JP4043909B2 - Centerhole load cell for civil engineering using optical fiber Bragg grating - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a center hole type load cell for civil engineering using an optical fiber Bragg diffraction grating [FBG (Fiber Bragg Grating)] for monitoring the tension of earth anchors and lock anchors that are frequently used in the field of civil engineering.
[0002]
[Prior art]
As a civil engineering center hole type load cell for monitoring the tension of earth anchors and lock anchors frequently used in the field of civil engineering, for example, Japanese Patent Application Laid-Open No. 2002-82001 comprises an upper and lower pressure receiving part and a stress cylindrical part. A cylindrical dynamometer of the type in which an electric strain gauge is bonded to the outer surface of the central portion of the cylindrical portion and is placed between upper and lower pressure plates to pressurize is described.
[0003]
However, since this cylindrical type force gauge uses an electric strain gauge, the insulation property tends to be lowered due to, for example, moisture and humidity, the lightning resistance is low, and the environment resistance is easily affected by noise caused by an electromagnetic field. There are difficulties. Further, since it is necessary to increase the number of scanners and cables in order to perform multipoint load measurement, the cost per measurement point increases. Further, since a weak distortion detection signal is handled, there is a difficulty in transmission of the distortion detection signal. For these reasons, the cylindrical force meter is not suitable for the civil engineering field.
[0004]
In order to solve such a problem of the electric strain gauge, one using an optical fiber has been proposed. This is because a detection element is an FBG in which the refractive index of the core portion of the single mode optical fiber for communication is periodically changed in the fiber axis direction, and a specific number corresponding to the refractive index period of the incident light to the FBG is used. This utilizes the phenomenon that only the wavelength (Bragg wavelength) is selectively reflected. That is, when distortion occurs in the FBG, the period of the diffraction grating changes, and therefore the wavelength of the reflected light shifts. Therefore, the load applied from the shift amount of this wavelength is measured.
[0005]
Here, when the FBG is used, since the Bragg wavelength described above has a property of changing depending on the temperature, the level of strain to be detected (for example, several hundred microstrain) changes in the surrounding temperature (for example, −20 ° C. to 70 °). There is a need for a method (temperature compensation) that is comparable to the strain level of the fiber itself based on C) and that excludes the effects of temperature changes.
[0006]
For example, Japanese Patent Laid-Open No. 11-83646 discloses an optical fiber type load cell in which FBG is bonded across two regions in an elastic body having two regions having the same temperature characteristics and different elastic moduli. Are listed. According to this, since reflected light having two wavelength components can be obtained, by measuring the difference between these wavelengths, it is possible to cancel the wavelength deviation due to the temperature change and to compensate the temperature of the distortion.
[0007]
[Problems to be solved by the invention]
In general, as a load meter for monitoring the tension of earth anchors and lock anchors frequently used in the civil engineering field, a load meter formed in a hollow cylindrical shape, that is, the earth anchor or lock anchor is passed through the hollow portion, and the outer circumference A center hole type load cell for civil engineering that can accurately measure the load by uniformly distorting the wall portion is desirable. However, the above-described conventional optical fiber load cell is formed in a solid cylindrical shape or a solid prismatic shape having a step or taper on the outer wall portion, as is apparent from the drawings of the above publication. For this reason, an earth anchor or a lock anchor cannot be set at the center, and the processing accuracy tends to be lower than that of the hollow cylindrical shape, so that it is difficult to obtain a uniform strain and the load measurement accuracy is lowered. There is a case. Therefore, this optical fiber type load cell is not suitable as a load cell for monitoring the tension of the earth anchor or the lock anchor.
[0008]
The present invention has been made for the above-mentioned circumstances, and an object of the present invention is for civil engineering using an FBG that is optimal as a load meter for monitoring the tension of earth anchors and lock anchors that are frequently used in the civil engineering field. It is to provide a center hall type load cell.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the civil engineering center hole type load cell using FBG according to claim 1 of the present invention has a hollow cylindrical portion in which ring-shaped flange portions are formed at both ends, and the axial direction. A strain generating portion that generates a strain due to a load applied to the FBG, a strain detecting FBG that is attached to a groove for protecting the FBG formed on the outer peripheral surface of the cylindrical portion, and an outer peripheral surface of the cylindrical portion And an FBG for temperature detection stuck on a non-strained plate disposed away from the plate. As a result, the processing accuracy of the outer peripheral wall can be easily increased, and the earth anchor or lock anchor can be set through the hollow portion, so that uniform and temperature compensated strain can be detected and high accuracy can be obtained. Load can be measured.
[0010]
Furthermore, in the invention according to claim 1 , a cylindrical cover that is spanned between the flange portions so as to cover the cylindrical portion, and a heat insulating material that is filled between the cylindrical portion and the cover; A partition plate that partitions the protective groove and the heat insulating material is provided. As a result, since the periphery of the strain detection FBG and the periphery of the temperature detection FBG are covered with the same heat insulating material, nonuniformity between the ambient temperature of the strain detection FBG and the ambient temperature of the temperature detection FBG is alleviated. The temperature characteristics can be improved. Further, since the partition plate prevents the heat insulating material from coming into direct contact with the strain detection FBG, it is possible to prevent the characteristics of the strain detection FBG from being deteriorated or the strain detection FBG from being damaged.
[0011]
According to a second aspect of the present invention, in the civil engineering centerhole type load cell using the FBG according to the first aspect, at least three of the strain detection FBGs are equally arranged in the outer circumferential direction of the cylindrical portion. It is characterized by. As a result, even if the applied load becomes a single contact in the circumferential direction of the cylindrical portion, the averaged strain can be detected.
[0012]
According to a third aspect of the present invention, in the center hole type load cell for civil engineering using the FBG according to any one of the first or second aspect , the temperature detecting FBG is on the cylindrical portion side of the unstrained plate. It is characterized by being attached to the surface of As a result, the heat-insulating material is prevented from directly contacting the temperature detection FBG by the unstrained plate, so that it is possible to prevent the temperature detection FBG from deteriorating or the temperature detection FBG from being damaged. it can.
[0013]
In the invention according to claim 4 , in the center hole type load cell for civil engineering using the FBG according to any one of claims 1 to 3 , the strain detection FBG and the temperature detection FBG are one. It is characterized by being connected by an optical fiber. This eliminates the need to increase the number of scanners, cables, and the like when performing multipoint load measurement, thereby reducing the cost per measurement point.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. Here, in the accompanying drawings, the same reference numerals are given to the same members, and duplicate descriptions are omitted. The embodiment of the invention is a particularly useful embodiment in which the present invention is implemented, and the present invention is not limited to the embodiment.
[0015]
1A and 1B are a plan view showing a center hole type load cell for civil engineering using an FBG according to an embodiment of the present invention, and a cross-sectional view taken along Ad-A0 and A2-A0. The civil engineering center hole type load cell 100 includes a strain generating section 110 that generates strain due to a load applied in the axial direction, three strain detecting FBGs 120 disposed on the outer periphery of the strain generating section 110, and one temperature detection. FBG130 is provided.
[0016]
The strain generating portion 110 has a hollow cylindrical portion 112 in which ring-shaped flange portions 111 are formed at both ends. As described above, since the strain generating portion 110 is formed in a hollow cylindrical shape, the processing accuracy of the outer peripheral wall portion can be easily increased, and an earth anchor or a lock anchor can be set through the hollow portion. Therefore, it is possible to detect a uniform strain and measure a highly accurate load.
[0017]
A groove 113 for accommodating and protecting the strain detection FBG 120 is formed on the outer peripheral surface of the cylindrical portion 112. The grooves 113 are formed in a rectangular parallelepiped shape extending in the axial direction at equal angular intervals of 120 ° in the outer peripheral direction of the cylindrical portion 112. Note that two or four or more grooves 113 may be formed as long as they are equiangularly spaced.
[0018]
As described above, since the plurality of strain detection FBGs 120 are evenly arranged on the outer peripheral surface of the cylindrical portion 112, the strain detected by each strain detection FBG 120 does not become uniform depending on the state of the contact surface of the flange portion 111. However, the strain applied to the total strain detection FBG 120 can be averaged, and the applied load can be measured with high accuracy from the strain measured by the calibration test performed in advance.
[0019]
Further, a non-strained dummy plate 140 for adhering the temperature detecting FBG 130 is separated from the outer peripheral surface by, for example, a screw or the like at a substantially intermediate position between the two grooves 113 on the outer peripheral surface of the cylindrical portion 112. Has been. The dummy plate 140 is a member that transmits only the temperature to the temperature detecting FBG 130 without transmitting the strain generated in the strain generating section 110. In this manner, since the temperature detecting FBG 130 is attached to the unstrained dummy plate 140, the apparent strain depending on the temperature can be compensated.
[0020]
Each strain detection FBG 120 is attached to the inner bottom surface of each groove 113 with an adhesive, for example, so as to extend in the axial direction. The temperature detecting FBG 130 is attached to the surface of the dummy plate 140 on the cylindrical portion 112 side, for example, with an adhesive. Each strain detection FBG 120 and temperature detection FBG 130 have different reflection center wavelengths. Each strain detection FBG 120 and temperature detection FBG 130 are connected by a single optical fiber 150 as shown in a development view of the outer peripheral surface of the strain generating section 110 in FIG.
[0021]
As described above, each strain detection FBG 120 and temperature detection FBG 130 having different reflection center wavelengths are connected by one optical fiber 150. Therefore, when performing multipoint load measurement, the following configuration is used. That's fine. That is, a plurality of civil engineering center-hole type load cells 100 are connected in a daisy chain and connected to an FBG strain measuring device and a computer, and when remote monitoring is performed, an optical channel selector, a modem, and the like corresponding to the number of measurement points are connected. Accordingly, there is no need to increase the number of scanners, cables, etc., so that the cost per measurement point can be kept low.
[0022]
Further, a rectangular partition plate 160 is attached with, for example, an adhesive so as to cover the opening of each groove 113 in which the strain detection FBG 120 is accommodated, and a cylindrical cover 170 covers the outer peripheral surface of the cylindrical portion 112. It is spanned between each flange part 111 so that it may cover, and is spot-welded. In addition to spot welding, it is possible to fix both by not only adhesion by an adhesive but also pressure welding such as gas pressure welding, as well as various fusion welding and brazing techniques. A heat insulating material 180 is filled between the cylindrical portion 112 and the cover 170.
[0023]
Here, it is important that the temperature of the strain detection FBG 120 and the temperature of the temperature detection FBG 130 are the same in order to compensate for the apparent strain depending on the temperature. For example, direct sunlight is applied to the civil engineering center hole load cell 100. In order to compensate for the non-uniform temperature distribution when hitting one side, in particular, the apparent distortion depending on the transient temperature non-uniformity, it is desirable to attach the temperature detection FBG 130 in the vicinity of each strain detection FBG 120. However, there is a problem that the cost becomes high.
[0024]
Thus, with the above-described configuration, the periphery of the strain detection FBG 120 and the periphery of the temperature detection FBG 130 are covered with the same heat insulating material 180, so the ambient temperature and temperature detection of the strain detection FBG 120 are detected. The nonuniformity of the ambient temperature of the FBG 130 can be alleviated, and the temperature characteristics thereof can be improved.
[0025]
Further, since the heat insulating material 180 is prevented from directly contacting the strain detection FBG 120 by the partition plate 160, it is possible to prevent the characteristics of the strain detection FBG 120 from being deteriorated or the strain detection FBG 120 from being damaged. it can. Further, since the dummy plate 140 prevents the heat insulating material 180 from coming into direct contact with the temperature detection FBG 130, it is possible to prevent the characteristics of the temperature detection FBG 130 from being deteriorated or the temperature detection FBG 130 from being damaged. it can.
[0026]
FIG. 3 is a cross-sectional view showing a case where the above-mentioned civil engineering center hole type load cell 100 is applied to tension monitoring of earth anchors and lock anchors that are frequently used in the civil engineering field. The lower anchor screw portion 11 of the anchor bolt 10 is screwed into the base portion 12, and the lower loading plate 13, the civil engineering center hole type load cell 100, and the upper loading plate 14 are inserted in this order into the anchor bolt 10. An anchor bolt fixing nut 16 is screwed into the upper anchor screw portion 15 and a load is applied. Thereby, for the reasons described above, it is possible to detect an accurate strain that is averaged and temperature-compensated, so that a highly accurate load monitoring system can be constructed.
[0027]
【The invention's effect】
As described above, according to the present invention, the processing accuracy of the outer peripheral wall portion can be easily increased, the earth anchor or the lock anchor can be set through the hollow portion, and the applied load can be increased. Since the averaged strain can be detected even if it comes to one side in the circumferential direction of the cylindrical portion, a highly accurate load can be measured. At this time, since the periphery of the strain detection FBG and the periphery of the temperature detection FBG are covered with the same heat insulating material, unevenness of the ambient temperature of the strain detection FBG and the ambient temperature of the temperature detection FBG is alleviated. The temperature characteristics can be improved.
[0028]
Further, since the heat insulating material is prevented from directly contacting the strain detection FBG and the temperature detection FBG by the partition plate and the non-strain plate, the characteristics of the strain detection FBG and the temperature detection FBG are deteriorated or the strain detection FBG is used. It is possible to prevent the FBG and the temperature detecting FBG from being damaged. In addition, when performing multipoint load measurement, it is not necessary to increase the number of scanners, cables, etc., so that the cost per measurement point can be kept low.
[Brief description of the drawings]
FIG. 1 is a plan view showing a center hole type load cell for civil engineering using FBG according to an embodiment of the present invention, and a view showing a cross section Ad-A0 and a cross section A2-A0.
2 is a development view of an outer peripheral surface of a strain generating portion of the civil engineering center hole type load cell. FIG.
3 is a cross-sectional view showing a case where the center hole load cell for civil engineering of FIG. 1 is applied to tension monitoring of earth anchors and lock anchors that are frequently used in the civil engineering field.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Anchor bolt 11 Lower anchor screw part 12 Base part 13 Lower loading board 14 Upper loading board 15 Upper anchor screw part 16 Anchor bolt fixing nut 100 Center hole type load cell 110 for civil engineering Strain part 111 Flange part 112 Cylindrical part 113 Groove 120 Strain FBG for detection
130 FBG for temperature detection
140 Dummy plate 150 Optical fiber 160 Partition plate 170 Cover 180 Heat insulating material

Claims (4)

It has a hollow cylindrical part with ring-shaped flanges formed at both ends,
A strain generating portion that generates strain due to a load applied in the axial direction;
A strain detection FBG attached in a protective groove of the FBG formed on the outer peripheral surface of the cylindrical portion;
FBG for temperature detection stuck on a non-strained plate disposed away from the outer peripheral surface of the cylindrical portion,
Furthermore, a cylindrical cover spanned between the flange portions so as to cover the cylindrical portion,
A heat insulating material filled between the cylindrical portion and the cover;
A civil engineering centerhole type load cell comprising a partition plate for partitioning the protective groove and the heat insulating material . In the centerhole type load cell for civil engineering using the FBG according to claim 1 ,
The center hole type load cell for civil engineering, wherein at least three of the strain detection FBGs are evenly arranged in the outer circumferential direction of the cylindrical portion. In the center hall type load cell for civil engineering using the FBG according to any one of claims 1 and 2 ,
The center hole type load cell for civil engineering, wherein the temperature detecting FBG is attached to a surface of the unstrained plate on the cylindrical portion side. In the center hall type load cell for civil engineering using the FBG according to any one of claims 1 to 3 ,
The strain detection FBG and the temperature detection FBG are connected by a single optical fiber.

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