Inspecting device

Abstract

This inspecting device is a device for inspecting an inner circumferential surface of an object under inspection that has a cylindrical shape. The device comprises: an inspecting unit for emitting terahertz waves toward the inner circumferential surface and detecting reflected waves of the terahertz waves; and a distance measuring unit for measuring the distance between the inspecting unit and the inner circumferential surface. The inspection target and the distance measuring unit are caused to rotate in the circumferential direction of the object under inspection. Further, the relative axial position of the inspecting unit with respect to the object under inspection is adjusted. Further, the position of the inspecting unit in a plane intersecting the axial direction of the object under inspection can be adjusted. Control of the position adjustment mechanism is performed on the basis of the measurement result from the distance measuring unit such that the center of rotation of a rotation unit is positioned on the central axis of the object under inspection.

Description

Inspection Equipment

[0001] This application claims priority to Japanese Patent Application No. 2023-139490, filed with the Japan Patent Office on August 30, 2023, the contents of which are incorporated herein by reference.

[0002] Patent Literature 1 discloses a reflection-type terahertz wave measuring device (inspection device) configured to be able to irradiate the surface of a structure with terahertz waves, which are a type of electromagnetic wave, and to detect terahertz waves reflected by the structure. This terahertz wave measuring device includes a terahertz wave transmitter as a terahertz wave transmitting means and a terahertz wave detector as a terahertz wave detecting means. In this terahertz wave measuring device, a terahertz wave generating element including a resonant tunneling diode (RTD) or a photoconductive antenna (PCA) is used as the terahertz wave transmitter, and a terahertz wave detecting element consisting of an RTD is used as the terahertz wave transmitter.

[0003] Japanese Patent Application Laid-Open No. 2020-26991

[0004] The above-mentioned inspection device using terahertz waves can be used to inspect objects such as cylindrical tubular members. In this case, the inspection device is positioned on the central axis of the interior space of the object and performs an inspection operation of irradiating the inner surface of the object with terahertz waves in the circumferential direction and detecting reflected waves while moving axially, thereby inspecting a wide area of ​​the object's inner surface. In this inspection, the signal strength of the reflected waves from the inner surface is approximately constant in areas where the inner surface is healthy, whereas the signal strength of the reflected waves decreases in areas where there is an abnormality (corrosion, water, etc.) on the inner surface. Therefore, by plotting the distribution of signal strength, it is possible to image the condition of the inner surface.

[0005] Terahertz waves are electromagnetic waves with high directionality and excellent linearity due to their high frequency. Therefore, if the irradiation position of the terahertz waves deviates from the central axis, when the terahertz waves are irradiated onto the inner surface along the circumferential direction, a substantially constant signal strength cannot be obtained even if the inner surface is in a healthy state, and anomalies (corrosion, water, etc.) based on the signal strength cannot be accurately detected.

[0006] At least one embodiment of the present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide an inspection device that can inspect the condition of the inner surface of an object to be inspected with high accuracy by irradiating terahertz waves from the central axis of the object to be inspected, having a cylindrical shape, along the circumferential direction onto the inner surface of the object to be inspected.

[0007] In order to solve the above-mentioned problems, an inspection device according to at least one embodiment of the present disclosure is an inspection device for inspecting the inner surface of an object to be inspected having a cylindrical shape, and includes: an inspection unit for irradiating terahertz waves onto the inner surface and detecting reflected waves of the terahertz waves; a distance measurement unit for measuring the distance between the inspection unit and the inner surface; a rotation unit for rotating the inspection unit and the distance measurement unit along the circumferential direction of the object to be inspected; a position adjustment mechanism for adjusting the position of the inspection unit on a plane intersecting the axial direction of the object to be inspected; and an axial position adjustment unit for adjusting the axial position of the inspection unit relative to the object to be inspected, and based on the measurement results of the distance measurement unit, the position adjustment mechanism is controlled so that the center of rotation of the rotation unit is located on the central axis of the object to be inspected.

[0008] According to at least one embodiment of the present disclosure, an inspection device can be provided that can inspect the condition of the inner surface of an object to be inspected with high accuracy by irradiating terahertz waves from the central axis of the object to be inspected, which has a cylindrical shape, along the circumferential direction of the inner surface of the object to be inspected.

[0009] 5 is a schematic external view of an inspection device according to one embodiment; FIG. 6 is a block diagram of the control device of FIG. 1; FIG. 7 is a flowchart showing an inspection method according to one embodiment; FIG. 8 is an example of an inspection result obtained in step S107 of FIG. 3; FIG. 9 is a flowchart showing an inspection method according to another embodiment; FIG. 10 is an example of correction data prepared in step S200 of FIG. 5; FIG. 11 is a flowchart showing an inspection method according to another embodiment;

[0010] Hereinafter, an inspection device according to an embodiment will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0011] The configuration of an inspection device 1 according to at least one embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a schematic external view of the inspection device 1 according to one embodiment.

[0012] The inspection device 1 is a device for inspecting an inspection object TG. The inspection object TG is a pipe member having a substantially cylindrical shape and made of a metal material, such as an iron pipe. The inspection object TG has an internal space 2 extending in the axial direction X. The inner peripheral surface of the internal space 2 has a substantially constant curvature in the YZ plane perpendicular to the axial direction X. The inner peripheral surface is also lined with a resin material RM. If this resin material RM deteriorates, water may penetrate and corrode the inner wall of the iron pipe. The inspection device 1 aims to detect corrosion on the inner peripheral surface of such an inspection object TG, or the presence of water that causes corrosion, as an abnormality.

[0013] The inspection device 1 has a main body 6 that houses an optical system 4 as an inspection unit for performing inspections. The optical system 4 includes a light source 8, a nonlinear optical crystal 10, a half mirror 12, a mirror 14, a condenser lens 16, and a detector 18.

[0014] The light source 8 is configured to output pulsed excitation light LB. The pulsed excitation light LB is output with a pulse duration of, for example, 1 microsecond or less, preferably 1 nanosecond or less. In this embodiment, the light source 8 outputs pulsed excitation light LB with a duration of 10 picoseconds to 10 nanoseconds. The light source 8 is configured, for example, as a beam light source such as a chip laser. Note that the light source 8 is not limited to being disposed inside the main body 6 as shown in FIG. 1 , but may also be disposed outside the main body 6. In this case, the pulsed excitation light from the light source 8 located outside the main body 6 may be transmitted to the inside of the main body 6 via an optical fiber or the like.

[0015] The nonlinear optical crystal 10 is configured to generate terahertz waves TH by converting the optical wavelength of the pulsed pump light LB. The nonlinear optical crystal 10 is, for example, a periodically poled lithium niobate (LiNbO ３ The periodically poled lithium niobate crystal generates terahertz waves TH by backward terahertz wave TH oscillation. １２ It is an electromagnetic wave in the range of around 1 trillion hertz (0.1 to 100 THz).

[0016] The terahertz waves TH generated by the nonlinear optical crystal 10 pass through the half mirror 12, are deflected by the mirror 14, and are irradiated onto the inner peripheral surface of the inspection object TG via the condenser lens 16. The reflected waves RW from the inspection object TG are collected by the condenser lens 16, deflected by the mirror 14, pass through the half mirror 12, and are detected by the detector 18. In this way, in the optical system 4, when inspecting the inspection object TG, the terahertz waves TH are collected by the condenser lens 16 and are irradiated onto the inspection object TG. Therefore, the terahertz waves TH are collected on the inspection object TG, and the reflected waves RW can be detected with high resolution by the detector 18.

[0017] In this way, in the optical system 4, pulsed excitation light LB with a time width of 10 picoseconds to 10 nanoseconds passes through the nonlinear optical crystal 10 to generate terahertz waves TH that have been wavelength-converted. This generates more powerful (higher output) terahertz waves than those emitted from semiconductor elements such as RTDs and PCAs. Therefore, the optical components (light source 8, nonlinear optical crystal 10, etc.) that make up the optical system 4 can be positioned at a distance from the test object TG. Furthermore, even if the resin material RM provided on the inner surface of the test object TG is a low-permeability material, the terahertz waves TH pass through the resin material RM and are reflected by the test object TG. Therefore, the test object TG can be inspected even if it is covered with a resin material RM containing a low-permeability material.

[0018] Furthermore, in imaging of difficult-to-transmit materials, ensuring a high signal-to-noise ratio requires a high output from the light source 8. However, continuous wave oscillation, such as with a gyrotron, consumes a lot of power and may burn the object. On the other hand, the light source 8 uses pulsed terahertz waves TH, ensuring high peak power while consuming low power. This allows for non-destructive imaging with high transmission performance without burning the object TG.

[0019] The main body 6 that houses the optical system 4 having such a configuration includes a housing 20 and an arm mechanism 22 that is rotatably attached to the housing 20 .

[0020] The housing 20 accommodates the light source 8, the nonlinear optical crystal 10, the half mirror 12, and the detection unit 18 of the optical system 4. The light source 8 and the nonlinear optical crystal 10 are arranged so that the terahertz wave TH output from the nonlinear optical crystal 10 passes through the rotation center C1 of the arm mechanism 22.

[0021] A multi-axis arm 24 is also provided on the outer periphery of the housing 20. The arms of the multi-axis arm 24 are provided at equal intervals around the periphery of the housing 20 and are configured to extend radially outward from the housing 20. These arms extend and contract to form a YZ direction position adjustment mechanism for adjusting the position of the inspection device 1 on the YZ plane (a plane perpendicular to the axial direction X). Each arm of the multi-axis arm 24 is pantograph-shaped, and a running wheel 26 is provided at its joint for supporting the housing 20 on the inner circumferential surface of the inspection object TG while allowing it to move along the axial direction X within the inspection object TG. Note that, although the present embodiment illustrates the multi-axis arm 24 as an example of a YZ direction position adjustment mechanism, the configuration of the YZ direction position adjustment mechanism is not limited.

[0022] The arm mechanism 22 is a rotating unit that can rotate the optical system 4, which is an inspection unit, and the distance measurement unit 28 along the circumferential direction. The arm mechanism 22 is rotatably attached to the housing 20 around a rotation center C1 along the axial direction X and houses the mirror 14 and the condenser lens 16 of the optical system 4. The arm mechanism 22 includes one end where the mirror 14 is provided and the other end where the condenser lens 16 is provided, and one end is rotatably attached to the housing 20. In particular, the mirror 14 is positioned on the rotation center C1 of the arm mechanism 22 so that it can receive the terahertz waves TH output from the nonlinear optical crystal 10 housed in the housing 20. The arm mechanism 22, whose one end is rotatably attached, is rotated by an actuator such as a motor (not shown). From the other end of the arm mechanism 22, the terahertz waves TH generated by the optical system 4 are irradiated onto the inner circumferential surface of the inspection object TG, and reflected waves RW from the inner circumferential surface are captured.

[0023] The arm mechanism 22 is also provided with a distance measurement unit 28 for measuring the distance between the arm mechanism 22 and the inner surface of the object under test TG. The distance measurement unit 28 is, for example, a laser distance measuring device capable of measuring distances using laser light LL. The distance measurement unit 28 can measure the distance between the arm mechanism 22 and the inner surface of the object under test TG by irradiating the inner surface of the object under test TG with laser light LL from approximately the same position as the terahertz waves TH and approximately parallel to the terahertz waves TH, and detecting reflected laser light LR from the inner surface of the object under test TG at approximately the same position as the reflected laser light RW. The distance measurement unit 28 is fixed to the arm mechanism 22 and can rotate around a rotation center C1 together with the arm mechanism 22. The distance measured by the distance measurement unit 28 can be converted to the distance from the rotation center C1 to the inner surface of the object under test TG by taking into account the length from the rotation center C1 to the irradiation position of the laser light LL or the detection position of the reflected laser light LR.

[0024] The inspection device 1 also includes a control device 30 for controlling the above-described components. The control device 30 is a control unit for controlling the inspection device 1 and is composed of, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and a computer-readable storage medium. A series of processes for realizing various functions is stored in a storage medium or the like in the form of a program, for example. The CPU reads this program into the RAM or the like and executes information processing and arithmetic operations to realize various functions. The program may be pre-installed in a ROM or other storage medium, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0025] 1, the control device 30 is configured as a separate unit from the main body 6 of the inspection device 1 and is configured to be able to communicate with the main body 6, but at least a part of the control device 30 may be configured as an integral part of the main body 6. Furthermore, the control device 30 can be connected to the main body 6 by wired or wireless communication means, thereby enabling transmission and reception of various data.

[0026] Fig. 2 is a block diagram of the control device 30 of Fig. 1. The control device 30 includes an inspection control unit 32, an X-direction position adjustment unit 34, a YZ-direction position adjustment unit 36, a data storage unit 38, and an analysis unit 40.

[0027] The inspection control unit 32 is configured to control the inspection operation performed by the inspection device 1. The inspection operation includes irradiating the inner circumferential surface of the inspection target TG with terahertz waves TH while rotating the arm mechanism 22 relative to the housing 20 and detecting reflected waves RW from the inner circumferential surface of the inspection target TG. The inspection operation may also include a distance measurement operation performed by the distance measurement unit 28 as part of such an inspection, as necessary. That is, when inspecting the inner circumferential surface of the inspection target TG while rotating the arm mechanism 22, distance measurement by the distance measurement unit 28 may be performed simultaneously. The inspection operation may also only involve distance measurement by the distance measurement unit 28 (this inspection operation is appropriately referred to as a "distance measurement operation"). Data (inspection data) acquired during these inspection operations are associated with each other along with the circumferential position on the inner circumferential surface and appropriately stored in a data storage unit 38, which will be described later.

[0028] In addition, when the inspection data is obtained as analog data by the inspection operation, the inspection control unit 32 may include an A / D converter for converting the analog data into digital data that can be calculated.

[0029] The X-direction position adjustment unit 34 is configured to adjust the position of the inspection device 1 along the axial direction X (axial position). The above-described inspection operation is repeatedly performed while changing the X-direction position, thereby making it possible to inspect a wide range of the inner circumferential surface of the inspection target TG. The X-direction position adjustment unit 34 adjusts the position of the inspection device 1 along the axial direction X (hereinafter referred to as "X-direction position adjustment operation") in conjunction with such inspection operation.

[0030] In this embodiment, the X-direction position adjustment operation is performed by moving the inspection device 1 inserted into the internal space 2 of the inspection target TG while the inspection target TG is fixed, so that the X-direction position of the inspection device 1 changes. However, in other embodiments, the X-direction position adjustment operation may be performed by changing the X-direction position of the inspection target TG while the inspection device 1 is fixed. Alternatively, the X-direction position adjustment operation may be performed by relatively changing the X-direction positions of both the inspection device 1 and the inspection target TG.

[0031] The YZ-direction position adjustment unit 36 ​​is configured to perform position adjustment (hereinafter referred to as "YZ-direction position adjustment operation") of the inspection device 1 in the YZ plane (a plane perpendicular to the axial direction X). The adjustment amount by the YZ-direction position adjustment unit 36 ​​is controlled based on the measurement results by the distance measurement unit 28. For example, with the axial position of the inspection device 1 fixed, the arm mechanism 22 is rotated while the distance measurement unit 28 obtains distance data, and the adjustment amount is determined so that the rotation center C1 is positioned on the central axis C2 of the inspection target TG. More specifically, the adjustment amount is determined by calculating the average value of distance data in the circumferential direction and minimizing the deviation of each distance data from the average value. As a result, the YZ-direction position adjustment operation suitably adjusts the position of the inspection device 1 in the YZ plane so that the rotation center C1 of the inspection device 1 coincides with the central axis C2. As a result, irradiation of the terahertz waves TH and detection of the reflected waves RW are performed on the central axis C2 of the object to be inspected TG, thereby enabling inspection to be performed with high accuracy using the terahertz waves TH, which are electromagnetic waves with high directionality and excellent linearity.

[0032] The data storage unit 38 is configured to store various data necessary for control calculations in the control device 30. The data stored in the data storage unit 38 includes inspection data acquired in the inspection operation (including distance data acquired in the distance measurement operation).

[0033] The analysis unit 40 is configured to analyze the various data stored in the data storage unit 38 to obtain the test results.

[0034] Next, a description will be given of an inspection method performed by the inspection device 1 having the above configuration. Fig. 3 is a flowchart showing an inspection method according to one embodiment.

[0035] First, the control device 30 adjusts the axial position of the inspection device 1 by performing an X-direction position adjustment operation using the X-direction position adjustment unit 34 (step S100). For example, if the inspection plan calls for inspection to be performed at multiple axial positions, the X-direction position is adjusted so that the inspection device 1 is at the first axial position.

[0036] Next, a distance measurement operation is performed at the X-axis position adjusted in step S100 (step S101). In the distance measurement operation, with the X-axis position fixed, distance measurement is performed while the distance measurement unit 28 is rotated together with the arm mechanism 22. The distance data measured by the distance measurement unit 28 is readably stored in the data storage unit 38 as appropriate.

[0037] Next, the YZ direction position adjustment unit 36 ​​analyzes the distance data acquired in step S101 (step S102) and determines whether the rotation center C1 is displaced from the central axis C2 of the test object TG in the YZ plane (step S103). In step S102, by analyzing the distance data acquired in step S101, for example, an average value of the distance data in the circumferential direction is calculated, and the deviation of each distance data from the average value is calculated. Then, in step S103, it is determined whether the rotation center C1 is displaced from the central axis C2 of the test object TG based on whether the deviation is greater than a preset threshold.

[0038] If it is determined that the rotation center C1 is deviated from the central axis C2 of the test object TG (step S103: YES), a YZ direction position adjustment operation is performed so that the rotation center C1 is positioned on the central axis C2 of the test object TG (step S104). The adjustment amount for the YZ direction position adjustment mechanism in step S104 is determined, for example, so that the deviation described above is equal to or smaller than a threshold value.

[0039] If the rotation center C1 is not displaced from the central axis C2 of the inspection target TG (step S103: NO), the YZ direction position adjustment operation in step S104 is not necessary.

[0040] Subsequently, the inspection control unit 32 performs an inspection operation (step S105). In step S105, the arm mechanism 22 is rotated at the axial position adjusted in step S100 (the same axial position as when the distance measurement operation was performed in step S101), thereby performing an inspection (irradiation of the terahertz waves TH and detection of the reflected waves RW) along the circumferential direction of the inner circumferential surface of the inspection target TG. The inspection data obtained by this inspection is readably stored in the data storage unit 38 as appropriate.

[0041] Next, the control device 30 determines whether the inspection content in the inspection plan has been completed (step S106). For example, when inspections are to be performed at multiple axial positions, whether the inspection content has been completed is determined based on whether the axial position moved to in step S100 is the last inspection position. If there is a next inspection position (step S106: NO), the inspection is deemed not to be completed, and the process returns to step S100, whereby the same process is repeatedly performed at the next axial position that is the inspection position.

[0042] When all the inspection contents in the inspection plan are completed (step S106: YES), the analysis unit 40 analyzes the data stored in the data storage unit 38 to obtain the inspection results (step S107).

[0043] Here, Fig. 4 shows an example of the inspection results obtained in step S107 of Fig. 3. In Fig. 4, the vertical axis represents the axial position (position in the X direction), and the horizontal axis represents the phase angle (0 to 360 degrees) corresponding to the circumferential position, and the surface condition of the inner circumferential surface of the inspection object TG is visualized as a distribution of the signal intensity of the reflected wave RW. As shown in Fig. 4, when the surface condition of the inner circumferential surface is sound, the signal intensity of the reflected wave RW is approximately constant, but areas with abnormalities such as water or corrosion can be visually distinguished by localized drops in signal intensity.

[0044] In particular, in the present embodiment, in the YZ direction position adjustment operation, the YZ direction position adjustment mechanism is adjusted based on the distance data so that the rotation center C1 coincides with the central axis C2 of the object to be inspected TG, and then the inspection operation is performed. Therefore, when terahertz waves TH, which have high directivity and excellent linearity, are used, if the surface condition of the inner circumferential surface is sound, the signal intensity of the reflected waves RW becomes approximately constant, making it possible to distinguishably display areas where there are abnormalities, and good inspection accuracy can be obtained.

[0045] Next, an inspection method according to another embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart showing an inspection method according to another embodiment.

[0046] In this embodiment, as a preliminary step, correction data for correcting the test data is first prepared (step S200). The correction data is prepared as correlation data that indicates the relationship between the propagation distance and signal strength of the reflected wave RW detected by the detection unit 18.

[0047] 6 shows an example of the correction data prepared in step S200 of FIG. 5. In this example, the correction data is prepared as data showing the relationship between the propagation distance of the reflected wave RW and the signal strength, and shows that the signal strength tends to decrease as the propagation distance increases. Such correction data is prepared by an experimental, theoretical, or simulation method under the same conditions as those of the inspection device 1 or similar conditions.

[0048] Next, the X-direction position adjusting unit 34 performs an X-direction position adjusting operation to adjust the axial position of the inspection device 1 in the same manner as in step S100 (step S201). For example, if the inspection plan calls for inspections to be performed at multiple axial positions, the X-direction position is adjusted so that the inspection device 1 is at the first axial position.

[0049] Next, at the X-axis position adjusted in step S201, a distance measurement operation is performed (step S202) in the same manner as in step S101 described above. In the distance measurement operation, with the X-axis position fixed, distance measurement is performed while the distance measurement unit 28 is rotated together with the arm mechanism 22. The distance data measured by the distance measurement unit 28 is readably stored in the data storage unit 38 as appropriate.

[0050] Next, the YZ direction position adjustment unit 36 ​​analyzes the distance data acquired in step S202 (step S203), similar to steps S102 and S103 described above, and determines whether the rotation center C1 is displaced from the central axis C2 of the test object TG in the YZ plane (step S204). In step S203, by analyzing the distance data acquired in step S202, for example, an average value of the distance data in the circumferential direction is calculated, and the deviation of each distance data from the average value is calculated. Then, in step S204, it is determined whether the rotation center C1 is displaced from the central axis C2 of the test object TG based on whether the deviation is greater than a preset threshold.

[0051] If it is determined that the rotation center C1 is deviated from the central axis C2 of the test object TG (step S204: YES), a YZ direction position adjustment operation is performed so that the rotation center C1 is positioned on the central axis C2 of the test object TG (step S205). The amount of adjustment for the YZ direction position adjustment mechanism in step S205 is determined, for example, so that the deviation described above is equal to or smaller than a threshold value.

[0052] If the rotation center C1 is not displaced from the central axis C2 of the inspection target TG (step S204: NO), the YZ direction position adjustment operation in step S205 is not necessary.

[0053] Subsequently, similar to step S105 described above, the inspection control unit 32 performs an inspection operation (step S206). In step S206, the arm mechanism 22 is rotated at the axial position adjusted in step S101 (the same axial position as when the distance measurement operation was performed in step S202), thereby performing an inspection (irradiation of terahertz waves TH and detection of reflected waves RW) along the circumferential direction of the inner circumferential surface of the inspection target TG. The inspection data obtained by this inspection is readably stored in the data storage unit 38 as appropriate.

[0054] Next, the control device 30 determines whether the inspection content in the inspection plan has been completed (step S207), similar to step S106 described above. For example, if inspections are to be performed at multiple axial positions, whether the inspection content has been completed is determined based on whether the axial position moved to in step S201 is the final inspection position. If there is a next inspection position (step S207: NO), the inspection is deemed incomplete, and the X-direction position adjustment operation is performed again (step S208). Processing then returns to step S206, and the same inspection operation is repeated at the next axial position, which is the next inspection position. In other words, in this embodiment, the YZ-direction position adjustment operation is performed only at the first axial position, and not at any subsequent axial positions. Therefore, the YZ-direction position adjustment operation is performed only once, significantly reducing the overall inspection time.

[0055] When the inspection operation is completed at each axial position in this manner (step S207: YES), the analysis unit 40 analyzes the data stored in the data storage unit 38 to obtain inspection results (step S209). The data analysis in step S209 includes a correction process for the inspection data using the correction data prepared in step S200. In this correction process, the distance from the rotation center C1 to the inner surface of the inspection target TG is determined based on the inspection data and distance data simultaneously. Therefore, the signal intensity that should be obtained when this distance is the propagation distance is determined based on the correction data prepared in step S200 (see FIG. 6). In the correction process, the signal intensity of the reflected wave RW obtained as an actual measurement value is corrected based on the signal intensity thus determined. This effectively prevents a decrease in inspection accuracy even if the rotation center C1 is displaced from the central axis C2 of the inspection target TG.

[0056] Next, still another embodiment will be described with reference to Fig. 7. Fig. 7 is a flowchart showing an inspection method according to another embodiment. In the above-described embodiments, the inspection is performed while moving in one direction along the axial direction of the inspection target TG, but in the following embodiment, the inspection is performed while moving in at least two directions (i.e., a forward direction and a backward direction) along the axial direction of the inspection target TG.

[0057] First, in the forward direction, the control device 30 adjusts the axial position of the inspection device 1 by performing an X-axis position adjustment operation (step S300) and then performs a distance measurement operation (step S301). That is, in the forward direction, the inspection operation (irradiation of terahertz waves TH and detection of reflected waves RW) is not performed, and only the distance to the inner peripheral surface of the inspection target TG is measured along the circumferential direction. (The distance measurement may be performed along the circumferential direction while the axial position is fixed, as in the above-described embodiments, or may be performed along a spiral by combining with adjustment of the axial position.) Steps S300 and S301 are repeatedly performed until the axial position reaches the forward direction end position specified in the inspection plan (step S302). As a result, distance data is obtained over the range specified in the inspection plan in the forward direction. These distance data are associated with the axial position and appropriately stored in the data storage unit 38.

[0058] Next, correction data is created using the distance data obtained in the forward direction (step S303). This correction data includes distance data (distance to the inner peripheral surface of the test object TG) for each axial position, and is used to correct the inspection data obtained in the backward direction. The correction data created in step S303 may be stored in the data storage unit 38 as appropriate.

[0059] Next, in the backward direction, the control device 30 adjusts the axial position of the inspection device by performing an X-direction position adjustment operation (step S304), and then performs an inspection operation (step S305). Steps S304 and S305 are repeatedly performed until the axial position reaches the backward end position (step S306). As a result, inspection data is obtained in the backward direction over the range specified in the inspection plan. This inspection data is associated with the axial position and stored in the data storage unit 38 as appropriate.

[0060] In steps S300 to S302 in the forward direction, the X-direction position adjustment operation and the distance measurement operation may be performed simultaneously, so that, for example, distance measurement may be performed spirally on the inner peripheral surface of the inspection target TG. In this case, in steps S304 to S306 in the backward direction, the X-direction position adjustment operation and the inspection operation may also be performed simultaneously, so that, for example, inspection may be performed spirally on the inner peripheral surface of the inspection target TG.

[0061] Next, steps S304 to S306 are repeated using the correction data created in step S303 to correct the acquired inspection data (step S307). In this embodiment, YZ position adjustment operations are not performed in steps S304 to S306, where inspection data is acquired in the backward direction. However, by performing correction processing using correction data created based on distance data acquired in the forward direction, the influence of deviation of the rotation center C1 from the central axis C2 of the inspection target TG can be reduced. As a result, compared to the previously described embodiment in which YZ position adjustment operations are performed each time an inspection operation is performed, it is possible to suitably improve inspection accuracy while shortening the time required for inspection.

[0062] In addition, within the scope of the present disclosure, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described embodiments may be combined as appropriate.

[0063] The contents described in each of the above embodiments can be understood, for example, as follows.

[0064] (1) An inspection device according to one embodiment is an inspection device for inspecting the inner surface of an inspection object having a cylindrical shape, and includes: an inspection unit for irradiating the inner surface with terahertz waves and detecting reflected waves of the terahertz waves; a distance measurement unit for measuring the distance between the inspection unit and the inner surface; a rotation unit for rotating the inspection unit and the distance measurement unit along the circumferential direction of the inspection object; a position adjustment mechanism for adjusting the position of the inspection unit on a plane intersecting the axial direction of the inspection object; and an axial position adjustment unit for adjusting the axial position of the inspection unit relative to the inspection object, and the position adjustment mechanism is controlled based on the measurement results of the distance measurement unit so that the center of rotation of the rotation unit is located on the central axis of the inspection object.

[0065] According to the above aspect (1), the inspection unit rotates in the circumferential direction while irradiating terahertz waves onto the inner peripheral surface of the object to be inspected, and detecting the waves reflected from the inner peripheral surface, thereby performing the inspection. The inspection device adjusts its position on a plane intersecting the axial direction based on the distance measurement results measured by the distance measurement unit, which rotates together with the inspection unit, so that the rotation center coincides with the central axis of the object to be inspected. This allows for accurate inspection using terahertz waves, which are electromagnetic waves with high directionality and excellent linearity.

[0066] (2) In another aspect, in the aspect (1) above, the adjustment amount of the position adjustment mechanism is determined based on the distance measured when the distance measuring unit is rotated circumferentially by the rotating unit while the axial position is fixed.

[0067] According to the above aspect (2), the rotation centers of the inspection unit and the distance measurement unit are suitably adjusted to the central axis of the object to be inspected, thereby effectively improving the inspection accuracy using terahertz waves.

[0068] (3) In another aspect, in the aspect (2) above, the adjustment amount is determined so that the deviation of the distance is minimized from the average value of the distance measured when the distance measuring unit is rotated circumferentially by the rotating unit while the axial position is fixed.

[0069] According to the above aspect (3), the adjustment amount of the position adjustment mechanism is determined so as to minimize the deviation of the distances measured while rotating the distance measurement unit in the circumferential direction with the axial position of the movable body fixed. By controlling the position adjustment mechanism based on the adjustment amount thus determined, the inspection unit can be suitably positioned on the central axis.

[0070] (4) In another aspect, in any one of the above aspects (1) to (3), the position adjustment mechanism is controlled each time the axial position changes, before the inner circumferential surface is inspected by the inspection unit.

[0071] According to the above aspect (4), each time the axial position of the inspection unit is changed, the position adjustment mechanism adjusts the rotation axis so that it is positioned on the central axis. By performing the inspection after such position adjustment, good inspection accuracy can be obtained.

[0072] (5) In another aspect, in any one of the above aspects (1) to (3), after the position adjustment mechanism is controlled, the inspection unit performs inspection at a plurality of axial positions.

[0073] According to the above aspect (5), after the position adjustment mechanism adjusts the rotation axis to be positioned on the central axis, inspection is performed at multiple axial positions, thereby making it possible to efficiently perform inspection at many axial positions while reducing the number of position adjustments.

[0074] (6) In another aspect, in the aspect (5) above, the relationship between the signal strength of the reflected wave detected by the inspection unit and the distance measured by the distance measurement unit is prepared in advance as correction data, and the signal strength of the reflected wave detected by the inspection unit is corrected using the correction data based on the distance measured by the distance measurement unit.

[0075] According to the above aspect (6), the relationship between the signal strength of the reflected wave detected by the inspection unit and the distance measured by the distance measurement unit is prepared in advance as correction data. By referring to this correction data, the signal strength of the reflected wave detected corresponding to the distance measured by the distance measurement unit is corrected, thereby improving the inspection accuracy while reducing the number of position adjustments by the position adjustment mechanism.

[0076] (7) In another aspect, in any one of the aspects (1) to (6) above, the signal strength of the reflected wave detected by the inspection unit is corrected using correction data that associates the signal strength of the reflected wave detected by the inspection unit while moving along the axial direction with the distance measured by the distance measurement unit.

[0077] According to the above aspect (7), the relationship between the signal strength of the reflected wave detected by the inspection unit while moving along the axial direction and the distance measured by the distance measurement unit is prepared in advance as correction data. This correction data is used when performing a subsequent inspection to correct the signal strength of the reflected wave detected by the inspection unit, thereby effectively improving the inspection accuracy.

[0078] (8) In another aspect, in any one of the above aspects (1) to (7), the distance measurement unit is a laser measurement device capable of measuring the distance using laser light.

[0079] According to the above aspect (8), by using a laser measuring device as the distance measuring unit, it is possible to suitably measure the distance between the inspection unit and the inner surface of the object to be inspected.

[0080] (9) In another aspect, in any one of the above aspects (1) to (8), the terahertz waves are generated by converting the wavelength of pulsed excitation light having a time width of 10 picoseconds to 10 nanoseconds using a nonlinear optical crystal.

[0081] According to the above aspect (9), the inspection unit converts the optical wavelength of pulsed excitation light having a time width of 10 picoseconds to 10 nanoseconds using a nonlinear optical crystal, thereby enabling the irradiation of powerful (high-output) terahertz waves compared to oscillators formed from semiconductor elements such as RTDs and PCAs. By using such powerful terahertz waves, it is possible to accurately inspect an object to be inspected that has a small signal-to-noise ratio (SNR) and is located beneath a difficult-to-permeate material.

[0082] REFERENCE SIGNS LIST 1 Inspection device 2 Internal space 4 Optical system 8 Light source 10 Nonlinear optical crystal 12 Half mirror 14 Mirror 16 Condenser lens 18 Detector 20 Housing 22 Arm mechanism 24 Multi-axis arm 26 Running wheel 28 Distance measurement unit 30 Control device 32 Inspection control unit 34 X-direction position adjustment unit 36 ​​YZ-direction position adjustment unit 38 Data storage unit 40 Analysis unit TG Inspection object RM Resin material LB Pulsed excitation light TH Terahertz wave RW Reflected wave LL Laser light LR Reflected laser light C1 Center of rotation C2 Central axis

Claims

1. An inspection device for inspecting an inner surface of a cylindrical object to be inspected, comprising: an inspection unit for irradiating the inner surface with terahertz waves and detecting reflected waves of the terahertz waves; a distance measurement unit for measuring the distance between the inspection unit and the inner surface; a rotation unit for rotating the inspection unit and the distance measurement unit along the circumferential direction of the object to be inspected; a position adjustment mechanism for adjusting the position of the inspection unit on a plane intersecting the axial direction of the object to be inspected; and an axial position adjustment unit for adjusting the axial position of the inspection unit relative to the object to be inspected, wherein the position adjustment mechanism is controlled so that the center of rotation of the rotation unit is located on the central axis of the object to be inspected based on the measurement results of the distance measurement unit.

2. An inspection device as described in claim 1, wherein the adjustment amount of the position adjustment mechanism is determined based on the distance measured when the distance measuring unit is rotated circumferentially by the rotating unit while the axial position is fixed.

3. An inspection device as described in claim 2, wherein the adjustment amount is determined so as to minimize the deviation of the distance from the average value of the distance measured when the distance measuring unit is rotated circumferentially by the rotating unit while the axial position is fixed.

4. An inspection device as described in claim 1 or 2, wherein the position adjustment mechanism is controlled each time the axial position changes and before the inner circumferential surface is inspected by the inspection section.

5. The inspection device according to claim 1 or 2, wherein after the position adjustment mechanism is controlled, inspection is performed by the inspection unit at a plurality of axial positions.

6. An inspection device as described in claim 5, which prepares in advance the relationship between the signal strength of the reflected wave detected by the inspection unit and the distance measured by the distance measuring unit as correction data, and uses the correction data to correct the signal strength of the reflected wave detected by the inspection unit based on the distance measured by the distance measuring unit.

7. A detection device as described in claim 1 or 2, which corrects the signal strength of the reflected wave detected by the inspection unit using correction data that correlates the signal strength of the reflected wave detected by the inspection unit while moving along the axial direction with the distance measured by the distance measuring unit.

8. The inspection device according to claim 1 or 2, wherein the distance measuring unit is a laser measuring device capable of measuring the distance using laser light.

9. An inspection device according to claim 1 or 2, wherein the terahertz waves are generated by optical wavelength conversion of pulsed excitation light having a time width of 10 picoseconds to 10 nanoseconds using a nonlinear optical crystal.

Images