Inspection method, inspection device, inspection system, and program

Abstract

To provide an inspection method, an inspection device, an inspection system, and a program with which it is possible to shorten a time of nondestructively inspecting the inside of a resin that covers electroconductive parts in an electric power apparatus.SOLUTION: According to an embodiment of the present invention, an inspection method for inspecting the inside of a resin that covers electroconductive parts in an electric power apparatus is provided. The inspection method comprises the steps of: acquiring a reflected wave signal that corresponds to a reflected wave, from an interface of foreign matter mixed in the inside of the resin, of a pulse wave irradiated on the basis of a plurality of irradiation points set to the resin; and generating an image that includes foreign matter, on the basis of the acquired reflective wave signal. The plurality of irradiation points are sparsely set to a plurality of pixels constituting the generated image.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an inspection method, an inspection device, an inspection system, and a program. [Background technology]

[0002] In general, electric power devices are often configured so that conductive parts (conductors) made of metal are covered with resin to maintain insulation.

[0003] However, in the process of covering the conductive portion with resin, foreign matter may be mixed into the resin, which may cause partial discharge or dielectric breakdown in the electric power equipment, resulting in failure of the electric power equipment.

[0004] For this reason, it is necessary to inspect the inside of the resin covering the conductive part for contamination with foreign matter. In this case, for example, it is possible to inspect whether or not foreign matter has been contaminated inside the resin by destroying the resin, but such an inspection method requires the destruction of the resin, which is not preferable from the viewpoint of the destruction cost and the labor required for the inspection. For this reason, it is desirable to inspect the inside of the resin without destroying the resin (i.e., non-destructively).

[0005] However, the resin covering the conductive parts is thick, and the structure (e.g., the shape of the resin) varies depending on the power equipment (product), making it difficult to inspect the inside of the resin nondestructively. Furthermore, while it is useful to identify the type of foreign matter that has entered the resin in order to take measures to prevent the intrusion of foreign matter, it is also difficult to identify (inspect) the type of foreign matter nondestructively. In particular, many of the foreign matter is small, requiring precise inspection. Therefore, inspecting the inside of the resin nondestructively takes a long time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-105649 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the problem that the present invention aims to solve is to provide an inspection method, an inspection device, an inspection system, and a program that can shorten the time required to non-destructively inspect the inside of the resin that covers the conductive parts in electric power equipment. [Means for solving the problem]

[0008] According to an embodiment, there is provided an inspection method for inspecting the inside of a resin covering a conductive part in an electric power device. The inspection method includes the steps of acquiring reflected wave signals corresponding to waves reflected from interfaces of foreign matter mixed inside the resin, the reflected wave signals being generated by irradiating pulse waves based on a plurality of irradiation points set on the resin, and generating an image including the foreign matter based on the acquired reflected wave signals. The plurality of irradiation points are set sparsely with respect to a plurality of pixels constituting the generated image. The generating step generates the image by applying a compressed sensing technique, and the number of the set irradiation points varies depending on the type of foreign matter that may be mixed inside the resin. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram showing an example of the functional configuration of an inspection apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a hardware configuration of an inspection apparatus. [Figure 3] FIG. 2 is a diagram schematically illustrating an electric power device. [Figure 4] FIG. 10 is a diagram showing an example of the positional relationship between an oscillator and a receiver that employs a lens system. [Figure 5] FIG. 1 is a diagram for explaining an oscillator and a receiver that employ a lensless system. [Figure 6] FIG. 10 is a diagram showing another example of the positional relationship between the oscillator and the receiver. [Figure 7] FIG. 10 is a diagram showing an example of a processing procedure of an inspection device. [Figure 8]FIG. 1 is a diagram for explaining an overview of a simulation model. [Figure 9] FIG. 4 is a diagram for explaining an example of a reflected wave reflected at an interface between a first material and a second material. [Figure 10] FIG. 4 is a diagram for explaining an example of a reflected wave reflected at an interface between a first material and a second material. [Figure 11] FIG. 4 is a diagram for explaining an example of a reflected wave reflected at an interface between a first material and a second material. [Figure 12] FIG. 10 is a diagram showing an example of a reflected waveform based on an actual inspection result. [Figure 13] FIG. 10 is a diagram showing an example of reflection intensity based on an actual inspection result. [Figure 14] FIG. 1 is a diagram for explaining an example of an image generated by applying compressed sensing technology. [Figure 15] 10A and 10B are diagrams for explaining the difference in characteristics of a reflected wave when a reflected wave from a foreign object is compared with a reflected wave from resin surrounding the foreign object; [Figure 16] FIG. 10 is a diagram showing an example of an image generated when a lens system is adopted. [Figure 17] FIG. 10 is a diagram showing an example of an image generated when a lensless system is adopted. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings. The inspection device of this embodiment is used to inspect the inside of resin without destroying it (i.e., to detect foreign matter mixed inside the resin) by irradiating pulse waves onto electric power equipment that is configured so that conductive parts (conductors) are covered with resin.

[0011] In this embodiment, the types of foreign matter mixed inside the resin are assumed to be, for example, metal, air bubbles, resin burrs, etc. The types of foreign matter may also be a concept that includes, for example, an abnormality (defect) in the power device, such as peeling between the conductive part and the resin or a crack occurring in the resin.

[0012] The electric power equipment includes, for example, a circuit breaker, a disconnecting switch, a current transformer, or a voltage transformer. Furthermore, the electric power equipment may be, for example, a power transformer, a gas-insulated switchgear, a generator, an electric motor, or a reactor, as long as it is an equipment that may generate partial discharge. Since such electric power equipment passes high voltage and large current from the outside via a power cable, the conductive parts of the electric power equipment are covered with resin to maintain insulation.

[0013] Here, the above-mentioned methods for non-destructively inspecting the inside of resin include methods using electromagnetic waves such as X-rays or infrared rays, and methods using ultrasonic waves. Below, we will briefly explain some of the methods used for such inspections.

[0014] First, X-rays have good penetration into resin, so they can be used to inspect the inside of resin. However, because X-rays have low penetration into metal, it may not be possible to properly inspect structures with embedded metal. For example, an X-ray CT scanner (X-ray CT inspection) can be used to inspect (observe) the inside of resin even when metal is embedded, but large electric power equipment cannot be inspected using a general X-ray CT scanner. Although there are X-ray CT scanners that can handle large electric power equipment, these X-ray CT scanners have special specifications, making inspection using them impractical. Furthermore, radiation management is required when using X-rays.

[0015] Furthermore, in order to take measures against contamination, it is useful to distinguish the type of foreign matter that has entered the resin, and from the viewpoint of distinguishing the type of foreign matter, when X-rays are used, it is thought that it is possible to distinguish metals, air bubbles, etc. that have entered the resin due to differences in density, but it is not possible to distinguish and detect objects with similar densities, such as resin burrs.

[0016] Next, infrared (thermography) can easily obtain information about the inside of resin, but it becomes difficult to obtain this information when the resin is thick (for example, 3 mm or thicker). Furthermore, infrared has low resolution, making it difficult to detect small foreign objects. Furthermore, the type of foreign object is determined by differences in thermal conductivity, making it difficult to distinguish the type of foreign object using infrared.

[0017] Ultrasonic waves can also provide information about the interior of resin with high resolution and in a relatively simple manner. However, ultrasonic waves are significantly attenuated in resin, making it difficult to inspect thick resin (for example, 10 mm or thicker) using conventional methods. Ultrasonic waves are also significantly attenuated in air, making inspections cumbersome, requiring immersion in water or passing through gel. The type of foreign matter can be determined by taking advantage of the fact that the reflectivity and propagation speed of ultrasonic waves vary depending on the material. Ultrasonic waves are an effective method for inspecting foreign matter on the surface of electrical equipment (resin).

[0018] In addition to the above-mentioned X-rays, infrared rays, and ultrasound, it is also possible to use electromagnetic waves in the high frequency band (for example, terahertz waves). Terahertz waves are electromagnetic waves that have good resin penetration properties, and can detect foreign matter mixed inside even thick resin (for example, about 60 mm). Furthermore, if a scanning mechanism or the like is provided, it is possible to handle large electric power equipment (i.e., inspect the inside of the resin of large electric power equipment). Furthermore, it may be possible to identify the type of foreign matter by taking advantage of the fact that the transmission characteristics of terahertz waves differ depending on the material.

[0019] Therefore, in this embodiment, an inspection device that uses the above-mentioned terahertz waves to inspect the inside of the resin covering the conductive parts of electric power equipment will be described. Note that the inspection of the inside of the resin in this embodiment includes detecting foreign matter (e.g., metal, air bubbles, resin burrs, etc.) mixed in the inside of the resin, and detecting the occurrence of the above-mentioned peeling or cracks (i.e., defects in the electric power equipment). Furthermore, the inspection of the inside of the resin may also include identifying the type of foreign matter mixed in the inside of the resin.

[0020] Fig. 1 shows an example of the functional configuration of an inspection device according to this embodiment. The inspection device 10 shown in Fig. 1 is an information processing device (electronic device) such as a personal computer, a smartphone, a tablet computer, or a server device.

[0021] 1, an inspection device 10 is connected to an oscillation device (oscillator) 20 and a receiving device (receiver) 30. In this embodiment, the inspection device 10, the oscillation device 20, and the receiving device 30 configure an inspection system.

[0022] The oscillator 20 functions as an irradiation device used to irradiate the electric power equipment (the resin covering the conductive portion) with a predetermined pulse wave (terahertz wave), and is configured to oscillate the terahertz wave in response to an instruction from, for example, the inspection device 10. The terahertz wave oscillated by the oscillator 20 is assumed to be an electromagnetic wave in a frequency band corresponding to, for example, a range of 0.05 to 10 THz.

[0023] As described above, when terahertz waves emitted from the oscillator 20 are irradiated onto a resin, the terahertz waves are reflected, for example, by (the interface of) foreign matter mixed inside the resin. The receiver (detector) 30 is configured to receive (detect) such reflected waves. The receiver 30 converts the received reflected waves into an electrical signal to generate a reflected wave signal corresponding to the reflected waves. This reflected wave signal includes the intensity (signal intensity) of the reflected waves received by the receiver 30, the peak value of the intensity of the reflected waves, and the time at which the peak is reached (hereinafter referred to as the peak arrival time).

[0024] In this embodiment, the measurement light delay time of the terahertz waves irradiated to the power equipment (i.e., the terahertz waves oscillated by the oscillator 20) is, for example, 160 seconds. When this measurement light delay time is converted into an optical path length, it becomes 48 mm. When using a reflective type, the measurable thickness is 24 mm (48 mm round trip, refractive index 1.0). The terahertz waveform acquisition speed is 1000 waveforms / second. The acquisition speed during imaging is 1000 pixels / second. The sampling interval is 0.1 psec. The terahertz wave oscillation band is greater than 2.0 THz.

[0025] There are various types of oscillator 20, such as high-output type and wideband type, and the type of oscillator 20 to be used should be appropriate depending on the material of the resin to be irradiated with the terahertz waves (i.e., the object to be inspected).

[0026] The inspection device 10 shown in FIG. 1 includes a propagation behavior prediction unit 11, a reflected wave signal acquisition unit 12, a waveform data generation unit 13, an image generation unit 14, a depth calculation unit 15, a discrimination unit 16, and an output unit 17.

[0027] The propagation behavior prediction unit 11 predicts the propagation behavior of terahertz waves when inspecting the inside of the resin covering a conductive part in the electric power equipment, based on at least one of the structure of the electric power equipment and the relative dielectric conductivity of the resin and foreign matter that may be mixed inside the resin. The frequency of the terahertz waves oscillated by the oscillator 20 during the inspection (i.e., the terahertz waves irradiated onto the resin), the position of the oscillator 20, and the position of the receiver 30 are set based on the prediction result by the propagation behavior prediction unit 11.

[0028] The reflected wave signal acquiring unit 12 acquires the reflected wave signal generated in the receiving device 30 from the receiving device 30.

[0029] The waveform data generating unit 13 generates waveform data indicating the waveform of the reflected wave (hereinafter referred to as the reflected waveform) based on the reflected wave signal acquired by the reflected wave signal acquiring unit 12. Specifically, the waveform data generating unit 13 generates waveform data that reflects the intensity of the reflected wave contained in the reflected wave signal, the peak value of the intensity of the reflected wave, the time when the peak is reached, and the like.

[0030] The image generating unit 14 generates an image (e.g., a planar image) based on the reflected wave signal acquired by the reflected wave signal acquiring unit 12. Specifically, the image generating unit 14 generates three-dimensional image data based on the reflected wave signal. The three-dimensional image data includes, for example, pixel values ​​corresponding to the intensity of the reflected wave included in the reflected wave signal for each coordinate value in a Cartesian coordinate system in three-dimensional space. The image generating unit 14 generates an image including a foreign object based on this three-dimensional image data. Specifically, the image generating unit 14 generates a planar image in which the value of one of the coordinate axes (x, y, z) in the three-dimensional space is fixed. For example, if the coordinate value of the Z axis is fixed, the image generating unit 14 can generate a planar image related to the XY plane at the fixed coordinate value of the Z axis.

[0031] The depth calculation unit 15 calculates the depth of a foreign object mixed inside the resin based on the reflected wave signal acquired by the reflected wave signal acquisition unit 12. The depth of the foreign object is the distance from the surface of the resin irradiated with the terahertz wave to the foreign object, and is calculated based on the peak arrival time (delay time) included in the reflected wave signal and the refractive index of the resin. The refractive index of the resin is assumed to be measured in advance and stored inside the inspection device 10, for example.

[0032] The discrimination unit 16 discriminates the type of foreign matter mixed inside the resin based on an index whose value varies depending on the type of foreign matter obtained by analyzing the reflected wave signal acquired by the reflected wave signal acquisition unit 12. In this embodiment, the type of foreign matter is discriminated using an index (characteristic) that appears on the waveform data generated by the waveform data generation unit 13, for example.

[0033] The output unit 17 outputs the waveform data generated by the waveform data generation unit 13, the image generated by the image generation unit 14, the depth of the foreign matter calculated by the depth calculation unit 15, and the type of foreign matter identified by the identification unit 16, etc.

[0034] Fig. 2 shows an example of the hardware configuration of the inspection device 10 shown in Fig. 1. The inspection device 10 includes a CPU 101, a nonvolatile memory 102, a RAM 103, and a communication device 104. The inspection device 10 also includes a bus 105 that interconnects the CPU 101, the nonvolatile memory 102, the RAM 103, and the communication device 104.

[0035] The CPU 101 is a processor for controlling the operation of each component in the inspection device 10. The CPU 101 may be a single processor or may be configured with multiple processors. The CPU 101 executes various programs loaded from the non-volatile memory 102 to the RAM 103. In this embodiment, the programs executed by the CPU 101 include an inspection program 103a.

[0036] 1, some or all of the propagation behavior prediction unit 11, reflected wave signal acquisition unit 12, waveform data generation unit 13, image generation unit 14, depth calculation unit 15, discrimination unit 16, and output unit 17 are realized by software, for example, when the CPU 101 (i.e., the computer of the inspection device 10) executes the inspection program 103a. This inspection program 103a may be stored in a computer-readable storage medium and distributed, or may be downloaded to the inspection device 10 via a network.

[0037] Here, it has been described that some or all of the above-mentioned units 11 to 17 are realized by software, but some or all of the units 11 to 17 may also be realized by hardware such as an IC (Integrated Circuit), or may be realized by a combination of software and hardware.

[0038] The nonvolatile memory 102 is a storage medium used as an auxiliary storage device. The RAM 103 is a storage medium used as a main storage device. Although only the nonvolatile memory 102 and the RAM 103 are shown in Fig. 2, the inspection device 10 may also include other storage devices such as a hard disk drive (HDD) and a solid state drive (SSD).

[0039] The communication device 104 is a device configured to perform wired or wireless communication with external devices.

[0040] Although not shown in FIG. 2, the inspection device 10 may further include an input device such as a mouse or a keyboard, and a display device such as a display.

[0041] Next, the principle of inspecting the inside of resin using the inspection device 10 according to this embodiment will be described.

[0042] Fig. 3 shows a schematic diagram of electric power equipment 40 arranged in a three-dimensional space defined by mutually orthogonal X, Y, and Z directions. As shown in Fig. 3, electric power equipment 40 is composed of conductive parts 41 made of a metal material and resin (insulator) 42 covering conductive parts 41. For convenience, only a portion of conductive part 41 and resin 42 is shown in Fig. 3.

[0043] Resin 42 is formed of, for example, an epoxy resin containing a filler. As the epoxy resin, for example, a bisphenol A type epoxy resin may be used. Furthermore, an acid anhydride-based hardener may be used for resin 42. As the filler, for example, silica is used. Note that resin 42 described here is only an example, and for example, dicyclopentadiene or the like may be used instead of bisphenol A type epoxy resin.

[0044] As described above, foreign matter 43 may be mixed into the resin 42 in the electric power device 40, and the foreign matter 43 may include metal, air bubbles, resin burrs, and the like.

[0045] Next, the oscillator 20 that oscillates the terahertz waves to be irradiated onto the power equipment 40 (resin 42) and the receiver 30 that receives the terahertz waves reflected from the power equipment 40 will be described.

[0046] FIG. 4 shows the positional relationship between the oscillator 20 and the receiver 30 when terahertz waves are irradiated from a direction perpendicular to the interface between the electric power device 40 and air, for example.

[0047] In this case, a portion of the terahertz waves emitted from oscillator 20 is reflected by beam splitter 51, but the terahertz waves that are not reflected by beam splitter 51 are transmitted through beam splitter 51. The terahertz waves that have transmitted through beam splitter 51 are converged by lens 52. The converged terahertz waves reach electric power equipment 40. A portion (reflected wave) of the terahertz waves reflected by electric power equipment 40 (the interface of foreign matter 43 mixed inside resin 42) is refracted by beam splitter 51 and received by receiver 30.

[0048] In Figure 4, we have described an oscillator 20 and a receiver 30 that are equipped with a lens 52 (i.e., an oscillator 20 and a receiver 30 that use a lens system), but the oscillator 20 and the receiver 30 may also be configured not to have a lens 52 (i.e., to use a lensless system) as shown in Figure 5.

[0049] FIG. 6 also shows the positional relationship between the oscillator 20 and the receiver 30 when terahertz waves are emitted from an angle that is not perpendicular to the interface between the power device 40 and air, for example.

[0050] In this case, the oscillator 20 is placed at a position where the terahertz waves oscillated by the oscillator 20 are irradiated onto the electric power equipment 40 at a predetermined angle. The predetermined angle is, for example, an angle that is not perpendicular to the interface between the electric power equipment 40 and the air. The terahertz waves oscillated from the oscillator 20 in this manner reach the electric power equipment 40. The terahertz waves (reflected waves) reflected by the electric power equipment 40 (the interface of the foreign matter 43 mixed inside the resin 42) are received by the receiver 30.

[0051] For example, when the oscillator 20 and the receiver 30 are used in the positional relationship described in FIG. 4, the beam splitter 51 theoretically causes a loss of 75% of the terahertz waves.

[0052] On the other hand, when the oscillator 20 and the receiver 30 are used in the positional relationship shown in FIG. 6, the receiver 30 can receive the terahertz waves (or their reflected waves) without going through the beam splitter 51, thereby reducing the loss caused by the beam splitter 51 and improving the reception (detection) capability of the reflected waves.

[0053] Furthermore, although FIG. 6 assumes that the oscillator 20 and the receiver 30 employ a lens system, the oscillator 20 and the receiver 30 shown in FIG. 6 may employ a lensless system.

[0054] The intensity of the reflected wave during inspection by the inspection device 10 varies depending on the angle of the terahertz wave irradiated onto the electric power equipment 40, and also on whether a lens system or a lensless system is adopted in the oscillator 20 and the receiver 30. Therefore, the angle of the terahertz wave irradiated onto the electric power equipment 40 (normal incidence or oblique incidence) and the system adopted in the oscillator 20 and the receiver 30 (lens system or lensless system) can be selected appropriately depending on the electric power equipment 40 (product).

[0055] Next, an example of a processing procedure of the inspection device 10 according to this embodiment will be described with reference to the flowchart of FIG.

[0056] In this embodiment, the inside of the resin 42 is inspected based on a reflected wave signal (a reflected wave signal generated by the receiving device 30) corresponding to the reflected wave received by the receiving device 30, and the intensity of the reflected wave, etc., is thought to differ depending on, for example, the frequency band of the terahertz wave and the angle at which the terahertz wave is irradiated.

[0057] Therefore, before inspecting the inside of resin 42 in electric power device 40, propagation behavior predicting unit 11 predicts (simulates) in advance the propagation behavior (or reflection behavior) of terahertz waves in resin 42 (step S1).

[0058] The following describes the prediction (processing) of the propagation behavior of terahertz waves by the propagation behavior prediction unit 11. The prediction of the propagation behavior of terahertz waves can be performed, for example, using the Finite-Difference Time-Domain method (FDTD) in electromagnetic field analysis, which analyzes the interaction between an object and an electromagnetic field. In this case, for example, a simulation model is constructed in the electromagnetic field analysis, taking into account the presence of foreign matter, and the oscillation point (oscillation position) of the terahertz waves and the reception point (reception position) of the reflected waves of the terahertz waves are set in the simulation model.

[0059] Here, an overview of the above-mentioned simulation model will be described with reference to Fig. 8. According to the simulation model shown in Fig. 8, for example, a first material 61 corresponding to resin 42 and a second material 62 corresponding to foreign matter 43 are defined. Furthermore, in first material 61, an oscillation point 63 that oscillates terahertz waves (spherical waves) in an arbitrary frequency band and a reception point 64 that receives the terahertz waves reflected from the interface between first material 61 and second material 62 are set.

[0060] Note that the example shown in Figure 8 shows a case where the propagation behavior of terahertz waves is predicted in the case of perpendicular incidence, where the terahertz waves are irradiated from a direction perpendicular to the first material 61 and the second material 62, as explained in Figure 4 above. However, by changing the positions (settings) of the oscillation point 63 and the reception point 64, it is also possible to predict the propagation behavior of terahertz waves in the case of oblique incidence, where the terahertz waves are irradiated from an angle that is not perpendicular to the first material 61 and the second material 62.

[0061] According to such a simulation model, by changing the frequency band, oscillation point, and reception point of the terahertz wave and predicting the intensity of the reflected wave of the terahertz wave received at the reception point (electric field value corresponding to the reflected wave) as the propagation behavior of the terahertz wave, it is possible to select terahertz wave irradiation conditions that will produce a useful (i.e., maximum) reflected wave intensity, even if, for example, power equipment 40 (resin 42) has a complex structure (shape).

[0062] 9 to 11, the reflected wave from the interface between the first material 61 and the second material 62 in the above-mentioned simulation model will be described.

[0063] 9 shows incident waves and reflected waves received at reception point 64 when, for example, terahertz waves in the 0.1 THz band are transmitted from oscillation point 63. That is, in FIG. 9, based on the positional relationship between oscillation point 63 and reception point 64 set in the simulation model described above, it is shown that the terahertz waves transmitted at oscillation point 63 are directly received at reception point 64 as incident waves, and then the reflected waves from the interface between first material 61 and second material 62 are received at reception point 64.

[0064] Moreover, Fig. 10 shows an enlarged view of the reflected waveform shown in Fig. 9. Specifically, Fig. 10 shows reflected waveforms 71 to 74 predicted in the simulation model by changing the relative dielectric constant of the second material 62. The respective relative dielectric constants of the first material 61 and the second material 62 are shown in Fig. 11.

[0065] Reflected waveform 71 shown in Fig. 10 is the waveform of a wave reflected from the interface between first material 61 and second material 62, which has a relative dielectric constant of 1. Reflected waveform 72 is the waveform of a wave reflected from the interface between first material 61 and second material 62, which has a relative dielectric constant of 2. Reflected waveform 73 is the waveform of a wave reflected from the interface between first material 61 and second material 62, which has a relative dielectric constant of 4. Reflected waveform 74 is the waveform of a wave reflected from the interface between first material 61 and second material 62, which has a relative dielectric constant of 5. It is assumed that the relative dielectric constant of first material 61 is 3, as shown in Fig. 11.

[0066] In this case, the amplitudes of the reflected waveforms 71 to 74 shown in FIG. 10 correspond to the intensity of the reflected waves, and the magnitude of the intensity of the reflected waves can be expressed using the relative dielectric constant of the second material 62 as 1>5>2>4.

[0067] The reflection coefficient R of the terahertz wave at the interface between the first material 61 and the second material 62 (hereinafter simply referred to as the reflection coefficient of the second material 62) can be calculated by the following formula (1).

number

[0068] In equation (1), Z1 is the characteristic impedance of the first material 61, and Z2 is the characteristic impedance of the second material 62. In addition, in equation (1), ε is the relative permittivity, and μ is the magnetic permeability. For convenience, in equation (1), the magnetic permeability μ is set to 1.

[0069] According to such equation (1), for example, by applying the relative dielectric constant of the first material 61 and the relative dielectric constant of the second material 62, the reflection coefficient of the second material 62 can be calculated.

[0070] The reflection coefficient of each of the second materials 62 having different relative dielectric constants calculated using the above-mentioned formula (1) is as shown in the following formula (2).

number

[0071] In addition, in equation (2), R1 is the reflection coefficient of the second material 62 having a relative dielectric constant of 1, R2 is the reflection coefficient of the second material 62 having a relative dielectric constant of 2, R4 is the reflection coefficient of the second material 62 having a relative dielectric constant of 4, and R5 is the reflection coefficient of the second material 62 having a relative dielectric constant of 5.

[0072] According to formula (2), it can be seen that the magnitude relationship of the amplitudes (i.e., the intensities of the reflected waves) of the reflected waveforms 71 to 74 corresponding to the above-mentioned respective relative dielectric constants roughly coincides with the magnitude relationship of the absolute values ​​of the reflection coefficients of the second material 62. Note that, as shown in Fig. 10, when the magnitude relationship between the relative dielectric constants of the first material 61 and the second material 62 differs, the reflected wave is inverted.

[0073] While the above simulation results show differences in the intensity and waveform of the reflected wave depending on the dielectric constant, similar trends have been confirmed in actual inspections (measurements). Specifically, FIG. 12 shows an example of a reflected waveform based on actual inspection results. FIG. 12 shows a reflected waveform obtained by placing various materials (metal, air bubbles, and resin burrs) corresponding to foreign matter 43 under a resin plate and irradiating the resin plate with terahertz waves from the top surface (i.e., performing an inspection). FIG. 13 shows the intensity of the reflected wave (reflection intensity) based on the inspection results shown in FIG. 12. The ratios in FIG. 13 indicate the ratio of the intensity of the reflected wave from other materials when the intensity of the reflected wave from the metal (Al plate) is taken as 100%. FIG. 13 shows that the intensity of the reflected wave decreases in the order of metal, air bubbles, and resin burrs.

[0074] As described above, the intensity of the reflected wave varies depending on the relative dielectric constants of the resin 42 (first material 61) and the foreign matter 43 (second material 62), and therefore, by knowing in advance the materials (relative dielectric constants) of the resin 42 and the foreign matter 43 that may be mixed inside the resin 42, it is possible to predict the propagation behavior of the terahertz wave more accurately. That is, in this embodiment, the irradiation conditions of the terahertz wave may be selected taking into account the materials of the resin 42 and the foreign matter 43.

[0075] As described above, in step S1, the propagation behavior of the terahertz waves is predicted based on at least one of the structure of the power equipment 40 (e.g., the shape of the conductive part 41 and the resin 42) and the relative dielectric constant (material) of the resin 42 and the foreign matter 43 that may be mixed inside the resin 42.

[0076] 7, irradiation conditions selected based on the propagation behavior of the terahertz waves predicted in step S1 are set (step S2). Note that the irradiation conditions set in step S2 include, for example, the frequency band of the terahertz waves and the positions of oscillator 20 and receiver 30 (the angle at which the terahertz waves are irradiated) based on oscillation point 63 and reception point 64 in the prediction of the propagation behavior of the terahertz waves described above, but may include at least one of the frequency band of the terahertz waves and the positions of oscillator 20 and receiver 30.

[0077] When the process of step S2 is executed, the inspection device 10 instructs the oscillator 20 to emit terahertz waves in a frequency band included in the irradiation conditions set in step S2. Furthermore, for example, if a mechanism for automatically adjusting the positions of the oscillator 20 and the receiver 30 (hereinafter referred to as a position adjustment mechanism) is provided, the positions of the oscillator 20 and the receiver 30 may be automatically adjusted (moved) based on the positions of the oscillator 20 and the receiver 30 included in the irradiation conditions set in step S2. If a position adjustment mechanism is not provided, an administrator of the inspection device 10 (inspection system) may confirm the positions of the oscillator 20 and the receiver 30 included in the irradiation conditions set in step S2, and the administrator may manually adjust the positions of the oscillator 20 and the receiver 30.

[0078] Here, the oscillator 20 and the receiver 30 (terahertz device) in this embodiment are configured with a scanning mechanism, which can scan, for example, the top surface (XY plane) of the electric power device 40 when inspecting the inside of the resin 42 covering the conductive portion 41 in the electric power device 40. With this configuration, terahertz waves are sequentially irradiated based on a plurality of irradiation points set on the top surface of the electric power device 40 (resin 42), so that reflected waves from the interface of the foreign matter 43 mixed inside the resin 42 can be received over a wide range of the resin 42. Note that if the oscillator 20 employs a lens system, it is also possible to irradiate terahertz waves while sequentially changing the focus in the depth direction (Z-axis direction) of the electric power device 40 (resin 42).

[0079] When the irradiation conditions are set in step S2, the oscillator 20 oscillates the terahertz waves according to the irradiation conditions while scanning the top surface of the electric power equipment 40 using the scanning mechanism. As a result, the receiver 30 receives reflected waves from the entire electric power equipment 40 (resin 42).

[0080] In this case, the reflected wave signal acquiring unit 12 acquires from the receiving device 30 a reflected wave signal corresponding to the reflected wave received by the receiving device 30 (step S3). The reflected wave signal acquired in step S3 includes the intensity of the reflected wave corresponding to the internal state of the resin 42, the peak value of the intensity of the reflected wave, and the time it takes to reach the peak. Note that since the reflected wave signal may contain noise, the reflected wave signal acquiring unit 12 may perform signal processing such as averaging on the reflected wave signal to reduce the noise level.

[0081] The waveform data generating unit 13 generates waveform data based on the intensity of the reflected wave included in the reflected wave signal acquired in step S3, the peak value of the intensity of the reflected wave, the time to reach the peak, etc. (step S4).

[0082] Based on the reflected wave signal acquired in step S3, image generation unit 14 can generate three-dimensional image data of resin 42 covering conductive portion 41 in power device 40. Image generation unit 14 generates an image of resin 42 based on the generated three-dimensional image data (step S5).

[0083] Here, the image (e.g., a planar image) of the resin 42 is composed of a plurality of pixels, and each of the plurality of pixels is assigned a pixel value corresponding to each reflected wave signal according to the reflected wave of the terahertz wave irradiated based on a plurality of irradiation points set on the resin 42 (electric power equipment 40) by the oscillator 20 and the receiver 30 scanning the top surface of the electric power equipment 40 as described above. In other words, in order to generate an image (three-dimensional image data) of the resin 42 that is clear enough to visually recognize the foreign matter 43, it is necessary to set a large number of irradiation points densely (i.e., at close intervals) on the plurality of pixels that make up the image.

[0084] However, it takes time to inspect the inside of the resin 42 by sequentially irradiating each of the many irradiation points set as described above with terahertz waves.

[0085] For this reason, in this embodiment, image processing is incorporated when generating an image in step S5, thereby reducing the number of irradiation points (i.e., observation points of reflected waves). Here, it is assumed that processing based on compressed sensing technology is performed as image processing (i.e., an image is generated by applying compressed sensing technology). Compressed sensing technology is, for example, a technology for restoring target data from a smaller number of data sets than the required number. When compressed sensing technology is applied in this embodiment, unknown reflected wave signals can be derived from a small number of reflected wave signals (an image generated based on) obtained by irradiating terahertz waves onto irradiation points sparsely set for multiple pixels constituting an image, and the derived reflected wave signals can be used to restore (generate) an image. For restoration, coefficients (called an observation matrix) for converting an image acquired at dense irradiation points to an image acquired at sparse irradiation points must be set in advance. By correctly setting this matrix, it is possible to convert a sparse image into a dense image.

[0086] Here, an example of an image generated by applying the compressed sensing technology in this embodiment will be described with reference to FIG.

[0087] 13 is an image generated based on reflected wave signals obtained by irradiating terahertz waves onto irradiation points that are densely set for a plurality of pixels that make up the image generated by the image generating unit 14 (i.e., the image output by the output unit 17). The original image 81 is a clear image, and foreign matter 43 in the original image 81 can be easily visually recognized. Note that it is assumed that the irradiation points are set at a pitch of, for example, 0.5 mm x 0.5 mm in the original image 81.

[0088] Next, the first thinned image 82 is an image generated based on reflected wave signals obtained by reducing the number of irradiation points by 75% compared to the original image 81 and irradiating the remaining 25% of the irradiation points with terahertz waves. That is, the pitch of the irradiation points in the first thinned image 82 is 1 mm × 1 mm. Because the number of irradiation points (i.e., reflected wave signals) in the first thinned image 82 is reduced compared to the original image 81, the clarity of the first thinned image 82 is lower than that of the original image 81. However, when compressed sensing technology is applied to the first thinned image 82 (the reflected wave signals used to generate the first thinned image 82), a first restored image 83 can be obtained. The clarity of the first restored image 83 is improved compared to the first thinned image 82.

[0089] Furthermore, the second thinned image 84 is an image generated based on reflected wave signals obtained by reducing the number of irradiation points by 96% compared to the original image 81 and irradiating the remaining 4% of irradiation points with terahertz waves. That is, the pitch of the irradiation points in the second thinned image 84 is 2 mm × 2 mm. Because the number of irradiation points in the second thinned image 84 is further reduced compared to the first thinned image 82, the clarity of the second thinned image 84 is further reduced compared to the first thinned image 82. However, when compressed sensing technology is applied to the second thinned image 84 (the reflected wave signals used to generate the second thinned image 84), a second restored image 85 can be obtained. The clarity of the second restored image 85 is improved compared to the second thinned image 84.

[0090] Furthermore, the third thinned image 86 is an image generated based on reflected wave signals obtained by reducing the number of irradiation points by 99% compared to the original image 81 and irradiating the remaining 1% of irradiation points with terahertz waves. That is, the pitch of the irradiation points in the third thinned image 86 is 5 mm × 5 mm. Because the number of irradiation points in the third thinned image 86 is further reduced compared to the second thinned image 84, the clarity of the third thinned image 86 is further reduced compared to the second thinned image 84. However, when compressed sensing technology is applied to the third thinned image 86 (the reflected wave signals used to generate the third thinned image 86), a third restored image 87 can be obtained. The clarity of the third restored image 87 is improved compared to the third thinned image 86.

[0091] According to the first restored image 83 and the second restored image 85 shown in FIG. 13, the foreign matter 43 can be easily seen, just like in the original image 81. Therefore, when compressed sensing technology is applied in this embodiment, it is considered possible to reduce the number of illumination points by up to 96% compared to the original image 81 (i.e., illumination points densely set for multiple pixels constituting the image).

[0092] That is, in this embodiment, by applying compressed sensing technology, even if irradiation points are sparsely set for a plurality of pixels constituting an image (i.e., the number of irradiation points is reduced), it is possible to obtain an image that is useful for recognizing (understanding) the foreign substance 43. Note that sparsely setting irradiation points for a plurality of pixels constituting an image means, for example, setting fewer irradiation points than the number of irradiation points set to obtain the original image 81 (i.e., setting irradiation points at wider intervals than the irradiation points set to obtain the original image 81).

[0093] Although the third restored image 87 has lower clarity (is unclear) compared to the original image 81, it is possible to visually recognize the foreign matter 43 depending on the type of the foreign matter 43. Therefore, if it is assumed that the foreign matter 43 mixed inside the resin 42 can be relatively easily visually recognized, it is acceptable to reduce 99% of the illumination points set to obtain the original image 81.

[0094] Step S5 shown in FIG. 7 is assumed to generate a planar image (an image on the XY plane), but a tomographic image (an image on the XZ plane or YZ plane) may also be generated in step S5.

[0095] Next, the depth calculation unit 15 calculates the depth of the foreign matter 43 mixed in the resin 42 based on the reflected wave signal acquired in step S3 (step S6). In this case, the depth of the foreign matter 43 is calculated based on the peak arrival time (measurement light delay time of the terahertz wave) included in the reflected wave signal and the refractive index of the resin 42.

[0096] 7, the processes of steps S5 and S6 are described as being executed based on the reflected wave signal acquired in step S3, but these processes may also be executed based on the waveform data generated in step S4. Furthermore, the process of step S6 may also be executed in consideration of the image (e.g., a tomographic image) generated in step S5.

[0097] Next, the discriminator 16 discriminates the type of foreign matter 43 mixed in the resin 42 based on the waveform data generated in step S4 (step S7).

[0098] The processing of step S7 will be described below. As described above, the propagation behavior and reflection behavior of terahertz waves differ depending on the dielectric constant of the material, and for example, terahertz waves are totally reflected by metal. In this embodiment, by utilizing such characteristics (properties), the type (material) of foreign matter 43 mixed inside resin 42 is determined (estimated) in a non-destructive manner.

[0099] 15 is a diagram for explaining the difference in characteristics between a reflected wave from a foreign particle (or defect) (hereinafter referred to as a first reflected wave) and a reflected wave from the resin surrounding the foreign particle (surrounding resin without foreign particles) (hereinafter referred to as a second reflected wave) when the reflected wave is compared. Note that the first and second reflected waves shown in FIG. 15 are reflected waves obtained as a result of actually inspecting (the inside of) the resin.

[0100] 15 shows the differences between the first and second reflected waves in terms of the reflected waveform characteristics, time delay characteristics, and frequency characteristics, and marks the differences with ◯, △, and × according to the degree of difference. Note that ◯ indicates that there is a difference in the characteristics, × indicates that there is no difference (or an extremely small difference) in the characteristics, and △ indicates that there is a difference between ◯ and ×.

[0101] First, we will explain the differences in the reflected waveform characteristics shown in Figure 15. The diagram shown here shows a reflected terahertz waveform, with the horizontal axis representing time and the vertical axis representing reflected wave intensity. If the foreign object is metal, the terahertz wave is totally reflected, and the amplitude of the first reflected wave becomes larger than that of the second reflected wave. Furthermore, the difference in amplitude between the first and second reflected waves occurs widely (within a range of several ps) around the depth of the foreign object. Therefore, if the foreign object is metal, it can be said that there is a difference in the reflected waveform characteristics between the first and second reflected waves.

[0102] If the foreign object is an air bubble, the reflectivity is small, but a slight difference in amplitude occurs due to the difference in dielectric constant with the surrounding resin. Therefore, if the foreign object is an air bubble, it can be said that there is a difference in the reflected waveform characteristics between the first and second reflected waves.

[0103] When the foreign object is a resin burr, the difference in dielectric constant with the surrounding resin is small, but because the surrounding resin is uniform and flat, while an interface exists at the location of the resin burr, a slight amplitude difference occurs. This amplitude difference is also thought to be influenced by the wrinkled shape of the resin burr within the resin. However, because this amplitude difference is smaller than when the foreign object is metal or when the foreign object is an air bubble, the difference between the first and second reflected waves in the reflected waveform characteristics when the foreign object is a resin burr is evaluated as fair.

[0104] Next, we will explain the differences in the time delay characteristics shown in Figure 15. The diagram shown here shows the correlation of the time difference between the first reflected wave and the second reflected wave, with the horizontal axis representing time and the vertical axis representing the correlation. When the foreign object is metal or an air bubble, the time delay difference is 0 and the correlation between the foreign object and the surrounding resin is at its maximum, so there is almost no time delay difference (i.e., there is no difference between the first and second reflected waves in the time delay characteristics). On the other hand, when the foreign object is a resin burr, there is a clear time delay difference (i.e., there is a difference between the first and second reflected waves in the time delay characteristics).

[0105] Finally, we will explain the difference in frequency characteristics shown in Figure 15. Here, the correlation between the foreign matter (first reflected wave) and the surrounding resin (second reflected wave) in the 0.05 to 2.5 THz band is shown as a frequency characteristic. If the foreign matter is metal, no difference can be confirmed between the first reflected wave and the second reflected wave, so it can be said that there is no difference in the frequency characteristics between the first and second reflected waves. If the foreign matter is an air bubble, a difference between the first reflected wave and the second reflected wave can be confirmed in some low-frequency components, so the difference in the frequency characteristics between the first and second reflected waves is evaluated as fair. Furthermore, if the foreign matter is a resin burr, a clear difference can be confirmed between the first reflected wave and the second reflected wave, especially in low-frequency components up to the 1 THz band, so it can be said that there is a difference in the frequency characteristics between the first and second reflected waves.

[0106] In this embodiment, the type of foreign matter is identified by grasping the above-mentioned characteristics (properties) and then using a predetermined foreign matter identification algorithm.

[0107] In the above-described impurity discrimination algorithm, for example, multiple waveform data are extracted by random sampling of the results (waveform data) of an actual resin inspection, and a correlation filter (a filter containing information about the surrounding resin without impurities) is created. The correlation filter is then shifted while performing a convolution process, thereby achieving consistency in amplitude and phase differences within each region. This allows the region furthest from the correlation filter to be detected as a location where a foreign object is present (or a defective location). In this case, by inputting waveform data indicating the reflected waves from the location where the foreign object is present (i.e., the amplitude, phase difference, and frequency characteristics related to the foreign object) into an identifier, the type of the object can be determined based on the correlation with the surrounding resin (waveform data indicating the reflected waves from the surrounding resin). Note that the identifier to which this waveform data is input can use a trained model that has previously trained on the correlation (type of foreign object based on) between the waveform data indicating the reflected waves from the interfaces of each of the above-described foreign objects and the waveform data indicating the reflected waves from the surroundings of the foreign object.

[0108] When the processing of step S7 is executed, the output unit 17 outputs, for example, the waveform data generated in step S4, the image generated in step S5, the depth of the foreign object 43 calculated in step S6, and the type of the foreign object 43 determined in step S7 as inspection results of the inside of the resin 42 covering the conductive part 41 in the electric power equipment 40 (step S8).

[0109] Specifically, in step S8, the waveform data, the image, the depth of the foreign matter 43, and the type of the foreign matter 43 are output to, for example, a display device provided in the inspection device 10 and displayed on the display device. This allows an inspector using the inspection device 10 to easily identify the foreign matter 43 that has entered the resin 42 by visually checking the waveform data, the image, the depth of the foreign matter 43, and the type of the foreign matter 43.

[0110] Note that various display modes for the waveform data, image, depth of foreign matter 43, and type of foreign matter 43 are possible. Specifically, for example, the waveform data and image may be displayed side by side on the same screen, or the depth of foreign matter 43 and type of foreign matter 43 may be displayed so as to be superimposed on the image. Furthermore, the waveform data, image, depth of foreign matter 43, and type of foreign matter 43 may be displayed after being processed as appropriate. In this case, for example, the position of foreign matter 43 (brightness value, area value, etc.) may be extracted from the image, and the image may be displayed in a mode that allows the foreign matter 43 (or the type of foreign matter 43) to be easily visually recognized.

[0111] Here, it has been explained that the waveform data, the image, the depth of the foreign matter 43, and the type of the foreign matter 43 are displayed on the display device, but the waveform data, the image, the depth of the foreign matter 43, and the type of the foreign matter 43 may be output (transmitted) to an external server device for further analysis processing, etc.

[0112] The inspection results output in step S8 may include at least one of waveform data, an image, the depth of the foreign matter 43, and the type of the foreign matter 43.

[0113] 7, the processes of steps S3 to S7 may be performed for each specific frequency band because the reflected wave from the interface of foreign matter 43 mixed in resin 42 covering conductive portion 41 in power device 40 described above may differ depending on the frequency band of the terahertz wave. Specifically, the processes of steps S3 to S7 may be performed for each frequency band subdivided (divided) into, for example, a range of 0.05 to 1 THz.

[0114] Further, for example, it may be configured to determine whether or not foreign matter is mixed inside the resin 42 based on the waveform data generated in step S4 and the image generated in step S5, and if it is determined that foreign matter is mixed inside the resin 42, the processing of steps S6 and S7 may be executed.

[0115] As described above, in this embodiment, a reflected wave signal corresponding to the reflected wave from the interface of a foreign substance 43 mixed inside the resin 42 of the terahertz wave (pulse wave) irradiated based on a plurality of irradiation points set on the resin 42 is obtained, and an image including the foreign substance 43 is generated based on the reflected wave signal, and the plurality of irradiation points are set sparsely with respect to the plurality of pixels that make up the generated image.

[0116] In this embodiment, this configuration makes it possible to reduce the number of irradiation points (i.e., the number of times terahertz waves are irradiated during inspection), thereby shortening the time (hereinafter simply referred to as inspection time) required to non-destructively inspect the inside of resin 42 covering conductive part 41 in power equipment 40.

[0117] In addition, when multiple irradiation points are set sparsely as described above, a restored image in which foreign objects are visible to the same extent as in the original image described above can be generated by applying compressed sensing technology.However, as long as it is possible to generate an image in which foreign objects are visible even when the irradiation points are set sparsely, a technology similar to compressed sensing technology or a technology other than the compressed sensing technology may also be applied.

[0118] Furthermore, in this embodiment, the propagation behavior of terahertz waves (pulse waves) is predicted based on at least one of the structure of electric power device 40 and the relative dielectric constants of resin 42 and foreign matter 43 that may be mixed inside resin 42, and irradiation conditions for the terahertz waves are set based on the predicted propagation behavior of the terahertz waves. In this embodiment, such a configuration makes it possible to set appropriate irradiation conditions for electric power device 40 and inspect the inside of resin 42, thereby reducing the possibility of obtaining a low-accuracy reflected wave signal, for example. That is, in this embodiment, an efficient inspection can be performed, and as a result, the inspection time can be shortened.

[0119] The above-mentioned irradiation conditions for the terahertz waves include, for example, the frequency band of the terahertz waves, and at least one of the position of the oscillator 20 configured to emit the terahertz waves and the position of the receiver 30 configured to receive the reflected waves of the terahertz waves, but may also include other conditions (for example, the intensity of the terahertz waves, etc.).

[0120] Furthermore, in this embodiment, waveform data indicating a reflected waveform is generated based on the reflected wave signal acquired from the receiving device 30, and the type of foreign matter 43 mixed in the resin 42 is determined based on the generated waveform data, but the type of the foreign matter 43 may be determined using a trained model that has previously trained the correlation between the waveform data and waveform data indicating a reflected waveform from the resin surrounding the foreign matter. In this embodiment, such a configuration makes it possible to non-destructively determine the type of foreign matter 43 mixed in the resin 42, and the determination result (type of foreign matter 43) can be used for checking the quality of the resin 42, analyzing the cause of the foreign matter being mixed in the resin 42, and taking measures against the mixing of the foreign matter 43.

[0121] In this embodiment, terahertz waves in a frequency band ranging from 0.05 to 10 THz are used. However, it is preferable to use terahertz waves in the 0.075 to 0.125 THz band. Furthermore, if the foreign matter 43 or defect in the resin 42 is, for example, at least one of metal, air bubbles, resin burrs, peeling, and cracks, terahertz waves in the 0.1 THz band can effectively visualize the foreign matter 43 in an image generated based on the reflected wave signal. Therefore, in this embodiment, terahertz waves in the 0.1 THz band, particularly in the 0.075 to 0.125 THz band, are preferably used. That is, in this embodiment, the 0.1 THz band is preferentially selected as the frequency band of terahertz waves included in the terahertz wave irradiation conditions over other frequency bands. However, depending on the results of the prediction of the propagation behavior of terahertz waves described above, frequency bands other than the 0.1 THz band may also be included in the terahertz wave irradiation conditions.

[0122] Furthermore, the oscillator 20 and the receiver 30 in this embodiment may employ a lens system (a configuration including a lens that converges the terahertz waves and the reflected waves of the terahertz waves) or a lensless system (a configuration that does not include a lens that converges the terahertz waves and the reflected waves of the terahertz waves), but if the oscillator 20 and the receiver 30 employ the lens system, they can receive reflected waves with high intensity, and therefore can generate an image in which a foreign object 43 can be easily visually recognized, for example, as shown in Fig. 16. In other words, the lens system can improve the inspection accuracy based on the reflected wave signal corresponding to the reflected wave.

[0123] On the other hand, when the oscillator 20 and receiver 30 employ a lensless system, the intensity of the reflected wave decreases, and therefore the visibility of the foreign object 43 in the image decreases, as shown in Fig. 17. However, the lensless system does not require work such as focusing, which can contribute to shortening the inspection time.

[0124] As described above, the lens type and the lensless type employed in the oscillator 20 and the receiver 30 have different advantages, so an appropriate type may be selected depending on the object to be inspected (electric power device 40).

[0125] In this embodiment, multiple averaging processes may be performed on the reflected wave signal to reduce the noise level of the reflected wave signal, but the number of averaging processes may be reduced to shorten the inspection time.

[0126] In this embodiment, the electric power device 40 is mainly irradiated with terahertz waves, but ultrasonic waves can also be used as the pulse waves in this embodiment.

[0127] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0128] 10...inspection device, 11...propagation behavior prediction unit, 12...reflected wave signal acquisition unit, 13...waveform data generation unit, 14...image generation unit, 15...depth calculation unit, 16...discrimination unit, 17...output unit, 20...oscillating device, 30...receiving device, 40...power equipment, 41...conductive part, 42...resin, 43...foreign matter, 51...beam splitter, 52...lens, 101...CPU, 102...non-volatile memory, 103...RAM, 103a...inspection program, 104...communication device.

Claims

1. An inspection method for inspecting the inside of a resin covering a conductive part in an electric power device, comprising: acquiring a reflected wave signal corresponding to a wave reflected from an interface of a foreign substance mixed inside the resin, the reflected wave being generated by a pulse wave irradiated based on a plurality of irradiation points set on the resin; generating an image including the foreign object based on the acquired reflected wave signal; Equipped with the plurality of illumination points are set sparsely with respect to the plurality of pixels constituting the generated image; the generating step generates the image by applying a compressed sensing technique; The number of the set irradiation points varies depending on the type of foreign matter that may be mixed inside the resin. Testing method.

2. and predicting a propagation behavior of the pulse wave based on at least one of a structure of the electric power device and a relative dielectric constant of the resin and a foreign matter that may be mixed in the resin, The pulse wave irradiation conditions are set based on the predicted pulse wave propagation behavior. The inspection method according to claim 1.

3. 3. The inspection method according to claim 2, wherein the pulse wave irradiation conditions include at least one of the frequency of the pulse wave, the position of an oscillator configured to oscillate the pulse wave, and the position of a receiver configured to receive the reflected wave.

4. generating waveform data representing a reflected waveform based on the acquired reflected wave signal; determining the type of the foreign matter based on the generated waveform data; Further comprising: The type of the foreign matter is determined using a trained model that has previously trained the correlation between waveform data showing a waveform reflected from the interface of the foreign matter and waveform data showing a waveform reflected from the resin surrounding the foreign matter. The inspection method according to any one of claims 1 to 3.

5. the foreign matter includes at least one of metal, air bubbles, resin burrs, peeling, and cracks; The pulsed wave includes at least a terahertz wave in the 0.1 terahertz band. The inspection method according to any one of claims 1 to 4.

6. The inspection method according to any one of claims 1 to 5, wherein an oscillator configured to oscillate the pulse wave and a receiver configured to receive the reflected wave are configured to include lenses that converge the pulse wave and the reflected wave.

7. The inspection method according to any one of claims 1 to 5, wherein an oscillator configured to oscillate the pulse wave and a receiver configured to receive the reflected wave are configured not to include a lens that converges the pulse wave and the reflected wave.

8. An inspection device for inspecting the inside of a resin covering a conductive part in an electric power device, an acquisition means for acquiring a reflected wave signal corresponding to a reflected wave from an interface of a foreign substance mixed in the resin, the reflected wave being generated by a pulse wave irradiated based on a plurality of irradiation points set on the resin; a generating means for generating an image including the foreign matter based on the acquired reflected wave signal; Equipped with the plurality of illumination points are set sparsely with respect to the plurality of pixels constituting the generated image; the generating means generates the image by applying a compressed sensing technique; The number of the set irradiation points varies depending on the type of foreign matter that may be mixed inside the resin. Inspection equipment.

9. An inspection system for inspecting the inside of a resin covering a conductive part in an electric power device, an oscillator configured to generate pulse waves to be irradiated based on a plurality of irradiation points set on the resin; a receiving device configured to receive a reflected wave of the pulse wave from an interface of a foreign substance mixed inside the resin; an inspection device including: an acquisition means for acquiring a reflected wave signal corresponding to the reflected wave received by the receiving device; and a generation means for generating an image including the foreign matter based on the acquired reflected wave signal; Equipped with the plurality of illumination points are set sparsely with respect to the plurality of pixels constituting the generated image; the generating means generates the image by applying a compressed sensing technique; The number of the set irradiation points varies depending on the type of foreign matter that may be mixed inside the resin. Inspection system.

10. A program executed by a computer of an inspection device that inspects the inside of a resin that covers a conductive part in an electric power device, The computer, acquiring a reflected wave signal corresponding to a wave reflected from an interface of a foreign substance mixed inside the resin, the reflected wave being generated by a pulse wave irradiated based on a plurality of irradiation points set on the resin; generating an image including the foreign object based on the acquired reflected wave signal; Execute the plurality of illumination points are set sparsely with respect to the plurality of pixels constituting the generated image; the generating step generates the image by applying a compressed sensing technique; The number of the set irradiation points varies depending on the type of foreign matter that may be mixed inside the resin. program.

Images