Bolt axial force estimation method, wind turbine preventive maintenance method and nut

Abstract

To provide a bolt axial force estimation method, a wind turbine preventive maintenance method, and a nut that can easily evaluate changes in bolt strain.MEANS FOR SOLVING THE PROBLEM: The bolt axial force estimation method of the present invention is a method for estimating bolt axial force when fastening a fixed member with a nut and a bolt, and includes the steps of measuring the distance between first two markings on a side surface of the nut near the fixed surface side and the distance between second two markings on a side surface of the nut on the side opposite the fixed surface, and estimating the bolt axial force by comparing the distance between the first two markings with the distance between the second two markings.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a bolt axial force estimation method, a wind turbine preventive maintenance method, and a nut. [Background technology]

[0002] Blades of wind turbines and other devices are fixed to their foundations by dozens of bolts tightened with nuts. Because the fastened objects are made of resins such as GFRP, even if the nuts do not loosen (they do not rotate), the strain generated in the bolts may decrease due to creep of the resin. Strain gauges are used to monitor bolt strain in critical locations, but because strain gauges are fixed with adhesive, their adhesive strength deteriorates due to moisture in the air and high temperature environments, so they need to be replaced every two years or so. For this reason, a non-contact strain measurement method that does not use adhesives is desired.

[0003] A known non-contact strain measurement method is described in, for example, Patent Document 1. In this method, strain is measured by laser interference (paragraph

[0008] ). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-235618 Summary of the Invention [Problem to be solved by the invention]

[0005] Strain measurement using laser interference requires large-scale equipment that cannot be brought to high places such as wind turbines, so there is a need for a bolt axial force estimation method, a preventive maintenance method for wind turbines, and a nut that are small and easy to use to evaluate bolt strain.

[0006] An object of the present invention is to provide a bolt axial force estimation method, a wind turbine preventive maintenance method, and a nut that can easily evaluate changes in bolt strain. [Means for solving the problem]

[0007] The bolt axial force estimation method of the present invention is a method for estimating bolt axial force when fastening a fixed member with a nut and a bolt, and includes the steps of measuring the distance between first two markings on a side surface of the nut near the fixed surface side and the distance between second two markings on a side surface of the nut near the opposite side to the fixed surface, and estimating the bolt axial force by comparing the distance between the first two markings with the distance between the second two markings.

[0008] Alternatively, a preventive maintenance method for a wind turbine of the present invention is characterized in that the above-mentioned bolt axial force estimation method is used for a fastening portion of a blade, which is a blade that rotates when exposed to wind in a wind turbine, and the axial force of the bolt at the fastening portion is estimated.

[0009] Alternatively, the nut of the present invention is a nut for fastening to a fixed surface together with a bolt, and is characterized in that it has first two markings provided on a side surface of the nut near the fixed surface side and second two markings provided on a side surface of the nut near the opposite side of the fixed surface for estimating the axial force of the bolt. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a bolt axial force estimation method, a wind turbine preventive maintenance method, and a nut that can easily evaluate changes in bolt strain. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an overall view of a method for measuring bolt strain using a nut according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the installation position of a strain gauge in this embodiment. [Figure 3] FIG. 10 is a diagram showing the axial force of the bolt and the strain generated by the strain gauge in this embodiment. [Figure 4] FIG. 10 is a diagram showing the strain generated when the bolt of this embodiment is subjected to an axial force of 4000 N. [Figure 5]FIG. 4 is a diagram showing strain distribution in the nut of the present embodiment. [Figure 6] FIG. 1 is a diagram illustrating the configuration of a wind turbine according to an embodiment of the present invention. [Figure 7] FIG. 2 is an enlarged view of a blade mounting portion of the wind turbine according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The inventors conducted extensive research to solve the problem and found that there is a correlation between the axial force of the bolt and the strain on the side of the nut. In particular, this is the strain on the side of the nut near the nut fixing surface. In other words, by understanding the axial force of the bolt, it is possible to understand the condition of the fastening part, and preventive maintenance of the fastening part becomes possible. Below, the estimation of the axial force of the bolt is specifically explained in the examples. However, the present invention is not limited to the embodiments discussed here, and appropriate combinations and improvements are possible within the scope that does not change the gist of the present invention. [Example]

[0013] FIG. 1 shows an overall view of a method for measuring bolt strain using a nut according to this embodiment. In this example, a bolt 1 and a nut 2 are fastened to a fixed region 3, and a load is applied downward in the drawing. When a load is applied to the bolt, a high strain region 4 and a low strain region 5 occur in the nut 2. The high strain region 4 is near the fixed surface side, and the low strain region 5 is near the opposite side of the fixed surface. Two first impressions, or indentations 6, are provided on the surface of the nut 2 in the high strain region 4 near the fixed surface side. Furthermore, two second impressions, or indentations 7, are provided on the surface of the nut 2 in the low strain region 5 near the opposite side of the fixed surface.

[0014] In this embodiment, the distance between each of the indentations 6 and 7 is measured. Here, a laser or a camera serving as an imaging means can be used as a means for measuring the distance A between two indentations 6 and the distance B between two indentations 7. Measuring devices such as lasers are complex and difficult to use for measurements at high altitudes such as wind turbines, but it is desirable to take images using a camera or other imaging means and measure the distance between each of the two indentations 6 and two indentations 7. In other words, by taking images using a camera or other imaging means and measuring the distance, measurements can be easily made even at high altitudes.

[0015] Next, we will explain how to estimate the bolt axial force before and after nut tightening. First, before tightening the nut 2, the distance A0 between the two indentations 6 and the distance B0 between the two indentations 7 are simultaneously photographed with a camera, and the distance is calculated using software or other tools. Then, the nut 2 is tightened and fastened to the fixed area 3. At this time, a load is applied to the bolt 1, generating an axial force. Next, the distance A1 between the two indentations 6 and the distance B1 between the two indentations 7 are simultaneously photographed with a camera, and the distance is calculated using software or other tools, just as before tightening the nut. Here, the images are taken simultaneously with the camera, but they can be taken almost simultaneously. Furthermore, the higher the accuracy of the photographing position and direction, the higher the measurement accuracy. By comparing the distance A0 with the distance A1, and the distance B0 with the distance B1, the axial force of the bolt 1 after tightening can be estimated based on these measurement results. However, it is desirable to separately obtain a construction curve of the load on the bolt 1 versus the distances A and B in advance.

[0016] We will also explain an example of preventive maintenance of fastening parts of equipment, etc., in which a check is made to see if there are any problems with the fastening parts several years after installation. During preventive maintenance, the distance A1 between two indentations 6 and the distance B1 between two indentations 7 are simultaneously photographed with a camera, and the distance is determined using software, etc. By comparing the distance A1 between two indentations 6, which is within the high strain region 4, with the distance B1 between two indentations 7, which is within the low strain region 5, the axial force of the bolt 1 can be estimated and the degree of strain can be determined. Comparisons within this region will be discussed later in the explanation of Figure 4.

[0017] Next, we will explain the correlation between the bolt axial force and the strain on the side of the nut. Figure 2 shows the strain gauge installation positions in this example. Multiple strain gauges were attached to the surface of the side of the nut 2 to obtain the relationship between the bolt axial force and strain. As shown in Figure 2, the attachment positions are A, B, C, D, E, and F, in order from the fixed area 3 side.

[0018] Figure 3 is a diagram showing the axial force of the bolt of this example and the strain generated by the strain gauge. The horizontal axis is the load equivalent to the axial force, and the vertical axis is the generated strain. A load of up to 4000 N was applied, and the strain was measured at A, B, C, D, E, and F. As can be seen from the diagram, there is a correlation between the load equivalent to the axial force and the strain at A, B, C, D, E, and F. It can be seen that A and B, which are close to the fixed area 3, have large generated strain, while E and F, which are far from the fixed area 3 and are on the opposite fixed surface side, have small generated strain.

[0019] Figure 4 is a diagram showing the strain generated when an axial force of 4000 N is applied to the bolt 1 of this example. A load of 4000 N was applied to the bolt 1, and strain values ​​were measured at positions A, B, C, D, E, and F. The horizontal axis represents the ratio of the strain gauge position to the thickness of the nut 2 in the thickness direction from the fixing region 3. A is the 10% position, B is the 50% position, C is the 60% position, D is the 65% position, E is the 70% position, and F is the 80% position. Note that the position of the fixing surface, which is the contact surface of the fixing region 3 with the nut 2, represents a ratio of 0%, and the thickness direction end of the nut 2 opposite the fixing region 3 represents a ratio of 100%.

[0020] As shown in Figure 4, A and B, high strain occurs at approximately the same value up to a ratio of the strain gauge position to the thickness of the nut 2 of approximately 50%. However, once the ratio exceeds 50%, the generated strain decreases. At strain gauge position E, where the ratio is 70%, the generated strain decreases to approximately 10% of the strain at A and B. At strain gauge position F, where the ratio is 80%, the generated strain decreases to approximately 50% of the strain at A and B. In other words, the region where the ratio of the strain gauge position to the thickness of the nut 2 is 50% or less is designated as high strain region 4, and the region where the ratio of the strain gauge position to the thickness of the nut 2 is 70% or more is designated as low strain region 5. By making indentations 6 and 7 in these two regions and measuring and comparing the spacing between the indentations, the axial force of the bolt 1 can be estimated. In this example, the difference between the indentations is used to estimate the axial force of the bolt.

[0021] Furthermore, the spacing between indentations 6 and the spacing between indentations 7 before the nut 2 is tightened can be evaluated by pointing the camera perpendicular to the indentation surface. After the nut 2 is attached, it is difficult to always keep the camera perpendicular to the indentation surface due to the equipment that holds the fastening part. Furthermore, if measurements cannot be taken under the same perpendicular conditions, the measurement accuracy of the spacing between indentations 6 and the spacing between indentations 7 will decrease. By assuming that the strain of indentations 7 in the low strain region 5 remains almost unchanged, the spacing between indentations 6 and the spacing between indentations 7 can be measured from an angle with a camera, and by comparing the spacing between indentations 6 and the spacing between indentations 7, it is possible to detect a decrease in the axial force of the bolt 1 with a certain degree of accuracy. This can be applied to preventive maintenance of the aforementioned wind turbines, etc. Figure 5 shows the strain distribution of the nut of this embodiment, and explains the reason for the strain distribution on the side of the nut. When the nut 2 is turned for tightening, a force is generated in the area where the nut 2 and bolt 1 contact, in the force direction 10, which is downward in the drawing. This force generates strain in the nut 2, resulting in high strain. On the other hand, the corners of the nut are not affected by this force and form a strain relief area 9, so the generated strain in these areas is small.

[0022] It should be noted that higher accuracy can be maintained if the spacing between indentations 6 and 7 is the same. Indentations may be made using a Vickers testing machine or the like. It is also desirable to make indentations 6 and 7 using a jig with two protrusions so that the spacing is the same.

[0023] Furthermore, high strain occurs when the ratio of the strain gauge position to the thickness of the nut 2 is up to about 50%, so it is preferable to make indentation 6 in this region. When the ratio of the strain gauge position to the thickness of the nut is 70% or more, low strain occurs, so it is preferable to make indentation 7 in this region. Furthermore, to improve accuracy, it is preferable to make indentation 7 when the ratio of the strain gauge position to the thickness of the nut is 80% or more. It is preferable to make indentations 6 and 7 arc-shaped, as this allows the center to be measured with high accuracy.

[0024] In this embodiment, the indentations 6 and 7 are made on one side of the nut, but it goes without saying that they may be made on multiple sides. Also, it is possible to add, delete, or replace part of the configuration of this embodiment without departing from the spirit of the present invention. [Example]

[0025] Next, an embodiment will be described in which the present invention is applied to the blade mounting portion of a wind turbine as preventive maintenance for a wind power generating wind turbine 11. Fig. 6 shows a configuration diagram of the wind turbine of this embodiment, and Fig. 7 shows an enlarged view of the blade mounting portion of the wind turbine of this embodiment.

[0026] The wind turbine 11 shown in Fig. 6 mainly comprises blades 14, which are wings that rotate when exposed to wind, a tower 12 that supports the wind turbine 11, a nacelle 13, a hub 15, a rotor 16, and a pitch slewing bearing 17. As shown in Fig. 7, each blade 14 is connected to the hub 15 via the pitch slewing bearing 17. This connection is fastened with bolts and nuts. When the present invention is applied to the fastening evaluation of the nuts and fastening parts during preventive maintenance of the wind turbine 11, This makes it possible to easily evaluate the tightening of fastening parts, and makes it possible to easily perform preventive maintenance of fastening parts, especially at high altitudes, without requiring complex equipment. [Explanation of symbols]

[0027] 1 volt 2 Nut 3...Fixed area 4. High strain region 5. Low strain region 6. Indentation 7. Indentation 8. Strain gauge 9. Strain relief region 10...Force direction 11...windmill 12 Tower 13. Nacelle 14 blades 15 Hub 16 Rotor 17 Pitch slewing bearing

Claims

1. A method for estimating bolt axial force when fastening a fixed member with a nut and a bolt, measuring the distance between first two markings on a side surface of the nut near the fixing surface side and the distance between second two markings on a side surface of the nut near the opposite side to the fixing surface; and estimating the axial force of the bolt by comparing the distance between the first two marks with the distance between the second two marks.

2. 2. The bolt axial tension estimation method according to claim 1, A method for estimating bolt axial force, comprising: measuring the distance between the first two marks and the distance between the second two marks by capturing images of the distance between the first two marks and the distance between the second two marks using an imaging device.

3. 2. The bolt axial tension estimation method according to claim 1, A method for estimating a bolt axial force, comprising: estimating the axial force of the bolt by comparing the distance between the first two markings and the distance between the second two markings before and after tightening the nut.

4. 2. The bolt axial tension estimation method according to claim 1, A method for estimating a bolt axial force, characterized in that the axial force of a bolt is estimated using a nut in which the first two markings are located within 50% of the thickness of the nut from the fixing surface in the thickness direction of the nut.

5. 2. The bolt axial tension estimation method according to claim 1, A method for estimating a bolt axial force, characterized in that the axial force of a bolt is estimated using a nut in which the second two markings are located at a thickness of 70% or more in the thickness direction of the nut from the fixing surface.

6. 2. The bolt axial tension estimation method according to claim 1, A method for estimating a bolt axial force, characterized in that the axial force of a bolt is estimated using a nut in which the second two markings are located at a thickness of 80% or more from the fixing surface in the thickness direction of the nut.

7. 2. The bolt axial tension estimation method according to claim 1, A method for estimating a bolt axial force, wherein the first two markings and the second two markings are spaced approximately the same apart before the nut is tightened, and the nut is used to estimate the axial force of the bolt.

8. A preventive maintenance method for a wind turbine, characterized in that the bolt axial force estimation method according to claim 1 is used for fastening parts of blades, which are wings that rotate when exposed to wind in a wind turbine, and the axial force of the bolts at the fastening parts is estimated.

9. A nut used to fasten a bolt to a fixed surface. A nut characterized in that it has two first markings provided on a side surface of the nut near the fixed surface side and two second markings provided on a side surface of the nut near the opposite side to the fixed surface for estimating the axial force of the bolt.

10. The nut according to claim 9, The nut is characterized in that the first two markings are located within 50% of the thickness of the nut from the fixing surface in the thickness direction of the nut.

11. The nut according to claim 9, The nut is characterized in that the second two markings are located at a thickness of 70% or more from the fixing surface in the nut thickness direction.

12. The nut according to claim 9, The nut is characterized in that the second two markings are present over a thickness of 80% or more in the nut thickness direction from the fixing surface.

13. The nut according to claim 9, A nut characterized in that the spacing between the first two markings and the spacing between the second two markings are approximately equal.

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