Method for measuring curve contour of deep blind hole based on point spectrum confocal sensor

Abstract

The invention discloses a deep blind hole curve contour measuring method based on a point spectrum confocal sensor, and belongs to the technical field of optical sensors. The measuring method comprises the following steps: establishing a coordinate system about the deep blind hole, and importing the design contour of the deep blind hole into the coordinate system; combining the coordinate system and the design contour of the deep blind hole to form a trajectory, and determining the coordinate of the trajectory and the distance between starting points; providing a machine tool, arranging a point spectrum confocal sensor on an output shaft of the machine tool, and inputting the coordinate system and the trajectory to the machine tool, so that the point spectrum confocal sensor sequentially performs point scanning on the curve contour of the deep blind hole between two adjacent trajectory points according to the trajectory, and constructing a curve by using the scanned point data, the starting point distance and the trajectory in the three-dimensional model, and rotating to obtain the curve contour of the deep blind hole. According to the method for measuring the curve profile of the deep blind hole based on the point spectrum confocal sensor provided by the embodiment of the invention, the accurate curve profile of the deep blind hole can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of optical sensors, and in particular relates to a method for measuring a deep blind hole curve profile based on a point spectrum confocal sensor. Background Art

[0002] As the proportion of large integral workpieces used in modern aircraft, ships, large precision instruments and other products continues to increase, the detection of deep blind holes also occurs frequently.

[0003] At present, the detection method for the curve profile of deep blind holes after addition (the inner diameter of deep blind holes in the axial direction is different) mainly adopts contact measurement tools or laser scanning methods. Among them, contact measurement tools (such as internal diameter micrometers and pneumatic measuring instruments) rely on mechanical probes to contact the inner wall, which is prone to errors due to probe wear or insufficient rigidity; in the actual measurement process, the detection efficiency is low through the contact method, and the detection data sampling density is not enough, resulting in the difficulty in ensuring the detection accuracy. The optical system corresponding to the laser scanning method is large and cannot be adapted to deep blind holes. In addition, due to the uneven reflection of the inner wall of the deep blind hole and the interference of oil and dust, the signal will be severely attenuated, resulting in the difficulty in ensuring the detection accuracy. Therefore, a detection method for detecting the curve profile of blind holes is urgently needed to improve the detection accuracy. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method for measuring the curve profile of a deep blind hole based on a point spectral confocal sensor, the purpose of which is to control the point spectral confocal sensor to scan and construct the curve according to the trajectory line in the coordinate system, so that the point spectral confocal sensor has high scanning accuracy and can obtain an accurate deep blind hole curve profile.

[0005] To achieve the above object, the present invention provides a method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor, the measuring method comprising:

[0006] Establishing a coordinate system for the deep blind hole, wherein the coordinate system establishes a two-dimensional coordinate system with the central axis of the deep blind hole as the Y-axis and a radial direction as the X-axis, and importing the design contour of the deep blind hole into the coordinate system;

[0007] In combination with the coordinate system and the design profile of the deep blind hole, on the reference plane formed by the X-axis and the Y-axis, trajectory points are set with the X-axis as the corresponding position and moving to the corresponding positions in sequence along the Y-axis direction, and any two adjacent trajectory points are connected by a connecting line to form a trajectory line and determine the coordinates and starting point spacing of the trajectory line;

[0008] A machine tool is provided, wherein a point spectral confocal sensor is arranged on an output shaft of the machine tool, and the coordinate system and the trajectory line are input into the machine tool, so that the point spectral confocal sensor sequentially performs point scanning on the deep blind hole curve profile between two adjacent trajectory points according to the trajectory line, and constructs a curve with the scanned point data, the starting point spacing and the trajectory line in a three-dimensional model and rotates the curve to obtain the deep blind hole curve profile;

[0009] Among them, the spacing between each point of the trajectory line and the designed contour of the deep blind hole in the X-axis direction does not exceed the working distance of the point spectral confocal sensor, the height difference on the designed contour of the deep blind hole corresponding to any two adjacent trajectory points in the X-axis direction does not exceed the measuring range of the point spectral confocal sensor, the starting point spacing is the radial distance between the corresponding position of the trajectory line on the X-axis and the deep blind hole, and the position of any point on each connecting line in the X-axis direction does not exceed the position range of the corresponding two trajectory points in the X-axis direction.

[0010] Optionally, the connecting line is a straight line segment.

[0011] Optionally, the connecting line is a broken line segment, and the broken line segment includes a first straight line segment and a second straight line segment connected to each other, the first straight line segment is parallel to the X-axis, and the second straight line segment is parallel to the Y-axis.

[0012] Optionally, 30 mm ≤ working distance ≤ 40 mm.

[0013] Optionally, the height difference between the positions on the design contour of the deep blind hole corresponding to any two adjacent trajectory points in the X-axis direction satisfies the following formula:

[0014] 80%≤Δx i / L≤90%;

[0015] Where Δx i is the height difference between the positions on the designed contour of the deep blind hole corresponding to any two adjacent trajectory points in the X-axis direction, mm; L is the measuring range of the point spectral confocal sensor, mm.

[0016] Optionally, a connecting piece is provided on the output shaft of the machine tool, and the point spectrum confocal sensor is located on the connecting piece.

[0017] Optionally, the connecting member is a support rod or a knife rod.

[0018] Optionally, a ratio of the depth to the diameter of the deep blind hole is ≥10.

[0019] Optionally, the maximum inner diameter of the deep blind hole is ≥100 mm, and the depth of the deep blind hole is ≥1 m.

[0020] The above-mentioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0021] In general, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

[0022] For a method for measuring the curve profile of a deep blind hole based on a point spectral confocal sensor provided in an embodiment of the present invention, when measuring the curve profile of the deep blind hole, first, a coordinate system for the deep blind hole is established, and a two-dimensional coordinate system is established with the center axis of the deep blind hole as the Y-axis and a radial direction as the X-axis, and the designed profile of the deep blind hole is imported into the coordinate system. Through the coordinate system, not only the coordinates of the trajectory points can be confirmed, but also the coordinates of the subsequent trajectory lines can be determined, and the coordinates can also be input, so that the spectral confocal sensor of the machine tool control point scans according to the coordinates of the trajectory line.

[0023] Then, in combination with the coordinate system and the design contour of the deep blind hole, on the reference plane formed by the X-axis and the Y-axis, the track points are set with the X-axis as the corresponding position and the corresponding position moved in sequence along the Y-axis direction, and any two adjacent track points are connected by connecting lines to form a track line and determine the coordinates and starting point spacing of the track line. Among them, setting multiple track points can enable the subsequent point spectrum confocal sensor to scan in sequence between two adjacent track points, which can not only avoid the problem that the height difference of the positions on the design contour of the deep blind hole corresponding to two adjacent track points in the subsequent spectral confocal sensor during the scanning process of a track exceeds the range of the point spectrum confocal sensor, resulting in insufficient scanning accuracy and large errors, but also avoid the problem that the distance between the point spectrum confocal sensor and the deep blind hole exceeds the working distance of the point spectrum confocal sensor during the subsequent scanning process and cannot be scanned. Finally, a machine tool is provided, on the output shaft of which a point spectral confocal sensor is arranged, and a coordinate system and a trajectory line are input into the machine tool, so that the point spectral confocal sensor performs point scanning on the deep blind hole curve profile between two adjacent trajectory points in turn according to the trajectory line, and constructs a curve with the scanned point data, starting point spacing and trajectory line in a three-dimensional model and rotates it to obtain the deep blind hole curve profile, thereby finally obtaining an accurate deep blind hole curve profile.

[0024] That is to say, an embodiment of the present invention provides a method for measuring the curve profile of a deep blind hole based on a point spectral confocal sensor. By controlling the point spectral confocal sensor to scan and construct a curve along a trajectory line in a coordinate system, the point spectral confocal sensor has high scanning accuracy and can obtain an accurate curve profile of the deep blind hole. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of a method for measuring a deep blind hole curve profile based on a point spectrum confocal sensor provided by an embodiment of the present invention;

[0026] Figure 2 is a schematic diagram of the arrangement of trajectory points provided by an embodiment of the present invention;

[0027] Figure 3 is a schematic diagram of the arrangement of a trajectory line provided by an embodiment of the present invention;

[0028] Figure 4 is a processing schematic diagram provided by an embodiment of the present invention;

[0029] Figure 5 It is a schematic diagram of the arrangement of a trajectory line provided by an embodiment of the present invention.

[0030] In all the drawings, the same reference numerals represent the same technical features, specifically:

[0031] 1. Deep blind hole; 2. Point spectrum confocal sensor; 3. Connector; 4. Trajectory line; 41. Connecting line; 5. Design outline. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0034] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0035] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0037] Example:

[0038] Figure 1 is a flow chart of a method for measuring a deep blind hole curve profile based on a point spectrum confocal sensor provided by an embodiment of the present invention, such as Figure 1 As shown, the measurement methods include:

[0039] S1. Establish a coordinate system for the deep blind hole 1. The coordinate system establishes a two-dimensional coordinate system with the center axis of the deep blind hole 1 as the Y axis and a radial direction (located on the end surface) as the X axis, and imports the design contour 5 of the deep blind hole 1 into the coordinate system.

[0040] It should be noted that the coordinate system can be established with the assistance of measuring tools.

[0041] S2. Combine the coordinate system and the designed outline 5 of the deep blind hole 1 (the central axis of the designed outline 5 of the deep blind hole 1 coincides with the Y axis in the coordinate system), and set the trajectory points on the reference plane formed by the X axis and the Y axis, taking the X axis as the corresponding position and moving to the corresponding position in sequence along the Y axis (see Figure 2 A1, A2, A3, etc.), and connect any two adjacent track points through a connecting line 41, thereby forming a track line 4 and determining the coordinates and starting point spacing of the track line 4 (see Figure 3 ).

[0042] S3, providing a machine tool, on which a point spectrum confocal sensor 2 is arranged on the output shaft of the machine tool, and inputting a coordinate system and a trajectory line 4 into the machine tool, so that the point spectrum confocal sensor 2 sequentially scans the curve profile of the deep blind hole 1 between two adjacent trajectory points according to the trajectory line 4 (see Figure 4 ), and in the three-dimensional model, the scanned point data, the starting point spacing and the trajectory line 4 are used to construct a curve and rotate it to obtain the curve profile of the deep blind hole 1.

[0043] The distance between each point of the track line 4 and the design contour 5 of the deep blind hole 1 in the X-axis direction does not exceed the working distance of the point spectrum confocal sensor 2, and the height difference Δx of the position on the design contour 5 of the deep blind hole 1 corresponding to any two adjacent track points in the X-axis direction is i It does not exceed the measuring range of the point spectrum confocal sensor 2, the starting point spacing (i.e. ΔL1) is the radial distance between the corresponding position of the trajectory line 4 on the X-axis and the deep blind hole 1 (which can be obtained by a measuring tool), and the position of any point on each connecting line in the X-axis direction does not exceed the position range of the corresponding two trajectory points in the X-axis direction.

[0044] For a method for measuring the curve profile of a deep blind hole based on a point spectral confocal sensor provided by an embodiment of the present invention, when measuring the curve profile of the deep blind hole 1, first, a coordinate system for the deep blind hole 1 is established, and a two-dimensional coordinate system is established with the center axis of the deep blind hole 1 as the Y-axis and a radial direction as the X-axis, and the designed profile 5 of the deep blind hole 1 is imported into the coordinate system. Through the coordinate system, not only the coordinates of the trajectory points can be confirmed, but also the coordinates of the subsequent trajectory line 4 can be determined, and the coordinates can also be input, so that the machine tool control point spectral confocal sensor 2 scans according to the coordinates of the trajectory line 4.

[0045] Then, in combination with the coordinate system and the design contour 5 of the deep blind hole 1, on the reference plane formed by the X-axis and the Y-axis, the track points are set with the X-axis as the corresponding position and the corresponding positions moved in sequence along the Y-axis direction, and any two adjacent track points are connected by connecting lines to form a track line 4 and determine the coordinates and starting point spacing of the track line 4. Among them, setting a plurality of track points can enable the subsequent point spectrum confocal sensor 2 to scan sequentially between two adjacent track points, which can not only avoid the problem that the height difference of the positions on the design contour 5 of the deep blind hole 1 corresponding to two adjacent track points during the scanning process of a track of the subsequent spectrum confocal sensor exceeds the range of the point spectrum confocal sensor 2, resulting in insufficient scanning accuracy and large errors, but also avoid the problem that the distance between the point spectrum confocal sensor 2 and the deep blind hole 1 exceeds the working distance of the point spectrum confocal sensor 2 during the subsequent scanning process and cannot be scanned. Finally, a machine tool is provided, on the output shaft of which a point spectral confocal sensor 2 is arranged, and a coordinate system and a trajectory line 4 are input into the machine tool, so that the point spectral confocal sensor 2 performs point scanning on the curve profile of the deep blind hole 1 according to the trajectory line 4 between two adjacent trajectory points in turn (i.e., scanning from the end surface of the deep blind hole to its bottom), and constructs a curve with the scanned point data, the starting point spacing and the trajectory line 4 in the three-dimensional model and rotates it to obtain the curve profile of the deep blind hole 1, thereby finally obtaining an accurate curve profile of the deep blind hole 1.

[0046] That is to say, an embodiment of the present invention provides a method for measuring the curve profile of a deep blind hole based on a point spectral confocal sensor. By controlling the point spectral confocal sensor 2 to scan and construct a curve according to the trajectory line 4 in the coordinate system, the point spectral confocal sensor 2 has high scanning accuracy and can obtain an accurate curve profile of the deep blind hole 1.

[0047] It is easy to understand that the point spectrum confocal sensor 2 is a device that uses optical principles for measurement. It forms a focal point on the surface of the object to be measured by emitting light of different wavelengths. When the distance between the focal point and the surface of the object to be measured changes, the wavelength of the reflected light will also change accordingly. The point spectrum confocal sensor 2 provided by the present invention can scan each point of the deep blind hole 1 and its corresponding elevation difference during the movement along the trajectory line 4, thereby forming the contour line of each segment of the trajectory line in the X-axis direction (at this time, the spacing of the contour line relative to the Y-axis and the starting point spacing are unknown). On this basis, and combined with the coordinates of the trajectory line 4 and the starting point spacing, a complete and known curve is finally formed through integration, and finally the curve contour of the deep blind hole 1 is obtained.

[0048] In addition, since the size of the deep blind hole 1 finally formed in the workpiece during the fine machining process is close to the design contour 5, that is, the actual inner contour of the deep blind hole 1 is not much different from the design contour 5 in size, in order to quickly determine the position of each trajectory point and reduce the number of trajectory points, the present invention uses the design contour 5 as a reference to select each trajectory point.

[0049] It is easy to understand that the position of any point on each connecting line in the X-axis direction does not exceed the position range of the corresponding two trajectory points in the X-axis direction, which can effectively constrain each point in the connecting line and avoid the problem that when the position of the connecting line in the X-axis direction exceeds the position range of the two trajectory points in the X-axis direction, there may be two points in the connecting line that exceed the range of the point spectrum confocal sensor 2, resulting in insufficient subsequent scanning accuracy.

[0050] Exemplarily, the ratio of the depth to the diameter of the deep blind hole 1 is ≥ 10. The maximum inner diameter of the deep blind hole 1 is ≥ 100 mm, and the depth of the deep blind hole 1 is ≥ 1 m.

[0051] In one implementation of the present invention, the connecting line is a straight line segment (see Figure 5 ). That is, at this time, the connecting line is a straight line connecting two corresponding trajectory points, so that the scanning path of the subsequent point spectral confocal sensor 2 is the shortest, thereby improving the scanning efficiency.

[0052] In another implementation of the present invention, the connecting line 41 is a broken line segment (see Figure 2 ), the broken line segment includes a first straight line segment and a second straight line segment connected to each other, the first straight line segment is parallel to the X-axis, and the second straight line segment is parallel to the Y-axis.

[0053] That is to say, setting the connecting line 41 as a broken line segment can make the scanning path move successively along two coordinate axis directions (i.e., X-axis direction and Y-axis direction), which can improve the accuracy of displacement scanning of the machine tool belt to the point spectral confocal sensor 2.

[0054] It is easy to understand that the output shaft of the machine tool has high precision control and a small error range when performing unidirectional displacement.

[0055] In this embodiment, 30 mm ≤ working distance ΔL i ≤40mm. That is to say, in the X-axis direction, the distance between each point on the track line 4 and the design contour 5 is smaller than the working distance, ensuring that scanning can be performed.

[0056] Preferably, the working distances corresponding to the various trajectory points are equal (ie, ΔL1 = ΔL2 = ΔL3).

[0057] In addition, the height difference between the positions on the design contour 5 of the deep blind hole 1 corresponding to any two adjacent trajectory points in the X-axis direction satisfies the following formula:

[0058] 80%≤Δx i / L≤90%;

[0059] Where Δx iis the height difference between any two adjacent track points on the design contour 5 of the deep blind hole 1 in the X-axis direction (i.e., Δx1, Δx2, etc.; for example, Δx1 is the position of the two track points A1 and A2 on the design contour 5 in the X-axis direction, respectively. 10 , A 20 , A 10 and A 20 The height difference in the X-axis direction is Δx1), mm; L is the measuring range of the point spectrum confocal sensor 2, mm.

[0060] In the above embodiment, Δx is controlled i The ratio of / L is between 80% and 90%, which can not only avoid the height difference on the design contour 5 of the deep blind hole 1 corresponding to any two adjacent track points in the X-axis direction being too large to exceed the range of the point spectrum confocal sensor 2, but also make it as close as possible to the range of the point spectrum confocal sensor 2, thus avoiding Δx while ensuring the scanning accuracy. i Too small will result in too many track points needing to be set.

[0061] See again Figure 4 A connecting piece 3 is provided on the output shaft of the machine tool, and the point spectrum confocal sensor 2 is located on the connecting piece 3. The connecting piece 3 serves to connect the output shaft of the machine tool and the point spectrum confocal sensor 2, and avoids interference during scanning.

[0062] Furthermore, the connecting member 3 may be a support rod or a knife rod.

[0063] It is easy to understand that the measurement method provided by the present invention is also applicable to deep blind holes 1 with the same diameter segments, that is, at this time, the point data corresponding to the scanning of the point spectrum confocal sensor 2 are the same in the X-axis direction.

[0064] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor, characterized in that: The measuring method comprises: Establishing a coordinate system for the deep blind hole, wherein the coordinate system establishes a two-dimensional coordinate system with the central axis of the deep blind hole as the Y-axis and a radial direction as the X-axis, and importing the design contour of the deep blind hole into the coordinate system; In combination with the coordinate system and the design profile of the deep blind hole, on the reference plane formed by the X-axis and the Y-axis, trajectory points are set with the X-axis as the corresponding position and moving to the corresponding positions in sequence along the Y-axis direction, and any two adjacent trajectory points are connected by a connecting line to form a trajectory line and determine the coordinates and starting point spacing of the trajectory line; A machine tool is provided, wherein a point spectral confocal sensor is arranged on an output shaft of the machine tool, and the coordinate system and the trajectory line are input into the machine tool, so that the point spectral confocal sensor sequentially performs point scanning on the deep blind hole curve profile between two adjacent trajectory points according to the trajectory line, and constructs a curve with the scanned point data, the starting point spacing and the trajectory line in a three-dimensional model and rotates the curve to obtain the deep blind hole curve profile; Among them, the spacing between each point of the trajectory line and the designed contour of the deep blind hole in the X-axis direction does not exceed the working distance of the point spectral confocal sensor, the height difference on the designed contour of the deep blind hole corresponding to any two adjacent trajectory points in the X-axis direction does not exceed the measuring range of the point spectral confocal sensor, the starting point spacing is the radial distance between the corresponding position of the trajectory line on the X-axis and the deep blind hole, and the position of any point on each connecting line in the X-axis direction does not exceed the position range of the corresponding two trajectory points in the X-axis direction.

2. The method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor according to claim 1, characterized in that: The connecting line is a straight line segment.

3. The method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor according to claim 1, characterized in that: The connecting line is a broken line segment, and the broken line segment includes a first straight line segment and a second straight line segment connected to each other, the first straight line segment is parallel to the X axis, and the second straight line segment is parallel to the Y axis.

4. The method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor according to claim 1, characterized in that: 30mm≤working distance≤40mm.

5. The method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor according to claim 1, characterized in that: The height difference of the positions on the design contour of the deep blind hole corresponding to any two adjacent trajectory points in the X-axis direction satisfies the following formula: 80%≤Δx i / L≤90%; Where Δx i is the height difference between the positions on the designed contour of the deep blind hole corresponding to any two adjacent trajectory points in the X-axis direction, mm; L is the measuring range of the point spectral confocal sensor, mm.

6. The method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor according to claim 1, characterized in that: A connecting piece is arranged on the output shaft of the machine tool, and the point spectrum confocal sensor is located on the connecting piece.

7. The method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor according to claim 6, characterized in that: The connecting piece is a support rod or a knife rod.

8. A method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor according to any one of claims 1 to 7, characterized in that: The ratio of the depth to the diameter of the deep blind hole is ≥10.

9. A method for measuring the curve profile of a deep blind hole based on a point spectrum confocal sensor according to any one of claims 1 to 7, characterized in that: The maximum inner diameter of the deep blind hole is ≥100 mm, and the depth of the deep blind hole is ≥1 m.

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