JP2001066116A - Strain sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect strain of a measuring object, by facing a light-emitting member to a light-receiving member, and by inserting a translucent resin between them, and by fixing the resin part on the measuring object. SOLUTION: A feeding lead wire 2 is connected to a light-emitting element 1, and the lead wire 2 is connected to a power supply 3. A light-receiving element 4 generates a voltage by receiving light, and is connected to a voltage measuring machine 5 through the lead wire 2. The light-emitting element 1 and the light-receiving element 4 are faced each other, and a transparent resin 6 is fixed between them. The resin 6 part is preferably transparent or translucent, such as an epoxy resin, an ABS resin or the like. The resin 6 is fixed to a member whose strain is required to be measured (measuring object) 7 by an adhesive or the like. When the measuring object 7 is deformed, the resin 6 part is deformed in response to the deformation. If the deformation quantity exceeds a fixed value, a striped pattern peculiar to the resin called a craze is generated on the resin 6 part, and if the deformation is repeated, minute cracks are generated inside the resin 6 part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strain sensor using light, and more particularly, to a strain sensor suitable for measuring a stress in a structure.

[0002]

2. Description of the Related Art As a conventional method for detecting distortion using light, there is a method described in Japanese Patent Application Laid-Open No. H10-111111. This is accomplished by disposing an optical fiber at least one turn or more in a part or the entire circumference in the circumferential direction over the entire area in the axial direction, and disposing the optical fiber in contact with the inner circumference of the solenoid so as to be parallel to each other. Are formed in an elliptical shape, and two formers each having one end limited to a measurement target portion are disclosed.

[0003]

However, in order to know whether or not various members forming a structure have undergone excessive deformation exceeding a design load during use, in the above-mentioned prior art, a strain signal is always recorded. Or keep some alarms active all the time and keep monitoring for strains that exceed the threshold. Amplifiers for measuring strain are expensive, and it is necessary to prepare equipment for each location where measurement is desired.
When the structure is large, it is difficult to constantly monitor the strain.
Moreover, since the destruction of a structure often occurs by receiving an excessive strain a plurality of times, the magnitude and the number of strains are important monitoring items.

An object of the present invention is to provide a simple strain sensor in which an excessive amount of strain received by an object to be measured and the number of times of the strain are accumulated, and a detecting device is externally connected to the sensor when not in use. It is an object of the present invention to provide a sensor capable of determining the number of times of excessive strain.

[0005]

According to the present invention, in order to achieve the above object, a light emitting member and a light receiving member are opposed to each other, a resin that transmits light is inserted between the members, and the resin portion is measured. By fixing to the object, the distortion of the object to be measured is detected.

[0006] Alternatively, instead of the light emitting element or the light receiving element, the end faces of the optical fibers are opposed to each other, and a resin that transmits light is inserted between them.

The optical fiber is sealed so as to cover the end face of one optical fiber, is covered with a cylindrical member, and a member for reflecting light is provided on the other end face of the cylinder in which no fiber is inserted.

[0008] The resin is made of a transparent or translucent thermosetting resin or thermoplastic resin.

Alternatively, the diameter of a part of the optical fiber made of plastic is made smaller than the diameter of the other part, and the part having the smaller diameter is fixed to the object to be measured.

[0010] A plurality of optical fibers are connected between the ends of the respective optical fibers by a cylinder filled with a resin through which light passes so as to cover the end faces of the fibers, and the end of the fiber having no cylinder is provided. One of the parts is connected to the light emitting element,
The other was connected to the light receiving element.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a front view of the strain sensor.

A power supply lead wire 2 is connected to the light emitting element 1, and the lead wire 2 is connected to a power supply 3. The light receiving element 4 generates a voltage by receiving light, and is connected to a voltage measuring device 5 via the lead wire 2. Light emitting element 1 and light receiving element 2
Are opposed to each other, and a transparent resin 6 is fixed between the two. Desirably, the resin 6 is transparent or translucent.
Epoxy resin, ABS resin and the like are conceivable.

The resin 6 is a member 7 whose strain is to be measured.
(Measurement member) is fixed with an adhesive 8 or the like. When the DUT 7 is deformed, the resin 6 is also deformed accordingly. If the amount of deformation exceeds a certain value, a stripe pattern called craze peculiar to the resin is generated in the resin 6 portion, and when the deformation is repeated, fine cracks are generated in the resin 6 portion. Since the light transmitted through the resin 6 is irregularly reflected by the crack, the amount of light reaching the light receiving element 4 from the light emitting element 1 changes.

The amount of strain required to generate craze, which is the starting point of the crack, differs depending on the type of resin.
As long as the resin 6 is deformed a plurality of times within a range not exceeding the strain threshold, no crack occurs in the resin.

According to the present embodiment, the amount of transmitted light changes in accordance with the magnitude of the strain of the object to be measured, and the history of the excessive strain once received is accumulated in the form of cracks in the resin 6. Therefore, the magnitude and the number of received strains can be determined based on a change in the voltage applied to the light-emitting element 1 and the voltage generated in the light-receiving element 4 at the time of inspection, without constantly monitoring the distortion of the device under test. Moreover, the history of the strain that does not exceed the threshold does not remain, and the history of only the abnormal strain remains.

This operation is shown in FIG. (a) shows the time change of the strain of the measured object. (B) shows the time change of the amount of light received by the light receiving element at this time.

While the resin is repeatedly subjected to a small strain that does not cause craze, the light amount of AB remains in the initial state. Once an excessive strain is applied at C, the light quantity decreases as shown in FIG. Thereafter, DE maintains the light amount while the small distortion is repeated. When excessive strain is again applied at F, FIG.
The light quantity further decreases as shown in FIG. By examining the relationship between the amount of decrease in light quantity and the number of repetitions of excessive strain, the history of excessive strain received by the structural member can be known from the change in light quantity at the time of inspection.

Another embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a sectional view of the strain sensor.

In the figure, two optical fibers 9 are inserted into a cylinder 10 such that their end faces face each other at a fixed distance. Both end faces of the fiber 9 are polished.
The resin 6 is sealed in the cylinder 10. Cylinder 1
Numeral 0 is used by being fixed to the object 7 using an adhesive 8 or the like. The fiber 9 is connected to a laser light source 11 and an optical power meter 12. Fiber 9 is single mode,
Any of multi-mode type may be used, and the material is quartz glass or plastic. The resin is desirably transparent or translucent, and may be an epoxy resin, an ABS resin, or the like. The material of the cylinder 10 is preferably the same material as the member 7 of the object to be measured or a material deforming close to the resin 6.

When the object 7 is deformed, the cylinder 10 and the resin 6 are also deformed accordingly. When the amount of deformation exceeds a certain value, resin-specific crazes occur in the resin 6 portion, and when the deformation is repeated, this grows into fine cracks in the resin portion 6. The light transmitted through the resin 6 due to the cracks is irregularly reflected.
Varies in the amount of light that reaches. By appropriately selecting the type of the resin 6 and the interval between the fibers 9, the strain threshold necessary for generating craze, which is the starting point of the crack, is adjusted. Even if the resin portion 6 is deformed a plurality of times within a range not exceeding the strain threshold, no crack is generated in the resin.

According to the present embodiment, the amount of transmitted light changes in accordance with the magnitude of the amount of distortion of the DUT 7, and the history of excessive distortion once received is accumulated in the form of cracks in the resin 6. Even if the distortion of the object to be measured is not constantly monitored, the magnitude and the number of the received distortion can be determined by changing the amount of light received by the optical power meter 12 by operating the laser light source 11 at the time of inspection. Moreover, the history of the strain that does not exceed the threshold does not remain, and the history of only the abnormal strain remains. Also, the use of optical fibers makes wiring as a sensor easier,
The sensor is strong against electromagnetic noise.

Another embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a sectional view of the strain sensor.

The end face of one end of the optical fiber 9 is polished,
It is inserted into the cylinder 10. The resin 6 is sealed in the cylinder 10, and the end face 13 of the cylinder is polished so as to be parallel to the end face 14 of the optical fiber. And the cylindrical end surface 1
1 is coated with a material that reflects light, for example, gold.
Gold may be deposited on the inner surface of the cylinder. The other end of the fiber 9 is connected to an optical directional coupler and a photocoupler 15. The fiber 9 connected to the laser light source 11 and the fiber 9 connected to the optical power meter 12 are connected to the photocoupler 15. Resin 6 is the same as in the previous embodiment.
Epoxy resin, ABS resin and the like are conceivable. The cylinder 10 is fixed to the object 7 via an adhesive 8 or the like. The light from the laser light source 11 passes through the photocoupler 14 and
After passing through the inside, the light is reflected by the cylindrical end face 13 and enters the photocoupler 15 again. The light that has entered the photocoupler 15 reaches the optical power meter 12.

The occurrence of craze and the like are the same as those in the embodiment of FIG. Due to the crack, light transmitted through the resin 6 is irregularly reflected, and the amount of light reflected on the cylindrical end face 13 changes. By appropriately selecting the type of the resin 6 and the distance between the fiber 9 and the reflecting surface, the strain threshold necessary for generating craze, which is the starting point of the crack, is adjusted. Other detection methods are the same as in the previous embodiment. In this embodiment, since there is a strain detecting unit at the tip of the optical fiber,
The strain history can be monitored simply by fixing one fiber at the measurement point.

Another embodiment of the present invention will be described with reference to FIG. FIG. 5 is a front view of the optical fiber sensor.

Optical fiber 9 connected to laser light source 11
Is cut at multiple locations. Then, a cylinder 10 is placed over each cut portion, and a resin 6 is sealed inside. The final end of the fiber 9 is connected to the optical power meter 12. Cylinder 1
Numeral 0 is fixed using adhesive 8 or the like at a plurality of locations where the strain of the object 7 is to be monitored. If the strain at any of the measurement points exceeds the threshold value, the resin 6 is cracked only at that portion, and the transmitted light amount changes. According to this embodiment, by monitoring the output of the optical power meter 12 periodically, the histories of excessive strain at a plurality of locations can be simultaneously known.

Another embodiment of the present invention will be described with reference to FIG.

In FIG. 1, light emitted from a laser light source 11 passes through a photocoupler 15 and then passes through a plurality of cylinders 10. Then, the light reflected on the fiber end face 16 inside each cylinder returns to the photocoupler 15, and the optical power meter 1
2 is incident. According to the present embodiment, simultaneous measurement at a plurality of locations is possible. Further, the position of the sensor can be specified by measuring the itinerary of the reflected light from each cylinder group or by counting the wave number.

Another embodiment of the present invention will be described with reference to FIG.

The optical fiber 9 has a portion 17 whose diameter is partially smaller than other portions. The material of the optical fiber is a plastic material. A fixture 18 is attached to the DUT 7.
And is fixed with an adhesive 8 or the like. When the DUT 7 is distorted, the small diameter optical fiber 17 is distorted more than the other large diameter fiber portions. For this reason, the plastic fiber itself is cracked, and the amount of transmitted light changes. According to this embodiment, since the optical fiber itself has a function as a strain sensor, the manufacturing cost can be reduced.

Another embodiment of the present invention will be described with reference to FIG. FIG. 8 is a perspective view of the generator.

The rotor 18 is provided with a field winding and is excited to rotate. The stator coil 19 for extracting electric power is fixed in the stator frame 20 by a resin rod or the like. A strain sensor 21 is fixed to the end of the stator coil 19. The stator coil vibrates due to the fluctuating magnetic field during rotation. In the unlikely event that the rod or the like fixing the coil is damaged and the vibration of the coil becomes excessive, there is a risk that the coil will break. The strain history of the fixed end portions of all the coils is monitored by the strain sensor 21, and it can be seen that the coil vibration has become excessive due to the change in the light transmitted through the fiber. In addition, since the optical fiber is used, it is not affected by electromagnetic noise even during inspection during operation.

Another embodiment of the present invention will be described with reference to the drawings. FIG. 9 is a sectional view of the strain sensor. In the embodiment of FIG. 4, there is a reflecting portion on the cylindrical end face, but this is an example in which another optical fiber 22 is inserted and a reflecting material is applied to the end face.

According to the present embodiment, the amount of transmitted light changes in accordance with the magnitude of the amount of distortion of the DUT 7, and the history of excessive distortion once received is accumulated in the form of cracks in the resin 6.
For this reason, the magnitude and the number of received strains can be determined based on a change in the amount of light received by the optical power meter 12 by activating the laser light source 11 at the time of inspection without constantly monitoring the strain of the DUT. Moreover, the history of the strain that does not exceed the threshold does not remain, and the history of only the abnormal strain remains. In addition, a smoother reflecting surface can be easily obtained than at the cylindrical end.

[0035]

According to the present invention, since the history of excessive strain received by the object to be measured is accumulated in the form of cracks in the resin in the sensor, it is not necessary to constantly monitor the strain of the object to be measured, and the inspection can be performed at the time of inspection. By activating the laser light source, the magnitude and the number of strains received can be determined by changes in the amount of light received by the optical power meter. Moreover, the history of the strain that does not exceed the threshold does not remain, and the history of only the abnormal strain remains. Further, by using an optical fiber, wiring as a sensor is facilitated, and the sensor is resistant to electromagnetic noise.

[Brief description of the drawings]

FIG. 1 is a front view of a strain sensor according to one embodiment of the present invention.

FIG. 2 is a time change diagram of distortion and light amount.

FIG. 3 is a sectional view of a strain sensor according to another embodiment.

FIG. 4 is a sectional view of a strain sensor according to another embodiment.

FIG. 5 is a front view of a strain sensor according to another embodiment.

FIG. 6 is a front view of a strain sensor according to another embodiment.

FIG. 7 is a front view of a strain sensor according to another embodiment.

FIG. 8 is a perspective view of a generator to which the strain sensor of the present invention is applied.

FIG. 9 is a sectional view of a strain sensor according to another embodiment.

[Explanation of symbols]

1 ... light-emitting element, 4 ... light-receiving element, 6 ... resin, 9 ... optical fiber, 10 ... cylinder, 15 ... photocoupler, 17 ... optical fiber with small diameter.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroyuki Watanabe 3-1-1, Sakaimachi, Hitachi, Hitachi City CA00 DA03 DA04 DA06 2H038 AA05

Claims (6)

[Claims] A light-transmitting resin inserted between the light-emitting member and the light-receiving member;
A strain sensor for measuring a strain amount of an object to be measured by fixing the resin portion to the object to be measured. 2. A strain sensor wherein two optical fibers are provided with end faces facing each other, and a light transmitting resin is inserted between the end faces. 3. An optical fiber is covered with a cylinder so as to cover an end face of the optical fiber, and a member for reflecting light is provided on another end face of the optical fiber in which the fiber of the cylinder is not inserted. A strain sensor characterized by being enclosed. 4. A strain sensor according to claim 1, wherein said resin is made of a transparent or translucent thermosetting resin or thermoplastic resin. 5. An object to be measured by forming a part of an optical fiber made of plastic to have a diameter smaller than that of the other part and fixing the part of the optical fiber having a smaller diameter to the object to be measured. A strain sensor for measuring a strain of a strain. 6. A plurality of optical fibers connected to each other by a cylinder filled with a resin that transmits light between the ends of the optical fibers so as to cover the end faces of the fibers. One of the ends of is connected to the light emitting element,
A strain sensor characterized in that the other is connected to a light receiving element.