JP2004257933A - Optical fiber type displacement gauge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber type displacement gauge hardly affected by external factors such as weather and high-voltage electrical power lines, having high durability and capable being monitored from a remote place. <P>SOLUTION: This optical fiber type displacement gauge comprises a plate member receiving the displacement in accordance with the displacement of a measured object and having a rack at least on a part of it, a gear engaged with the rack, a displacement converting part for converting the rotation in accompany with the displacement of the plate member, of the gear into the displacement in the rotating axis direction, of the rotation, an elastic member having the cylindrical shape rotationally symmetric to the rotating axis of the gear, an elastic member elastically deformed in the direction approximately perpendicular to the moving direction in accordance with the movement in the rotating axis direction, of the gear on the basis of the conversion by a displacement converting part, and an optical fiber approximately orthogonal to the displacement direction of the elastic member, and wound around the elastic member. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber type displacement meter which is suitable for, for example, installing on a large civil engineering structure such as a bridge girder of a bridge and monitoring a state change, particularly a displacement, of the civil engineering structure due to seismic motion or the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, state changes of large civil engineering structures are monitored by patrol inspections by security personnel, electric displacement meters (for example, see Non-Patent Documents 1 to 3) and the like.
[0003]
[Non-patent document 1]
"Measurement equipment for civil engineering and construction, displacement meter", [online], Kyowa Dengyo Co., Ltd., [searched on February 25, 2003], Internet <URL: http: // www. kyowa-ei. co. jp / japanese / product / index_2002-10. htm>
[0004]
[Non-patent document 2]
"Displacement meter", [online], Tokyo Sokki Laboratory, [searched on February 25, 2003], Internet <URL: http: // www. tokyosoki. co. jp / product / transducer / displacement. html>
[0005]
[Non-Patent Document 3]
"Multi Displacement Meter", [online], Kowa Co., Ltd., [searched on February 25, 2003], Internet <URL: http: // www. kowa-net. co. jp / product / multi / multi. htm>
[0006]
[Problems to be solved by the invention]
Among the above-mentioned prior arts, the patrol inspection by security personnel lacks responsiveness and has a problem in safety.
[0007]
In addition, although the electric displacement meter has high accuracy, it has a problem in that it is affected by lightning damage and the like, and requires durability and frequent maintenance.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an optical fiber displacement meter which is hardly affected by external factors such as weather and high-voltage wires, has excellent durability, and can be monitored remotely. Is to provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is an optical fiber type displacement meter for detecting a displacement of a measurement target, which receives a displacement following the displacement of the measurement target, and at least a part of which receives a rack. Provided, a gear that meshes with the rack, a displacement conversion unit that converts rotation of the gear due to the displacement of the plate member into a displacement of the rotation in the rotation axis direction, An elastic member having a cylindrical shape that is rotationally symmetric with respect to the rotation axis, and elastically deforming in a direction substantially orthogonal to the moving direction in accordance with the movement of the gear in the rotation axis direction based on the conversion by the displacement conversion unit; An optical fiber wound substantially around the elastic member and substantially orthogonal to the deformation direction of the elastic member.
[0010]
According to the first aspect of the present invention, since the optical fiber is used as a sensor and a transmission line, it can be monitored from a remote place. Further, since no electrical parts are used for the optical fiber type displacement meter, there is no need to be affected by induction such as lightning and high-voltage electric wires.
[0011]
According to a second aspect of the present invention, in the first aspect of the present invention, in the displacement conversion section, the rotation shaft surface of the gear is processed into a spiral shape, and the gear is processed into a spiral shape similarly to the rotation shaft surface. The gist is that it is screwed to the center of the.
[0012]
According to a third aspect of the present invention, in the first or second aspect, the elastic member is disposed between the gear and a substantially hollow disk-shaped member fixed to a rotation shaft of the gear. Make a summary.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0014]
FIG. 1 is an explanatory diagram showing a schematic configuration of an optical fiber displacement meter according to one embodiment of the present invention. The optical fiber type displacement meter 1 shown in FIG. 1 detects displacement of an object to be measured by using a tensile strain caused by a tensile load applied to the optical fiber 11. FIG. 2 is a view in the direction of arrow A in FIG. The measurement targets of the optical fiber type displacement meter 1 are, for example, displacements caused by earthquakes and secular changes of large civil engineering structures such as tunnels, bridges, dams, buildings, river embankments, port facilities, and the like. And the collapse of snow and ice on the slopes of mountainous areas, but it is needless to say that the present invention is not necessarily limited thereto.
[0015]
The optical fiber type displacement meter 1 shown in FIGS. 1 and 2 has a plate-like member 12 which moves following the displacement of a measurement object on which the optical fiber-type displacement meter 1 is installed, and a movement of the plate-like member 12. And a plurality of rollers 16 fixedly arranged with respect to the measurement object. A rack 13 is provided on at least a part of the upper surface of FIG. 1 of the plate-like member 12. A shaft 15, which is a rotation shaft of a gear 14 meshing with the rack 13, has a helical surface. The screw 14 is screwed to the center of a gear 14 formed into a spiral shape in the same manner as the surface of the shaft 15, so that the gear 14 rotates with the shaft 15 as a rotation axis in the axial direction of the shaft 15. (Vertical direction in FIG. 2). That is, the shaft 15 is processed so as to convert the displacement of the plate-shaped member 12 accompanying the displacement of the measurement target into the displacement of the gear 14 in the axial direction (the upward direction in FIG. 2). In this sense, the gear 14 and the shaft 15 each have a structure corresponding to a nut and a bolt, and both of them rotate the gear 14 in the direction of the shaft 15 in accordance with the displacement of the plate member 12 as a whole. A displacement conversion unit for converting the displacement into a displacement.
[0016]
A deformed portion 17 having a substantially hollow cylindrical shape formed of an elastic member having a wide elastic range such as rubber and having a large Poisson's ratio is fixed to the gear 14, which shares a shaft 15 with the gear. At the end of the deformed portion 17 different from the gear 14 side, a disk portion 18 made of a substantially hollow disk-shaped member coaxially mounted is fixedly attached to the shaft 15. Has an optical fiber 11 wound therearound.
[0017]
Next, the operation of the optical fiber displacement meter 1 of the present embodiment will be described with reference to the explanatory diagram of FIG. In the figure, for comparison, the state of the optical fiber type displacement meter 1 before and after the displacement of the measurement target is generated (FIG. 3A) and after the displacement is generated (FIG. 3B) are also shown above and below.
[0018]
In the state (initial state) before the occurrence of displacement shown in FIG. 3A, the strain (strain) distribution of the optical fiber 11 has a value corresponding to the initial tension in the portion wound around the deformed portion 17.
[0019]
Next, when the measurement target is displaced rightward in FIG. 3, the plate-like member 12 is displaced rightward with the displacement, and the gear 14 is rotated by the movement of the rack 13. Incidentally, the rotation direction of the gear 14 at this time is a counterclockwise direction in FIG. The gear 14 moves upward along the axis 15 in FIG. 2 by rotation. On the other hand, the disk portion 18 is fixed to the shaft 15 as described above, and the deformed portion 17 is formed of the above-described elastic member, so that the deformed portion is deformed according to the displacement of the gear 14 toward the disk portion 18. The portion 17 is pressed in the axial direction of the shaft 15 and elastically deforms in a barrel shape in a direction away from the shaft 15 (outward from the shaft 15) in a direction substantially perpendicular to the moving direction of the gear 14. Due to this elastic deformation, a tensile load is applied to the optical fiber 11 wound around the deformed portion 17, and tensile strain is generated.
[0020]
As described above, according to the present embodiment, when a position change (displacement) occurs in the measurement target portion and thus in the plate member 12, the amount of the displacement can be detected by the tensile strain generated in the optical fiber 11. Therefore, after the optical fiber type displacement meter 1 of the present embodiment is installed at the measurement target site, a strain distribution measuring device for measuring the strain distribution of the optical fiber 11 is connected to the optical fiber type displacement meter 1, and the initial position before the displacement is measured. From the difference from the state, the displacement amount of the measurement target part can be detected and converted.
[0021]
That is, according to the present embodiment, the physical quantity based on the position change (displacement) of the measurement target portion can be measured according to the tensile strain of the optical fiber 11 based on the position change, rather than electrically. For example, it is less susceptible to weather changes such as lightning and external factors such as high-voltage wires, so that measurement accuracy can be improved, durability can be improved, and malfunction can be prevented.
[0022]
Further, according to the present embodiment, it is possible to measure a physical quantity based on a change in load on a measurement target portion without using an electrical component, and thus it is possible to reduce the cost of the optical fiber displacement meter 1 itself. .
[0023]
As a result, it is possible to reduce the cost (initial installation cost) when the optical fiber displacement meter 1 is first installed for detecting a change in the load of the measurement target site and the maintenance cost involved in maintenance such as replacement. .
[0024]
Note that the rack 13 may be provided on at least a part of the plate member 12, and the length of the rack 13, the diameter of the gear 14, and the number of teeth are determined according to the allowable displacement of the structure to be monitored. It goes without saying that it is decided. Further, it is a matter of course that the displacement of the object to be measured is measured by providing at least a plurality of sets of (the rack 13, the gear 14, the shaft 15, the deformed portion 17, and the disk portion 18) on the plate member 12. It is possible.
[0025]
FIG. 4 is an explanatory diagram illustrating a schematic configuration of a displacement measurement system that measures displacement of a measurement target using a plurality of optical fiber displacement meters 1 of the present embodiment. The displacement measurement system 100 shown in FIG. 1 detects a tensile strain generated in the optical fiber 11 by using a plurality of optical fiber displacement meters 1. In the following description, a plurality of optical fiber displacement meters are represented as 1-1, 1-2,..., 1-n (n is a positive integer of 2 or more).
[0026]
Each of the optical fiber displacement meters 1-1, 1-2,..., 1-n shown in FIG. 4 is connected in series via the same optical fiber 11, and each of them is, for example, a measurement target site. It is installed in. A more specific example will be described later with reference to FIG. The other components of the optical fiber type displacement meters 1-1, 1-2,..., 1-n are the same as those of the optical fiber type displacement meter 1 described with reference to FIG. The description is omitted.
[0027]
Also, the plurality of optical fiber type displacement meters 1-1,..., 1-n connected in series via the same optical fiber 11 are pulled out from the optical fiber type displacement meter 1-1 on one end side. The optical fiber 11 is connected to a strain distribution measuring device 20 that measures a strain distribution of the optical fiber 11, converts the strain distribution into electrical strain data, and outputs the data. The distortion distribution measuring device 20 is communicably connected to a computer 30 which is an electronic computer such as a personal computer via a communication network such as a LAN, a public line, and a dedicated line. The calculator 30 receives the strain data output from the strain distribution measuring device 20, calculates a load change amount and a change position of the measurement target based on the received strain data, and sets a predetermined threshold based on the calculation result. The presence or absence of the corresponding position change is determined, and an alarm or the like is issued.
[0028]
Here, a schematic configuration of the strain distribution measuring device 20 will be described with reference to FIG. A strain distribution measuring device 20 shown in FIG. 4 is a Brillouin optical-fiber time domain reflectometer (BOTDR) using Brillouin backscattered light capable of continuously measuring a strain distribution along the optical fiber 11. ).
[0029]
That is, the strain distribution measuring device 20 includes a light source 21 that outputs the signal light S1 such as a laser beam and the reference light S2, and an optical frequency of the signal light S1 output from the light source 21 raised to, for example, about 10 GHz. An optical frequency converter 22 for conversion; an optical pulse modulator 23 for pulse-modulating the signal light S1 frequency-converted by the optical frequency converter 22 to generate and output an optical pulse P1; A beam splitter that outputs the optical pulse P1 output from the optical fiber 11 to the optical fiber 11, splits the backscattered light B1 due to Brillouin scattering returning to itself, and outputs the split light to a coherent optical receiver 25 described later. 24.
[0030]
Further, the strain distribution measuring device 20 receives the backscattered light B1 returning from the plurality of optical fiber displacement meters 1-1, 1-2,..., 1-n via the beam splitter 24, By comparing the received backscattered light B1 with the reference light S2, the strain distribution in the entire optical fiber 11, that is, the plurality of optical fiber displacement meters 1-1,..., 1-n is measured. And a coherent optical receiver 25 that converts the measured strain distribution into electrical strain data and outputs the converted data to the computer 30.
[0031]
Next, the operation of the entire displacement measurement system 100 will be described.
[0032]
An optical pulse P1 is sent from the strain distribution measuring device 20 to the optical fiber type displacement meters 1-1, 1-2,..., 1-n.
[0033]
At this time, at least one optical fiber displacement meter 1-j (1 ≦ j ≦ n; j is an integer) among the plurality of optical fiber displacement meters 1-1, 1-2,..., 1-n. When the displacement occurs in the measurement target portion where the is installed, the deformed portion 17-j of the optical fiber type displacement meter 1-j causes the gear 14-j to move the rack 13 in accordance with the displacement amount of the plate member 12-j. -J, and is pressed between the gear 14-j and the disk portion 18-j fixed to the shaft 15-j, thereby being substantially orthogonal to the axial direction of the shaft 15-j. In the barrel direction (radial direction) (see FIG. 2). Due to this elastic deformation, a tensile load is applied to a portion (hereinafter, this portion is referred to as a fiber portion) of the optical fiber 11 wound around the annular side surface of the deformed portion 17-j in the optical fiber displacement meter 1-j. Applied, which results in tensile strain at the fiber site. Here, "-j" is added to all the reference numerals of the components of the optical fiber type displacement meter 1-j.
[0034]
At this time, the optical pulse P1 incident on the optical fiber 11 generates backscattered light B1 (return light; frequency of about 10 GHz is reduced) based on Brillouin scattering while propagating in the optical fiber 11.
[0035]
In particular, since tensile strain occurs in at least one or more fiber portions of the optical fiber 11, a frequency shift occurs in the backscattered light from the fiber portion due to the tensile strain.
[0036]
The backscattered light B1 generated in this manner propagates through the optical fiber 11 toward the optical pulse incident side, that is, toward the strain distribution measuring device 20, and branches via the beam splitter 24 to the coherent optical receiver 25. Incident.
[0037]
In the coherent light receiver 25, for example, optical heterodyne detection is performed between the incident backscattered light B1 and the reference light S2, and a distribution (frequency distribution) representing a frequency difference between the backscattered light B1 and the reference light S2 is obtained. , That is, strain data representing the distribution (strain distribution) of the frequency difference corresponding to the frequency shift portion caused by the tensile strain.
[0038]
The generated distortion data is transmitted to the computer 30. The computer 30 performs an analysis process based on the strain data, and calculates a load change amount and a position change (displacement) of the measurement target portion.
[0039]
Also, based on the calculated load change amount and position change of the measurement target portion, it is determined whether or not a load change has occurred according to a preset threshold value (for example, representing a maximum allowable load displacement level of the measurement target). As a result, when it is determined that a load change exceeding the threshold value has occurred, the calculator 30 outputs an alarm.
[0040]
As described above, even when the displacement measurement system 100 is configured using a plurality of optical fiber displacement meters 1 shown in FIG. 1, for example, weather changes such as lightning, external factors such as high-voltage wires, etc. , Greatly improve the measurement accuracy, and further reduce the cost of the entire displacement measurement system 100 based on the cost reduction of each of the optical fiber displacement meters 1-1,..., 1-n. And the initial installation cost and the maintenance cost can be reduced.
[0041]
Such a displacement measurement system 100 is particularly suitable for measuring a large measurement target at a plurality of locations. That is, the optical fiber displacement gauges 1-1,..., 1-n provided at the respective measurement sites and one strain distribution measuring device 20 are wired in series using one optical fiber 11. Since it is not necessary to individually wire each of the optical fiber displacement meters 1-1,..., 1-n, the entire displacement measurement system 100 can be simplified.
[0042]
Further, no power supply is required for each of the optical fiber displacement meters 1-1,..., 1-n, so that the cost for the power supply is reduced, and maintenance such as power supply replacement is also unnecessary.
[0043]
As described above, since the optical fiber type displacement gauges 1-1,..., 1-n and the strain distribution measuring instrument 20 can be wired with only the optical fiber 11, only the strain distribution measuring instrument 20 can be used. Is remotely arranged with respect to the optical fiber displacement gauges 1-1,..., 1-n, and a change in the load of the measurement target portion can be integrally monitored on the remote side.
[0044]
The displacement measurement system 100 according to the present embodiment is installed, for example, at a connection portion of a bridge girder in a bridge, and can be applied to a case where movement of the bridge girder is detected. FIG. 5 is a side view when the optical fiber type displacement meter according to the present embodiment is attached to a connecting portion of a bridge girder. The two bridge girders 41 and 42 shown in the figure are connected with a pier 51 as a pedestal, and both bridge girders 41 and 42 are provided with a fall prevention device 61 connected thereto.
[0045]
For convenience, the reference numeral 1-j (1 ≦ j ≦ n; j is an integer) is given to the optical fiber type displacement meter installed on the side surface of the connecting portion, and the reference number of each part of the optical fiber type displacement meter 1-j. "-J" is additionally described. The right end of the plate member 12-j is fixedly attached to the bridge girder 42, and the rotating shaft of each roller 16 is also attached to the bridge girder 41 or 42. A shaft 15-j is also attached to the bridge girder 41. Accordingly, the plate member 12-j is also displaced rightward as the bridge girder 42 is displaced rightward in FIG. As a result, the deformed portion 17-j undergoes elastic deformation, and the optical fiber 11 wound around the deformed portion 17-j undergoes a tensile strain, whereby the displacement of the bridge girder 42 can be detected. I can do it.
[0046]
In the case shown in the figure, the displacement in the left direction cannot be handled, but this can be detected, for example, by providing a similar optical fiber type displacement meter 1 on the opposite side of the figure (opposite side of the paper). You can do it.
[0047]
If the optical fiber type displacement meter 1-j is subjected to a treatment such as coating using a cover member as appropriate, the durability can be further increased.
[0048]
【The invention's effect】
As is clear from the above description, according to the present invention, there is provided an optical fiber type displacement meter which is hardly affected by external factors such as weather and high voltage wires, has excellent durability, and can be monitored remotely. be able to.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a schematic configuration of an optical fiber displacement meter according to an embodiment of the present invention.
FIG. 2 is a side view in the direction of arrow A in FIG.
FIG. 3 is an explanatory diagram showing a change of an optical fiber type displacement meter before and after displacement.
FIG. 4 is an explanatory diagram illustrating a schematic configuration of a displacement measurement system including a plurality of optical fiber displacement meters according to an embodiment of the present invention.
FIG. 5 is a side view of a connection portion of a bridge showing one application example of the displacement measurement system shown in FIG. 4;
[Explanation of symbols]
1, 1-1, 1-2,..., 1-n Optical fiber displacement meter 11 Optical fiber 12 Plate member 13 Rack 14 Gear 15 Shaft 16 Roller 17 Deformed portion 18 Disk portion 20 Strain distribution measuring device 21 Light source 22 Optical frequency converter 23 Optical pulse modulator 24 Beam splitter 25 Coherent optical receiver 30 Computers 41 and 42 Bridge girder 51 Bridge pier 61 Falling bridge prevention device 100 Displacement measurement system

Claims (3)

An optical fiber displacement meter that detects a displacement of a measurement object,
A plate-shaped member that receives a displacement following the displacement of the measurement target and at least a part of which is provided with a rack,
A gear that meshes with the rack;
A displacement conversion unit that converts the rotation of the gear due to the displacement of the plate-like member into a displacement of the gear in the rotation axis direction,
The gear has a cylindrical shape that is rotationally symmetric with respect to the rotation axis of the gear, and elastically deforms in a direction substantially orthogonal to the moving direction in accordance with the movement of the gear in the rotation axis direction based on the conversion by the displacement conversion unit. An elastic member;
An optical fiber which is substantially perpendicular to the direction of deformation of the elastic member and which is wound around the elastic member. 2. The displacement converter, wherein a surface of a rotation shaft of the gear is formed into a helical shape, and screwed to a center of the gear processed into a helical shape similarly to the surface of the rotation shaft. 3. An optical fiber type displacement meter as described in the above. The optical fiber type displacement meter according to claim 1, wherein the elastic member is disposed between the gear and a substantially hollow disk-shaped member fixed to a rotation shaft of the gear.

Images