula of material mechanics, it may not be possible to derive an appropriate amount of bending.

[0008] When measuring the amount of bending of a rod-shaped body while gripping it at its end, it is affected by the deflection due to its own weight, and the amount of bending is calculated to be larger than the actual state. Depending on the gripping state, it may not be possible to derive an appropriate amount of bending with correction by calculating the amount of deflection based on the formula of material mechanics. Therefore, the present invention has been made in view of the above, and an object thereof is to provide a method for measuring the amount of bending of a rod-shaped body that can measure the amount of bending of the rod-shaped body held at the end portion without being affected by the deflection due to its own weight.

Means for Solving the Problems

[0009] The method for measuring the amount of bending of a rod-shaped body according to the present invention is a method for measuring the amount of bending of a rod-shaped body in which at least one end of the rod-shaped body is supported by a support that can rotate 360° about a horizontal axis. When the measurement range of the amount of bending of the rod-shaped body is L, the coordinates obtained by projecting the radial center positions of the rod-shaped body at the longitudinal distances of 0, n, and L from the measurement start end onto the plane defined by the axis and the direction of gravity are (X0, YA0), (Xn, YAn), and (XL, YAL), respectively. The line connecting the measured radial center positions at each distance is defined as line (A). When the rotation angle at the time of measuring line (A) is set to 0°, further, the rod-shaped body is rotated by 90°, 180°, and 270°. Similarly, in the longitudinal direction of the rod-shaped body, the lines connecting the measured center positions of the rod-shaped body are defined as line (B), line (C), and line (D), respectively. When the coordinates of the center position of the rod-shaped body at the distance n from the measurement start end of line (B), line (C), and line (D) are (Xn, YBn), (Xn, YCn), and (Xn, YDn), respectively, the following formula, (Xn, (YAn - YCn) / 2 - { (YAL - YCL) / 2 - (YA0 - YC0) / 2} / (XL - X0) * Xn + (YA0 - YC0) / 2) The line connecting these is defined as the amount of bending of the rod-shaped body in the V direction at each position. Similarly, the following formula, (Xn, (YBn - YDn) / 2 - { (YBL - YDL) / 2 - (YB0 - YD0) / 2} / (XL - X0) * Xn + (YB0 - YD0) / 2) The line connecting these is defined as the amount of bending of the rod-shaped body in the H direction at each position. Further, the square root of the sum of the square of the amount of bending in the V direction and the square of the amount of bending in the H direction, where the distances from the measurement end in the longitudinal direction of the rod-shaped body are at the same point, is defined as the amount of bending of the rod-shaped body at that point.

[0010] In the present invention, it is preferable that the rod-shaped body is a glass preform for an optical fiber and is welded to a dummy glass portion gripped by a support that can rotate 360°. The difference between the outer diameter of the glass preform for an optical fiber and the outer diameter of the dummy glass portion is set to be 5 mm or more. Also, it is preferable that the glass preform for an optical fiber and the dummy glass portion are connected in a state where the diameter is reduced.

Advantages of the Invention

[0011] According to the method for measuring the amount of bending of the rod-shaped body of the present invention, at the radial center position in the longitudinal direction obtained by rotating the rod-shaped body to the positions of 0°, 90°, 180°, and 270°, by performing correction using, as the amount of deflection, the center portion where the distances from the measurement start end of the radial center position at the opposing angular positions are at the same point, it is possible to perform measurement of the amount of bending while avoiding the influence of deflection, and it is possible to easily and accurately measure the amount of bending in a state where it is installed on a glass lathe.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] The method for measuring the bending amount of the rod-shaped body of the present invention specifically is, in the rod-shaped body supported by a support capable of rotating 360° about the horizontal axis at at least one end of the rod-shaped body, when the measurement range of the bending amount of the rod-shaped body is L, taking the coordinates projected onto the plane defined by the axis and the gravity direction of the radial center positions of the rod-shaped body at the longitudinal distances of 0, n, and L from the measurement start end as (X0, YA0), (Xn, YAn), and (XL, YAL) respectively, taking the line connecting the measured center positions as line (A), and setting the rotation angle at the time of measuring the line (A) as 0°. Furthermore, the rod-shaped body is rotated by 90°, 180°, and 270°, and similarly, in the longitudinal direction of the rod-shaped body, the lines connecting the measured center positions of the rod-shaped body are taken as line (B), line (C), and line (D) respectively, and taking the coordinates of the center positions of the rod-shaped body at the distance n from the measurement start end of line (B), line (C), and line (D) as (Xn, YBn), (Xn, YCn), and (Xn, YDn).

[0014] In this case, focusing on line (A) and line (C) with a rotation angle difference of 180°, the line connecting the coordinates (Xn, (YAn + YCn) / 2) will be a straight line if the rod-shaped body has no deflection. However, in reality, since the rod-shaped body is deflected, it becomes a line reflecting the deflection. That is, the line connecting the coordinates (Xn, (YAn + YCn) / 2) can be used as the deflection amount in the V direction of the rod-shaped body. Therefore, (Xn, YAn - (YAn + YCn) / 2) = (Xn, (YAn - YCn) / 2), which is the coordinates of the center position in the V direction with the deflection amount subtracted from the coordinates (Xn, YAn) of line (A), becomes the coordinates of the center position in the V direction with the deflection amount subtracted. Furthermore, by subtracting the value of the Y coordinate of (Xn, (YAn - YCn) / 2), which is the coordinates of the center position in the V direction with the deflection amount subtracted, from the straight line connecting (X0, (YA0 - YC0) / 2) and (XL, (YAL - YCL) / 2), it can be corrected so that the Y values at the measurement start end and the measurement end become zero. As a result of the above correction, at a distance of Xn from the measurement start end, (Xn, (YAn - YCn) / 2 - { (YAL - YCL) / 2 - (YA0 - YC0) / 2} / (XL - X0) * Xn + (YA0 - YC0) / 2) The line connecting them can be used as the amount of bending in the V direction with the amount of deflection corrected.

[0015] Similarly, by focusing on line (B) and line (D) and performing the same correction as above, at a distance of Xn from the measurement start end (Xn, (YBn - YDn) / 2 - { (YBL - YDL) / 2 - (YB0 - YD0) / 2} / (XL - X0) * Xn + (YB0 - YD0) / 2) The line connecting them can be used as the amount of bending in the H direction with the amount of deflection corrected.

[0016] By taking the square root of the sum of the squares of the amounts of bending in the V direction and the H direction at the same point with the same distance from the measurement start end obtained in this way as the amount of bending of the rod-shaped body at each point, the amount of bending of the rod-shaped body not affected by deflection can be calculated.

[0017] When the outer diameter of the rod-shaped body shape at the end portion is not uniform and is partially thickened or thinned, or when the outer diameter of the end portion and the outer diameter of the measurement portion are significantly different, the amount of deflection calculated from the beam deflection formula is often different from the reality. Therefore, more complex calculations and corrections are required. On the other hand, the amount of deflection obtained in the present invention is not affected by the shape of the rod-shaped body at the end portion, and thus can be used for calculating the amount of bending in line with reality.

[0018] In the present invention, the rod-shaped body may be a glass base material for an optical fiber connected to a dummy glass held by a chuck of a glass lathe. Generally, a glass lathe is equipped with a set of laser outer diameter measuring devices, and the outer diameter of the glass base material within the measurement range of the laser outer diameter measuring devices is often measured to confirm the shape before and after processing. When measuring the amount of bending of a glass base material connected to a dummy glass held by a chuck at the end, it is necessary to eliminate the influence of deflection due to the self-weight of the glass base material. However, since there is often an outer diameter difference between the dummy glass and the glass base material, appropriate correction by calculating the amount of deflection based on the formula of material mechanics may not be able to derive the appropriate amount of bending. Therefore, calculating the amount of bending that is not affected by the above-mentioned deflection becomes effective.

[0019] When the outer diameter difference between the dummy glass and the glass base material is less than 5 mm, there is no major problem with the correction of the amount of deflection based on the formula of material mechanics. However, when it is 5 mm or more, it is often not possible to perform appropriate correction for the amount of deflection compared to the case derived from the above formula. Therefore, calculating the amount of bending that is not affected by the above-mentioned deflection becomes effective.

[0020] In order to enable wire drawing to start with a small amount of heating, the glass base material may be necked down by reducing the diameter at the end portion. The necking process can be performed by pulling the dummy glass and the glass base material away from each other while heating near the connection end of the dummy glass and the glass base material. The necking process may be stopped once in the diameter-reduced state before completely separating the dummy glass and the glass base material, and the amount of bending may be measured. Also in such a case, since it is difficult to correct the amount of deflection based on the formula of material mechanics, calculating the amount of bending that is not affected by the above-mentioned deflection becomes effective.

[0021] Next, an example of a method for measuring the amount of bending of the rod-shaped body according to the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited by the embodiments described below. Also, although there are parts that explain the outer diameter of a circle, it is not limited to a perfect circle, and it may be non-circular to such an extent that the function as an optical fiber preform is not impaired. FIG. 1 is a configuration diagram of a glass lathe used for processing a glass preform for an optical fiber of a rod-shaped body according to the present embodiment. A dummy glass 1 is gripped by a chuck 6 that can rotate 360° about a fixed horizontal axis, and a dummy glass 5 is gripped by a chuck 7 that can rotate 360° about a horizontal axis that can move in the longitudinal direction. Combustible gas such as hydrogen is supplied to a burner 3 that can move in the longitudinal direction to generate a flame, and the glass preform 2 is welded to the dummy glasses 1 and 5 while continuously rotating, and then processing is performed. A laser outer diameter measuring device 4 can also move in the longitudinal direction, measures the shape of the entire longitudinal direction of the glass preform 2, and the data is used for processing.

[0022] FIG. 2 shows the flow when measuring the amount of deflection V corrected in the V direction of a glass preform connected to dummy glasses at both ends. First, by moving a laser outer diameter measuring device L mm in the longitudinal direction from the measurement start end, the work center position distribution projected onto the plane defined by the axis and the gravity direction in the longitudinal direction of the glass preform is obtained. Let the work center position coordinates at distances of 0, n, and L from the measurement start end be (X0, YA0), (Xn, YAn), and (XL, YAL), respectively, and the line connecting these is defined as the work center position distribution (A) at the 0° position (see FIG. 2(a)). Next, the chuck is rotated 180°, and similarly, the work center position coordinates at distances of 0, n, and L from the measurement start end are obtained as (X0, YC0), (Xn, YCn), and (XL, YCL), respectively, and the line connecting these is defined as the work center position distribution (C) at the 180° position (see FIG. 2(b)). The line connecting the above (A) and (C) at positions having the same distance from the measurement start end in the longitudinal direction, that is, the line connecting (Xn, (YAn + YCn) / 2), can be used as the longitudinal distribution of the amount of deflection in the V direction of the glass preform. Therefore, (Xn, YAn - (YAn + YCn) / 2) = (Xn, (YAn - YCn) / 2), where the amount of deflection is corrected at the coordinate (Xn, YAn) of the line (A), becomes the coordinate of the center position in the V direction with the amount of deflection subtracted (see FIG. 2(c)). Furthermore, by subtracting the Y - coordinate value of (Xn, (YAn - YCn) / 2), which is the coordinate of the center position in the V direction after subtracting the amount of deflection, from the straight line connecting (X0, (YA0 - YC0) / 2) and (XL, (YAL - YCL) / 2), it is possible to correct the Y - values at the measurement start end and the measurement end to be zero. As a result of the above correction, at a distance of Xn from the measurement start end (Xn, (YAn - YCn) / 2 - { (YAL - YCL) / 2 - (YA0 - YC0) / 2} / (XL - X0) * Xn + (YA0 - YC0) / 2) The line connecting these points can be made the amount of bend in the V direction with the amount of deflection corrected (see Fig. 2(d)). By performing the same process for 90° and 270°, at a distance of Xn from the measurement start end (Xn, (YBn - YDn) / 2 - { (YBL - YDL) / 2 - (YB0 - YD0) / 2} / (XL - X0) * Xn + (YB0 - YD0) / 2) The line connecting these points can be made the amount of bend in the H direction with the amount of deflection corrected. The square root of the sum of the squares of the amounts of bend in the V direction and the H direction with the amount of deflection corrected at the same position at the same distance from the measurement start end is the amount of bend of the glass base material at each position.

[0023] Fig. 2 shows a state where dummy glass is connected to both ends of the glass base material. However, there may be cases where the amount of bend of the glass base material is measured in a state where dummy glass is connected to only one end and nothing is connected to the other end. Regardless of whether it is in a one - side support state or a two - side support state, it is possible to calculate the amount of bend with the amount of deflection corrected by the above method. Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples at all.

Examples

[0024] A large glass preform for an optical fiber with an average outer diameter of 150 mm and a length of 3000 mm manufactured by the OVD method was drawn in an electric furnace to produce five glass preforms for optical fibers in a cylindrical shape with an average outer diameter of 80 mm and a length of 2000 mm. [Comparative Example 1] One of the five was set in a shape measuring device while being suspended vertically with the end being gripped by a robot arm. The shape measuring device was a laser outer diameter measuring device LDM-306H manufactured by Takikawa Engineering Co., Ltd. set in a state of being perpendicular at 90°. While moving in the longitudinal direction, it acquired the distribution of the center positions of the glass preform at a pitch of 1 mm, corrected the distribution of the center positions so that it became zero at the measurement start position and the measurement end position, and took the square root of the sum of the squares of the center positions of the corrected glass preform at the same point as the distance from the measurement start position as the amount of bending at that point, and took the maximum value obtained as the amount of bending of the glass preform. The amount of bending measured by this method was 0.9 mm.

[0025] [Comparative Example 2] The glass preform measured in Comparative Example 1 was gripped by a movable chuck of a glass lathe using the glass lathe shown in FIG. 1. Further, a dummy glass in a cylindrical shape with an average outer diameter of 80 mm and a length of 500 mm was gripped by a fixed chuck of the glass lathe, and the end faces of the respective glasses were brought close to each other. By supplying hydrogen and oxygen to a movable burner of the glass lathe to eject a flame, the end faces of the glass preform and the dummy glass were each heated while rotating, and then the movable chuck was pressed against the fixed chuck to weld the glass preform and the dummy glass. Next, after releasing the movable chuck, a dummy glass in a cylindrical shape with an average outer diameter of 80 mm and a length of 500 mm was gripped by the movable chuck, and the end face of the glass preform that was not welded to the dummy glass and the end face of the dummy glass gripped by the movable chuck were brought close to each other. Then, by welding the glass preform and the dummy glass, the setting of the glass preform for an optical fiber with dummy glasses welded to both ends on the glass lathe was completed.

[0026] Regarding the glass base material with dummy glass welded to both ends as described above, the laser outer diameter measuring instrument LDM-306H manufactured by Takikawa Engineering Co., Ltd. was moved in the longitudinal direction at a pitch of 1 mm without rotating the chuck, and the center position distribution of the glass base material at each position in the longitudinal direction was measured. After correcting the amount of deflection obtained from the formula for the deflection of a simply supported beam subjected to a uniformly distributed load with respect to this center position distribution in the longitudinal direction, correction was performed so that the measurement start end and the end became zero, and the maximum value obtained as a result was taken as the amount of bending. The amount of bending measured by this method was 1.3 mm.

[0027] [Example 1] On the other hand, by moving the laser outer diameter measuring instrument LDM-306H manufactured by Takikawa Engineering Co., Ltd. in the longitudinal direction at a pitch of 1 mm without rotating the chuck, the distribution of the coordinates projected onto the plane defined by the chuck rotation axis and the gravitational direction of the center position in the longitudinal direction of the glass base material is acquired. This is taken as the line (A) at the 0° position. Further, after rotating to the 90° position, the distribution of the center position in the longitudinal direction is similarly acquired, and this is taken as the line (B) at the 90° position. Further, after rotating to the 180° position, the distribution of the center position in the longitudinal direction is similarly acquired, and this is taken as the line (C) at the 180° position. Further, after rotating to the 270° position, the distribution of the center position in the longitudinal direction is similarly acquired, and this is taken as the line (D) at the 270° position. The line connecting the center positions of the line (A) and the line (C) at the same position from the measurement start end can be used as the longitudinal distribution of the amount of deflection in the V direction of the glass base material. By subtracting this longitudinal distribution of the amount of deflection in the V direction from (A) in FIG. 2, the center position distribution in the V direction with the amount of deflection corrected can be obtained. From this straight line connecting the measurement start point in the longitudinal direction in the V direction and the center position in the V direction with the amount of deflection corrected at this point, and the measurement end point and the center position in the V direction with the amount of deflection corrected at this point, by subtracting the center position in the V direction with the amount of deflection corrected at each position in the longitudinal direction of the rod-shaped body at each position, the amount of bending in the V direction of the glass base material at each position can be calculated. By performing the same process on line (B) and line (D), the amount of bending of the glass base material in the H direction at each position can be calculated. The square root of the sum of the squares of the amounts of bending in the V direction and the H direction, where the distance from the measurement start end is at the same position, is taken as the amount of bending of the glass base material at that position, and the maximum value obtained as a result is taken as the amount of bending of the glass base material. The amount of bending measured by this method was 0.9 mm.

[0028] As a result, the same amount of bending was measured for Comparative Example 1 and Example 1, but a deviated amount of bending was measured for Comparative Example 2. Since Comparative Example 1 measures the amount of bending of the glass base material suspended vertically, it is not affected by the deflection due to the self-weight of the glass base material. Example 1 corrects the influence of deflection that conforms to reality, so it is not affected by the influence of deflection. On the other hand, in Comparative Example 2, since the amount of deflection used for correction was derived from the calculation, there is a part that does not conform to reality, so it is considered that a deviation occurs.

[0029] As a separate consideration, a dummy glass held by the lathe chuck was connected to both ends of the glass base material with an average outer diameter of 75 mm and a length of 500 mm. [Example 2] After that, the amount of bending of the glass base material was measured in the same manner as in Example 1. As a result, the obtained amount of bending was 0.9 mm. [Comparative Example 3] On the other hand, the amount of bending of the glass base material was measured in the same manner as in Comparative Example 2. As a result, the obtained amount of bending was 1.6 mm.

[0030] Furthermore, as a separate consideration, a dummy glass held by the lathe chuck was connected to both ends of the glass base material with an average outer diameter of 70 mm and a length of 500 mm. [Example 3] After that, the amount of bending of the glass base material was measured in the same manner as in Example 1. As a result, the obtained amount of bending was 0.9 mm. [Comparative Example 4] On the other hand, the amount of bending of the glass base material was measured in the same manner as in Comparative Example 2. As a result, the obtained amount of bending was 2.2 mm.

[0031] From the above results, it was found that when the average outer diameter of the dummy glass becomes thinner than that of the glass base material, the amount of bending measured in the comparative example increases. When the average outer diameter difference is up to 5 mm, it is within the range that can be used as a reference amount of bending. However, when it exceeds this value, the amount of bending is calculated too large, making it difficult to use as a reference. When the difference in the average outer diameter between the dummy glass and the glass base material becomes large, it becomes difficult to accurately calculate the amount of deflection according to the deflection formula. To prevent this, a thick dummy glass can be used, but if the dummy glass is too large, it becomes difficult to handle and is also costly, which is not preferable. In the method of this example, it is possible to calculate the amount of bending similar to that of Comparative Example 1 while suppressing the cost by using a thin dummy glass.

[0032] Separately, as another consideration, at a position 10 mm from the welded end surface of the glass base material and the dummy glass of the glass base material for an optical fiber set on the glass lathe toward the glass base material side, while rotating the glass base material, a movable chuck was pulled away from the fixed chuck so as to move while heating with a burner, thereby generating reduced diameter portions with a minimum diameter of 20 mm at both ends of the glass base material. The glass base material for an optical fiber having such reduced diameter portions can smoothly start wire drawing to the optical fiber. [Example 4] With the glass base material for an optical fiber having reduced diameter portions at both ends still set on the glass lathe, the amount of bending of the glass base material was measured in the same manner as in Example 1. As a result, the obtained amount of bending was 0.9 mm. [Comparative Example 5] On the other hand, in the same manner as in Comparative Example 2, the amount of bending of the glass base material having reduced diameter portions at both ends was measured while it was set on the glass lathe. As a result, the obtained amount of bending was 2.1 mm.

[0033] When the glass base material having reduced-diameter portions at both ends is set on a glass lathe, the formula for correcting the influence of deflection becomes complicated and does not conform to reality, so the amount of bending is calculated to be large by the method of Comparative Example 5. On the other hand, in the present embodiment, since the amount of deflection is the value actually measured, accurate measurement can be performed without being affected by the shape of both ends. Note that the present invention is not limited to the above-described embodiments, and can be freely deformed, improved, etc.

Explanation of Reference Numerals

[0034] 1: Dummy glass held by a fixed chuck 2: Glass base material for optical fiber 3: Burner 4: Outer diameter measuring device 5: Dummy glass held by a movable chuck 6: Fixed chuck 7: Movable chuck x: Outer diameter of the glass base material for optical fiber y: Outer diameter of the dummy glass held by the fixed chuck z: Outer diameter of the dummy glass held by the movable chuck

Claims

Claim 1 In the rod-shaped body in which at least one end of the rod-shaped body is supported by a support body that can rotate 360° about a horizontal axis, when the bending measurement range of the rod-shaped body is L, the radial center positions of the rod-shaped body at longitudinal distances of 0, n, and L from the measurement start end are projected onto a plane defined by the axis and the gravitational direction, and the coordinates are (X0, YA0), (Xn, YAn), and (XL, YAL), respectively. A line connecting the measured radial center positions at each distance is defined as line (A). When the rotation angle at which line (A) is measured is 0°, further, the rod-shaped body is rotated by 90°, 180°, and 270°. Similarly, lines connecting the measured center positions of the rod-shaped body in the longitudinal direction of the rod-shaped body are defined as line (B), line (C), and line (D), respectively. When the coordinates of the center position of the rod-shaped body at a distance n from the measurement start end of lines (B), (C), and (D) are (Xn, YBn), (Xn, YCn), and (Xn, YDn), respectively, a line obtained by connecting the following [Equation 1] is defined as the amount of bending of the rod-shaped body in the V direction at each position. Similarly, a line obtained by connecting the following [Equation 2] is defined as the amount of bending of the rod-shaped body in the H direction at each position. Further, the square root of the sum of the square of the amount of bending in the V direction and the square of the amount of bending in the H direction, where the distances from the measurement ends in the longitudinal direction of the rod-shaped body are at the same point, is defined as the amount of bending of the rod-shaped body at that point. A method for measuring the amount of bending of a rod-shaped body, characterized in that. [Equation 1] (Xn, (YAn - YCn) / 2 - { (YAL - YCL) / 2 - (YA0 - YC0) / 2} / (XL - X0) * Xn + (YA0 - YC0) / 2) [Equation 2] (Xn, (YBn - YDn) / 2 - { (YBL - YDL) / 2 - (YB0 - YD0) / 2} / (XL - X0) * Xn + (YB0 - YD0) / 2) Claim 2 The method for measuring the amount of bending of a rod-shaped body according to claim 1, wherein the rod-shaped body is a glass preform for an optical fiber, and a dummy glass portion held by the support body that can rotate 360° is welded to the glass preform for the optical fiber. Claim 3 The method for measuring the amount of bending of a rod-shaped body according to claim 2, wherein the difference between the outer diameter of the glass preform for the optical fiber and the outer diameter of the dummy glass portion is 5 mm or more. Claim 4 The method for measuring the amount of bending of a rod-shaped body according to claim 2 or claim 3, characterized in that the glass preform for the optical fiber and the dummy glass portion are connected in a state where the diameter is reduced.

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