A non-contact pipe interior calibration method and system

Abstract

The present invention provides a non-contact pipeline interior calibration method and system. The system includes a laser for emitting laser light, an optical device, a stripe grating, a transparent pipeline device, and a camera. The optical device is matched and arranged on the laser output side of the laser to receive the laser light output and convert it for output. The stripe grating is matched and arranged on the beam output side of the optical device to receive the laser light output by the optical device and convert it into equally spaced and uniformly thick stripes of laser light for output. The transparent pipeline device is matched and arranged on the beam output side of the stripe grating to receive the stripes of laser light output by the stripe grating. The camera is matched and arranged outside the transparent pipeline device and spatially perpendicular to the laser light path to capture the stripes of laser light in real time. The present invention has strong operability and low calibration error, and can solve the problem of complex calibration procedures in pipeline flow experiments at this stage.

Description

Technical Field

[0001] The present invention relates to the technical field of experimental fluid mechanics measurement, and in particular to a non-contact pipe interior calibration method and system. Background Art

[0002] Pipeline flow is widely used in engineering fields such as biomedicine and pipeline transportation. For example, tap water is delivered to thousands of households through pipelines, tens of thousands of tons of oil are distributed across the country through pipelines, and high-pressure fire hoses spray water. Studying the basic characteristics and mechanisms of pipeline flow can help achieve flow resistance reduction, thereby significantly reducing water and oil transportation costs, increasing the outlet pressure of high-pressure hoses, and achieving low-cost, high-efficiency engineering goals. To further explore the laws of pipeline flow, similarity experiments are often conducted using experimental devices to reveal their physical mechanisms. However, due to the arc-shaped pipe wall and the different refractive indices of air, pipes, and internal media, internal flow images captured directly by the camera are prone to distortion. To ensure the accuracy of experimental measurements, the resulting images need to be calibrated.

[0003] Currently, image calibration methods for pipeline flow experiments fall into two main categories. The first involves placing the pipeline in a rectangular transparent box filled with water or oil of uniform refractive index, with the box walls perpendicular to the camera's optical axis. Assuming the refractive indices of the fluid in the pipeline, the pipeline walls, the liquid in the box, and the box walls are identical, the internal image captured by the camera can be considered undistorted. This method requires multiple assumptions: that the camera's optical axis is perfectly perpendicular to the box walls and the pipeline axis, and that the refractive indices of all media are consistent. These assumptions are difficult to fully implement, resulting in large calibration errors. The second method involves placing a semi-cylindrical calibration plate in the pipeline, securing it so that its calibration plane is flush against the measurement plane, and acquiring calibration information through the camera. However, this contact-based calibration cannot be performed simultaneously with the experiment. The calibration plate is cumbersome to install and can easily scratch or deflect the pipeline, resulting in incomplete agreement between the calibration results and the experimental measurements. Furthermore, precisely adjusting and securing the calibration plate to align with the measurement plane remains a technical challenge. Summary of the Invention

[0004] In response to the technical problems existing in the above-mentioned background technology, the present invention proposes a non-contact pipeline internal calibration method and system to solve the problem of complex pipeline flow experiment calibration process at this stage.

[0005] In order to solve the above technical problems, the present invention provides a non-contact pipe interior calibration system, which includes a laser for emitting laser, an optical tool, a strip grating, a transparent pipe device and a camera;

[0006] The optical device is matched and arranged at the laser output side of the laser, and is used to receive the laser light output by the laser and convert it before outputting it;

[0007] The stripe grating is matched and arranged on the beam output side of the optical device, and is used to receive the laser beam output by the optical device and convert it into stripe lasers with equal spacing and uniform thickness for output;

[0008] The transparent pipe device is matched and arranged on the light beam output side of the stripe grating, and is used to receive the stripe laser output by the stripe grating;

[0009] The camera is matched and arranged outside the transparent pipe device and is vertical to the laser light path in space, and is used for real-time shooting of the striped laser.

[0010] The non-contact pipe internal calibration system, wherein: the optical device is composed of a concave lens and a convex lens arranged in sequence and side by side on the laser output light path of the laser;

[0011] The concave lens is used to diverge the laser light emitted by the laser so that it can illuminate the experimental area; the convex lens is used to converge the laser light diverged by the concave lens and turn it into parallel laser light, so that stripe laser light with known spacing and thickness can be obtained after the laser light passes through the strip grating.

[0012] The non-contact pipe internal calibration system, wherein when the camera takes real-time photos of the stripe laser:

[0013] Only the state after the stripe laser enters the transparent pipe device is captured. This method requires that the upper and lower walls of the transparent pipe device be captured at the same time and the inner diameter of the pipe is known;

[0014] Alternatively, the camera field of view is capable of simultaneously capturing the states of the stripe laser before and after entering the transparent pipe device.

[0015] A non-contact pipe interior calibration method is based on the above-mentioned non-contact pipe interior calibration system; the method mainly comprises the following steps:

[0016] Step 1: First, the laser is emitted by the laser. After passing through the optical tool and grating stripes, the laser forms uniform stripes with equal spacing. The stripes of laser light in the air or any medium with uniform refractive index are photographed by a camera to obtain a reference image I0. The actual physical coordinates of the stripes of laser light are then obtained by the camera magnification.

[0017] Step 2: Input the stripe laser into a transparent pipe device filled with a transparent fluid medium. At the same time, use a camera to capture the stripe laser entering the transparent pipe device to obtain a measurement image I1 and the obtained stripe image coordinates;

[0018] Step 3: The real physical coordinates of the stripe laser in the reference image I0 are matched with the image coordinates of the stripe laser in the measurement image I1 one by one to obtain the relationship between the image coordinates and the real physical coordinates at different radial positions, which is recorded as f ,this f This is the calibration function of the pipeline system;

[0019] Step 4: Obtain the calibration function f In subsequent experiments, the camera can be used to directly shoot the transparent pipe device, and then the coordinates can be corrected through this function to convert the image coordinate information into real physical world information.

[0020] By adopting the above technical solution, the present invention has the following beneficial effects:

[0021] The calibration method and system for the non-contact interior of a pipeline of the present invention are rationally designed, highly operable, and have a small calibration error, and can solve the problem of the complex calibration process of pipeline flow experiments at this stage. Compared with the calibration method of placing the pipeline in a rectangular transparent box, the present invention does not require the establishment of new experimental components, does not require the assumption that the camera optical axis is completely perpendicular to the box wall and the pipeline axis, and that the refractive index of each medium is consistent. It is easier to implement in terms of operation method and is easier to obtain more accurate calibration results. Compared with the calibration method of placing a semi-cylindrical calibration plate in a pipeline, the present invention is a contactless calibration method that can be carried out synchronously with the experiment and will not change the state of the device during the experiment. It only requires a stripe grating to be set up on the laser light path to directly obtain a calibration result that is highly consistent with the experimental situation, avoiding the cumbersome installation steps of the calibration plate, and does not require the assumption that the calibration plate is strictly fixed and accurately fits the measurement plane. At the same time, it avoids the risk of scratching or offsetting the pipeline by the contact calibration method. In summary, the present invention is easy to operate, reduces the error sources in the two existing calibration methods, and has a small calibration error. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A flow chart (algorithm flow chart) of the non-contact pipe interior calibration method and system of the present invention;

[0024] Figure 2 Schematic diagram of the structure of the non-contact pipe interior calibration method according to an embodiment of the present invention;

[0025] Figure 3The reference image and the measurement image captured in the embodiment of the present invention, and the fitting function graph;

[0026] Figure 4 3. Comparison of the turbulent velocity profile in the pipeline before and after calibration and the velocity profile obtained by numerical calculation in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] The present invention will be further explained below with reference to specific embodiments.

[0029] like Figure 1 As shown, this embodiment provides a non-contact pipe interior calibration system, which includes a laser 1, an optical device 2, a strip grating 3, a transparent pipe device 5 and a camera 6.

[0030] The laser 1 is used to emit laser light. The optical device 2 is matched with the laser output side of the laser 1 and is used to receive the laser light output by the laser 1 and filter it before output. The optical device 2 consists of a concave lens and a convex lens arranged side by side, one in front of the other. The concave lens is matched with the laser output optical path of the laser 1 and is used to diverge the laser light emitted by the laser 1 so that it can illuminate the experimental area. The convex lens is matched with the beam output optical path of the concave lens and is used to converge the laser light diverged by the concave lens and convert it into parallel laser light. After the laser light passes through the stripe grating 3, the stripe laser 4 with a known spacing and thickness is obtained.

[0031] The strip grating 3 is matched and arranged on the beam output side of the optical device 2, and is used to receive the laser beam output by the optical device 2 and convert it into stripe lasers 4 with equal spacing and uniform thickness for output.

[0032] The transparent pipe device 5 is matched and arranged on the light beam output side of the stripe grating 3 , and receives the stripe laser 4 output by the stripe grating 3 .

[0033] The camera 6 is matched and arranged outside the output optical path of the stripe laser 4, and is used to take real-time pictures of the stripe laser 4. The pictures can be taken in either of the following two ways: one way is to only take pictures of the state after the stripe laser 4 enters the transparent pipe device 5 (in the experimental section of the pipe fluid experiment). This method requires that the upper and lower walls of the pipe be taken at the same time and the inner diameter of the pipe is known; the other way is to take pictures of the stripe laser 4 after entering the transparent pipe device 5 (in the experimental section of the pipe fluid experiment). Figure 2As shown, the camera 6 can simultaneously capture the states of the stripe laser 4 before and after entering the transparent pipe device 5 .

[0034] After the laser passes through the strip grating 3, it forms striped laser light 4 with equal spacing and uniform thickness. A reference image of the striped laser light 4 at this time is obtained by the camera 6. Subsequently, the striped laser light 4 is shot into the transparent pipe device 5 along the pipe direction. The camera 6 is used to capture the striped laser light at this time to obtain a measurement image. By establishing a relationship between the reference image and the measurement image, the physical dimensions of the camera's image of each location in the pipe can be obtained.

[0035] The non-contact pipe interior calibration method of the present invention specifically comprises the following steps:

[0036] First, laser light is emitted from laser 1, which passes through optical tool 2 and grating stripes 3 to form uniform stripe laser light 4 with equal spacing. The stripe laser light 4 is photographed by camera 6 in the air or any medium with uniform refractive index (such as a rectangular acrylic water tank with uniform wall thickness, perpendicular to the camera optical axis, and filled with a medium with uniform refractive index such as water or air). Figure 3 The right half of the image is recorded as the reference image I0; the real physical coordinates of the stripe laser 4 (or the light and dark transition point of the stripe) are obtained through the magnification of the camera 6, that is, y 1, y 2, y 3, … , y n coordinate;

[0037] Secondly, the stripe laser 4 enters a transparent pipe device 5 (such as a transparent acrylic pipe) filled with a transparent fluid medium (such as water). Because the refraction light paths at different radial positions of the pipe are different, different parts of the stripe laser 4 will be stretched and scaled to different degrees. At this time, the stripe laser 4 is photographed using a camera 6 to obtain Figure 3 The left half of the image is recorded as the measurement image I1; the coordinates of the obtained fringe image are y 1', y 2', y 3' ,…, y n'; The coordinates here represent the pixel coordinates of the stripe laser 4 (or the light-dark transition point of the stripe) in the image captured by the camera 6. There are two ways to obtain them: the first way is to read the grayscale value of the image captured by the camera 6, average it along the direction parallel to the stripe laser 4, and obtain an average grayscale value curve. The coordinates of the maximum and minimum points of the average grayscale value curve are taken as the pixel coordinates of the stripe laser 4; the second way is to obtain the average grayscale value curve and then assign a threshold value (such as the average of the maximum and minimum values). The portion with a grayscale value above the threshold is considered to be illuminated by the laser, and the portion below the threshold is considered not to be illuminated by the laser. The coordinates corresponding to the intersection of the threshold and the average grayscale value curve can be regarded as the coordinates of the light-dark transition point of the stripe laser 4.

[0038] The real physical coordinates of the stripe laser 4 in the reference image I0 (i.e., the coordinates y 1, y 2, y 3, … , y n ) and the image coordinates (i.e., coordinates) of the stripe laser 4 of the measurement image I1 y 1', y 2', y 3' ,…, y n ') one-to-one correspondence, the relationship between the image coordinates and the real physical coordinates at different radial positions can be obtained, which is recorded as f ,this f This is the calibration function of the pipeline system (in actual operation, the following two forms of coordinate relationships can be selected as calibration functions f , the first form of the calibration function f The second form of calibration function is the mapping from the pixel coordinates of the stripe laser 4 refracted through the pipe and captured by the camera to the real physical coordinates of the stripe laser 4 with equal spacing in the homogeneous medium. f is the ratio of the stripe width in the pipe at different radial positions to the actual stripe width, indicating the deformation rate of the coordinate grid at different radial positions. The latter form is used in the embodiment of the present invention, and the fitting function is a quadratic function.

[0039] Get the calibration function f In subsequent experiments, the camera 6 can be used to directly shoot the transparent pipe device 5, and then the calibration function f Correct the coordinates and convert the image coordinate information into real physical world information. Specifically, for the first form of calibration function f , given any pixel coordinate, substitute into the calibration function f , the corresponding real physical coordinates can be calculated. For the second form of calibration function f , can be calculated based on the calibration function fDeform the uniform pixel grid to convert it into a non-uniform physical coordinate grid.

[0040] The present invention has strong operability and small calibration error, and can solve the problem of complex calibration process of pipeline flow experiments at the current stage.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A non-contact pipe interior calibration system, characterized by: The calibration system includes a laser (1) for emitting laser light, an optical device (2), a strip grating (3), a transparent pipe device (5), and a camera (6); The optical device (2) is matched and arranged on the laser output side of the laser (1), and is used to receive the laser light output by the laser (1) and convert it before outputting it; The strip grating (3) is matched and arranged on the beam output side of the optical device (2), and is used to receive the laser beam output by the optical device (2) and convert it into stripe lasers (4) with equal spacing and uniform thickness for output; The transparent pipe device (5) is matched and arranged on the light beam output side of the strip grating (3), and is used to receive the stripe laser (4) output by the strip grating (3); The camera (6) is matched and arranged outside the transparent pipe device (5) and is vertical to the laser light path in space, and is used to shoot the striped laser (4) in real time.

2. The non-contact pipe interior calibration system according to claim 1, characterized in that: The optical device (2) is composed of a concave lens and a convex lens which are sequentially arranged side by side on the laser output light path of the laser (1); The concave lens is used to diverge the laser light emitted by the laser (1) so that it can illuminate the experimental area; the convex lens is used to converge the laser light diverged by the concave lens so that it becomes parallel laser light, so that stripe laser light with known spacing and thickness can be obtained after the laser light passes through the stripe grating (3).

3. The non-contact pipe interior calibration system according to claim 1, characterized in that: When the camera (6) takes real-time photos of the stripe laser (4): Only the state of the stripe laser (4) after entering the transparent pipe device (5) is photographed. This method requires that the upper and lower walls of the transparent pipe device (5) be photographed at the same time and the inner diameter of the pipe is known; Alternatively, the camera (6) is capable of simultaneously capturing the states of the striped laser (4) before and after entering the transparent pipe device (5).

4. A non-contact pipe interior calibration method, based on the non-contact pipe interior calibration system according to any one of claims 1 to 3; characterized in that: The process mainly includes the following steps: Step 1: First, a laser is emitted from a laser (1). After passing through an optical device (2) and grating stripes (3), a uniform stripe laser (4) with equal spacing is formed. The stripe laser (4) in air or any medium with a uniform refractive index is photographed by a camera (6) to obtain a reference image I0. The actual physical coordinates of the stripe laser (4) are then obtained by adjusting the magnification of the camera (6). Step 2: Input the stripe laser (4) into the transparent pipe device (5) filled with a transparent fluid medium. At the same time, use a camera (6) to shoot the stripe laser (4) entering the transparent pipe device (5) to obtain a measurement image I1 and the obtained stripe image coordinates; Step 3: The real physical coordinates of the stripe laser (4) in the reference image I0 are matched with the image coordinates of the stripe laser in the measurement image I1 to obtain the relationship between the image coordinates and the real physical coordinates at different radial positions, which is recorded as f ,this f This is the calibration function of the transparent pipe device (5); Step 4: Obtain the calibration function f In subsequent experiments, the camera (6) can be used to directly photograph the transparent pipe device (5), and then the coordinates can be corrected through this function to convert the image coordinate information into real physical world information.

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