A method for measuring defocused droplet size based on quantitative calibration of defocus distance

Abstract

The present invention discloses a method for measuring the size of defocused droplets based on quantitative calibration of defocus distance. The method obtains the law between the defocused droplet size and the real droplet size through experiments. A high-speed camera is used in conjunction with a telephoto microscope lens to capture clear droplet images and droplet-free background images of hanging drops of different diameters D at different telephoto microscope working distances L. The electric displacement stage is adjusted to only change the front and rear positions of the droplets to obtain droplet photos at different defocus distances ε. The obtained droplet images are converted into grayscale images using a program to obtain the grayscale diameter D of the droplets. g And the average gray gradient K on both sides of the droplet; by fitting, L, D, ε and D g , K; in the specific calibration, L and droplet grayscale image are known from the shooting situation, and D is obtained through the program g and K; finally, ε and the actual droplet diameter D are obtained according to the functional relationship. The present invention realizes the accurate measurement of the actual data of the defocused droplet size measurement under conditions of different sizes and magnifications.

Description

Technical Field

[0001] The present invention relates to a method for measuring droplet particle size, and in particular to a method for measuring defocused droplet size based on quantitative calibration of defocus distance. Background Art

[0002] The method of measuring droplet size is the basis for studying droplet impact, droplet evaporation, and droplet combustion. The collection and measurement of droplet size distribution is crucial. Research on droplet impact, droplet evaporation, and droplet combustion is also an important stage of combustion in the engine cylinder. The droplets generated in real engine operating conditions are all small droplets on the sub-millimeter level. In experimental research, high-speed microscopy with high magnification is required to capture clear droplets under such conditions. However, the droplets under such imaging effects are easily separated from the focal plane of the high-speed microscopy due to the narrow focal plane of the high-speed microscopy, resulting in inaccurate measurement and affecting the reliability of the experimental research.

[0003] Defects and shortcomings of existing technology:

[0004] 1. Numerous methods exist for measuring droplet size, including simulation programs and commercial software that process and measure grayscale images converted from droplet images. These methods use the grayscale threshold reached by the droplet's grayscale image to determine whether it represents a droplet boundary, thereby obtaining droplet size data. However, these methods can introduce measurement errors when processing droplets that are slightly out of focus due to grayscale variations at the droplet's boundary, affecting experimental accuracy.

[0005] 2. High-speed microscopy, as a high-magnification imaging method, can capture submillimeter droplets. However, due to the narrow focal plane, some moving droplets can easily escape the focal plane, resulting in inaccurate measurements and affecting the reliability of experimental research.

[0006] 3. Existing technologies lack correction methods for particle size measurement of defocused droplet imaging, which poses a great challenge for some experiments with high precision requirements and brings great difficulties to the experimental process and data processing.

[0007] High-speed microscopy utilizes a high-speed camera (Phantom V611) and a telephoto microscope lens (Questar QM1) to create a high-magnification imaging system. It can microscopically magnify distant objects with continuously adjustable focal length. The telephoto microscope features a spare port on the top for adding a light source, as well as an axial port for connecting other imaging devices. Adjusting the focus screw allows for viewing objects at varying distances. When the light source is inserted into the microscope, a prism adjuster and a magnification adjuster assist in adjusting the light and focus. The telephoto microscope has a working distance range of 530-1520 mm. During the imaging system design process, a 1 mm ruler was used to calibrate the 1 mm dimension at various distances from the microscope lens. Specific calibration parameters are shown in Table 1. The difficulty in optical path arrangement lies in combining the precise measurement of droplet size parameters for microscopic imaging with the control of the imaging window range. When the droplet is farther from the telephoto microscope lens, the magnification is lower and the field of view is larger. Conversely, when the droplet is closer to the lens, the magnification is higher and the field of view decreases. When the high-speed camera window adopts a resolution of 1280×800, the observable field of view varies with the distance between the droplet and the telephoto microscope, as shown in Table 2.

[0008] Table 1 Dimension calibration table

[0009]

[0010] Table 2 Relationship between field of view and distance

[0011]

[0012] Summary of the Invention

[0013] The purpose of the present invention is to provide a defocused droplet size measurement method based on quantitative calibration of defocus distance. By conducting experimental shooting of defocused droplets of different sizes, information such as the grayscale diameter and grayscale gradient of the droplet imaging at different defocus distances and different magnifications is obtained, and a calibration function relationship between the defocus distance, droplet size, magnification, grayscale diameter and grayscale gradient is established, thereby achieving accurate measurement of the real data of defocused droplet size measurement under conditions of different sizes and magnifications, and providing a correction method that is more in line with the actual droplet size and has smaller errors.

[0014] The present invention is achieved through the following technical solutions:

[0015] A defocused droplet size measurement method based on quantitative calibration of defocus distance is provided. The method obtains the regularity between the defocused droplet size and the actual droplet size through experiments, and includes the following steps:

[0016] Step 1: Using a high-speed camera with a telephoto microscope lens, a droplet is suspended on a high-precision motorized translation stage capable of three-dimensional movement using a capillary tube. The optical path is adjusted to obtain a clear image of the droplet and a droplet-free background image at the same magnification. The number of pixels in the viewing window is calibrated using a calibration plate to determine the actual length represented by each pixel.

[0017] Step 2: By adjusting the electric translation stage, the vertical and horizontal positions of the droplet are kept unchanged, and the front and back positions are changed to obtain the droplet imaging photos at different defocus distances ε;

[0018] Step 3, changing the telephoto microscope magnification, i.e., the telephoto microscope working distance L and the hanging droplet size D, respectively, and repeating the operations of steps 1 and 2 to obtain multiple droplet images;

[0019] Step 4: Convert each droplet image into a grayscale image using the Matlab program and set a grayscale threshold. Find the location of the droplet midpoint and obtain the number of pixels in the interval that reaches this grayscale threshold for the first and last time under this vertical coordinate. At the same time, obtain the grayscale diameter D based on the calibration value. g , and the average value K of the grayscale change gradient on the left and right sides of the droplet;

[0020] Step 5: Fit the function to the data obtained under different conditions. The data under different conditions include independent variables: telephoto microscope working distance L, droplet size D and defocus distance ε, and dependent variable: grayscale diameter D g And the gray gradient K, get the corresponding relationship between them:

[0021] K=f(ε,L) (1)

[0022] D g =g(D,ε,L) (2)

[0023] The actual particle size of the defocused droplets is corrected using the obtained functional relationship;

[0024] Step 6: When obtaining the defocused droplet image, the magnification or the working distance L of the telephoto microscope is known through the shooting situation. The grayscale image and grayscale diameter D of the droplet image are obtained in the matlab program by using the method of step 4. g , and the average value K of the grayscale change gradient on the left and right sides of the droplet;

[0025] Step 7: According to the function correspondence (1) obtained in step 5 and L and K obtained in step 6, the defocus distance ε of the defocused droplet image is obtained. Then, according to the function correspondence (2), the grayscale diameter D obtained in step 6 is used to calculate the defocus distance ε of the defocused droplet image. g The corrected droplet true particle size D is obtained.

[0026] A further improvement of the present invention is that the model of the high-speed camera is Phantom V611.

[0027] A further improvement of the present invention is that the working distance range of the telephoto microscope is 530 to 1520 mm.

[0028] A further improvement of the present invention is that the model of the telephoto microscope lens is Questar QM1.

[0029] A further improvement of the present invention is that, in step 1, the calibration plate used has a size of 1 mm.

[0030] A further improvement of the present invention is that, in step 1, a calibration plate is used to calibrate the number of pixels within 1 mm of the viewing window.

[0031] A further improvement of the present invention is that the droplet particle size distribution is between 0.9 and 2 mm.

[0032] A further improvement of the present invention is that the defocus distance is between 0.5 and 15 mm.

[0033] The present invention has at least the following beneficial technical effects:

[0034] The present invention provides a method for measuring the size of defocused droplets based on quantitative calibration of defocus distance. This method obtains information such as the grayscale diameter and grayscale gradient of droplet images at different defocus distances and magnifications by experimentally photographing the defocused state of droplets of different sizes. A calibration function relationship is established between the defocus distance, droplet size, magnification, and grayscale diameter and grayscale gradient, thereby achieving accurate measurement of the size of defocused droplets under conditions of different sizes and magnifications. This method has the following advantages:

[0035] 1. The present invention obtains experimental data under different working conditions by conducting experiments under various working conditions and summarizes a set of change rules between experimental variables with universal significance through the obtained experimental data. The independent variables are the telephoto microscope working distance L, the droplet particle size D, the defocus distance ε, and the dependent variables are the grayscale diameter D. g , and the functional relationship contained in the gray gradient K, the results of which are applicable to all high-speed microscopy imaging situations.

[0036] 2. The present invention adopts the forward method to obtain the changing law of the experimental dependent variable, and obtains the actual data of all independent variables in this case through the dependent variable obtained by the grayscale image of the droplet image during the reverse correction, thereby correcting the real particle size data of the defocused droplets.

[0037] 3. Compared with other methods for droplet size measurement, the present invention adds a correction for the true particle size of blurred and defocused droplets, which is conducive to obtaining droplet size data that is more consistent with the actual droplet size and has smaller errors, thereby improving the accuracy and reliability of experimental data.

[0038] 4. The present invention is consistent with the situation where the defocus distance is less than or equal to twice the droplet diameter, the error of the obtained correction data is small, and it includes a droplet correction method within a larger defocus range.

[0039] 5. The correction method of the present invention is simple to operate and can obtain the real size correction data of the decoked droplets without going through more complicated steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is an experimental system diagram of a defocused droplet size measurement method based on quantitative calibration of defocus distance used in the present invention.

[0041] Figure 2 The present invention provides a method for measuring the size of defocused droplets based on quantitative calibration of defocus distance, and obtains droplet images at different defocus distances. Figure 2 (a) is the defocus distance 0mm, Figure 2 (b) is the defocus distance 2mm, Figure 2 (c) is the defocus distance 5mm, Figure 2 (d) is the defocus distance of 10 mm.

[0042] Figure 3 The present invention provides a method for measuring the size of defocused droplets based on quantitative calibration of the defocus distance, which is an experimentally obtained grayscale change image of the vertical coordinate of the position of the midpoint of the droplet at different debonding distances.

[0043] Figure 4 This is a defocused droplet image obtained by implementing a defocused droplet size measurement method based on quantitative calibration of defocus distance provided by the present invention.

[0044] Figure 5 It is a grayscale image of defocused droplets obtained by implementing a defocused droplet size measurement method based on quantitative calibration of defocus distance provided by the present invention. DETAILED DESCRIPTION

[0045] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0046] The present invention provides a method for measuring the size of defocused droplets based on quantitative calibration of defocus distance. The method obtains the regularity between the defocused droplet size and the actual droplet size through experiments, and comprises the following steps:

[0047] In step 1, a high-speed camera (Phantom V611) was used in conjunction with a telephoto microscope lens (Questar QM1). A capillary was used to suspend a droplet on a high-precision motorized translation stage capable of three-dimensional movement. The optical path was adjusted to obtain a clear image of the droplet and a droplet-free background image at the same magnification. The number of pixels within the 1mm window was calibrated using a 1mm calibration plate to determine the actual length represented by each pixel.

[0048] Step 2: By adjusting the electric translation stage, the up, down, left, and right positions of the droplet are kept unchanged, and the front and back positions are changed to obtain the droplet imaging photos at different defocus distances ε.

[0049] Step 3: Repeat steps 1 and 2 by changing the telephoto microscope magnification, i.e., the telephoto microscope working distance L, and the hanging droplet particle size D.

[0050] Step 4: Convert each droplet image into a grayscale image using the Matlab program and set a grayscale threshold. Find the location of the droplet midpoint and obtain the number of pixels in the interval that reaches this grayscale threshold for the first and last time under this vertical coordinate. At the same time, obtain the grayscale diameter D based on the calibration value. g , and the average value K of the grayscale change gradient on the left and right sides of the droplet.

[0051] Step 5: The data obtained under different conditions (independent variables: telephoto microscope working distance L, droplet size D, defocus distance ε, dependent variable: grayscale diameter D) are g , gray gradient K) to perform function fitting and obtain the corresponding relationship between them:

[0052] K=f(ε,L) (1)

[0053] D g =g(D,ε,L) (2)

[0054] Correcting the actual particle size of the defocused droplets using the obtained functional relationship includes the following steps:

[0055] Step 6: When obtaining the defocused droplet image, the magnification (or the working distance L of the telephoto microscope) is known through the shooting situation. The grayscale image and grayscale diameter D of the droplet image are obtained in the matlab program by using the method in step 4. g , and the average value K of the grayscale change gradient on the left and right sides of the droplet.

[0056] Step 7: According to the function correspondence (1) obtained in step 5 and L and K obtained in step 6, the defocus distance ε of the defocused droplet image is obtained. Then, according to the function correspondence (2), the grayscale diameter D obtained in step 6 is used to calculate the defocus distance ε of the defocused droplet image. g The corrected droplet true particle size D can be obtained.

[0057] Example

[0058] Experiments were conducted based on the capillary hanging drop method for different droplets with diameters of 0.9, 1.17, 1.6, and 2 mm. The same droplet was imaged at different telephoto working distances of 530 / 630 / 730 / 930 / 1130 mm using a high-precision motorized stage, with each photo taken every 0.5 mm away from the focal plane (the experimental system is shown in Figure 2). Figure 1 ), each droplet image ( Figure 2 ) were converted into grayscale images using the Matlab program and the grayscale change images of the vertical coordinates of the droplet midpoint position at different degumming distances were obtained ( Figure 3 ), according to steps 4 and 5, the data of the respective variables and dependent variables are obtained (Table 3 and Table 4), and the specific functional correspondence between them is obtained by fitting the functional relationship of the data:

[0059] K=0.015Lε 0.613 -1.376 (1)

[0060] D g =(-0.116L-0.374ε 2 -2.27ε+204.9)×D

[0061] Table 3 Average K of the grayscale gradient on the left and right sides of the droplet at different defocus distances and telephoto working distances

[0062]

[0063] Table 4 Maximum grayscale diameter D of droplets reaching grayscale threshold at different defocus distances and telephoto working distances g / Pixel

[0064]

[0065] Specifically, when calibrating the defocused droplet, the experimental image of a random droplet is known ( Figure 4 ) with a telephoto microscope working distance of L = 530 mm (or magnification), and the grayscale image of the defocused droplet is obtained by the program ( Figure 5 ), and get the grayscale diameter D g The pixel size is 226, the grayscale gradient K = 5.1, and the defocus distance ε = 1.39 mm can be obtained from test 1. Then according to the obtained ε, L, D g The three data from Test 2 indicate that the estimated droplet diameter D = 1.6198 mm. The actual droplet diameter is 1.61 mm. The error of the calibrated droplet size in the specific case does not exceed 5%.

[0066] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for measuring the size of defocused droplets based on quantitative calibration of defocus distance, characterized in that: This method obtains the law of defocused droplet size and real droplet size through experiments, including the following steps: Step 1: Using a high-speed camera with a telephoto microscope lens, a droplet is suspended on a high-precision motorized translation stage capable of three-dimensional movement using a capillary tube. The optical path is adjusted to obtain a clear image of the droplet and a droplet-free background image at the same magnification. The number of pixels in the viewing window is calibrated using a calibration plate to determine the actual length represented by each pixel. Step 2: By adjusting the electric translation stage, the vertical and horizontal positions of the droplet are kept unchanged, and the front and back positions are changed to obtain the droplet imaging photos at different defocus distances ε; Step 3, changing the telephoto microscope magnification, i.e., the telephoto microscope working distance L and the hanging droplet size D, respectively, and repeating the operations of steps 1 and 2 to obtain multiple droplet images; Step 4: Convert each droplet image into a grayscale image using the Matlab program and set a grayscale threshold. Find the location of the droplet midpoint and obtain the number of pixels in the interval that reaches this grayscale threshold for the first and last time under this vertical coordinate. At the same time, obtain the grayscale diameter D based on the calibration value. g , and the average value K of the grayscale change gradient on the left and right sides of the droplet; Step 5: Fit the function to the data obtained under different conditions. The data under different conditions include independent variables: telephoto microscope working distance L, droplet size D and defocus distance ε, and dependent variable: grayscale diameter D g And the gray gradient K, get the corresponding relationship between them: K=f(ε,L) (1) D g =g(D,ε,L) (2) The actual particle size of the defocused droplets is corrected using the obtained functional relationship; Step 6: When obtaining the defocused droplet image, the magnification or the working distance L of the telephoto microscope is known through the shooting situation. The grayscale image and grayscale diameter D of the droplet image are obtained in the matlab program by using the method of step 4. g , and the average value K of the grayscale change gradient on the left and right sides of the droplet; Step 7: According to the function correspondence (1) obtained in step 5 and L and K obtained in step 6, the defocus distance ε of the defocused droplet image is obtained. Then, according to the function correspondence (2), the grayscale diameter D obtained in step 6 is used to calculate the defocus distance ε of the defocused droplet image. g The corrected droplet true particle size D is obtained.

2. The method for measuring the size of defocused droplets based on quantitative calibration of defocus distance according to claim 1, characterized in that: The model of the high-speed camera is Phantom V611.

3. The method for measuring the size of defocused droplets based on quantitative calibration of defocus distance according to claim 1, characterized in that: The working distance range of telephoto microscope is 530~1520mm.

4. The method for measuring the size of defocused droplets based on quantitative calibration of defocus distance according to claim 3, characterized in that: The working distance range for telephoto microscopes is 530mm, 630mm, 730mm, 930mm, or 1130mm.

5. The method for measuring the size of defocused droplets based on quantitative calibration of defocus distance according to claim 1, characterized in that: The model of the telephoto microscope lens is Questar QM1.

6. The method for measuring the size of defocused droplets based on quantitative calibration of defocus distance according to claim 1, characterized in that: In step 1, the calibration plate size is 1 mm.

7. The method for measuring the size of defocused droplets based on quantitative calibration of defocus distance according to claim 1, characterized in that: In step 1, the number of pixels within the 1mm window is calibrated using a calibration plate.

8. The method for measuring the size of defocused droplets based on quantitative calibration of defocus distance according to claim 1, characterized in that: The droplet size distribution is between 0.9 and 2 mm.

9. The method for measuring the size of defocused droplets based on quantitative calibration of defocus distance according to claim 1, characterized in that: The defocus distance is between 0.5 and 15 mm.

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