JP6803268B2 - Current observation system, current observation method and aircraft - Google Patents

Description

Embodiments of the present invention relate to current observation systems, current observation methods and aircraft.

When designing an aircraft, it is necessary to take measures against lightning strikes. Therefore, a technique for detecting a lightning strike on an aircraft has been proposed (see, for example, Patent Document 1 and Patent Document 2). When an aircraft is hit by a lightning strike, current flows through the aircraft, which can cause damage. In particular, carbon fiber reinforced plastic (CFRP: Carbon Fiber Reinforced Plastics), which is one of the composite materials, may be a path for lightning current because carbon fiber serves as a conductor. For this reason, the standards set by the Society of Automotive Engineers (SAE) set standards so that sufficient strength is ensured even when a lightning current flows through an aircraft.

JP-A-2009-229465 Japanese Patent Publication No. 2014-534437

However, it is difficult to actually measure the lightning current flowing through an aircraft. For this reason, there is a risk that the strength design will be excessive with respect to the lightning current. In particular, composites, unlike metals, are susceptible to damage by lightning currents. Therefore, it is desired to be able to estimate the current value flowing through each part when the aircraft is hit by a lightning strike.

Further, it is desired to be able to easily measure the current flowing through an object such as a composite material partially containing a conductor, not limited to an aircraft.

Therefore, it is an object of the present invention to be able to measure a lightning strike current when an aircraft is hit by a lightning strike.

Another object of the present invention is to make it possible to easily measure the current flowing through an object such as a composite material partially containing a conductor.

The current observation system according to the embodiment of the present invention includes a storage device, an optical fiber sensor, and a current acquisition unit. The storage device stores information representing the relationship between the current flowing through the test object and the amount of strain generated in the test object due to the current. The optical fiber sensor detects the amount of strain of the test object. The current acquisition unit obtains the current flowing through the test object based on the information and the amount of strain detected by the optical fiber sensor.

Further, the aircraft according to the embodiment of the present invention is equipped with the above-mentioned current observation system.

Further, in the current observation method according to the embodiment of the present invention, information representing the relationship between the current flowing through the test object and the amount of strain generated in the test object due to the current is acquired and stored in the storage device. A step, a step of detecting the amount of strain of the test object by the optical fiber sensor, and a step of obtaining a current flowing through the test object based on the information and the amount of strain detected by the optical fiber sensor. Has.

FIG. 1 is a block diagram of a current observation system according to an embodiment of the present invention. The figure which shows the example which made it possible to detect the current flowing through CFRP by an optical fiber sensor when the object to be examined is CFRP. The figure which shows another example which made it possible to detect the current flowing through CFRP by an optical fiber sensor when the object under test is CFRP. The figure which shows the example which arranged the optical fiber sensor shown in FIG. 1 in a plurality of parts of an aircraft. The figure which shows an example of the lightning current distribution map which flows through an aircraft which can be acquired by the current observation system shown in FIG. The flowchart which shows an example of the flow of the current observation method using the current observation system shown in FIG. The block diagram of the current observation system which concerns on 2nd Embodiment of this invention.

The current observation system, the current observation method, and the aircraft according to the embodiment of the present invention will be described with reference to the accompanying drawings.

(First Embodiment)
(Configuration and function)
FIG. 1 is a block diagram of a current observation system according to an embodiment of the present invention.

The current observation system 1 is a system that monitors the current flowing through the test object O by measuring the amount of strain of the test object O. Therefore, the current observation system 1 has a distortion detection system 2 and a signal processing unit 3. When the current value is measured at a plurality of positions of the object O to be inspected, a plurality of strain detection systems 2 can be arranged at the current value measurement positions as illustrated in FIG.

Each strain detection system 2 is configured by connecting an optical fiber sensor 4, a light source 5, and a photodetector 6 with an optical waveguide 7. That is, the strain detection system 2 is a system that detects the amount of strain of the test object O by using the optical fiber sensor 4. When the current observation system 1 is provided with a plurality of strain detection systems 2, the light source 5 may be shared among the plurality of strain detection systems 2 as illustrated in FIG.

The optical fiber sensor 4 is a sensor for converting the amount of distortion generated in the test object O into the amount of change in optical characteristics such as light transmission characteristics or light reflection characteristics for detection. Therefore, the optical fiber sensor 4 is attached to the test object O so as to expand and contract due to the strain generated in the test object O. Further, as illustrated in FIG. 1, a plurality of optical fiber sensors 4 can be attached to a desired position of the test object O according to the number of locations where the strain amount should be measured.

When the amount of distortion of the test object O is detected as a change in the light transmission characteristics of the optical fiber sensor 4, the transmitted light of the optical fiber sensor 4 is used as an optical signal representing the amount of distortion of the test object O from the optical fiber sensor 4. To be acquired. On the other hand, when the amount of distortion of the test object O is detected as a change in the light reflection characteristic of the optical fiber sensor 4, the reflected light from the optical fiber sensor 4 is an optical fiber as an optical signal representing the amount of distortion of the test object O. Obtained from sensor 4.

Examples of the optical fiber sensor 4 include a fiber Bragg grating (FBG) sensor and a phase shift FBG (PS-FBG: Phase-shifted FBG) sensor. The PS-FBG is an FBG that introduces a local phase shift into the periodic fluctuation of the refractive index. Therefore, when the PS-FBG sensor is used, the detection sensitivity can be dramatically improved as compared with the case where the FBG sensor is used.

The light source 5 is connected to the optical waveguide 7 so that the laser beam can be incident on the optical fiber sensor 4. As illustrated in FIG. 1, when a plurality of optical fiber sensors 4 are attached to the test object O as a component of one strain detection system 2, not only between the plurality of strain detection systems 2 but also a plurality of lights. The light source 5 can be shared among the fiber sensors 4.

The photodetector 6 is a photoelectric conversion device that detects an optical signal output from an optical fiber sensor 4 whose optical characteristics have changed according to the amount of distortion of the object O to be inspected and outputs it as an electric signal. By changing the wavelength band of the optical signals output from the plurality of optical fiber sensors 4, the optical signals output from the plurality of optical fiber sensors 4 can be distinguished according to the wavelength band. Therefore, the common photodetector 6 It can also be detected with.

In the example shown in FIG. 1, the transmitted light from the plurality of optical fiber sensors 4 is configured to be detected by a common photodetector 6. When the reflected light from the plurality of optical fiber sensors 4 is detected by a dedicated or common photodetector 6, the reflected light from the plurality of optical fiber sensors 4 is dedicated or by arranging an optical element such as an optical circulator. It is configured so that it can be detected by a common photodetector 6.

The output side of the photodetector 6 is connected to the signal processing unit 3. Then, the optical signal detected as the distortion amount detection signal by the photodetector 6 is configured to be output to the signal processing unit 3 as an electric signal.

The optical waveguide 7 is a medium for transmitting the laser light emitted from the light source 5 and the optical signal output from the optical fiber sensor 4. The optical waveguide 7 can be composed of an optical fiber, but can also be composed of an inorganic optical waveguide such as a glass optical waveguide or a polymer optical waveguide. The polymer optical waveguide is originally an optical element for a printed circuit board using an optical signal, and is also called an organic optical waveguide, a plastic optical waveguide, a polymer optical wiring, a polymer optical circuit, or the like.

The polymer optical waveguide has a core layer formed inside the clad layer, and the core layer can be formed of a polymer material, while the clad layer can be formed of a resin sheet or the like. The features of the polymer optical waveguide are that there is no light loss in the direction perpendicular to the length direction, that it is easy to process, that it is possible to increase the density, and that it is easy to mount. Further, there is an advantage that the polymer optical waveguides can be easily intersected with each other without causing unevenness.

On the other hand, the signal processing unit 3 can be composed of an arithmetic unit 8, a storage device 9, a display device 10, and an input device 11. That is, the signal processing unit 3 can be configured by using an electronic circuit such as a computer in which the signal processing program is read. Therefore, an A / D (analog-to-digital) converter is provided on the input side of the signal processing unit 3 or the output side of the photodetector 6 as needed. Further, a desired circuit such as a noise filter for analog signals or digital signals can be connected to the front stage or the rear stage of the A / D converter.

By reading the information processing program, the arithmetic unit 8 functions as a current acquisition unit 8A, a current distribution acquisition unit 8B, a timing recording unit 8C, a damage detection unit 8D, and an observation data display unit 8E. Further, the storage device 9 functions as a distortion amount / current value conversion information storage unit 9A and an observation data storage unit 9B by loading the information processing program into the arithmetic unit 8.

The strain amount / current value conversion information storage unit 9A stores information representing the relationship between the current flowing through the test object O and the strain amount generated in the test object O due to the current. Information indicating the relationship between the amount of strain generated in the test object O when a current flows through the test object O and the current value is stored in the strain amount / current value conversion information storage unit 9A as a table or a function. Can be done. Therefore, by referring to the table or function stored in the strain amount / current value conversion information storage unit 9A, the amount of strain generated in the test object O is converted into the current value of the current flowing through the test object O. Can be converted.

The current acquisition unit 8A contains information for converting the strain amount into a current value stored in the strain amount / current value conversion information storage unit 9A, and the strain amount of the test object O detected by each optical fiber sensor 4. It has a function of obtaining the current flowing through the test object O based on the output signal from the photodetector 6 representing the above. The current value obtained by the current acquisition unit 8A can be stored in the observation data storage unit 9B so that other components can be referred to in association with desired information such as the detection timing and the detection position of the strain amount.

When a plurality of optical fiber sensors 4 are attached to the object O, the current distribution acquisition unit 8B includes a plurality of distortion generation positions and a current value corresponding to each strain amount obtained by the current acquisition unit 8A. Has a function of obtaining the current distribution flowing through the test object O by associating and grouping the two. That is, the current distribution acquisition unit 8B acquires the current distribution of the test object O by obtaining the value of each current flowing through the plurality of test sites of the test object O corresponding to the mounting positions of the plurality of optical fiber sensors 4. Has the function of The current distribution of the test object O acquired by the current distribution acquisition unit 8B can be stored in the observation data storage unit 9B so that other components can be referred to. On the contrary, the information necessary for obtaining the current distribution of the test object O can be obtained from the observation data storage unit 9B.

When a plurality of optical fiber sensors 4 are mounted on the test object O, the timing recording unit 8C flows through a plurality of test sites of the test object O corresponding to the mounting positions of the plurality of optical fiber sensors 4. It has a function to specify the timing of the current. The timing of the current acquired by the timing recording unit 8C can be stored in the observation data storage unit 9B in association with the current value and the test site where the current value is detected so that other components can refer to it. On the contrary, the information necessary for specifying the timing of the current flowing through the plurality of test sites can be acquired from the observation data storage unit 9B.

The damage detection unit 8D has a function of detecting whether or not damage has occurred to the test object O due to the current flowing when a current flows through the test object O. Therefore, the damage detection unit 8D is provided as necessary when there is a risk that the test object O may be damaged due to the current flowing through the test object O. When damage is detected in the damage detection unit 8D, it can be stored in the observation data storage unit 9B so that other components can be referred to in association with the test site where the damage is detected. On the contrary, the information necessary for detecting the presence or absence of damage can be obtained from the observation data storage unit 9B.

Whether or not the test object O is damaged can be determined based on the amount of strain of the test object O detected by the optical fiber sensor 4. That is, it is possible to detect whether or not damage has occurred in the test portion of the test object O through which the current has flowed by the damage test using the optical fiber sensor 4 for detecting the amount of strain.

More specifically, a threshold value is set for the amount of strain, and when the amount of strain of the test object O detected by the optical fiber sensor 4 exceeds or exceeds the threshold value, the test object O is set. It can be determined that damage has occurred. The threshold value for determining whether or not damage has occurred to the test object O can be empirically determined by a test in which an electric current is passed through a test piece or the like that simulates the test object O to cause damage. Alternatively, the threshold value may be determined based on the physical property value representing the mechanical strength of the test object O with respect to the electric current.

When the damage detection unit 8D is provided in the signal processing unit 3, the current observation system 1 functions as a damage detection system that detects whether or not the test object O is damaged by using the optical fiber sensor 4. Will also have. On the contrary, the electronic circuit of the existing damage detection system that detects whether or not the test object O is damaged by measuring the amount of distortion of the test object O with the optical fiber sensor 4 is used in the electronic circuit of the test object O. By installing a signal processing program that converts the amount of distortion into the current value of the current flowing through the test object O, the damage detection system may be provided with the function of the current observation system 1.

In this case, the current detection in the test object O and the damage detection can be performed by using the common optical fiber sensor 4. Therefore, the configuration can be simplified by reducing the number of parts.

The observation data display unit 8E has a function of referring to the information stored in the observation data storage unit 9B and creating observation information to be displayed on the display device 10. That is, the observation data display unit 8E has a function of acquiring the information stored in the observation data storage unit 9B, creating various observation data, and displaying the created observation data on the display device 10. Further, the observation data once created can be stored in the observation data storage unit 9B so that it can be referred to again.

The content of the observation data to be displayed on the display device 10 can be specified by operating the input device 11. As a specific example, when a current having a different current value flows through the same position or region of the test object O multiple times, a plurality of current values corresponding to different dates and times are stored in the observation data storage unit 9B. Can be accumulated in. Therefore, statistical values such as the average value of a plurality of current values in the same position or region of the test object O can be created and displayed as observation data.

Further, even when currents flow through a plurality of positions or regions of the test object O at different dates and times, a plurality of current values corresponding to different dates and times can be stored in the observation data storage unit 9B. Therefore, it is also possible to combine the detection results of the current values at a plurality of different positions or regions to create and display a current value map irrelevant to the date and time as observation data. Of course, it is also possible to create and display observation data irrelevant to the date and time by synthesizing statistical values such as the average value of a plurality of current values at a plurality of different positions or regions.

As another example, the observation data display unit 8E can create and display observation data indicating the path through which the current flows by arranging the detection timings of the current values in chronological order. In particular, the time resolution of the optical fiber sensor 4 is in microseconds. Therefore, it is possible to grasp the direction of current flow by specifying the current detection timings at a plurality of different positions and creating time-series current value data.

Next, a method of acquiring information representing the relationship between the current flowing through the test object O and the amount of strain generated in the test object O due to the current will be described.

When a current flows through the test object O, the test object O is distorted by an electromagnetic force (Lorentz force) with a strain amount corresponding to the current value. This applies not only when the test object O is a metal, but also when the test object O is made of a metal or a material containing a conductor other than the metal. An example of a material containing a conductor as a part is CFRP, which is mainly used as a material for aircraft.

FIG. 2 is a diagram showing an example in which the optical fiber sensor 4 can detect the current flowing through the CFRP when the test object O is the CFRP.

As shown in FIG. 2, CFRP has a structure in which carbon fiber O1 is impregnated with epoxy resin O2 and cured by laminating a carbon fiber reinforced resin layer O3. Therefore, since the filamentous carbon fiber O1 constituting the CFRP serves as a conductor of the current I, the current I may flow through the CFRP.

When the current I flows through the conductors parallel to each other in the same direction, the conductors are magnetically attracted to each other by the Lorentz force F. Therefore, when the current I flows through the two filamentous carbon fibers O1 arranged in parallel as shown in FIG. 2, a Lorentz force F that attracts each other is generated between the two carbon fibers O1.

The direction of the Lorentz force F at which the two carbon fibers O1 attract each other is perpendicular to the direction in which the current I flows, and the magnitude depends on the magnitude of the current I flowing through the two carbon fibers O1. As a result, compressive stress is generated in CFRP, and minute strain is generated by the amount of strain depending on the magnitude of the current I flowing through the two carbon fibers O1. That is, when the current I flows through the CFRP, the CFRP is distorted in the direction perpendicular to the direction in which the current I flows with the amount of distortion corresponding to the magnitude of the current I flowing through the CFRP.

In principle, the force F (t) generated between the two carbon fibers O1 is expressed by Eq. (1) as a function of the current values I ₁ (t) and I ₂ (t) flowing through the two carbon fibers O1. Will be done.
F (t) = μ · I ₁ (t) · I ₂ (t) / (2π) · L / D ... (1)
However, in equation (1),
t: Time F (t): magnitude of force at time t μ: magnetic permeability of epoxy resin I ₁ (t): magnitude of current flowing through one carbon fiber at time t I ₂ (t): magnitude of current at time t Magnitude of current flowing through the other carbon fiber L: Length of carbon fiber D: Distance between carbon fibers.

Therefore, as illustrated in FIG. 2, the surface of the CFRP is such that the length direction of the optical fiber sensor 4, which is the measurement direction of the strain amount, is perpendicular to the length direction of the carbon fiber O1, that is, the strengthening direction of the CFRP. By arranging the optical fiber sensor 4 in the CFRP, the amount of compression strain generated in the CFRP can be detected with high sensitivity.

FIG. 3 is a diagram showing another example in which the optical fiber sensor 4 can detect the current flowing through the CFRP when the test object O is the CFRP.

As shown in FIG. 3, CFRP has a structure in which carbon fiber O1 is impregnated with epoxy resin O2 and cured by laminating a carbon fiber reinforced resin layer O3. Therefore, the Lorentz force F that attracts each other is generated even between the carbon fiber reinforced resin layers O3 reinforced with innumerable filamentous fibers. That is, when a current I flows through the two carbon fiber reinforced resin layers O3, a Lorentz force F that attracts each other is generated between the carbon fiber reinforced resin layers O3. The magnitude of the Lorentz force F generated between the carbon fiber reinforced resin layers O3 is also represented by the formula (1). However, in the formula (1), I ₁ (t) is the magnitude of the current I flowing through one carbon fiber reinforced resin layer O3, and I ₂ (t) is the magnitude of the current I flowing through the other carbon fiber reinforced resin layer O3. L is the length of the carbon fiber reinforced resin layer O3, and D is the distance between the carbon fiber reinforced resin layers O3.

Therefore, as illustrated in FIG. 3, the optical fiber sensor 4 is arranged on the side surface of the CFRP so that the length direction of the optical fiber sensor 4 which is the measurement direction of the strain amount is the stacking direction of the carbon fiber reinforced resin layer O3. This makes it possible to detect the amount of compression strain generated in CFRP with high sensitivity. In a typical optical fiber sensor 4, the light transmission characteristic and the light reflection characteristic have peaks, and the length of the portion that actually functions as a sensor is about several mm. Therefore, if the CFRP has a thickness of about several mm, a commercially available optical fiber sensor 4 can be arranged in the stacking direction of the carbon fiber reinforced resin layer O3.

However, in reality, CFRP has a multilayer structure in which a large number of carbon fiber reinforced resin layers O3 are laminated, and innumerable carbon fibers O1 are also present in each carbon fiber reinforced resin layer O3. Moreover, there are CFRPs in which carbon fiber reinforced resin layers O3 having different length directions of carbon fibers O1 are laminated, and CFRPs shaped into a special shape. Therefore, in the CFRP, the Lorentz force F causes a stress distribution according to the number and arrangement of the carbon fibers O1, and a strain amount distribution according to the stress distribution. Therefore, it is often difficult to analytically obtain the relationship between the current value of the current I flowing through the CFRP and the amount of strain generated in the CFRP using the equation (1).

Therefore, on the premise that the amount of distortion of CFRP changes depending on the magnitude of the current flowing through CFRP, a current with a known current value is passed through the test object O itself actually composed of CFRP, and an optical fiber is used. By measuring the strain amount of the test object O with the sensor 4, the relationship between the current value and the strain amount can be obtained. That is, the relationship between the current value and the amount of strain can be obtained by calibration. Alternatively, a current having a known current value is passed through a CFRP test piece or test piece that simulates the test object O, and the strain amount of the test object O is measured by the optical fiber sensor 4, so that the current value and the strain are measured. You may want to find the relationship with the quantity.

In this case, the strain amount corresponding to the unknown current value can be obtained by interpolation processing based on the relationship between the known current value and the strain amount. That is, the relationship between the current value and the amount of strain in the required range can be obtained by interpolation processing such as interpolation, extrapolation, curve fitting, straight line approximation, and curve approximation. In particular, when a current is passed through the test object O itself, the test is performed by passing a current at a safe current value that does not cause damage to the test object O, and corresponds to the current value that can be damaged by extrapolation. The amount of distortion can also be obtained.

Of course, if the CFRP having a simple structure is the test object O, the relationship between the current value and the strain amount is theoretically obtained by modeling and simulation applying the relationship of the equation (1) or the equation (1). You may do so.

Information such as functions and tables representing the relationship between the current value and the amount of strain can be similarly obtained not only for CFRP but also for a composite material made of a resin reinforced with conductive fibers. Therefore, in the case of the test object O made of a composite material reinforced with conductive fibers, the current of the current flowing through the test object O by detecting the amount of strain of the test object O with the optical fiber sensor 4 The value can be calculated.

Examples of conductive fibers include carbon fibers, fibers in which a conductive substance is dispersed in synthetic fibers, metal fibers, fibers whose surface is coated with metal, and whose surface is coated with a resin containing a conductive substance. Examples include fibers.

The direction of the current flowing through the composite material is considered to be approximately the length direction of the conductive fiber. Therefore, it is effective to arrange the optical fiber sensor 4 so as to be perpendicular to the length direction of the filamentous conductive fibers or the plurality of filamentous conductive fibers arranged in the form of a sheet from the viewpoint of satisfactorily detecting the amount of strain. Is considered to be.

Further, when the length directions of the conductive fibers are not uniform or when the optical fiber sensors 4 cannot be arranged in the length directions of the conductive fibers, the two or three optical fiber sensors 4 are oriented in different directions. For example, the amount of strain of the test object O may be detected two-dimensionally or three-dimensionally by arranging them so that their length directions are perpendicular to each other. In that case, the relationship between the combination of the strain amounts of the test object O in the two or three directions and the current value of the current flowing through the test object O may be obtained.

Further, the optical fiber is not limited to the composite material reinforced with the conductive fiber, and even if it is the test object O in which a plurality of parallel conductors are arranged with an insulator in between, such as a printed circuit board protected by a resin film. If the detection sensitivity of the strain amount of the sensor 4 is sufficient, it is possible to detect the current based on the same strain amount.

(Aircraft equipped with a current observation system)
Next, an example will be described in which the current observation system 1 is mounted on the aircraft so that the lightning current flowing through the structure can be obtained by using the structure of the aircraft as the test object O.

FIG. 4 is a diagram showing an example in which the optical fiber sensor 4 shown in FIG. 1 is arranged at a plurality of parts of the aircraft 20.

As shown in FIG. 4, an optical waveguide 7 can be stretched around the airframe of the aircraft 20, and an optical fiber sensor 4 can be attached to each part of the airframe. That is, each structure such as the left and right main wings, the left and right tails, the vertical stabilizer, and the fuselage of the aircraft 20 in which a current may flow due to a lightning strike is set as the test object O, and the optical fiber sensors 4 are applied to a plurality of test sites. Can be installed.

Then, in the current acquisition unit 8A of the current observation system 1, when the aircraft 20 is hit by a lightning strike, the lightning strike current flowing through a plurality of test sites can be obtained. That is, the lightning current value can be measured for each part of the airframe. Therefore, the current distribution acquisition unit 8B can acquire the lightning current distribution of the aircraft 20. Further, if the aircraft 20 is repeatedly hit by lightning strikes, lightning currents may flow through the aircraft 20 through various routes. Therefore, the lightning current distribution map flowing through the aircraft 20 can be created by performing statistical processing and synthesis processing of a plurality of lightning current distributions on the observation data display unit 8E.

FIG. 5 is a diagram showing an example of a lightning current distribution map flowing through the aircraft 20 that can be acquired by the current observation system 1 shown in FIG.

As illustrated in FIG. 5, it is possible to obtain a lightning current distribution map representing representative values such as temporal and spatial average values of lightning current values for each region of the aircraft 20. That is, the lightning current distribution map can be obtained by repeatedly measuring the lightning current value on the actual aircraft, accumulating it as an actual value, and performing statistical processing on the accumulated lightning current value.

For example, the strength of the lightning current value can be expressed by changing the color or pattern. Of course, the lightning current value itself may be displayed as illustrated in FIG. Further, a rough lightning current distribution map may be created according to the purpose as in the three-stage map illustrated in FIG.

It is empirically known that lightning strikes structurally sharp parts such as the wing tip of the aircraft 20, the tip of the fuselage, and the rear edge of the fuselage. When the aircraft 20 is hit by lightning, a lightning current flows from the lightning strike position and is discharged into the atmosphere again. Therefore, when the aircraft 20 is hit by a lightning strike, an inlet and an outlet for the lightning strike current are generated. It is also known that lightning currents may branch and be discharged into the atmosphere from multiple outlets. It is also known that lightning current outlets also tend to occur in sharp parts of the aircraft 20.

At the inlet and outlet of the lightning current, the current value is generally higher. Therefore, when a lightning current distribution map of the aircraft 20 is created, a map showing a large value in a sharp portion of the aircraft 20 can be obtained as illustrated in FIG. Therefore, it is possible to additionally equip and repair the aircraft 20 so as to secure the mechanical characteristics that can withstand the lightning current. Further, when designing an aircraft having a similar structure, it is possible to design the aircraft so as to secure mechanical characteristics that can withstand a lightning current.

In particular, the current observation system 1 can measure the current value of the lightning strike current flowing through CFRP as well as metal. Therefore, even in the aircraft 20 where CFRP is often used as a material, a lightning current distribution map can be easily obtained.

As one of the measures to ensure the safety when the aircraft is hit by a lightning strike, there is a measure to prevent the lightning current from flowing through the CFRP. This is because CFRP has a large electrical resistance and may be heated by a lightning current or spark may occur. As a measure to prevent the lightning current from flowing through the CFRP, a metal mesh is attached to the CFRP or the position of the fastener is appropriately determined so that the lightning current avoids the CFRP and the conductor has low electrical resistance. There is a way to make it flow.

When designing an aircraft structure so that lightning current does not flow through CFRP, it is important to confirm by testing that lightning current does not actually flow through CFRP. This also applies when designing an aircraft structure using a composite material reinforced with conductive fibers other than CFRP as a material.

Therefore, the composite material constituting the structure of the aircraft is a composite material made of a resin reinforced with conductive fibers, and a conductor for forming a lightning current path so that the lightning current does not flow through the composite material. Is attached to the structure, a simulated current is passed through the structure with the composite material as the test object O, and the current observation system 1 determines that the current flowing through the composite material is below or below the permissible value. You can check. This makes it possible to confirm the effectiveness of lightning current countermeasures.

On the contrary, a lightning current or a current simulating a lightning current is applied to an aircraft structure composed of a composite material made of a resin reinforced with conductive fibers without attaching a conductor for forming a lightning current path. If the current distribution is obtained by the current observation system 1, it is possible to determine the presence or absence of a portion where the value of the current flowing through the composite material becomes so large that it cannot be ignored. Then, only when a part where the value of the lightning current becomes so large that it cannot be ignored is confirmed, take measures against the lightning current by attaching a conductor such as a metal mesh which is a path of the lightning current so that the lightning current does not flow to the part. Can be done. Therefore, it is possible to avoid excessive measures against lightning current such as attachment of an unnecessary lightning current conductor such as a metal mesh.

Of course, not limited to the aircraft itself, a test body or test piece simulating the entire structure of the aircraft or a part of the aircraft is used as the test object O to pass a current simulating a lightning current, and the current distribution is observed by the current observation system 1. You can also do it.

In addition to the current distribution, useful information for considering the safety of an aircraft when it is hit by a lightning strike includes the inlet and outlet patterns of the lightning strike current. Therefore, if time-series current distribution data is created in the observation data display unit 8E based on the detection timing of the lightning strike current recorded in the timing recording unit 8C, the inlet and outlet of the lightning strike current can be specified. That is, by detecting the timing at which the lightning current flows through a plurality of test sites, it is possible to identify the test site on the inlet side of the lightning current to the aircraft and the test site on the outlet side of the lightning current from the aircraft. ..

As described above, the optical fiber sensor 4 can capture the change in the amount of strain in microsecond units. Therefore, it is possible to determine the inlet and outlet of the lightning current to the aircraft based on the time difference in the detection timing of the lightning current. Further, by observing the lightning current over a plurality of times, it is possible to grasp the correlation between the inlet and the outlet of the lightning current in addition to the frequency with which the test site becomes the inlet or the outlet of the lightning current. That is, when a certain test site becomes the inlet of the lightning current, the test site with a high probability of becoming the outlet of the lightning current can be specified. In other words, it is possible to grasp the path of the lightning current that can be formed in the aircraft together with the probability of occurrence.

Therefore, the observation data display unit 8E can create not only a distribution map of the lightning current value when the aircraft is hit by a lightning strike, but also a frequency distribution map in which the lightning current flows. Then, when the aircraft is actually hit by a lightning strike, it is possible to quickly identify the lightning strike point and perform an inspection by referring to the frequency distribution map in which the lightning strike current flows. For example, the inspection time can be shortened by performing the inspection in order from the test site where the lightning current flows frequently and the lightning current value is large.

Moreover, when the current observation system 1 is mounted on an aircraft, not only the lightning current flowing through the aircraft can be detected, but also the damage detection unit 8D can detect the presence or absence of damage due to lightning strikes. That is, by the damage inspection using the optical fiber sensor 4, it is possible to detect whether or not the damage has occurred at the inspection site of the aircraft through which the lightning current has flowed. A system for diagnosing structural soundness with a sensor such as an optical fiber sensor 4 is called a Structural Health Monitoring (SHM) system.

In general, there is a high possibility of severe damage at the part where the lightning current enters the aircraft and the part where the lightning current exits the aircraft. If the structure of the aircraft is damaged, it will need to be repaired or replaced. Therefore, by mounting the current observation system 1 on an aircraft, it is possible to quickly detect not only the inlet and outlet of the lightning current but also the presence or absence of damage. As a result, it is possible to reduce the labor and time required for inspection and repair when the aircraft is hit by a lightning strike. As a result, it is possible to improve the efficiency of aircraft operation.

In addition to the above example, it is also possible to observe the lightning current with the current observation system 1 for a plurality of aircraft having the same structure. In that case, it is possible to create a current value distribution map and a frequency distribution map of the lightning current that are statistically more reliable.

The current value distribution map and frequency distribution map of the lightning current are considered to depend on the flight path in addition to the structure of the aircraft. That is, it is considered that the lightning current value map and frequency distribution map change depending on the climate of the area where the aircraft flies. Therefore, for example, the current value distribution map and the frequency distribution map of the lightning current may be created for each flight path or flight area by using the operation information of the same type of aircraft in the world. In this case, it is possible to obtain a more accurate lightning current current value map and frequency distribution map for aircraft flying in the same flight path or flight area.

As a result, more appropriate lightning current countermeasures can be taken by making minor changes in the design of aircraft of the same type and adding or omitting parts. In addition, it is possible to grasp whether the standard set as a countermeasure against lightning current is excessive or insufficient and review it. Furthermore, as a measure against lightning currents, it is possible to set detailed and lean standards for each region. That is, depending on whether or not the aircraft flies in an area susceptible to lightning strikes, it is possible to set the necessary standards for lightning strike countermeasures so as not to be excessive.

(Operation and action)
Next, an example of a current observation method using the current observation system 1 will be described.

FIG. 6 is a flowchart showing an example of the flow of the current observation method using the current observation system 1 shown in FIG.

First, in step S1, information representing the relationship between the current flowing through the test object O and the amount of strain generated in the test object O due to the current is acquired by a test or the like. For example, in the case where the optical fiber sensor 4 is attached to each part of the airframe of the aircraft 20 as illustrated in FIG. 4, the current and the amount of distortion are calculated for each part to which the optical fiber sensor 4 is attached. Information representing the relationship between the two is acquired. The acquired information is stored in the strain amount / current value conversion information storage unit 9A of the storage device 9 as reference information for converting the strain amount into the current value.

On the other hand, the optical fiber sensor 4 is irradiated with laser light from the light source 5. This makes it possible to observe the current value using the current observation system 1.

When the monitoring of the current flowing through the test object O is started and the current actually flows through the test object O, the test object O is distorted by the electromagnetic force. As a specific example, when an aircraft 20 having an optical fiber sensor 4 attached to each part of the airframe is hit by lightning as illustrated in FIG. 4, a lightning current flows through the aircraft 20. Distortion occurs in each part of the aircraft 20 through which the lightning current has flowed. When the test object O such as the aircraft 20 is composed of a plurality of conductors such as CFRP and an insulator, the Lorentz force causes the test object O to be distorted.

Then, in step S2, the amount of distortion of the object O to be inspected is detected by each optical fiber sensor 4 arranged at the portion where a current such as a lightning strike current flows. Specifically, when the test object O is distorted, the optical fiber sensor 4 expands and contracts together with the test object O. As a result, the optical characteristics such as the light reflection characteristic and the light transmission characteristic of the optical fiber sensor 4 change. The amount of change in the optical characteristics of the optical fiber sensor 4 depends on the amount of distortion of the test object O. Therefore, the optical fiber sensor 4 outputs an optical signal having a wavelength distribution corresponding to the changed optical characteristics as a distortion amount detection signal.

The distortion amount detection signal output as an optical signal from each optical fiber sensor 4 is detected by the photodetector 6. The distortion amount detection signal detected by the photodetector 6 is converted from an optical signal into an electric signal and output to the signal processing unit 3.

Next, in step S3, the amount of distortion of the test object O is converted into a current value by the current acquisition unit 8A. Specifically, the information for converting the strain amount into the current value stored in the strain amount / current value conversion information storage unit 9A, and the strain amount of the test object O detected by each optical fiber sensor 4. The magnitude of the current flowing through the test object O is obtained based on the above. Therefore, when the strain amount is detected at a plurality of positions of the test object O, the magnitude of the current flowing through the test object O is obtained for each position where the strain amount is detected by the current acquisition unit 8A. The magnitude of the obtained current can be displayed on the display device 10. Further, the current value can be stored in the observation data storage unit 9B in association with the detection position of the strain amount.

Next, in step S4, when the strain amount is detected at a plurality of positions of the test object O, the current distribution acquisition unit 8B acquires the current distribution. That is, the detection position of the strain amount and the current value corresponding to the strain amount are associated with each other. This makes it possible to obtain a one-dimensional, two-dimensional or three-dimensional current distribution map having a spatial axis. The acquired current distribution map can be displayed on the display device 10. Further, the current distribution map can be stored in the observation data storage unit 9B.

As a specific example, if a lightning current flows through an aircraft 20 in which an optical fiber sensor 4 is attached to each part of the airframe as illustrated in FIG. 4, current distribution information is provided along the path through which the lightning current flows. Can be obtained.

Next, in step S5, the direction in which the current flows is specified as needed. For example, when a lightning current flows through an aircraft 20 as illustrated in FIG. 4, the inlet and outlet of the lightning current can be specified. In that case, the timing recording unit 8C associates the distortion amount detection timing with the strain amount detection position and the current value. Then, the observation data display unit 8E creates spatially and temporally continuous time-series current value distribution data. The created time-series current value distribution data can be displayed on the display device 10. Further, the time-series current value distribution data can be stored in the observation data storage unit 9B.

Next, in step S6, the presence or absence of damage is detected as needed. Specifically, the damage detection unit 8D executes threshold processing for the amount of strain of the test object O detected by each optical fiber sensor 4. Then, when at least one of the detected strain amounts exceeds the threshold value or exceeds the threshold value, it can be determined that the test object O has been damaged. When it is determined that damage has occurred, the display device 10 can display the detection position of the corresponding strain amount as the damage occurrence position. Further, the damage occurrence position can be stored in the observation data storage unit 9B in association with the strain amount.

Next, in step S7, desired statistical information can be acquired as needed. For example, the repetitive current value can be measured for the same test object O or a plurality of different test objects O. In that case, the observation data display unit 8E can create a distribution map of the average value of the current values and the like. Further, if the path through which the current flows changes, it is possible to create a current value map or a frequency map in which the current value map is spatially synthesized.

Therefore, if the test object O is an aircraft 20 as illustrated in FIG. 4, a lightning current distribution map and a frequency map can be created. Further, by repeatedly detecting the inlet and outlet of the lightning current, it is possible to create a probability distribution map in which each part of the aircraft 20 becomes the inlet and outlet of the lightning current.

The statistical information created by the observation data display unit 8E can be displayed on the display device 10. Further, it can be saved in the observation data storage unit 9B so that the statistical information can be updated.

(effect)
In the current observation system 1 and the current observation method as described above, the relationship between the amount of strain generated when a current flows through the object O to be inspected and the current value is acquired in advance, and the strain detected by the optical fiber sensor 4 is obtained. The magnitude of the current flowing through the test object O is observed based on the quantity.

Therefore, according to the current observation system 1 and the current observation method, the magnitude of the current flowing through the conductor covered with the insulator, such as a composite material such as CFRP in which the resin is reinforced with conductive fibers as well as the metal, is used. Even if there is, it can be measured as long as the test object O has a detectable magnitude and distortion occurs. It is also possible to detect the presence or absence of damage in addition to the current value.

In particular, when the object O to be inspected is the aircraft itself or a test body or test piece that simulates all or part of the aircraft, the current value distribution and frequency distribution of the lightning current, the inlet and outlet of the electric shock current, and each part are the lightning current. It is possible to obtain various statistical data on the lightning current such as the probability distribution that becomes the entrance and exit of the.

It is also possible to obtain various statistical data on lightning currents with actual lightning using an actual aircraft without manufacturing test specimens or test pieces. In that case, it is possible to eliminate the need for a test in which a current simulating a lightning strike current is passed through an aircraft body or a test piece.

In addition, the effect of lightning current on the airframe of the aircraft can be evaluated. As a result, for example, it is possible to alleviate excessive conditions for lightning strike countermeasures in an aircraft structure composed of a conductive composite material such as CFRP. As a more specific example, when the value of the lightning strike current is negligible, it is possible to eliminate the need for lightning strike countermeasures such as attaching a metal mesh or intentionally providing a fastener for passing the lightning strike current.

On the contrary, for places where the value of the lightning current is large, it is possible to eliminate the need for repair or replacement of parts in the event of a lightning strike due to a minor design change or addition of parts. As a result, it is possible to improve the efficiency of aircraft operation.

In addition, it is possible to quickly grasp the lightning point and the part where the lightning current is emitted in the event of a lightning strike and inspect for damage. Even if the aircraft structure is damaged, the labor and time required for identifying the damaged position, repairing the damage, and replacing parts can be reduced. Therefore, it is possible to improve the efficiency of aircraft operation.

Moreover, the sensor required to measure the current value at one location is only one very light optical fiber sensor 4. Therefore, it is possible to suppress the amount of increase in weight required for measuring the current value at each part of the aircraft. That is, it is possible to measure the lightning current value at each part of the aircraft as a countermeasure against the lightning current while reducing the weight of the aircraft.

(Second Embodiment)
FIG. 7 is a block diagram of the current observation system according to the second embodiment of the present invention.

In the current observation system 1A according to the second embodiment shown in FIG. 7, the first point is that an ultrasonic inspection can be performed to detect whether or not the test object O has been damaged. It is different from the current observation system 1 in the embodiment of. Since the other configurations and operations of the current observation system 1A in the second embodiment are not substantially different from those of the current observation system 1 in the first embodiment, the same configuration or the corresponding configurations are designated by the same reference numerals. The explanation is omitted.

The current observation system 1A includes a distortion / ultrasonic detection system 30 and a signal processing unit 3. In the strain / ultrasonic detection system 30, in addition to the optical fiber sensor 4, the light source 5, and the optical detector 6 constituting the strain detection system 2 of the current observation system 1 in the first embodiment, the test object O is superposed. A single or a plurality of ultrasonic vibrators 31 that oscillate sound waves, a transmission circuit 32 that applies a transmission signal to the single or a plurality of ultrasonic vibrators 31, respectively, and a single or a plurality of transmission circuits 32 by supplying power. A power supply 33 for driving each of the ultrasonic vibrators 31 and a start circuit 34 for activating the power supply 33 are provided.

Therefore, in order to determine whether or not the test object O has been damaged, ultrasonic waves can be transmitted from the ultrasonic vibrator 31 toward the test site of the test object O. When ultrasonic waves are transmitted from the ultrasonic vibrator 31, electric power is supplied from the power supply 33 to the transmission circuit 32, and an electric signal is output to the ultrasonic vibrator 31 as a transmission signal from the transmission circuit 32. As a result, in the ultrasonic vibrator 31, the electric signal is converted into ultrasonic waves and transmitted to the test site.

Therefore, when transmitting ultrasonic waves from the ultrasonic vibrator 31, a trigger for driving the power supply 33, the transmission circuit 32, and the ultrasonic vibrator 31 is required. The trigger can be manually generated by operating the input device 11, but it is often practical to be able to generate it automatically.

Therefore, the start circuit 34 can automatically start the power supply 33 when the current acquisition unit 8A acquires a current value equal to or higher than the threshold value or exceeds the threshold value. That is, the activation circuit 34 of the distortion / ultrasonic detection system 30 can be controlled by the current acquisition unit 8A of the signal processing unit 3. As a result, only when a current having a large current value that can cause damage to the test site of the test object O flows, the power supply 33 that consumes power is started and the current flows. An ultrasonic flaw detection test of the site can be performed.

When ultrasonic waves are transmitted from the ultrasonic vibrator 31 to the test site, the transmitted ultrasonic waves pass through the test site. If there is damage to the test site, the waveform of the ultrasonic waves transmitted through the test site will change under the influence of the damage. If there is damage to the test site, the ultrasonic waves transmitted to the test site are reflected by the damage. The result is an ultrasonic reflected wave with a peak that would not occur in the absence of damage.

Therefore, the optical fiber sensor 4 can detect the vibration of the ultrasonic wave transmitted through the test site of the test object O or the vibration of the reflected wave of the ultrasonic wave reflected by the test site. Specifically, when ultrasonic vibration propagates to the optical fiber sensor 4, minute distortion is generated in the optical fiber sensor 4 due to the ultrasonic vibration. Therefore, the optical characteristics of the optical fiber sensor 4 change according to the waveform of the ultrasonic vibration. Therefore, the optical fiber sensor 4 outputs an optical signal corresponding to the waveform of the ultrasonic vibration. The optical signal output from the optical fiber sensor 4 is detected by the photodetector 6 as a detection signal of ultrasonic vibration. The ultrasonic vibration detection signal detected by the photodetector 6 is converted from an optical signal into an electric signal and output to the signal processing unit 3.

The ultrasonic vibration detection signal output to the signal processing unit 3 is given to the damage detection unit 8D. Therefore, the damage detection unit 8D can acquire the waveform of the ultrasonic wave transmitted through the test site of the test object O or the waveform of the ultrasonic reflection reflected at the test site. Then, the damage detection unit 8D can detect whether or not damage has occurred in the test portion of the test object O based on the waveform of the vibration of the transmitted ultrasonic wave or the reflected wave detected by the optical fiber sensor 4. it can.

Therefore, the damage detection unit 8D is based on the waveform of the ultrasonic wave transmitted through the test site or the waveform of the ultrasonic reflection reflected at the test site when there is no damage in the test site of the test object O in advance. Saved as a waveform. Then, in the damage detection unit 8D, damage occurs in the test site by comparing the reference waveform with the waveform of the ultrasonic wave actually transmitted through the test site or the waveform of the ultrasonic reflection reflected in the test site. It can be determined whether or not it has been done. Specifically, an index value representing the amount of deviation between the reference waveform and the waveform of ultrasonic waves actually transmitted through the test site or the waveform of ultrasonic reflection reflected at the test site was empirically determined. When the threshold value is exceeded or the threshold value is exceeded, it can be determined that the test site has been damaged.

Specific examples of the index value to be subjected to the threshold processing include a least squares error, an intercorrelation coefficient, a difference or ratio of peak values, a difference or ratio of the area surrounded by a waveform, and the like. Further, signal processing such as averaging processing, noise removal processing, and envelope detection processing may be executed prior to the waveform comparison processing. These signal processes may be executed on the electric signal output from the photodetector 6 or may be executed on the optical signal input to the photodetector 6.

In this way, the optical fiber sensor 4 for detecting the amount of strain can also be used as a sensor for detecting ultrasonic vibration. As a result, it is possible to perform both measurement of the current value by detecting the amount of strain and detection of damage while suppressing an increase in the number of parts and weight.

According to the current observation system 1A in the second embodiment as described above, in addition to the same effect as the current observation system 1 in the first embodiment, the damage detection ability is improved by performing ultrasonic inspection. You can get the effect of being able to. In particular, even if damage occurs at a position far from the optical fiber sensor 4 so that the optical fiber sensor 4 is large enough and distortion does not occur, the damage can be detected by performing an ultrasonic inspection. it can.

Further, by arranging the plurality of ultrasonic vibrators 31 and the plurality of optical fiber sensors 4 at different positions, it is possible to detect not only the presence or absence of damage but also the position where damage occurs with high accuracy. In particular, if damage is detected using ultrasonic reflected waves, the damage occurrence position can be more accurately determined based on the time difference and sound velocity from the ultrasonic oscillation timing to the ultrasonic reflected wave detection timing. It becomes possible to identify.

Moreover, the start circuit 34 can automatically start the power supply 33 for ultrasonic inspection only when the current is detected by the measurement of the amount of strain using the optical fiber sensor 4. Therefore, the current observation system 1A can be mounted on an aircraft in which it is important to reduce power consumption. That is, ultrasonic flaw detection inspection can be performed on an aircraft in which it is important to reduce power consumption.

(Other embodiments)
Although the specific embodiments have been described above, the described embodiments are merely examples and do not limit the scope of the invention. The novel methods and devices described herein can be embodied in a variety of other modes. In addition, various omissions, substitutions and changes can be made in the methods and devices described herein without departing from the gist of the invention. The appended claims and their equivalents include such various modalities and variations as incorporated in the scope and gist of the invention.

1, 1A Current observation system 2 Distortion detection system 3 Signal processing unit 4 Optical fiber sensor 5 Light source 6 Optical detector 7 Optical waveguide 8 Computing device 8A Current acquisition unit 8B Current distribution acquisition unit 8C Timing recording unit 8D Damage detection unit 8E Observation data Display 9 Storage device 9A Distortion amount / current value conversion information storage unit 9B Observation data storage unit 10 Display device 11 Input device 20 Aircraft 30 Strain / ultrasonic detection system 31 Ultrasonic transducer 32 Transmission circuit 33 Power supply 34 Start circuit O Object O1 Carbon fiber O2 Epoxy resin O3 Fiber reinforced resin layer I Current F Lorentz force

Claims (12)

A storage device that stores information representing the relationship between the current flowing through the test object and the amount of strain generated in the test object due to the current.
An optical fiber sensor that detects the amount of distortion of the test object,
A current acquisition unit that obtains a current flowing through the test object based on the information and the amount of strain detected by the optical fiber sensor.
Current observation system with. An ultrasonic oscillator that oscillates ultrasonic waves to the object to be inspected,
A power supply for driving the ultrasonic oscillator and
A start circuit that activates the power supply when a current value equal to or greater than the threshold value or exceeds the threshold value is acquired by the current acquisition unit.
Based on the vibration of the ultrasonic wave transmitted through the test site of the test object or the vibration of the reflected wave of the ultrasonic wave reflected by the test site and detected by the optical fiber sensor. A damage detection unit that detects whether or not damage has occurred to the test object, and
The current observation system according to claim 1, further comprising. An aircraft equipped with the current observation system according to claim 1 or 2. A step of acquiring information representing the relationship between the current flowing through the test object and the amount of strain generated in the test object due to the current and storing the information in the storage device.
A step of detecting the amount of strain of the test object with an optical fiber sensor,
A step of obtaining the current flowing through the test object based on the information and the amount of strain detected by the optical fiber sensor, and
Current observation method with. The current observation method according to claim 4, wherein a composite material made of a resin reinforced with conductive fibers is used as the test object to obtain a current flowing through the composite material. The current observation method according to claim 4 or 5, wherein the lightning current flowing through the structure is obtained by using the structure of the aircraft as the test object. The current observation method according to claim 6, wherein the optical fiber sensor is attached to a plurality of test sites of an aircraft to obtain a lightning strike current flowing through the plurality of test sites. The current observation method according to claim 7, wherein the lightning current distribution of the aircraft is obtained by obtaining the lightning current flowing through the plurality of test sites. By detecting the timing at which the lightning current flows through the plurality of test sites, the test site on the inlet side of the lightning current to the aircraft and the test site on the outlet side of the lightning current from the aircraft are specified. The current observation method according to claim 7 or 8. The current observation method according to any one of claims 7 to 9, wherein the damage inspection using the optical fiber sensor detects whether or not damage has occurred in the test site through which the lightning current has flowed. The current observation method according to claim 5, wherein the optical fiber sensor is arranged so that the length direction of the optical fiber sensor, which is the measurement direction of the strain amount, is perpendicular to the length direction of the fiber. The structure to which a conductor for forming a path of a lightning current is attached, using the composite material made of a resin reinforced with conductive fibers and constituting the structure of an aircraft as the test object. The current observation method according to claim 4, wherein a simulated current is passed through the composite material to confirm that the current flowing through the composite material is equal to or less than the allowable value or less than the allowable value.

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