A high-precision detection method for the meniscus profile of liquid in a capillary tube

Abstract

The present invention belongs to the field of image spectrum detection, and specifically relates to a high-precision detection method for the contour of the meniscus of liquid in a capillary tube. It comprises a telecentric lens, an industrial camera, a displacement platform, a light source, a capillary tube and a culture dish; the industrial camera, the capillary tube and the culture dish are respectively mounted on different displacement platforms. The light source is provided with a rotating telescopic rod to achieve all-round movement. When photographing the contour of the meniscus of liquid in the capillary tube, the light source, the meniscus of the capillary tube and the industrial camera are adjusted to be aligned on the same horizontal plane. Based on the principle of telecentric imaging and the principle of light refraction, a distortion correction function for the contour of the meniscus in the capillary tube is derived. The present invention uses an industrial camera in combination with a telecentric lens, thereby avoiding the problem of shape distortion caused by changes in the distance between the object and reducing the difficulty of image distortion correction. The meniscus contour distortion correction function derived based on the telecentric imaging principle can accurately calculate the actual value of the meniscus contour and restore the actual contour of the meniscus.

Description

Technical Field

[0001] The present invention belongs to the field of image spectrum detection, and in particular relates to a high-precision detection method for the contour of a liquid meniscus in a capillary tube. Background Art

[0002] Capillary action is widely used in fields such as geology, petroleum engineering, and bioengineering. Accurately characterizing the capillary process can help us better understand the dynamic behavior of liquids in capillary tubes, which requires reliable measurement technology.

[0003] Existing research typically focuses on liquid columns in cylindrical capillaries. However, due to light refraction, the directly captured meniscus profile of the liquid column is optically distorted. There are two common methods for reducing or correcting this distortion: Method 1: Place the capillary in a chamber filled with a specific liquid to minimize optical distortion by matching the refractive index of the liquid and the tube wall. Method 2: Considering that the capillary tube is not distorted in the vertical direction, the curvature radius of the meniscus profile is calculated using the height of the liquid below the meniscus in the capillary tube.

[0004] Regarding method 1: Since there is air in the middle of the meniscus, light will still refract from the liquid to the air, and the direction of light propagation will still be offset, making it difficult to completely eliminate optical distortion. Regarding method 2: The formula for the radius of curvature is obtained under the premise that the contour of the meniscus is a circular arc. This correction method has systematic errors. In order to obtain accurate measurement results, X-ray measurement technology can also be used to measure the contour of the meniscus. However, the cost of using this technology is high and X-rays are harmful to the human body, which is not conducive to long-term experiments. Therefore, it is urgent for those skilled in the art to solve the above technical problems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that in the above-mentioned prior art, since there is air in the middle of the meniscus, light will still be refracted from liquid to air, the direction of light propagation will still be offset, and optical distortion is difficult to completely eliminate; the meniscus is approximated as an arc, and the formula for the curvature radius of the meniscus is obtained to correct the meniscus profile, but the correction method has systematic errors; using X-rays to measure the meniscus profile is harmful to the human body and is not conducive to long-term experiments.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A high-precision detection device for the contour of a liquid meniscus in a capillary tube comprises a telecentric lens, an industrial camera, a displacement platform, a light source, a capillary tube, and a culture dish. The industrial camera, capillary tube, and culture dish are respectively mounted on the displacement platform. A rotating telescopic rod is further provided on the optical platform. The light source is mounted on the rotating telescopic rod. The capillary tube is fixed directly above the culture dish via a V-shaped serrated clamp. The light source, the liquid meniscus in the capillary tube, and the industrial camera are aligned on the same horizontal plane.

[0008] By adopting the above technical solution, the industrial camera is mounted on a displacement platform and used in conjunction with a telecentric lens. This ensures that regardless of changes in the capillary diameter and the height of the liquid column within the tube, the captured meniscus profile image maintains the same proportion and resolution as the actual meniscus profile, thus avoiding shape distortion caused by changes in object distance. The capillary is fixed directly above the culture dish with a V-shaped serrated clamp, which not only provides stable support but also facilitates rapid adjustment of the capillary position to accommodate different experimental conditions. Furthermore, the displacement platform allows for precise adjustment of the industrial camera's height and angle, further enhancing the system's flexibility and operability. The design of aligning the light source with the industrial camera, combined with appropriate light shielding measures, provides uniform and interference-free illumination, fully preserving the details of the meniscus profile and reducing interference from excess light. This makes the captured meniscus profile image clearer and more accurate, facilitating subsequent data analysis. The entire device is compact and rationally structured, with all components centrally arranged on a single platform, simplifying the experimental setup process and reducing operational difficulty. In addition, this integrated design is also conducive to the daily maintenance and calibration of the equipment. Compared with expensive X-ray imaging technology, the solution proposed by the present invention is not only economical and affordable, but also harmless to the human body. It is suitable for long-term experimental research, greatly reducing scientific research costs, while also ensuring the safety of researchers. Through the above-mentioned carefully designed experimental device, optical distortion can be effectively reduced, the accuracy of meniscus profile measurement can be improved, and more reliable data support can be provided for the study of the dynamic behavior of liquids in capillaries.

[0009] Furthermore, the telecentric lens includes an object lens, an aperture stop and an image lens; the distance between the object lens and the image lens is the sum of their focal lengths, and the aperture stop is located at the common focus of the object lens and the image lens.

[0010] By adopting the above technical solution, a key feature of the telecentric lens is its large depth of field range and more flexible focusing. This means that for the same object, the image size remains consistent regardless of how far or near the object is from the lens. This eliminates perspective distortion caused by changes in viewing angle, allowing the meniscus profile at different distances to be recorded at the same scale, improving measurement consistency and accuracy. By adjusting the camera target surface, the height of the capillary meniscus, and the alignment of the light source on the same horizontal plane, the parallel light rays passing through the capillary meniscus are received by the telecentric lens. After passing through the lens group inside the telecentric lens, the flat light rays are inverted in the radial direction of the meniscus and proportionally reduced in the circumferential direction of the meniscus, and are received by the camera target surface, thereby reducing the blurring effect caused by differences in refractive index, improving the overall clarity and detail expression of the image, and maintaining good focusing effect throughout the entire range even if the height of the liquid column in the capillary changes. This is particularly important for studies that require observing the dynamic changes of liquid columns, as it allows for obtaining clear image sequences without adjusting the focal length. Since the images produced by the telecentric lens are distortion-free, subsequent data processing does not require complex geometric distortion correction algorithms, simplifying the data processing process and speeding up experimental analysis.

[0011] Furthermore, the bottom of the industrial camera also includes an optical platform, and a computer is also arranged on the optical platform; the industrial camera is electrically connected to the computer.

[0012] By adopting the above technical solution, a stable base is provided, which reduces the impact of external vibration on the imaging process and ensures the clarity of the image and the accuracy of the data. Fixing devices such as the V-shaped sawtooth clamp and the displacement platform further enhance the overall stability of the system. The electrical connection between the industrial camera and the computer enables the collected data to be immediately transmitted to the computer for processing and analysis, improving work efficiency. The image acquisition software supporting the camera can set the image white balance parameters and exposure time. While ensuring that the image is not overexposed, the light and dark contrast of the meniscus image is enhanced, and the detailed information of the meniscus contour is quickly and accurately extracted. The special optical path and light source design in the detection device makes the gas-liquid interface contour in the meniscus grayscale image clear and distinct. The contour curve is extracted based on the grayscale difference in MATLAB. The extracted contour curve is subjected to distortion correction according to the distortion correction formula (19). The scale set behind the light source provides a reference for the actual size of the image, which facilitates the conversion of pixel units into physical units, thereby achieving more accurate measurement. The displacement platform under the culture dish allows the experimenter to adjust the height and horizontal position of the culture dish as needed to adapt to different experimental conditions or research purposes, enhancing the flexibility of the system. The industrial camera is installed on the displacement platform, which can precisely control the position and angle of the camera to ensure the optimal imaging perspective. All components (including industrial camera, telecentric lens, light source, capillary, culture dish and computer) are integrated on one platform, which simplifies the construction and maintenance of the experimental device. The integrated design makes the entire system easier to operate, reduces experimental preparation time, and facilitates daily maintenance work.

[0013] The present invention also includes a high-precision detection method for the contour of a liquid meniscus in a capillary tube. The detection of the contour of a liquid meniscus in a capillary tube is performed using the high-precision detection device for the contour of a liquid meniscus in a capillary tube. The method includes fixing the industrial camera to the optical platform via the displacement platform. Before the experiment, the industrial camera is adjusted to a horizontal position using a spirit level. The capillary tube is fixed and suspended in the culture dish filled with liquid via the V-shaped serrated clamp. The tail of the V-shaped serrated clamp is connected to the displacement platform. The displacement platform is adjusted so that the capillary tube is perpendicular to the horizontal plane. The light source is arranged on the right side of the capillary tube. The light source is a diffuse reflection surface light source. A shielding member is used to limit the axial width of the light source to reduce the light reaching the imaging system through the air in the meniscus.

[0014] By adopting the above technical solution, the capillary is adjusted to be perpendicular to the horizontal plane through the displacement platform, which helps to accurately capture the contour of the meniscus and avoid measurement errors caused by tilt. The use of a diffuse surface light source can provide soft and uniform lighting, reducing highlights and shadows caused by direct light, thereby improving the overall clarity and contrast of the image. By limiting the axial width of the light source through the shielding part, the light refracted from the air in the meniscus can be effectively reduced, reducing noise interference and making the imaging clearer. The displacement platform is not only used to fix the industrial camera, but also connected to the V-shaped serrated clamp, allowing precise fine-tuning of the position of the capillary, further enhancing the stability of the entire system. All key components (such as industrial camera, capillary, light source, etc.) are integrated on one platform, which simplifies the construction process of the experimental device and facilitates quick setup and start of the experiment. The design of the displacement platform and V-shaped serrated clamp makes it simple and quick to adjust the position of the capillary and industrial camera, allowing experimenters to flexibly adjust according to their needs.

[0015] Furthermore, the displacement platform is adjusted so that the liquid in the culture dish is in full contact with the lower end of the capillary. After the height of the liquid column in the capillary is stabilized, the position of the light source is adjusted and the meniscus image is captured using the industrial camera.

[0016] By adopting the above technical solution, the displacement platform adjusts the height of the culture dish to ensure that the liquid column in the capillary starts to rise from the same initial height in each experiment, thereby ensuring the consistency of the experimental conditions and allowing the liquid column to reach a stable state before the experiment begins, avoiding measurement errors caused by unstable liquid columns. Adjusting the position of the light source after the height of the liquid column is stable can ensure that the light is evenly irradiated on the meniscus, avoiding uneven illumination caused by changes in the liquid column, thereby improving the quality of the image. Imaging when the liquid column is stable reduces image blur or distortion caused by liquid column fluctuations, making the collected meniscus contour clearer. Only when the liquid column height is stable can the true shape of the meniscus be accurately captured, which is crucial for subsequent data analysis. By ensuring the stability of the liquid column and uniform lighting, the systematic errors caused by external factors can be minimized, and the reliability of the measurement results can be improved.

[0017] Furthermore, the parallel light rays are received by the target surface of the industrial camera;

[0018] Wherein, F'C' is the incident light, θ4' is the incident angle of F'C', θ3' is the refraction angle of F'C', θ2' is the incident angle of C'B', θ1' is the refraction angle of C'B', θ1 is the incident angle of B'B, θ2 is the refraction angle of B'B, θ3 is the incident angle of BC, θ4 is the refraction angle of BC, the point of tangency of the light path of CF with the meniscus when passing through the liquid is point P, the distance P0 from point P to the center of the circle O is the object radial distance, point A" is the midpoint of the length of the reverse extension line of CF in the capillary, the distance A"O from point A" to the center of the circle O is the image radial distance, and the refractive indices of the liquid, capillary wall, and air in the capillary are n1, n2, and n3, respectively;

[0019] According to Snell's law:

[0020] n1sinθ1=n2sinθ2 (1)

[0021] n1sinθ1'=n2sinθ2' (2)

[0022] In ΔB'OB, |OB'|=|OB|, so θ1=θ1', that is:

[0023] θ2=θ2' (3)

[0024] A is the intersection of the extended line BC and OA". According to the sine theorem, in ΔOAB:

[0025] ∠OBA=θ2

[0026]

[0027] In ΔOAC:

[0028]

[0029] Right now:

[0030]

[0031] D is the intersection of the extended line of B'C' and the inner diameter. According to the law of sine, in ΔODB':

[0032] ∠OB'D=θ2'

[0033]

[0034] In ΔODC':

[0035]

[0036] Right now:

[0037]

[0038] According to formulas (3), (6), and (9), we can get:

[0039] θ3=θ3'(10)

[0040] According to Snell's law:

[0041] n2sinθ3=n3sinθ4 (11)

[0042] n2sinθ3'=n3sinθ4' (12)

[0043] have to

[0044] θ4=θ4' (13)

[0045] In ΔB'PO

[0046] |OP|=sinθ1'·R i (14)

[0047] From formula (2) and formula (12), we can get:

[0048]

[0049] and:

[0050]

[0051] Substituting formula (9) into formula (15) yields:

[0052]

[0053] In ΔOA”C:

[0054]

[0055] Substituting formula (17) into formula (16), we get

[0056]

[0057] Substituting formula (18) into formula (14) yields:

[0058] |OP|=|A”O|·n 31 (19)

[0059] When the refractive index of air (n3) is 1, the above formula is:

[0060] |OP|=|A”O| / n1 (20)

[0061] That is: image radial distance = object radial distance × liquid refractive index;

[0062] In the capture of the capillary meniscus profile image, the ratio of the outer diameter to the inner diameter of the capillary is greater than the refractive index of the liquid in the capillary.

[0063] By adopting the above technical solution, the refraction path of light in different media (liquid, capillary wall, air) is analyzed in detail, and Snell's law is used for calculation. The image distortion caused by light refraction can be accurately corrected. According to formula (19), the image radial distance is equal to the object radial distance multiplied by the liquid refractive index. This provides a direct and accurate method to correct the radial size in the image. The corrected image data is more consistent, reducing the systematic error caused by optical distortion and improving the repeatability and reliability of the measurement. The corrected image radial distance can be directly converted into the actual object radial distance, simplifying the subsequent data processing and analysis process. Complex geometric correction algorithms are not required, because the telecentric lens already provides an image with almost no distortion, which further simplifies the data analysis process. The entire correction process is based on known physical laws and simple mathematical operations, which is easy to program and implement, making it convenient for researchers to quickly apply. Through clear physical models and mathematical formulas, researchers can more intuitively understand the formation mechanism of the meniscus profile and the cause of its distortion, thereby better optimizing the experimental design. This method is not only applicable to water, but can also be applied to other liquids with different refractive indices, enhancing the versatility of the method. As long as the ratio of the capillary outer diameter to the inner diameter is greater than the refractive index of the liquid, this method can be used for capillaries of various specifications and has strong adaptability.

[0064] The present invention has the following beneficial effects:

[0065] 1. This invention effectively eliminates image distortion caused by light refraction by using a telecentric lens and an optical distortion correction method based on Snell's law. The image-side radial distance is equal to the object-side radial distance multiplied by the liquid's refractive index, thus achieving precise radial dimension correction. This method ensures high consistency and accuracy of imaging results and significantly improves the accuracy of meniscus profile measurement.

[0066] 2. This invention utilizes an optimized experimental setup, including an integrated layout of an industrial camera, a displacement platform, a light source, and a displacement platform, making experimental setup simpler and faster. A correction method based on physical laws and mathematical formulas simplifies the data processing process and reduces the need for complex geometric correction algorithms. This not only improves experimental efficiency but also enhances the intuitiveness and operability of data processing.

[0067] 3. The present invention is applicable to a variety of liquids with different refractive indices and can be used for capillaries of various specifications. Compared with expensive and harmful X-ray imaging technology, the conventional optical elements and computer software used in the present invention greatly reduce experimental costs, are suitable for long-term and frequent experimental operations, and provide an economical and efficient solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 Schematic diagram of the telecentric lens structure of the present invention;

[0069] Figure 2 This is a schematic diagram of the meniscus profile distortion correction principle of the present invention;

[0070] Figure 3 This is a graph showing the extraction and correction of the lower edge contour of a steel ball used for inspection according to the present invention;

[0071] Figure 4 This is a comparison chart of the measured and actual values of the steel ball profile of the present invention;

[0072] Figure 5 is an image of the liquid surface of ultrapure water in the capillary tube of the present invention;

[0073] Figure 6 This is a comparison of the ultrapure water meniscus profile before and after correction of the present invention. DETAILED DESCRIPTION

[0074] The present invention will be further described in detail below with reference to the accompanying drawings and specific preferred embodiments.

[0075] In the description of the present invention, it should be understood that the terms "left side," "right side," "upper," "lower," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Terms such as "first" and "second" do not indicate the importance of components and therefore should not be construed as limitations on the present invention. The specific dimensions used in this embodiment are intended only to illustrate the technical solution and do not limit the scope of protection of the present invention.

[0076] like Figure 1 and Figure 2As shown, a high-precision detection device for the contour of a liquid meniscus in a capillary tube, an optical platform is located at the bottom of the device, a computer and an industrial camera are respectively arranged on the optical platform, the industrial camera is mounted on a displacement platform, a telecentric lens is also mounted on the displacement platform, the industrial camera is electrically connected to the computer, the displacement platform is used to adjust the position of the industrial camera to ensure horizontal alignment, a V-shaped serrated clamp is mounted on the displacement platform, fixes the capillary tube to ensure that it is perpendicular to the horizontal plane, the capillary tube is located directly above the culture dish for observing the liquid meniscus, and contains liquid, and the height is adjusted by the displacement platform, the displacement platform is arranged below the culture dish for adjusting the height of the culture dish and controlling the height of the liquid column, the light source provides uniform illumination, the telecentric lens includes an object lens, an aperture diaphragm and an image lens, the distance between the object lens and the image lens is the sum of their focal lengths, the aperture diaphragm is located at the common focus of the object lens and the image lens, and black tape is used as a shielding member to limit the axial width of the light source to minimize the light reaching the imaging system through the air in the meniscus;

[0077] When the aperture is small enough, almost only parallel light can pass through the entire imaging system to reach the target surface. The shape of the meniscus in the capillary is equivalent to being scaled to the imaging target surface at a certain ratio. This avoids the problem of object shape changing with imaging distance in high-speed cameras and high-magnification lenses, thereby improving the accuracy of image data. The scaling ratio can be calculated using the following formula:

[0078]

[0079] Where: H1 is the actual meniscus height, H2 is the photographed meniscus height. f1 is the focal length of the object lens, and f2 is the focal length of the image lens.

[0080] The imaging system mainly consists of an industrial camera and a telecentric lens. The industrial camera model is AVT Prosilica GT1290C, which is fixed to the optical platform via a high-precision displacement platform. Before the experiment, the industrial camera was adjusted to a horizontal position using a spirit level. The clean and dry capillary tube was fixed with a V-shaped serrated clamp and suspended in a petri dish filled with liquid. The tail of the V-shaped serrated clamp was connected to the high-precision displacement platform. The displacement platform was adjusted to make the capillary tube perpendicular to the horizontal plane. A diffuse reflective surface light source was placed on the right side of the capillary tube. While ensuring that the light source covered the outline of the meniscus, the axial width of the light source was limited with black tape to minimize the light reaching the imaging system through the air inside the meniscus. During the experiment, the displacement platform under the petri dish was adjusted to ensure that the liquid in the petri dish was in full contact with the lower end of the capillary tube. After the height of the liquid column in the capillary tube stabilized, the light source, capillary meniscus, and camera target surface were aligned on the same horizontal plane. When using an industrial camera to capture meniscus images, the exposure time should be set to ensure that the image has a high signal-to-noise ratio without overexposure, and that sufficient details of the meniscus are captured.

[0081] When light propagates in two different media, it will be refracted at the interface of the media, and the propagation direction of the light will change. When collecting the contour of the meniscus of the liquid column in a cylindrical capillary, the light will have two propagation paths. The first: the light passes through the external air-tube wall-liquid under the meniscus-air inside the meniscus-liquid under the meniscus-tube wall-external air to the imaging system. The second: the light passes through the external air-tube wall-liquid under the meniscus-tube wall-external air to the imaging system. For the first case, the direction of the light changes in both the radial and axial directions. When the light source is narrow in the axial direction, the telecentric imaging system cannot receive the light that passes through the air inside the meniscus, and the corresponding area in the grayscale image appears black. In the second case, the direction of the light only changes in the radial direction and can be received by the telecentric imaging system, but the distortion caused by the change in the radial direction of the light needs to be corrected;

[0082] The telecentric lens used in the experiment only receives parallel light. Assuming that CF is a beam of parallel light received by the target surface of the industrial camera, according to the principle of light refraction, the optical path diagram of CF in the capillary is reversed. Figure 2 The red arrowhead line is shown in the figure. The light passes through points C', B', B, and C, and is received by point F on the target surface of the industrial camera. F'C' is the incident light, θ4' is the angle of incidence at F'C', and θ3' is the angle of refraction at F'C'. θ2' is the angle of incidence at C'B', and θ1' is the angle of refraction at C'B'. θ1 is the angle of incidence at B'B, and θ2 is the angle of refraction at B'B. θ3 is the angle of incidence at BC, and θ4 is the angle of refraction at BC. The point of tangency between the light path of CF and the meniscus when passing through the liquid is point P. The distance from point P to the center of the circle, point O, is the object-side radial distance. Point A" is the midpoint of the reverse extension of CF within the capillary tube. The distance from point A" to the center of the circle, point O, is the image-side radial distance. The refractive indices of the liquid, capillary wall, and air in the capillary tube are n1, n2, and n3, respectively.

[0083] According to Snell's law:

[0084] n1sinθ1=n2sinθ2 (2)

[0085] n1sinθ1'=n2sinθ2' (3)

[0086] In ΔB'OB, |OB'|=|OB|, so θ1=θ1', that is: θ2=θ2'

[0087] A is the intersection of the extended line BC and OA". According to the sine theorem, in ΔOAB:

[0088] ∠OBA=θ2

[0089]

[0090] In ΔOAC:

[0091]

[0092] Right now:

[0093]

[0094] D is the intersection of the extended line of B'C' and the inner diameter. According to the sine theorem, in ΔODB': ∠OB'D=θ2'

[0095]

[0096] In ΔODC':

[0097]

[0098] Right now:

[0099]

[0100] According to formulas (3), (6), and (9), we can get:

[0101] θ3=θ3'

[0102] According to Snell's law:

[0103] n2sinθ3=n3sinθ4 (10)

[0104] n2sinθ3'=n3sinθ4'(11)

[0105] have to

[0106] θ4=θ4'(12)

[0107] In ΔB'PO

[0108] |OP|=sinθ1'R i (13)

[0109] From formula (2) and formula (11), we can get:

[0110]

[0111] and:

[0112]

[0113] Substituting formula (9) into formula (14) yields:

[0114]

[0115] In ΔOA”C:

[0116]

[0117] Substituting formula (17) into formula (16), we get

[0118]

[0119] Substituting formula (17) into formula (13) yields:

[0120]

[0121] When the refractive index of air (n3) is 1, the above formula is:

[0122] |OP|=|A”O| / n1 (19)

[0123] That is: image radial distance = object radial distance × liquid refractive index.

[0124] In the capture of capillary meniscus profile images, the ratio of the outer diameter to the inner diameter of the selected capillary must be greater than the refractive index of the liquid in the capillary; otherwise, a complete meniscus image cannot be captured.

[0125] like Figure 3 and Figure 4 As shown, the accuracy of the measurement method is verified by measuring the contour of a standard spherical steel ball in a capillary. In order to simulate the imaging conditions of the meniscus, the experiment needs to use a steel ball with a diameter that is the same as the inner diameter of the capillary as much as possible. Limited by the specifications of the steel ball and capillary, the present invention uses a standard spherical steel ball with a diameter of 1.400mm and a capillary with an inner diameter of 1.402mm to carry out the accuracy verification experiment. It should be noted that the inner diameter of the selected capillary is 0.14% larger than the diameter of the steel ball, which is conducive to easily placing the steel ball into the capillary, and the resulting measurement error is acceptable.

[0126] In the experiment, a steel ball was immersed in a pure water column in a capillary tube. The image of the steel ball in pure water was captured using the measurement method proposed in the present invention. The contour of the steel ball was extracted and corrected. The contour curves of the steel ball before and after correction are shown in Fig. Figure 3 shown. Figure 4 A comparison of the corrected capillary steel ball profile curve and the actual steel ball profile is presented, showing that the two are almost completely consistent, with a relative root mean square error of only 1.34%. This error stems from two aspects: on the one hand, the inner diameter of the selected capillary is larger than the diameter of the steel ball; on the other hand, due to the limitation of pixel density, the extracted steel ball profile is stepped. The error caused by limited pixel density also exists in the measurement of the liquid column meniscus profile and is the only source of error in the measurement method proposed in this invention. The accuracy of the measurement method of the liquid column meniscus profile in the capillary proposed in this invention has been verified.

[0127] The meniscus images of ultrapure water in four sizes of quartz capillaries were obtained in the experiment. Figure 5 As shown, each meniscus image is scaled to the same scale, and the scale bar is given in the figure. Figure 5 It can be seen that the meniscus of the capillary liquid column under all experimental conditions is complete. This is attributed to the fact that the ratio of the outer diameter to the inner diameter of the capillary selected in the experiment is greater than the refractive index of the liquid. Due to the special optical path and light source design in the experiment, the gas-liquid interface contour in the meniscus grayscale image is clear and distinct, and the contour curve can be easily extracted based on the grayscale difference. According to formula (19), the meniscus contour is corrected in the radial direction. The meniscus contour curves before and after correction are shown as follows: Figure 6 shown.

[0128] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the scope of protection of the present invention.

Claims

1. A high-precision detection method for the meniscus profile of a liquid in a capillary tube, characterized by: The device comprises a telecentric lens, an industrial camera, a displacement platform, an optical platform, a rotating telescopic rod, a light source, a capillary tube, and a culture dish; the industrial camera, capillary tube, and culture dish are respectively mounted on the displacement platform, the rotating telescopic rod is mounted on the optical platform, the light source is mounted on the rotating telescopic rod, the capillary tube is fixed directly above the culture dish via a V-shaped serrated clamp, and the light source, the meniscus of the liquid in the capillary tube, and the industrial camera are aligned on the same horizontal plane; The telecentric lens includes an object lens, an aperture stop, and an image lens; the distance between the object lens and the image lens is the sum of their focal lengths, and the aperture stop is located at the common focus of the object lens and the image lens; A computer is also provided on the optical platform, and the industrial camera is electrically connected to the computer; The industrial camera is fixed on the optical platform via the displacement platform; Before the experiment, the industrial camera was adjusted to a horizontal position using a spirit level. The capillary was fixed by the V-shaped serrated clamp and suspended in the culture dish filled with liquid. The tail of the V-shaped serrated clamp was connected to the displacement platform. The displacement platform was adjusted so that the capillary was perpendicular to the horizontal plane. The light source was arranged on the right side of the capillary. The light source was a diffuse reflection surface light source. A shielding member was used to limit the axial width of the light source to reduce the light reaching the imaging system through the air in the meniscus. Adjusting the displacement platform so that the liquid in the culture dish is in full contact with the lower end of the capillary tube, adjusting the position of the light source after the height of the liquid column in the capillary tube is stabilized, and using the industrial camera to capture a meniscus image; The parallel light is received by the target surface of the industrial camera; Wherein, F'C' is the incident light, θ4' is the incident angle of F'C', θ3' is the refraction angle of F'C', θ2' is the incident angle of C'B', θ1' is the refraction angle of C'B', θ1 is the incident angle of B'B, θ2 is the refraction angle of B'B, θ3 is the incident angle of BC, θ4 is the refraction angle of BC, the point of tangency of the light path of CF with the meniscus when passing through the liquid is point P, the distance P0 from point P to the center of the circle O is the object radial distance, point A" is the midpoint of the length of the reverse extension line of CF in the capillary, the distance A"O from point A" to the center of the circle O is the image radial distance, and the refractive indices of the liquid, capillary wall, and air in the capillary are n1, n2, and n3, respectively; According to Snell's law: n1sinθ1=n2sinθ2 (1) n1sinθ1'=n2sinθ2' (2) In ΔB'OB, |OB'|=|OB|, so θ1=θ1', that is: θ2=θ2'(3) A is the intersection of the extended line BC and OA". According to the sine theorem, in ΔOAB: ∠OBA=θ2 In ΔOAC: Right now: D is for B ' C ' The intersection of the extension line and the inner diameter, according to the sine theorem, is ΔODB ' middle: ∠OB'D=θ2' In ΔODC ' middle: Right now: According to formulas (3), (6), and (9), we can get: θ3=θ3' (10) According to Snell's law: n2sinθ3=n3sinθ4 (11) n2sinθ3'=n3sinθ4' (12) have to θ4=θ4' (13) In ΔB'PO |OP|=sinθ1'·R i (14) From formula (2) and formula (12), we can get: and: Substituting formula (9) into formula (15) yields: In ΔOA”C: Substituting formula (17) into formula (16), we get Substituting formula (18) into formula (14) yields: |OP|=|A”O|·n 31 (19) When the refractive index of air (n3) is 1, the above formula is: |OP|=|A”O| / n1 (20) That is: image radial distance = object radial distance × liquid refractive index; In capturing the capillary meniscus profile image, the ratio of the outer diameter to the inner diameter of the capillary is greater than the refractive index of the liquid in the capillary.

2. The high-precision detection method of the meniscus profile of a liquid in a capillary tube according to claim 1, characterized in that: After the measurement, the accuracy of the measurement method was verified by adding a standard spherical steel ball with a size close to that of the liquid meniscus into the measuring capillary and measuring the profile of the standard spherical steel ball. The inner diameter of the selected capillary was 0.14% larger than the diameter of the standard spherical steel ball.

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