Optical fiber diameter measuring device

Abstract

The application discloses a kind of optical fiber diameter measuring device, comprising: object platform, base and first displacement table are provided on object platform;Second displacement table is arranged on base;Optical fiber fixing device is located on second displacement table, at least one optical fiber to be measured is fixed on optical fiber fixing device;Image acquisition device and the image processing device connected with image acquisition device, image acquisition device is located on first displacement table, for collecting the topographic image of at least one optical fiber to be measured, and output to image processing device, so that image processing device determines the diameter of at least one optical fiber to be measured according to topographic image.The application not only realizes the non-contact measurement of optical fiber diameter by image acquisition device and image processing device, ensures that the surface of the optical fiber to be measured is not damaged, but also avoids the optical fiber to be measured from shaking or oscillating during the measurement by moving the image acquisition device along the first direction, which is conducive to improving the accuracy of optical fiber diameter measurement.

Description

Technical Field

[0001] This application relates to the field of measurement technology, and in particular to a fiber optic diameter measuring device. Background Technology

[0002] In the manufacturing process of optical fibers, quality analysis is typically required for finished or prototype products to assess yield. This quality analysis usually involves measuring the fiber diameter. The diameter can be measured using either contact or non-contact methods. However, because optical fibers are pressure-sensitive devices, contact measurements can easily damage the fiber surface. Furthermore, non-contact methods can lead to fiber wobbling during measurement, resulting in decreased accuracy.

[0003] Therefore, the relevant technologies have shortcomings and need to be improved and developed. Summary of the Invention

[0004] This application provides an optical fiber diameter measuring device, which aims to at least partially solve one of the technical problems in the related art.

[0005] To address the aforementioned problems, this application provides an optical fiber diameter measuring device, comprising: a platform on which a base and a first displacement stage are disposed; a second displacement stage disposed on the base; an optical fiber fixing device located on the second displacement stage, on which at least one optical fiber to be measured is fixed; an image acquisition device and an image processing device connected to the image acquisition device; the image acquisition device being located on the first displacement stage, used to acquire morphological images of the at least one optical fiber to be measured and output them to the image processing device, so that the image processing device determines the diameter of the at least one optical fiber to be measured based on the morphological images; wherein, the image acquisition device moves along a first direction under the drive of the first displacement stage to acquire morphological images of each of the at least one optical fiber to be measured at the same height; the at least one optical fiber to be measured moves along a second direction under the drive of the second displacement stage to acquire morphological images of the at least one optical fiber to be measured at different heights, wherein the first direction and the second direction are perpendicular to each other.

[0006] The image acquisition device includes a camera, a light source, and multiple through-beam fiber optic sensors. The camera is positioned opposite to the light source, and a gap is formed between the camera and the light source. The multiple through-beam fiber optic sensors are arranged around the gap, and the gap is used to accommodate the portion of each fiber optic cable to be tested.

[0007] The plurality of through-beam fiber optic sensors include two pairs of through-beam fiber optic sensors arranged orthogonally.

[0008] The first displacement stage is provided with a first adapter plate and a second adapter plate fixed on the first adapter plate, and the plurality of through-beam fiber optic sensors are mounted on the second adapter plate.

[0009] The first adapter plate is also fixed with a third displacement stage, and the camera is set on the third displacement stage. The third displacement stage is used to drive the camera to move along the first direction or the third direction, wherein the first direction, the second direction and the third direction are perpendicular to each other.

[0010] The length of the portion to be tested in each optical fiber ranges from 45mm to 70mm.

[0011] The optical fiber fixing device is provided with an adsorption hole, which is used to adsorb and fix the at least one optical fiber to be tested on the optical fiber fixing device.

[0012] The platform is also equipped with a safety light curtain.

[0013] The number of optical fibers to be tested ranges from 1 to 60.

[0014] The at least one optical fiber under test includes multiple optical fibers under test, which are arranged at equal intervals along the first direction.

[0015] The beneficial effects of this application are as follows: This application realizes non-contact measurement of optical fiber diameter through image acquisition device and image processing device, ensuring that the surface of the optical fiber under test is not damaged. Furthermore, by moving the image acquisition device along the first direction to acquire the morphological image of each optical fiber under test at least one optical fiber under test at the same height, the optical fiber under test is prevented from moving along the first direction during the measurement process, thus avoiding shaking or oscillation. This solves the problem that the optical fiber diameter is difficult to determine due to motion blur in the first direction in the morphological image, which is beneficial to improving the accuracy of optical fiber diameter measurement. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the optical fiber diameter measuring device provided in the embodiments of this application;

[0018] Figure 2 yes Figure 1 A magnified schematic diagram of the local structure at point A;

[0019] Figure 3 This is a schematic diagram of the assembly structure of the image acquisition device, the first adapter plate, the second adapter plate, and the third displacement stage provided in the embodiments of this application;

[0020] Figure 4 yes Figure 3 A top view of the assembly structure;

[0021] Figure 5 This is a topographic image of a single optical fiber under test provided in an embodiment of this application. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0024] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0026] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, various specific examples of processes and materials are provided in this application, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0027] Please see Figure 1 , Figure 1 This is a schematic diagram of the diameter measuring device provided in the embodiments of this application. Figure 1 In the diagram, the first direction, the second direction, and the third direction correspond to the x-direction, the z-direction, and the y-direction, respectively, and the x-direction, y-direction, and z-direction are perpendicular to each other.

[0028] like Figure 1As shown, the diameter measuring device 10 includes a platform 11, a base 12, a first displacement stage 13, a second displacement stage 14, an optical fiber fixing device 15, an image acquisition device 17, and an image processing device (not shown in the figure). The base 12 and the first displacement stage 13 are mounted on the platform 11, the second displacement stage 14 is mounted on the base 12, and the optical fiber fixing device 15 is located on the second displacement stage 14. At least one optical fiber 16 to be measured is fixed on the optical fiber fixing device 15. The image acquisition device 17 is connected to the image processing device and is located on the second displacement stage 14. It is used to acquire morphological images of the at least one optical fiber 16 to be measured and output them to the image processing device, so that the image processing device can determine the diameter of the at least one optical fiber 16 to be measured based on the morphological images. The at least one optical fiber 16 to be measured moves along the z-direction under the drive of the second displacement stage 14, so that the image acquisition device 17 acquires morphological images of the at least one optical fiber 16 to be measured at different heights. The image acquisition device 17 moves along the x-direction under the drive of the first displacement stage 13 to acquire the shape image of each of the at least one optical fiber under test 16 at the same height, with the x-direction perpendicular to the z-direction.

[0029] Specifically, the second displacement stage 14 is positioned on the base 12 at the end away from the loading platform 11. Therefore, the fiber optic fixing device 15 located on the second displacement stage 14 has a certain height relative to the loading platform 11 in the z-direction, and this height can change as the fiber optic fixing device 15 moves in the z-direction. The at least one fiber optic cable 16 to be tested extends along the z-direction on the fiber optic fixing device 15. Therefore, when the height changes, the image acquisition device 17 can acquire morphological images at different lengths of each fiber optic cable 16. Since the z-direction, where the height is located, is also the direction of gravity acting on each fiber optic cable 16, each fiber optic cable 16 naturally extends along the z-direction. Therefore, when the at least one fiber optic cable 16 moves along the z-direction, its sway is very weak. Furthermore, since the z-direction is not the direction of the diameter of each fiber optic cable 16, the movement of the at least one fiber optic cable 16 along the z-direction will not affect the accuracy of the diameter measurement process.

[0030] It should be further explained that, in the embodiments of this application, topographic images of at least two locations on each fiber 16 under test can be acquired at at least two different heights. The image analysis device can obtain the diameter of the at least two locations based on the topographic images. By comparing the diameters of the at least two locations, the morphological uniformity of each fiber 16 under test can be evaluated. The average diameter of each fiber 16 under test can be calculated from the diameters of the at least two locations. By comparing the average diameter of each fiber 16 under test, the uniformity among the individual fibers 16 under test can be evaluated. The uniformity reflects the quality and yield of the fiber 16 under test.

[0031] In this embodiment, the number of optical fibers 16 to be tested can be one or more. In this embodiment, the number of optical fibers 16 to be tested can range from 1 to 60. When there are multiple optical fibers 16 to be tested, the multiple optical fibers 16 to be tested are arranged at equal intervals along the x-direction on the optical fiber fixing device 15. Therefore, when acquiring the morphological image of each of the at least one optical fiber 16 to be tested at the same height, each acquisition only requires moving the image acquisition device 17 the same distance along the x-direction.

[0032] It should be further explained that, in their research, the inventors of this application discovered that when the second displacement stage 14 moves the fiber optic fixing device 15 along the x-direction so that the image acquisition device 17 can acquire the morphological image of each of the at least one fiber optic cable 16 under test at the same height, although the at least one fiber optic cable 16 under test is fixed to the fiber optic fixing device 15, it has a certain inertia during the movement following the second displacement stage 14. Especially after the fiber optic fixing device 15 moves along the x-direction, the at least one fiber optic cable 16 under test has a certain inertia in the x-direction, that is, in the diameter direction of each fiber optic cable 16. This inertia caused by the following movement leads to oscillation or shaking of each fiber optic cable 16 in the x-direction when the second displacement stage 14 stops moving. This results in the morphological image acquired by the image acquisition device 17 being unclear, exhibiting motion blur. This phenomenon will ultimately lead to inaccurate determination of the fiber diameter by the image processing device, and if the topographic image is acquired only after each fiber 16 under test stops shaking, the measurement cycle will be greatly extended.

[0033] To address the aforementioned problems, in this embodiment, the image acquisition device 17 is moved along the x-direction by the first displacement stage 13 to acquire morphological images along the x-direction, ensuring that the at least one fiber 16 under test remains stationary. This avoids oscillations or shaking of the fiber 16 itself, which could lead to a decrease in measurement accuracy. Therefore, by moving the image acquisition device 17 along the x-direction under the influence of the first displacement stage 13, and acquiring morphological images of each of the at least one fiber 16 under test at the same height, the accuracy of fiber diameter measurement can be improved. Furthermore, since the image acquisition device 17 has a certain acquisition range, it only needs to move a short distance in the x-direction to achieve comprehensive acquisition of the at least one fiber 16 under test, which is beneficial for improving measurement efficiency.

[0034] Specifically, the connection between the image acquisition device 17 and the image processing device is a communication connection. Images acquired by the image acquisition device 17 can be transmitted to the image processing device, which can then display and analyze the received images. Please refer to [link / reference]. Figure 5 , Figure 5 This is a topographic image of a single optical fiber 16 under test provided in this application embodiment, acquired by the image acquisition device 17 as shown below. Figure 5 After obtaining the topographic image shown, the image analysis device can analyze and process the topographic image, for example, determine the first boundary and the second boundary on the topographic image, and calculate the distance between the first boundary and the second boundary to determine the fiber diameter. The image processing device can be a computer or other device with image processing capabilities. The image processing device can also include the function of driving the first displacement stage 13 and the second displacement stage 14. The image processing device can drive the first displacement stage 13 to move along the x-direction or the y-direction, or move simultaneously in the x and y directions; the image processing device can also drive the second displacement stage 14 to move along the x-direction or the z-direction, but in this embodiment, it is chosen to avoid moving the second displacement stage 14 along the x-direction, thereby avoiding the at least one fiber under test 16 from shaking or oscillating in the x-direction.

[0035] Please see Figure 2 , Figure 2 This is a magnified schematic diagram of the structure at point A, as shown below. Figure 2 As shown, the image acquisition device 17 includes a camera 171, a light source 172, and multiple through-beam fiber optic sensors 173. Please refer to... Figure 3 and Figure 4The camera 171 is positioned opposite the light source 172, and a gap region 100 is formed between the camera 171 and the light source 172. The plurality of through-beam fiber optic sensors 173 are arranged around the gap region 100, which is used to accommodate, for example... Figure 2 The portion 161 to be tested in each optical fiber 16 to be tested is shown.

[0036] Specifically, the portion to be tested 161 is the portion of each fiber 16 to be tested that protrudes downward from the fiber fixing device 15 along the z-direction. In the process of measuring the fiber diameter of at least one fiber 16 to be tested, in order to ensure the efficiency of the measurement, a portion of the at least one fiber 16 to be tested will be selected for measurement. The diameter of the portion to be tested 161 of each fiber 16 to be tested can represent the diameter of the entire fiber 16 to be tested. That is, the image acquisition device 17 specifically acquires the morphological image of the portion to be tested 161.

[0037] The length of the portion 161 under test in each optical fiber 16 under test ranges from 45mm to 70mm.

[0038] Specifically, when the length of the test portion 161 is different, it means that the test fiber 16 has different specifications. For example, when the length of the test portion 161 is longer, it indicates that there are more positions on the test fiber 16 that need to ensure uniformity, reflecting that the specification of the test fiber 16 is higher.

[0039] It needs to be further explained that, such as Figure 2 As shown, the part under test 161 is suspended during the measurement process, ensuring that the light emitted by the light source 172 towards the part under test 161 is not blocked by the fiber optic fixing device 15, thus not affecting the light intake of the camera 171. Consequently, the camera 171 can capture a clearer and brighter image. Specifically, each fiber under test 16 also includes a part fixed to the fiber optic fixing device 15 and not shaking (not shown in the figure). The fiber optic fixing device 15 is also provided with an adsorption hole (not shown in the figure), which adsorbs and fixes the part to the fiber optic fixing device 15. Thus, at least one fiber under test 16 is adsorbed and fixed to the fiber optic fixing device 15 as a whole. Since the part under test 161 is suspended, the aforementioned motion blur phenomenon is caused by the oscillation or shaking of the part under test 161.

[0040] Specifically, the camera 171 can be a CCD (Charge Coupled Device) camera, which can have a 2x or 2.5x lens, 1M to 1.3M pixels, and autofocus. The through-beam fiber optic sensor 173 is specifically used to locate the portion 161 to be tested in each fiber optic cable 16. When multiple through-beam fiber optic sensors 173 are used, more accurate positioning can be achieved compared to a single through-beam fiber optic sensor 173.

[0041] In this embodiment, the camera 171 and the light source 172 are arranged opposite each other, specifically meaning that the center line of the camera 171 and the center of the light source 172 are coaxial, which can minimize the occurrence of uneven brightness in the topographic image captured by the camera 171. The plurality of through-beam fiber optic sensors 173 may specifically include, for example... Figure 3 and Figure 4 The diagram shows through-beam fiber optic sensors 173A, 173B, 173C, and 173D. Through-beam fiber optic sensor 173A and 173C can form a first pair of through-beam fiber optic sensors 173 (hereinafter referred to as the first pair), while through-beam fiber optic sensor 173B and 173D can form a second pair of through-beam fiber optic sensors 173 (hereinafter referred to as the second pair). The first and second pairs are orthogonally arranged, that is, the first and second pairs are perpendicular to each other, and the center line of the first or second pair (…) Figure 4 The AC or BD of the light source 172 forms a 45° angle with the center line of the light source 172, and the center lines AC of the first pair, BD of the second pair, and the center line of the camera 171 intersect at a point (intersection point).

[0042] By moving the image acquisition device 17 to sequentially place the intersection point onto each of the at least one fiber 16 under test, and combining it with the preset algorithm in the image processing device, the approximate position of the at least one fiber 16 under test can be sensed (i.e., coarse positioning, specifically referring to obtaining millimeter-level positioning accuracy), and the proximity coordinates of the at least one fiber 16 under test can be calculated. Based on the proximity coordinates, the image acquisition device 17 can be moved to a position that is convenient for observation and acquisition of each fiber 16 under test. This avoids the time-consuming process of moving the image acquisition device 17 to a position that is convenient for observation and acquisition of each fiber 16 under test by relying solely on manual judgment of the approximate position of the at least one fiber 16 under test, which is not conducive to improving measurement efficiency.

[0043] When moving the image acquisition device 17 to the proximity coordinate, it is necessary to move the first displacement stage 13 not only along the x-direction but also along the y-direction. After moving the image acquisition device 17 to the proximity coordinate, the at least one optical fiber 16 under test is within the focal length range of the camera 171. Furthermore, after moving the at least one optical fiber 16 under test to the proximity coordinate, a higher level of positioning accuracy can be achieved by micro-movement of the first displacement stage 13 in the x-direction. The first displacement stage 13 has micrometer-level positioning accuracy; therefore, the image acquisition device 17 can be moved to a more ideal position using the first displacement stage 13, thus enabling the acquisition of an ideal morphological image for each optical fiber 16 under test. The micro-movement of the first displacement stage 13 in the y-direction assists the camera 171 in focusing.

[0044] Please see Figure 2 and Figure 3 The first displacement stage 13 is provided with a first adapter plate 18 and a second adapter plate 19 fixed on the first adapter plate 18, and the plurality of through-beam fiber optic sensors 173 are mounted on the second adapter plate 19.

[0045] Specifically, since the through-beam fiber optic sensor 173 has its own installation specifications, which do not match the mounting holes on the first displacement stage 13, it cannot be directly installed on the first displacement stage 13. Therefore, it needs to be transferred to the first displacement stage 13 in sequence through the second adapter plate 19 and the first adapter plate 18. The second adapter plate 19 is set up to ensure that the height of the multiple through-beam fiber optic sensors 173 meets the usage requirements.

[0046] Please see Figure 3 and Figure 4 The first adapter plate 18 is also fixed with a third displacement stage 20, and the camera 171 is set on the third displacement stage 20. The third displacement stage 20 is used to drive the camera 171 to move along the x direction or y direction.

[0047] Specifically, the camera 171 is mounted on the first adapter plate 18 via the third displacement stage 20. The third displacement stage 20 can be a manual displacement stage, used to move the camera 171 along the x-direction or y-direction, so that when the camera 171 moves along the x-direction, its centerline can be adjusted to be coaxial with the centerline of the light source 172. The third displacement stage 20 can also adjust the distance between the camera 171 and the part to be measured 161 when the camera 171 moves along the y-direction, thus enabling the third displacement stage 20 to assist the camera 171 in focusing, thereby obtaining a clearer image of the shape.

[0048] The cargo platform 11 is also equipped with a safety light curtain (not shown in the figure).

[0049] The safety light curtain is used to ensure that the diameter measuring device 10 only starts working after human operation has ended, thus avoiding interference from human operation in the measurement process.

[0050] This application, on the one hand, outputs the topographic image of at least one optical fiber under test acquired by the image acquisition device to the image processing device, so that the image processing device can determine the diameter of at least one optical fiber under test based on the topographic image, thereby realizing non-contact measurement of the optical fiber diameter and ensuring that the surface of the optical fiber under test is not damaged. On the other hand, by moving the image acquisition device along a first direction to acquire the topographic image of each of the at least one optical fiber under test at the same height, it ensures that the optical fiber under test does not move along the first direction during the measurement process, thus avoiding the optical fiber under test from shaking or oscillating. This solves the problem that the diameter is difficult to determine due to motion blur in the direction of the optical fiber diameter in the topographic image, which is beneficial to improving the accuracy of optical fiber diameter measurement.

[0051] In addition to the embodiments described above, this application may have other implementation methods. All technical solutions formed by equivalent substitutions or equivalent replacements fall within the protection scope claimed in this application.

[0052] In summary, although the preferred embodiments have been disclosed above, the above preferred embodiments are not intended to limit the present application. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be determined by the scope defined in the claims.

Claims

1. A fiber optic diameter measuring device, characterized in that, include: A loading platform, wherein a base and a first displacement stage are provided on the loading platform; A second displacement stage is mounted on the base; An optical fiber fixing device is located on the second displacement stage, and at least one optical fiber to be tested is fixed on the optical fiber fixing device, and the at least one optical fiber to be tested extends along the second direction on the optical fiber fixing device. An image acquisition device and an image processing device connected to the image acquisition device, wherein the image acquisition device is located on the first displacement stage and is used to acquire the morphological image of the at least one optical fiber under test and output it to the image processing device so that the image processing device can determine the diameter of the at least one optical fiber under test based on the morphological image; The image acquisition device moves along a first direction under the drive of the first displacement stage to acquire the morphological image of each of the at least one optical fiber under test at the same height; the at least one optical fiber under test moves along a second direction under the drive of the second displacement stage to acquire the morphological image of the at least one optical fiber under test at different heights, wherein the first direction and the second direction are perpendicular to each other. The image acquisition device includes a camera, a light source, and multiple through-beam fiber optic sensors; the camera is positioned opposite to the light source, and a gap is formed between the camera and the light source; the multiple through-beam fiber optic sensors include two pairs of through-beam fiber optic sensors arranged orthogonally; the multiple through-beam fiber optic sensors are arranged around the gap, and the gap is used to accommodate the portion of each fiber under test.

2. The optical fiber diameter measuring device according to claim 1, characterized in that, The first displacement stage is provided with a first adapter plate and a second adapter plate fixed on the first adapter plate, and the plurality of through-beam fiber optic sensors are mounted on the second adapter plate.

3. The optical fiber diameter measuring device according to claim 2, characterized in that, A third displacement stage is also fixed on the first adapter plate. The camera is mounted on the third displacement stage. The third displacement stage is used to drive the camera to move along the first direction or the third direction. The first direction, the second direction, and the third direction are perpendicular to each other.

4. The optical fiber diameter measuring device according to claim 1, characterized in that, The length of the portion to be tested in each optical fiber ranges from 45mm to 70mm.

5. The optical fiber diameter measuring device according to claim 1, characterized in that, The optical fiber fixing device is provided with an adsorption hole, which is used to adsorb and fix the at least one optical fiber to be tested onto the optical fiber fixing device.

6. The optical fiber diameter measuring device according to claim 1, characterized in that, The cargo platform is also equipped with a safety light curtain.

7. The optical fiber diameter measuring device according to claim 1, characterized in that, The number of optical fibers to be tested ranges from 1 to 60.

8. The optical fiber diameter measuring device according to claim 1, characterized in that, The at least one optical fiber under test includes multiple optical fibers under test, which are arranged at equal intervals along the first direction.

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