Measurement device and measurement method using terahertz waves

Abstract

To provide a terahertz wave measurement device and measurement method with which it is possible to freely move while measuring and visually and simultaneously confirm all of the results of measurements carried out multiple times.SOLUTION: The terahertz wave measurement device includes, accommodated in one case: a terahertz wave measurer 2 for generating a terahertz wave, with which to irradiate a measurement object 101, and outputting the generated wave, as well as detecting the terahertz wave inputted after being reflected; a SLAM processor 3 having a RGB camera that captures images while moving; a computation processing unit 5; and a display unit 6. An optical axis center P of the terahertz wave from the terahertz wave measurer 2 with which the measurement object 101 is irradiated and an optical axis center Q of the RGB camera match each other. The computation processing unit 5 accepts as input a terahertz wave detection signal from the terahertz wave measurer 2 and a measurement data signal from the SLAM processor 3, and when the data obtained from both of these synchronized signals is not point cloud data, converts the inputted signals into point cloud data, and generates a display image in which these point cloud data are displayed in the same coordinate system, with the generated data displayed on the display unit 6.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a measurement device and a measurement method using terahertz waves. [Background technology]

[0002] Terahertz waves, which are electromagnetic waves with a frequency of approximately 0.1 THz to 10 THz, are highly permeable to materials such as plastic, paper, cloth, ceramics, and gypsum, and can therefore be used to visualize objects hidden by these materials by irradiating the objects with terahertz waves and detecting the transmitted or reflected waves. For example, internal structures that cannot be seen by the human eye, such as those inside the walls of architectural structures or behind the ceiling, can be visualized. In addition, the thickness of the materials through which visible light is difficult to transmit can be measured. Various configurations of measuring devices using this type of terahertz waves (hereinafter referred to as "terahertz wave measuring devices") have been known in the past.

[0003] For example, Patent Document 1 describes an inspection system that uses an electromagnetic wave generating source having an oscillation frequency of 10 GHz to 10 THz, which is composed of a terahertz generator, combines multiple oscillation elements with different oscillation frequencies, or uses multiple detectors, irradiates the generated electromagnetic wave on a building and obtains a transmitted or reflected image, thereby enabling imaging of defect distribution on the surface and inside of the building. The two probes having oscillation elements with different oscillation frequencies perform scanning in the XY directions with the same driving mechanism, and adjustment in the focal depth direction is performed by the same driving mechanism that is separate from the above driving mechanism.

[0004] For example, Patent Document 2 describes a real-time non-contact non-destructive thickness measurement device using terahertz waves that can measure the thickness of a sample. This measurement device inputs a fixed wavelength laser and a wavelength sweep laser into a coupler, inputs the mixed light formed into a generator that generates terahertz waves, inputs the terahertz waves emitted from the generator and transmitted or reflected by the sample into a detector, and the detector biases the photocarriers excited by the mixed light with the electric field of the terahertz waves to generate a photocurrent, and the data acquisition unit acquires the photocurrent in the form of digital data, outputs it to a calculation unit to convert it into frequency domain data, performs a fast Fourier transform on the frequency domain data to generate time domain data, and calculates the thickness of the sample based on the time domain data. Patent Document 2 does not describe measuring the thickness of the sample, which is the measurement target, while moving the measurement device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2007-132915 [Patent Document 2] Patent Publication No. 2017-15681 Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned conventional inspection system or measuring device has a problem that the size of the measurement target that can be measured in one scan is limited to the range that can be moved by the drive system, that is, the range in which the position / angle coordinates can be acquired. In addition, when performing multiple scans, the installation position of the probe or measuring device must be changed each time, and this installation change work is a heavy burden. Furthermore, since it is difficult to check the overall arrangement state of the internal structure that is invisible and covers a wide area, there is also a problem that repair work or additional installation work of the internal structure cannot be performed smoothly and reliably.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a terahertz wave measurement device and a terahertz wave measurement method that can measure while moving freely, and can image not only the results of a single measurement but also all the results of multiple measurements, allowing the object to be measured and its internal structure to be visually confirmed at the same time. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, a first aspect of the terahertz wave measuring device of the present invention comprises a terahertz wave measuring instrument that generates and outputs terahertz waves to be irradiated onto a measurement object that is opaque to visible light, and detects the terahertz waves reflected and input by the measurement object and internal structures, a SLAM (Simultaneous Localization and Mapping) processor having a camera, a calculation processing unit, and a display unit, and at least everything except the display unit is contained in a single case, and the center of the optical axis that outputs the terahertz waves from the terahertz wave measuring instrument, i.e., the center of the optical axis that irradiates the measurement object with terahertz waves, coincides with the center of the optical axis of the camera, and the calculation processing unit receives a terahertz wave detection signal from the terahertz wave measuring instrument and a measurement data signal from the SLAM processor, converts the data obtained from the two synchronized signals into point cloud data, generates a display image in which these point cloud data are displayed on the same coordinate system, and displays this display image on the display unit.

[0009] The SLAM processor is a Visual SLAM having a camera, and by capturing images while moving the camera and analyzing the trajectories of feature points contained in the captured images, it is possible to estimate the three-dimensional positions of the feature points as well as the position and orientation of the camera, and also to create a map of the surroundings using the three-dimensional information of the feature points. By simultaneously performing this process of self-position and orientation estimation and map creation, it is possible to grasp the position and orientation and movement state of the terahertz wave measuring device in the same case as the SLAM processor with respect to the measurement object. The SLAM processor may have its own internal arithmetic processing unit, which processes the image data of the camera and converts it into point cloud data.

[0010] The center of the optical axis of the terahertz wave measuring instrument for irradiating the measurement object with the terahertz wave coincides with the center of the optical axis of the camera. This coincidence of the optical axis centers can be achieved by using, for example, a beam splitter.

[0011] The arithmetic processing unit converts the tomography data obtained from the input synchronous terahertz wave detection signal and the map point cloud data obtained from the measurement data signal into the same coordinate system, generates a display image displaying these point cloud data on this coordinate system, and displays this display image on the display unit. If the map data obtained from the measurement data signal is not point cloud data, it is converted into point cloud data and then converted into the same coordinate system. This allows the measurement object and the internal structure that was hidden by the measurement object to be displayed simultaneously. This process is performed for each scan, and a display image that is consistent with all the results of multiple measurements is generated and displayed, allowing all the measurement results from the first to the final measurement to be visually confirmed.

[0012] The display unit may be housed in the same case together with the terahertz wave measuring instrument, the SLAM processor, and the arithmetic processing unit, or may be provided in a separate location from the case. In this case, the person performing the measurement cannot see the map image of the SLAM processor or the image of the internal structure taken by the terahertz measuring instrument during the measurement operation, but can visually check all the measurement results from the first to the last measurement by the display image that has been aligned after the measurement operation.

[0013] In order to achieve the above object as well, in a second aspect of the terahertz wave measuring device according to the present invention, the camera of the SLAM processor is a 360-degree RGB camera. In addition to this second aspect, it is also possible to configure the device to preferably include a LiDAR, and more preferably include an IMU (Inertial Measurement Unit). When a 360-degree RGB camera is used, the shooting range can be expanded to include areas other than the measurement object, so that it is effective for SLAM processing when the measurement object has few feature points. Furthermore, LiDAR is more accurate than cameras such as RGB cameras, and can measure the distance to the measurement object. Furthermore, when an IMU is provided, the accuracy of the orientation information of the SLAM processor is improved. The combined use of this IMU is effective for creating a map in an environment with few feature points, similar to the 360-degree RGB camera.

[0014] In the first and second aspects, the synchronization of the terahertz wave detection signal from the terahertz wave measuring instrument and the measurement data signal from the SLAM processor is preferably performed by a synchronization signal generating unit such as an oscillator circuit that transmits a synchronization signal such as a shutter trigger to the terahertz wave measuring instrument and the SLAM processor provided in the case. Also, the synchronization of the terahertz wave detection signal and the measurement data signal may be preferably configured so that the arithmetic processing unit synchronizes the terahertz wave detection signal and the measurement data signal input at the same time.

[0015] In order to achieve the above object, the present invention provides a terahertz wave measurement method, which uses a terahertz wave measurement device that generates and outputs terahertz waves to be irradiated onto a measurement object that is opaque to visible light, and detects the terahertz waves reflected and input by the measurement object and an internal structure, a SLAM (Simultaneous Localization and Mapping) processor having a camera, a calculation processing unit, and a display unit, and at least the display unit is housed in a single case, in which the center of the optical axis of the terahertz wave measurement device that outputs the terahertz waves, i.e., irradiates the measurement object with the terahertz waves, is aligned with the center of the optical axis of the camera, and the calculation processing unit converts data obtained from the terahertz wave detection signal input from the terahertz wave measurement device and the measurement data signal input from the SLAM processor, which are synchronized with each other, into point cloud data, generates a display image in which the point cloud data are displayed on the same coordinate system, and displays the display image on the display unit. It is preferable to use a 360-degree RGB camera as the camera. In addition, if the SLAM processor has an internal calculation processing unit, the measurement data is processed into point cloud data before being output. Effect of the Invention

[0016] According to the present invention, the terahertz wave measuring device, at least except for the display unit, is contained in a single case, making it possible to perform measurements while moving freely.Furthermore, the internal structures measured by the terahertz wave measuring instrument and converted into a point cloud are aligned and overlaid on a map that has been converted into a point cloud using SLAM processing, and thus, in multiple measurement processes, it is possible to simultaneously visually confirm the measurement target positions of all measurement results from the first to the final measurement, and the existence of internal structures corresponding to these measurement target positions.Based on this confirmation, renovation work or additional placement work for the internal structures can be carried out smoothly and reliably. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing the relationship between a terahertz wave measuring device according to the present invention and a measurement object. [Diagram 2]FIG. [Diagram 3] FIG. 4 is a front view showing a display state of the display unit; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings, FIGS. As shown in Fig. 1, the terahertz wave measurement device 1 includes a terahertz wave measuring instrument 2, a SLAM processor 3, a synchronization signal generating unit 4, a calculation processing unit 5, a display unit 6, an operation unit 7, a memory unit 8, and a beam splitter 9, all of which are housed in a single case 10 (see Fig. 2). As shown in Fig. 2, the case 10 is of a size and weight that allows a measurer M to carry it in his or her hand and perform measurement work while moving around.

[0019] 1, in order to detect an internal structure behind an object to be measured, for example, an opaque wall 101 of an architectural structure, the terahertz wave measuring instrument 2 has a terahertz wave generator 21 that generates and outputs a terahertz wave having a frequency of 0.1 THz to 10 THz, preferably 75 GHz to 110 GHz or 20 GHz to 30 GHz to be irradiated onto a wall surface 110, and a terahertz wave detector 22 that detects the input terahertz wave reflected by the wall surface 110 and the internal structure. On the back side of the wall 101, there are provided, as internal structures, a metal pipe 201 that extends vertically, and a metal pipe 202 that extends horizontally, bends at one end of the wall 101, and reaches the back side of the adjacent wall 102 (see FIG. 2). The terahertz waves output from the terahertz wave generator 21 are partially reflected by the wall 101, while the remainder passes through and reaches the pipes 201, 202, and a further portion is reflected by the peripheral surface of each pipe 201, 202 and input to the terahertz wave detector 22, thereby enabling the presence of these pipes 201, 202 and the distance to their installation position to be detected.

[0020] The SLAM processor 3 is a Visual SLAM having a 360-degree RGB camera, and captures images while moving the 360-degree RGB camera, and analyzes the trajectories of feature points included in the captured images, such as the pot of the plant T in FIG. 2, or (not shown) the corners of desks and shelves arranged in the room, the corners of window frames, the edges of pillars, and air conditioning equipment on the ceiling, to estimate the three-dimensional positions of the feature points and to estimate the position and orientation of the SLAM processor 3. It is also possible to create a map of the wall 101 and its surroundings using the three-dimensional information of the feature points. By performing this process of estimating the self-position and orientation and creating a map simultaneously, the position and orientation and moving state of the SLAM processor 3 and the terahertz wave measuring device 2 in the same case 10 as the SLAM processor 3 with respect to the wall 101 can be grasped.

[0021] The optical axis center P of the terahertz wave measuring instrument 2, which irradiates the wall surface 110 with the terahertz wave, and the optical axis center Q of the 360-degree RGB camera are made to coincide with each other by a beam splitter 9. The beam splitter 9 is made of, for example, a glass plate coated with an ITO (indium tin oxide) film, and transmits visible light but reflects terahertz waves. By making the optical axis center P of the terahertz wave measuring instrument 2, which irradiates the wall surface 110 with the terahertz wave, and the optical axis center Q of the 360-degree RGB camera coincide with each other, the irradiation position (which is also the reflection position) of the terahertz wave on the wall surface 110 corresponds to the center position of the image captured by the 360-degree RGB camera.

[0022] The terahertz wave detection signal sent from the terahertz wave detector 22 and the measurement data signal from the SLAM processor 3 are input to the arithmetic processing unit 5 in synchronization with a synchronization signal from a synchronization signal generating unit 4. The map data, which is the measurement data signal of the SLAM processor 3 input to the arithmetic processing unit 5, is usually point cloud data, but if it is not point cloud data, it is converted into point cloud data. The arithmetic processing unit 5 also converts the terahertz wave reflection positions of the wall surface 110 and the periphery of each pipe 201, 202 into point cloud data based on the tomography data obtained from the input terahertz wave detection signal. The arithmetic processing unit 5 integrates each of the point cloud data into the same coordinate system, for example, a world coordinate system, and generates a display image 60 in which the map point cloud and the reflection position point cloud are integrated into the same image. Then, the arithmetic processing unit 5 displays the display image 60 on a display unit 6 consisting of a liquid crystal display or the like.

[0023] The operation unit 7 allows the measurer M to perform various operations on the terahertz wave measuring device 1, and includes, for example, a power key, numeric keys, an execution key, etc. The storage unit 8 includes a ROM in which the arithmetic program of the arithmetic processing unit 5 and the like are stored, and a RAM in which point cloud data and the like are temporarily stored.

[0024] In this embodiment, the first measurement is performed by targeting the wall 101 and detecting the internal structure behind the wall 101, and then the second measurement is performed by targeting the wall 102 and detecting the internal structure behind the wall 102. First, the first measurement is described. As shown in FIG. 2, the measurer M holds the above-mentioned terahertz wave measuring device 1 in his / her hand and moves back and forth parallel to the wall surface 110 while irradiating the wall surface 110 with terahertz waves from the top to the bottom in a zigzag pattern to detect the internal structure behind the wall 101. At this time, the SLAM processor 3 obtains image data of the wall surface 110 by the 360-degree RBG camera. However, since the wall surface 110 does not have clear features such as patterns or unevenness, it is difficult to perform self-location estimation and map creation processing using only the image data of the wall surface 110. However, since the 360-degree RGB camera can capture not only the wall surface 110 but also other structures in the room as image data, it is possible to reliably execute the SLAM process that simultaneously estimates the self-position and creates a map by acquiring features that can be used as feature points, such as the plant T shown in Fig. 2 and the structures on the opposing sides of the walls 101 and 102 (not shown). This map data and self-position estimation data are output to the calculation processing unit 5 as measurement data signals. Note that marks that can be used as feature points may be provided in advance at appropriate positions on the wall surface 110.

[0025] As shown in FIG. 1, the terahertz waves irradiated to the wall surface 110 are reflected at a reflectance corresponding to the material of the wall surface 110 and pass through the inside of the wall 101, and when they hit the pipe 201, they are reflected at a reflectance corresponding to the material. The pipe 201 is made of metal, so it is reflected at a high reflectance. The same is true for the pipe 202 extending perpendicularly to the pipe 201. The reflected terahertz waves are input to the terahertz wave detector 22 by the beam splitter 9, converted into detection data, and sent to the calculation processing unit 5, where the distance to the wall surface 101 and its material are specified, and the distance to each of the pipes 201 and 202 and their materials are specified. The calculation processing unit 5 further converts the reflection positions of the terahertz waves into a point group. Here, a threshold value is set for the received light reflection intensity, and when the threshold value is exceeded or when a peak is detected in the peak search, the data is considered valid, and only metal substances with a light reflection intensity higher than the threshold value are detected and converted into a point group. In addition, in Fig. 1, the irradiated terahertz wave is indicated by a solid line, and the reflected wave is indicated by a dashed line. For convenience of illustration, the irradiated wave and the reflected wave are shown at different positions.

[0026] The arithmetic processing unit 5 converts the map data acquired by the SLAM processing into point cloud data if it has not been converted into a point cloud, and sets the distance to the point of the map point cloud that is closest to the terahertz wave optical axis obtained from the self-position and orientation of the terahertz wave measuring instrument 2 as the distance value obtained by the terahertz wave measuring instrument 2, and determines each distance value of the map point cloud based on this distance value. Then, it obtains the coordinates of each map point cloud and the coordinates of the reflection positions converted into point clouds as described above, and integrates these coordinates into the same coordinate system, for example the world coordinate system, to generate an intermediate display image.

[0027] Next, in the second measurement, wall 102 is targeted to detect the internal structure behind it. The second measurement is similar to the first measurement described above, except that the internal structure is only pipe 202, so a description thereof will be omitted. The display image obtained in this second measurement is integrated with the intermediate display image obtained in the first measurement to generate a final display image 60, which is displayed on display unit 6. This integration of the display images can be easily performed because each display image is shown in the same coordinate system.

[0028] 3, the display image 60 displayed on the display unit 6 is a point cloud image of the positions and shapes of pipes 201, 202 present behind opaque walls 101, 102 that do not transmit visible light, together with the shapes of the walls 101, 102. This allows the entire results of the first and second measurements to be visually confirmed.

[0029] The present invention is not limited to the above-mentioned embodiments, and for example, the number of measurements, i.e., the number of scans, is not limited to two, but can be implemented once or three or more times. Furthermore, if the SLAM processor 3 is equipped with a LiDAR in addition to the 360-degree RGB camera, more accurate image data can be obtained and the distance to the measurement object can also be measured. Furthermore, although the SLAM processor is equipped, map point cloud data may be obtained by SfM / MVS (Structure-from-Motion / Multi-View-Stereo) processing as post-processing after measurement. This SfM / MVS processing can be performed by the terahertz wave measurement device 1, but considering the processing time, it is preferable to transfer the measurement data to an external personal computer with a high processing speed by wire or wirelessly. Furthermore, the terahertz wave measurement device 1 can be held by the measurer M for measurement, or if it is larger and heavier, it can be mounted on a cart or the like and measured while the measurer M moves the cart or the like. Furthermore, the above-mentioned embodiments can be modified based on the knowledge of a person skilled in the art, and it goes without saying that such forms are also included in the scope of the present invention. [Explanation of symbols]

[0030] 1. Terahertz wave measurement device 2. Terahertz wave measuring instrument 3 SLAM processor 4. Synchronization signal generator 5. Processing section 6 Display section 7 Control section 8 Memory section 9 Beam splitter 21 Terahertz Wave Generator 22 Terahertz wave detector 60 Display Images 101,102 Wall 110 Wall surface 201,202 Pipes P: Center of terahertz wave irradiation optical axis Q RGB camera optical axis center

Claims

1. The present invention includes a terahertz wave measuring device that generates and outputs terahertz waves and detects reflected and input terahertz waves, a SLAM processor having a camera, a calculation processing unit, and a display unit, At least the components other than the display unit are housed in one case, the center of an optical axis of the terahertz wave measuring instrument for irradiating the terahertz wave toward a measurement object coincides with the center of an optical axis of the camera; The arithmetic processing unit receives an input of a terahertz wave detection signal from the terahertz wave measuring instrument and a measurement data signal from the SLAM processor, converts data obtained from the two synchronized signals into point cloud data if the data is not point cloud data, generates a display image in which the point cloud data is displayed on the same coordinate system, and displays the display image on the display unit. A measuring device using terahertz waves.

2. The camera of the SLAM processor is a 360-degree RGB camera.

2. The measuring device using terahertz waves according to claim 1 .

3. The synchronization of the terahertz wave detection signal from the terahertz wave measuring instrument and the measurement data signal from the SLAM processor is performed by a synchronization signal generating unit provided in the case, which sends a synchronization signal to the terahertz wave measuring instrument and the SLAM processor.

3. A measuring device using terahertz waves according to claim 1 or 2.

4. The terahertz wave detection signal from the terahertz wave measuring instrument and the measurement data signal from the SLAM processor are synchronized in the arithmetic processing unit with respect to the terahertz wave detection signal and the measurement data signal input at the same time.

3. A measuring device using terahertz waves according to claim 1 or 2.

5. A measurement method using a terahertz wave measurement device including a terahertz wave measurement instrument that generates and outputs terahertz waves and detects reflected and input terahertz waves, a SLAM processor having a camera, an arithmetic processing unit, and a display unit, the measurement method including the use of a terahertz wave measurement instrument, the terahertz wave measurement instrument including a terahertz wave measurement instrument that generates and outputs terahertz waves and detects reflected and input terahertz waves, a SLAM processor having a camera, an arithmetic processing unit, and a display unit, the measurement method including the use of a terahertz wave measurement instrument that includes a terahertz wave measurement instrument that generates and outputs terahertz waves and detects reflected and input terahertz waves, the terahertz wave measurement instrument including ... measurement instrument including a terahertz wave measurement instrument that generates and outputs terahertz waves and detects reflected and input terahertz waves, the measurement instrument including a SLAM processor having a camera, an arithmetic processing unit, and a display unit, the measurement instrument including a terahertz wave measurement instrument that includes a SLAM processor having a camera, The optical axis center of the terahertz wave measuring instrument for irradiating the terahertz wave on the measurement object is aligned with the optical axis center of the camera, The arithmetic processing unit converts data obtained from the terahertz wave detection signal input from the terahertz wave measuring instrument and the measurement data signal input from the SLAM processor, which are synchronized with each other, into point cloud data, generates a display image in which the point cloud data are displayed on the same coordinate system, and displays the display image on the display unit. A measurement method using terahertz waves.

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