Non-contact pipeline interior calibration method and system

Abstract

The invention provides a non-contact pipeline interior calibration method and system. The system comprises a laser for emitting laser, an optical tool, a strip-shaped grating, a transparent pipeline device and a camera. The optical tool is arranged on the laser output side of the laser in a matched mode and used for receiving laser output by the laser, converting the laser and outputting the converted laser. The strip-shaped grating is arranged on the light beam output side of the light tool in a matched mode and used for receiving the laser beams output by the light tool, converting the laser beams into stripe lasers which are equal in interval and uniform in thickness and then outputting the stripe lasers. The transparent pipeline device is arranged on the light beam output side of the strip-shaped grating in a matched mode and used for receiving the stripe laser output by the strip-shaped grating. The camera is arranged on the outer side of the transparent pipeline device in a matched mode, is perpendicular to the laser light path in space and is used for shooting the stripe laser in real time. The method is high in operability and small in calibration error, and can solve the problem that the calibration process of the pipeline flow experiment at the present stage is complex.

Description

Technical Field

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

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

[0003] Currently, the calibration methods for pipeline flow experimental images are mainly divided into two categories. The first category is to place the pipeline in a cuboid transparent box filled with water or oil with a uniform refractive index, and make the box wall perpendicular to the camera optical axis. Assuming that the refractive indices of the fluid inside the pipeline, the pipeline wall, the liquid inside the box, and the box wall are the same, the internal images captured by the camera can be regarded as undistorted. This method requires multiple assumptions: the camera optical axis is completely perpendicular to the box wall and the pipeline axis, and the refractive indices of all media are the same. These assumptions are difficult to fully achieve, resulting in large calibration errors. The second category of methods is to place a semi-cylindrical calibration plate inside the pipeline, make its calibration plane closely adhere to the measurement plane and fix it, and obtain calibration information through the camera. However, this contact calibration cannot be carried out synchronously with the experiment, the installation of the calibration plate is cumbersome, and it is easy to scratch or shift the pipeline, resulting in the calibration result not fully matching the experimental measurement. In addition, how to accurately adjust and fix the calibration plate to fit the measurement plane is still a technical difficulty. Summary of the Invention

[0004] In view of the technical problems existing in the above background art, the present invention proposes a non-contact calibration method and system for the interior of a pipeline to solve the problem of the complex calibration process in current pipeline flow experiments.

[0005] To solve the above technical problems, a non-contact calibration system for the interior of a pipeline provided by the present invention includes a laser for emitting laser light, an optical tool, a bar-shaped grating, a transparent pipeline device, and a camera; The optical tool is arranged on the laser output side of the laser in a matching manner, and is used for receiving the laser output by the laser and outputting it after conversion; The bar grating is 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 laser with equal spacing and uniform thickness and then output it; The transparent pipeline device is arranged on the beam output side of the bar grating, and is used to receive the stripe laser output by the bar grating; The camera is arranged outside the transparent pipeline device and is perpendicular to the laser optical path in space, and is used to take real-time pictures of the stripe laser.

[0006] The non-contact calibration system inside the pipeline, wherein: the optical device is composed of a concave lens and a convex lens which are arranged side by side in sequence on the laser output optical path of the laser; The concave lens is used to diverge the laser emitted by the laser so that it can illuminate the experimental area; the convex lens is used to converge the laser diverged by the concave lens so that it becomes parallel laser, so as to obtain stripe laser with known spacing and thickness after the laser passes through the bar grating.

[0007] The non-contact calibration system inside the pipeline, wherein, when the camera takes real-time pictures of the stripe laser: Only the state after the stripe laser enters the transparent pipeline device is photographed, and this method requires photographing the upper and lower wall surfaces of the transparent pipeline device at the same time and the inner diameter of the pipeline is known; Or, the camera field of view can simultaneously photograph the state before the stripe laser enters the transparent pipeline device and the state after the stripe laser enters the transparent pipeline device.

[0008] A non-contact calibration method for the inside of a pipeline, based on the above non-contact calibration system for the inside of a pipeline; it mainly includes the following steps: Step 1: First, the laser is emitted by the laser, and after passing through the optical device and the grating stripes, stripe laser with equal spacing and uniform thickness is formed. The stripe laser in the air or any medium with uniform refractive index is photographed by the camera to obtain the reference image I0; then through the camera magnification, the true physical coordinates of the stripe laser are obtained; Step 2: The stripe laser is input into the transparent pipeline device filled with a transparent fluid medium. At the same time, the camera is used to photograph the stripe laser entering the transparent pipeline device to obtain the measurement image I1 and the obtained stripe image coordinates; Step 3: The true physical coordinates of the stripe laser in the reference image I0 are corresponded one by one with the image coordinates of the stripe laser in the measurement image I1 to obtain the relationship between the image coordinates and the true physical coordinates at different radial positions, denoted as f This f is the calibration function of this pipeline system; Step 4: Obtain the calibration function f, in subsequent experiments, the transparent pipeline device can be directly photographed by a camera, and then the coordinates can be corrected by this function to convert the image coordinate information into real physical world information.

[0009] Adopting the above technical solution, the present invention has the following beneficial effects: The non-contact calibration method and system for the interior of a pipeline of the present invention are reasonably conceived, highly operable, and have small calibration errors, and can solve the problem of the complex calibration process in current pipeline flow experiments. Compared with the calibration method of placing the pipeline in a cuboid transparent box, the present invention does not require the erection of new experimental components, nor the two assumptions that the optical axis of the camera is completely perpendicular to the box wall and the pipeline axis, and the refractive indices of various media are the same. It is easier to implement in terms of the operation method and easier to obtain relatively accurate calibration results. Compared with the calibration method of placing a semi-cylindrical calibration plate inside the pipeline, the present invention is a non-contact calibration method that can be carried out synchronously with the experiment and does not change the state of the device during the experiment. Only one fringe grating needs to be erected on the laser optical path to directly obtain a calibration result highly consistent with the experimental situation, avoiding the cumbersome installation steps of the calibration plate and the assumption that the calibration plate is strictly fixed and accurately fitted to the measurement plane, and at the same time avoiding 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 existing two types of calibration methods, and has small calibration errors. Description of the Drawings

[0010] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0011] Figure 1 It is a flowchart (algorithm flowchart) of the non-contact calibration method and system for the interior of a pipeline of the present invention; Figure 2 It is a structural schematic diagram of the non-contact calibration method for the interior of a pipeline in an embodiment of the present invention; Figure 3 It is a reference image, a measurement image, and a fitting function graph obtained by photographing in an embodiment of the present invention; Figure 4 It is a comparison of the turbulent velocity profiles inside the pipeline before and after calibration and the velocity profiles obtained by numerical calculation in an embodiment of the present invention. Detailed Embodiments

[0012] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0013] The present invention will be further explained below in conjunction with specific embodiments.

[0014] As Figure 1 shown, a calibration system inside a non-contact pipeline provided in this embodiment includes a laser 1, an optical tool 2, a bar grating 3, a transparent pipeline device 5, and a camera 6.

[0015] The laser 1 is used to emit laser light. The optical tool 2 is arranged on the laser output side of the laser 1 in a matching manner, and is used to receive the laser output by the laser 1, filter it and then output it. It is composed of a concave lens and a convex lens arranged side by side, one in front of the other; the concave lens is arranged on the laser output optical path of the laser 1 in a matching manner, and is used to diverge the laser emitted by the laser 1 so that it can illuminate the experimental area; the convex lens is arranged on the beam output optical path of the concave lens in a matching manner, and is used to converge the laser diverged by the concave lens to make it into parallel laser light, so as to obtain striped laser light 4 with known spacing and thickness after the laser passes through the bar grating 3.

[0016] The bar grating 3 is arranged on the beam output side of the optical tool 2 in a matching manner, and is used to receive the laser beam output by the optical tool 2 and convert it into striped laser light 4 with equal spacing and uniform thickness and then output it.

[0017] The transparent pipeline device 5 is arranged on the beam output side of the bar grating 3 in a matching manner, and receives the striped laser light 4 output by the bar grating 3.

[0018] The camera 6 is arranged on the outside of the output optical path of the striped laser light 4 in a matching manner, and is used to take real-time pictures of the striped laser light 4; among them, the shooting here can be realized by any one of the following two methods: one method is to only shoot the state of the striped laser light 4 after it enters the transparent pipeline device 5 (in the experimental section of the pipeline fluid experiment), and this method requires shooting the upper and lower wall surfaces of the pipeline at the same time and the inner diameter of the pipeline is known; the other method is as Figure 2 shown, so that the field of view of the camera 6 can simultaneously shoot the state of the striped laser light 4 before it enters the transparent pipeline device 5 and after it enters the transparent pipeline device 5.

[0019] After the laser passes through the bar grating 3, a striped laser 4 with equal spacing and uniform thickness is formed. The reference image of the striped laser 4 at this time is obtained through the camera 6. Subsequently, the striped laser 4 is injected into the transparent pipe device 5 along the pipe direction, and the camera 6 is used to photograph the striped laser at this time to obtain a measurement image. By establishing the relationship between the reference image and the measurement image, the physical dimensions of the images at various positions in the pipe can be obtained by the camera.

[0020] The non-contact calibration method for the interior of a pipe of the present invention specifically includes the following steps: First, a laser is emitted by the laser 1. After passing through the optical device 2 and the grating stripes 3, a striped laser 4 with equal spacing and uniformity is formed. The camera 6 is used to photograph the striped laser 4 in the air or any medium with a uniform refractive index (such as a rectangular acrylic water tank with a uniform wall thickness, a wall surface perpendicular to the optical axis of the camera, and filled with a medium with a uniform refractive index such as water or air) to obtain Figure 3 the right half of the image, which is recorded as the reference image I0; through the magnification of the camera 6, the true physical coordinates of the striped laser 4 (or the turning points of the stripe brightness) are obtained, that is y 1, y 2, y 3, …, y n coordinates; Secondly, the striped laser 4 enters the 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 striped laser 4 will be stretched and scaled to different degrees. At this time, the camera 6 is used to photograph the striped laser 4 to obtain Figure 3 the left half of the image, which is recorded as the measurement image I1; the obtained stripe image coordinates are recorded as y 1', y 2', y 3',…, y n '; Here, the coordinates represent the pixel coordinates of the striped laser 4 (or the turning points of the stripe brightness) in the image photographed by the camera 6, and there are two ways to obtain them: The first way is to read the gray value of the image photographed by the camera 6, make an average along the direction parallel to the striped laser 4 to obtain the average gray value curve, and take the coordinates of the maximum value point and the minimum value point as the pixel coordinates of the striped laser 4; The second way is after obtaining the average gray value curve, a threshold (such as the average value of the maximum value and the minimum value) is given. The part with a gray value higher than the threshold is regarded as being illuminated by the laser, and the part with a gray value lower than the threshold is regarded as not being illuminated by the laser. The coordinates corresponding to the intersection points of the threshold and the average gray value curve can be regarded as the coordinates of the turning points of the stripe brightness of the striped laser 4.

[0021] From the true physical coordinates of the striped laser 4 in the reference image I0 (that is, the coordinates y 1,y 2, y 3, … , y n ) corresponding one-to-one with the image coordinates of the fringe laser 4 in the measured image I1 (i.e., the coordinates y 1', y 2', y 3', …, y n '), the relationship between the image coordinates and the true physical coordinates at different radial positions can be obtained, denoted as f , and this f is the calibration function of the pipeline system (in actual operation, the following two forms of coordinate relationships can be selected as the calibration function f . The calibration function of the first form f is the mapping from the pixel coordinates obtained by the camera shooting the fringe laser 4 refracted through the pipeline to the true physical coordinates of the equally spaced fringe laser 4 in the homogeneous medium. The calibration function of the second form f is the ratio of the fringe width in the pipeline at different radial positions to the true fringe width, representing the deformation rate of the coordinate grid at different radial positions. In the embodiments of the present invention, the latter form is adopted, and the fitting function form is a quadratic function).

[0022] Obtain the calibration function f . In subsequent experiments, the camera 6 can directly shoot the transparent pipeline device 5, and then correct the coordinates through this calibration function f to convert the image coordinate information into true physical world information. Specifically, for the calibration function f of the first form above, given any pixel coordinate and substituting it into this calibration function f , the corresponding true physical coordinate can be calculated. For the calibration function f of the second form above, the uniform pixel grid can be deformed according to the calibration function f and converted into a non-uniform physical coordinate grid.

[0023] The present invention has strong operability and small calibration error, and can solve the problem of complex calibration process in current pipeline flow experiments.

[0024] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A non-contact calibration system inside a pipeline, characterized in that: The calibration system includes a laser (1) for emitting laser light, an optical device (2), a bar grating (3), a transparent pipe device (5), and a camera (6); The optical device (2) is arranged on the laser output side of the laser (1) in a matching manner, and is used to receive the laser output by the laser (1) and output it after conversion; The bar grating (3) is arranged on the light beam output side of the optical device (2) in a matching manner, and is used to receive the laser beam output by the optical device (2) and convert it into stripe laser light (4) with equal spacing and uniform thickness before outputting; The transparent pipe device (5) is arranged on the light beam output side of the bar grating (3) in a matching manner, and is used to receive the stripe laser light (4) output by the bar grating (3); The camera (6) is arranged outside the transparent pipe device (5) and is perpendicular to the laser light path in space, and is used to perform real-time shooting on the stripe laser light (4).

2. The non-contact calibration system inside the pipeline according to claim 1, wherein: The optical device (2) is composed of a concave lens and a convex lens that are successively 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 as to obtain stripe laser light with known spacing and thickness after the laser passes through the bar grating (3).

3. The non-contact calibration system inside the pipeline according to claim 1, characterized in that, When the camera (6) performs real-time shooting on the stripe laser light (4): Only shoot the state of the stripe laser light (4) after it enters the transparent pipe device (5). This method requires shooting the upper and lower wall surfaces of the transparent pipe device (5) at the same time and the inner diameter of the pipe is known; Or, enable the field of view of the camera (6) to simultaneously shoot the state of the stripe laser light (4) before it enters the transparent pipe device (5) and after it enters the transparent pipe device (5).

4. A calibration method for the interior of a non-contact pipeline, based on the calibration system for the interior of a non-contact pipeline according to any one of the above-mentioned claims 1 to 3; characterized in that, It mainly includes the following steps: Step 1: First, emit laser light through the laser (1). After the laser passes through the optical device (2) and the grating stripes (3), stripe laser light (4) with equal spacing and uniformity is formed. Shoot the stripe laser light (4) in the air or any medium with uniform refractive index through the camera (6) to obtain a reference image I0; then, through the magnification of the camera (6), obtain the true physical coordinates of the stripe laser light (4); Step 2: Input the stripe laser light (4) into the transparent pipe device (5) filled with a transparent fluid medium. At the same time, use the camera (6) to shoot the stripe laser light (4) entering the transparent pipe device (5) to obtain a measurement image I1 and the obtained stripe image coordinates; Step 3: One-to-one correspondence between the true physical coordinates of the stripe laser (4) in the reference image I0 and the image coordinates of the stripe laser in the measurement image I1 is performed to obtain the relationship between the image coordinates and the true physical coordinates at different radial positions, denoted as f , this f is the calibration function of the pipeline system; Step 4: Obtain the calibration function f , in subsequent experiments, the camera (6) can be directly used to 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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