PTV device for measuring spray particle size and three-dimensional velocity using a single camera

Abstract

A PTV device for measuring spray particle size and three-dimensional velocity using a single camera solves the problem of obtaining three-dimensional velocity and position information using a single camera, belonging to laser velocity measurement technology. The invention comprises: a laser transmitter emitting laser light of a set frequency, which is incident on a laser beam expander. After beam expansion, the expanded laser light generates non-correlated light to illuminate the observation area. A microscope lens is directed toward the observation area, and a high-speed camera is connected to the microscope lens. The microscope lens captures spray images of the observation area and transmits the spray images to a processor. The processor is used to store all spray images in chronological order, obtain the shape and position characteristics of all droplets in each spray image, determine the average particle size of the droplets, and obtain the defocus distance using the half-wavelength value of the point spread function (PSF). This eliminates unreasonable defocus distances, matches the droplets corresponding to two adjacent spray images, and obtains the three-dimensional velocity based on the distance and interval between the two matched droplets.

Description

Technical Field

[0001] The present invention relates to a PTV (Particle Tracking Velocimetry) device. Background Art

[0002] Digital image processing is the process of batch processing of images captured by the camera through program language control, screening of particle information, calculation and analysis, and measurement of the average particle size in the measured area. It is widely used in experiments such as spray measurement.

[0003] PTV velocimetry is a modern, non-contact laser velocimetry technique. By tracking and matching target particles captured by a laser camera system and digitally processing their images, the displacement of the particles between two adjacent frames is determined, enabling the measurement of the velocity of moving particles in a flow field. It is widely used in spray flow field experiments. Currently, the technology for obtaining the two-dimensional position and velocity of droplets is generally considered mature. However, obtaining three-dimensional velocity and position information requires increasing the number of high-speed cameras to capture more and more accurate information, which significantly increases the cost. Therefore, the current PTV velocimetry method of obtaining the three-dimensional velocity of target particles using a single camera is relatively novel.

[0004] High-speed cameras have a certain depth of field. When the measured droplet particles exceed the camera's depth of field, defocus will occur. At this time, using only the defocused image captured by the camera cannot determine whether the imaged object is in front of or behind the focus, which is the so-called defocus ambiguity problem. It is difficult to obtain the specific defocus position of the droplet. Summary of the Invention

[0005] In order to solve the problems of how to obtain three-dimensional velocity and position information using a single camera and how to resolve the defocus ambiguity, the present invention provides a PTV device for measuring spray particle size and three-dimensional velocity using a single camera.

[0006] The present invention provides a single-camera PTV device for measuring spray particle size and three-dimensional velocity, comprising a high-speed camera 1, a microscope lens 2, a laser beam expander 6, a laser transmitter 8, and a processor 12;

[0007] The laser emitter 8 emits a laser of a set frequency, which is incident on the laser beam expander 6. After the laser beam expander 6 expands the beam, it generates incoherent light 5 to illuminate the observation area. The microscope lens 2 is facing the observation area. The high-speed camera 1 is connected to the microscope lens 2. The microscope lens 2 captures the spray image of the observation area and sends the spray image to the processor 12.

[0008] Processor 12 is used to store the time sequence of all spray images taken, process the spray images, obtain the shape and position characteristics of all droplets in each spray image, determine the average particle size SMD of the droplets, obtain the defocus distance through the relationship between the half-wavelength value of the PSF point spread function and the defocus distance, eliminate unreasonable defocus distances, use the position and shape characteristics of the droplets in each spray image to match the corresponding droplets in two adjacent spray images, obtain the droplet movement speed based on the distance and interval time between the two matched droplets, and complete three-dimensional speed measurement.

[0009] Preferably, the processor 12 includes an image import and preprocessing module, an adaptive threshold cutting module, a droplet labeling module, a droplet defocus distance ambiguity elimination module and a feature matching module;

[0010] The image import and preprocessing module is connected to the adaptive threshold cutting module and the feature matching module. It is used to store all spray images in the chronological order of shooting, preprocess each image: remove the background and detect the contour, and send the preprocessed image to the adaptive threshold cutting module.

[0011] The adaptive threshold cutting module is connected to the droplet defocus distance ambiguity elimination module to grayscale the pre-processed image and binarize the image through the adaptive threshold function. It traverses all the droplets in the image to obtain the shape and position characteristics of each droplet and determine the average particle size (SMD) of the droplets.

[0012] Droplet defocus distance ambiguity elimination module is used to use the PSF point spread function half wavelength value χ est Calculate the defocus distance z of the droplet being measured, use the maximum gradient method to eliminate unreasonable defocus distance z, and obtain the true defocus distance of the droplet;

[0013] Get the half-wavelength value of the PSF point spread function χ est , according to χ est =f1(z) to obtain the defocus distance z;

[0014] f1() represents χ est and the fitting relationship of the defocus distance z;

[0015]

[0016] Where f is the focal length of the camera, l represents the distance between the measured droplet and the lens;

[0017] Get the focus parameter lnf of the droplet being measured L3 :

[0018]

[0019] in, Indicates the maximum gradient of the measured droplet; d ei is the diameter of the droplet being measured; I max is the maximum gray level of the measured droplet; I min is the minimum gray level of the measured droplet;

[0020] According to lnf Lq =f2(z,d ei ) respectively obtain the focal parameters lnf corresponding to z1 and z2 L1 and the intra-focus parameter lnf L2 ;

[0021] f2() represents the focus parameter lnf Lq With z, d ei The fitting relationship of

[0022] According to lnf L1 、lnf L2 and lnf L3 The relationship between the measured droplet and the actual defocus distance is determined as z1 or z2:

[0023]

[0024] The feature matching module is used to use the position and shape features of the droplets in each spray image to match the corresponding droplets in two adjacent spray images based on the two factors of features and close distance, and calculate the movement speed of the droplets by V=L / t, where L represents the movement distance of the same droplet in two adjacent images, and t represents the interval time between the capture of two adjacent images.

[0025] Preferably, the processor 12 further includes a droplet labeling module;

[0026] The droplet labeling module is connected to the adaptive threshold cutting module, and the droplet labeling module marks and labels the droplets identified by the adaptive threshold cutting module.

[0027] Preferably, the processor 12 also includes a calculation result visualization display and storage module for displaying and storing the processing results of the image import and preprocessing module, the adaptive threshold cutting module, the droplet labeling module, the droplet defocus distance ambiguity elimination module and the feature matching module.

[0028] The beneficial effects of the present invention are as follows: the present invention realizes the acquisition of spray particle size and three-dimensional velocity by a single camera through a specific image information processing method of digital image processing; and on this basis, the ambiguity of the droplet defocus distance is eliminated by using the half-wavelength value of the PSF point spread function and the maximum gradient contrast method, thereby achieving the purpose of accurately acquiring the spray particle size, three-dimensional velocity and defocus distance, and then obtaining the basis for objective evaluation of the nozzle atomization performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the present invention;

[0030] Figure 2 Schematic diagram of the workflow of the processor of the present invention;

[0031] Figure 3 This is a diagram showing the actual effect of droplet matching in the present invention;

[0032] Figure 4 This is an actual effect diagram of the droplet size distribution of the present invention;

[0033] Figure 5 This is an actual effect diagram of the droplet size distribution statistics of the present invention;

[0034] Figure 6 Schematic diagram of the principle of the droplet defocus ambiguity elimination module of the present invention. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other.

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0038] The single-camera PTV device for measuring spray particle size and three-dimensional velocity in this embodiment includes a high-speed camera 1, a microscope lens 2, a laser beam expander 6, a laser transmitter 8, and a processor 12;

[0039] The laser emitter 8 emits a laser of a set frequency, which is incident on the laser beam expander 6. After the laser beam expander 6 expands the beam, it generates incoherent light 5 to illuminate the observation area. The microscope lens 2 is facing the observation area. The high-speed camera 1 is connected to the microscope lens 2. The microscope lens 2 captures the spray image of the observation area and sends the spray image to the processor 12.

[0040] The high-speed camera 1 is used to capture the spray image of the observation area 4 illuminated by the laser and capture the instantaneous characteristics of the spray;

[0041] The microscope lens 2 is used to provide a smaller field of view and depth of field, which is convenient for forming the defocus phenomenon of the droplets and provides an environment for photographing the defocused droplets;

[0042] The laser emitter 8 is used to emit a high-frequency laser with a specific frequency to form a laser light path;

[0043] The laser beam expander 6 is used to expand the laser beam emitted by the laser emitter 8, increase the beam area, and at the same time destroy the strong coherence of the emitted laser beam, turning it into incoherent light 5 to illuminate the observation area 4;

[0044] The laser emitter 8 in this embodiment uses a diode laser emitter, which can emit higher frequencies and is less expensive than other instruments. The position of the laser beam expander 6 is adjusted to generate a laser beam 5 of the desired width and area to illuminate and pass through the observation area 4.

[0045] After information collection, the spray images obtained under different working conditions can be imported into the processor for analysis of the spray particle size, three-dimensional speed and position, and to eliminate defocus ambiguity; the processor 12 is used to store the time sequence of all spray images taken, process the spray images, obtain the shape and position characteristics of all droplets in each spray image, determine the average particle size SMD of the droplets, and obtain the defocus distance through the relationship between the half-wavelength value of the PSF point spread function and the defocus distance. The maximum gradient method is used to eliminate unreasonable defocus distances, and the position and shape characteristics of the droplets in each spray image are used to match the corresponding droplets of the two adjacent spray images. According to the distance and interval time of the two matched droplets, the droplet movement speed is obtained to complete the three-dimensional speed measurement.

[0046] This embodiment uses a specific image information processing method for digital image processing, utilizing the half-wavelength value of the point spread function (PSF) and the maximum gradient contrast method to eliminate the ambiguity of the droplet defocus distance, thereby achieving the purpose of accurately obtaining the spray particle size, three-dimensional velocity, and defocus distance. In a preferred embodiment, the processor 12 of this embodiment includes an image import and preprocessing module, an adaptive threshold cutting module, a droplet labeling module, a droplet defocus distance ambiguity elimination module, and a feature matching module.

[0047] The image import and preprocessing module, connected to the adaptive threshold cropping module and the feature matching module, stores all spray images in chronological order. It then performs preprocessing on each image, removing background and performing contour detection, before sending the processed images to the adaptive threshold cropping module. This self-programmed image import and preprocessing module imports and processes batches of captured droplet images and creates a table to store the processed information. During operation, the high-speed camera images are batch processed, renaming them in chronological order to prepare for further digital image processing.

[0048] The adaptive threshold segmentation module, connected to the droplet defocus distance ambiguity elimination module, grayscales the preprocessed image and binarizes it using an adaptive threshold function. It then iterates over all droplets in the image, extracts the shape and position characteristics of individual droplets, and determines the average droplet size (SMD). This adaptive threshold segmentation module, in this embodiment, includes a series of functions for background removal and image binarization. During operation, it analyzes, detects, and identifies the captured droplets in the preprocessed image, and calculates the droplet perimeter and area using a function. This yields the average droplet size (SMD) for all droplets in the image.

[0049] The droplet defocus distance ambiguity elimination module is used to calculate the droplet defocus distance using the half-wavelength value of the PSF point spread function. It then compares the measured droplet position using the maximum image gradient to eliminate unreasonable defocus distances and obtain the true relative droplet defocus distance. The droplet defocus ambiguity elimination module includes calculating the droplet defocus distance z and eliminating unreasonable cases. During operation, the droplet defocus distance is first calculated using the half-wavelength χ value of the PSF point spread function. Then, the maximum gradient method is used to compare the measured droplet position to eliminate unreasonable defocus distances and obtain the true relative droplet defocus distance z.

[0050] The feature matching module is used to use the position and shape features of the droplets in each spray image to match the corresponding droplets in two adjacent spray images based on the two factors of features and close distance. The moving speed of the droplets is calculated by V=L / t, and the calculated speed is stored separately according to the X, Y, and Z three-dimensional components. L represents the moving distance of the same droplet in two adjacent images, and t represents the interval time between the shooting of two adjacent pictures.

[0051] The PTV device of this embodiment further includes a droplet labeling module;

[0052] The droplet labeling module, connected to the adaptive threshold segmentation module, is responsible for marking and labeling droplets identified by the adaptive threshold segmentation module. This embodiment of the droplet labeling module includes two parts: drawing a rectangle and drawing a number in the upper left corner of the droplet. This module also includes a function to turn it on and off, specifically considering computational time costs.

[0053] The processor 12 in this embodiment includes a calculation result visualization and storage module, which is used to display and store the processing results of the image import and preprocessing module, the adaptive threshold cutting module, the droplet labeling module, the droplet defocus distance ambiguity elimination module, and the feature matching module. This calculation result visualization and storage module directly stores the calculation results in a table at the end of each module and finally aggregates all calculation results into an image for visual display. This includes the image drawing function within the programming language library, which draws relevant images based on the information obtained from the previous calculation modules and stores the results.

[0054] The PTV device of this embodiment further includes a controller 11 for adjusting the operating frequency of the laser emitter 8 and the high-speed camera 1 so that they operate at the same frequency to achieve the highest acquisition efficiency;

[0055] The controller 11 in this embodiment adjusts the laser emitter 8 and the high-speed camera 1 to the same operating frequency to improve image acquisition efficiency.

[0056] This embodiment further includes a power supply 10 for providing power to the controller 11 and the laser emitter 8;

[0057] The PTV device of this embodiment further includes an optical fiber 7 ; the laser emitter 8 is connected to the laser beam expander 6 via the optical fiber 7 , so as to transmit the laser light generated by the laser emitter 8 to the laser beam expander 6 in a directionally directed manner.

[0058] Optical fiber 7 is used to conduct the laser light generated by the laser transmitter in a direction and input it into the laser beam expander for further processing while reducing the loss of laser energy.

[0059] The PTV device of this embodiment further includes a fixing frame 9;

[0060] The laser beam expander 6 and the laser emitter 8 are installed on the fixing frame 9 at the same time and fixed as one. The light output direction of the laser beam expander 6 can be adjusted according to the placement of the fixing frame 9. During operation, by adjusting the placement position of the fixing frame 9, it is ensured that the laser light is always emitted from the end of the laser beam expander 6 to illuminate the observation area 4.

[0061] In this embodiment, the laser emitter 8 and high-speed camera 1 are positioned on opposite sides of the observation area, ensuring that the fully exposed spray is clearly and accurately recorded by the high-speed camera. The PTV apparatus also includes a micro-displacement platform 3, on which the spray nozzle is mounted, providing angular displacement for the nozzle.

[0062] The micro-displacement platform 3 is used to install the nozzle that emits the spray and can provide the nozzle with a certain angular displacement. When the nozzle is fixed on the micro-displacement platform 3, the nozzle is arranged vertically downward to form a conical spray in the working area. The controller 11 is turned on to collect the spray image and store the image for processing. At the same time, the micro-displacement platform 3 can give the nozzle a certain angular displacement under the same working conditions, so that when the high-speed camera 1 and the laser emitter 8 are fixed, more abundant spray information can be obtained.

[0063] Example 1: This example uses a laser emitter, a high-speed camera, a microscope lens, an optical fiber, a laser beam expander, and other necessary devices to capture and record spray images. The processor uses six modules to process the obtained images, obtain spray particle size and three-dimensional velocity information, and eliminate the ambiguity of droplet defocus. The device and method are applied to nozzle spray measurement experiments. The schematic diagram of the device structure is shown in the figure below. Figure 1 As shown, the light path arrangement of this embodiment forms a backlight shooting condition, thereby improving the utilization rate of light energy.

[0064] When working, first arrange the device according to the optical path position, adjust the coordination between the optical path and the camera, and fix the centrifugal nozzle above the shooting area to ensure that the spray can appear in the shooting area;

[0065] Secondly, connect the processor 12, controller 11, and power supply 10 lines and power on; open the nozzle valve in sequence, adjust the spray flow, turn on the laser generator 8 and the high-speed camera 1, and start collecting images by operating the processor 12 and controller 11. The images are transmitted to the processor for storage via the high-speed data line for processing.

[0066] Compared with other PTV image acquisition devices, this embodiment only uses one camera to record the behavior information of the spray droplets.

[0067] In this embodiment, the instrument calibration work will be performed after the spray information is collected. The specific operation steps are as follows:

[0068] Step 1: Mark standard circles ranging in size from 10 μm to 170 μm on the glass chrome plate used for calibration, and place it in the observation area 4 to wait for information to be obtained.

[0069] Step 2: Adjust the glass chrome plate to the clearest position where all patterns are clearly visible, turn on the power and controller to take pictures and samples, and store them in the processor for processing.

[0070] Step 3: Adjust the glass chrome plate forward and backward to obtain images at corresponding positions, obtain images corresponding to each position, and store them in the processor for processing.

[0071] Step 4: Process the acquired image, calculate the distance information in the image with pixels, and compare it with the actual distance on the glass chrome plate to obtain the relationship between the image features and the defocus distance, thus completing the calibration work.

[0072] The flowchart of the processor in this embodiment is as follows Figure 2 Shown, including:

[0073] Step 1: Obtain the spray image of the specified working condition of the centrifugal nozzle spray experiment, and store all images of the working condition in the same file in the chronological order of capture for processing; the images are all derived from the original images taken by the above-mentioned high-speed camera 1 and imported into the processor through the data cable and stored.

[0074] Step 2: Image import and preprocessing module, specifically:

[0075] Step 2.1: First, batch-import the above images into the calculation program. Then, use the Python programming language to number all images in preparation for individual processing. At the same time, create an Excel table and name the header to store the calculation results.

[0076] Step 2.2: First, use the image subtraction command to remove the background of all images, remove obvious impurities and erroneous information caused by lens dirt; then use the opening operation to remove image noise, perform contour detection, and draw the contour.

[0077] Step 3: Adaptive threshold cutting module, specifically:

[0078] Step 3.1: After converting the image to grayscale format, the image is binarized using an adaptive threshold function to highlight the droplets and perform calculations.

[0079] Step 3.2: Traverse the image to identify all droplets, obtain the shape and position characteristics of each droplet, and determine the average particle size (SMD) of the droplets.

[0080] Step 4: Droplet defocus ambiguity elimination module, specifically:

[0081] Step 4.1: Use the half-wavelength χ value of the PSF point spread function to obtain the defocus distance z.

[0082] By measuring different levels of the PTV device, the half-width difference Δr of the droplet image edge can be obtained according to the shape and position characteristics of the droplet. meas , we get the half-wavelength value expression of the PSF point spread function:

[0083]

[0084] Where C0 is the normalized image contrast;

[0085] At the same time, under the premise of considering aberration and PTV device, according to the conclusion drawn from the relationship between aberration and defocus distance, χ est It has nothing to do with the droplet diameter, but only with the defocus distance z, so the following expression can be obtained:

[0086] χ est =f1(z) (2)

[0087] Using formula (1), we can get the χ at different defocus positions: est , and fitting it with the defocus distance z can determine χ est The functional relationship with the defocus distance z, f1() represents χ est The fitting relationship between and the defocus distance z is as follows: Figure 6 The calibrated χ est Since equation (2) contains two solutions, positive and negative, about the defocus distance z, i.e., the same χ est There will be two defocus distances z1 and z2 in the value. This is the ambiguity problem mentioned in the method, and the expression is as follows:

[0088]

[0089] Where f is the focal length of the camera; l is the distance between the droplet and the lens;

[0090] When the droplet is on the side away from the camera, z is positive, otherwise it is negative.

[0091] Step 4.2: Use the maximum gradient of the image to eliminate unreasonable defocus distance z and obtain the actual defocus distance of the droplet:

[0092]

[0093] Among them, lnf Lq is the in-focus parameter, is the average value of the absolute value of the gradient of the droplet at the two end points of the long axis measured in this embodiment, that is, the maximum gradient; d ei is the droplet diameter; I max is the maximum gray level of the measured droplet image; I min is the minimum gray level of the measured droplet image;

[0094] Using formula (4), we can get lnf under different defocus distances z: Lq value, and lnf Lq With z, d ei Fitting, we can get the following formula:

[0095] lnf Lq =f2(z,d ei ) (5)

[0096] Among them, lnf Lq is a Gaussian distribution, such as Figure 6 The calibrated lnf Lq curve;

[0097] At the same defocus distance, we can use formula (1) to get a χ est value, and put it in Figure 6 In the figure, we get points a and b corresponding to the two defocus distances z1 and z2 respectively; by drawing a line parallel to the vertical axis through z1 and z2, we can get lnf L1 with lnf L2 ; Then through formula (4) we can get a lnf L3 Value, compare the lnf L3 with lnf L1 、lnf L2 The z values with larger differences are excluded, while the z values with smaller differences are considered to be the defocus distance z of the final droplet, as shown in the following formula (6).

[0098]

[0099] Step 5: Droplet matching module, including:

[0100] Step 5.1: Use the position and shape features of the images to match the corresponding droplets in the two images.

[0101] Step 5.2: The two droplets that are successfully paired are considered to be the same droplet in the two adjacent images. The movement distance L can be calculated based on the coordinates. The interval t between the two adjacent images is determined by the operating frequency of the high-speed camera. The movement speed of the droplet can be calculated according to the formula V = L / t.

[0102] Step 6: The calculation result visualization and storage module prints and stores the necessary calculation results when each module is processed. In addition, after the final calculation is completed, the image drawing function in the programming language matplotlib library is used to draw graphics, display and store the results.

[0103] This embodiment uses a single camera to shoot and calculates the spray particle size and three-dimensional velocity through a specific algorithm, eliminating the ambiguity of droplet defocus, achieving the purpose of accurately obtaining spray information and providing a basis for objective evaluation of nozzle atomization performance.

[0104] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be employed in conjunction with other described embodiments.

Claims

1. A single-camera PTV device for measuring spray particle size and three-dimensional velocity, characterized by: It includes a high-speed camera (1), a microscope lens (2), a laser beam expander (6), a laser emitter (8) and a processor (12); The laser emitter (8) emits a laser of a set frequency, which is incident on the laser beam expander (6). The laser beam expander (6) generates incoherent light 5 after beam expansion to illuminate the observation area. The microscope lens (2) is directed toward the observation area. The high-speed camera (1) is connected to the microscope lens (2). The microscope lens (2) captures a spray image of the observation area and sends the spray image to the processor (12). The processor (12) is used to store the time sequence of all spray images taken, process the spray images, obtain the shape and position characteristics of all droplets in each spray image, determine the average particle size SMD of the droplets, obtain the defocus distance through the relationship between the half wavelength value of the PSF point spread function and the defocus distance, eliminate unreasonable defocus distances, use the position and shape characteristics of the droplets in each spray image to match the droplets corresponding to two adjacent spray images, obtain the droplet movement speed based on the distance and interval time between the two matched droplets, and complete three-dimensional speed measurement; The processor (12) includes an image import and preprocessing module, an adaptive threshold cutting module, a droplet labeling module, a droplet defocus distance ambiguity elimination module and a feature matching module; The image import and preprocessing module is connected to the adaptive threshold cutting module and the feature matching module. It is used to store all spray images in the chronological order of shooting, preprocess each image: remove the background and detect the contour, and send the preprocessed image to the adaptive threshold cutting module. The adaptive threshold cutting module is connected to the droplet defocus distance ambiguity elimination module to grayscale the pre-processed image and binarize the image through the adaptive threshold function. It traverses all the droplets in the image to obtain the shape and position characteristics of each droplet and determine the average particle size (SMD) of the droplets. Droplet defocus distance ambiguity elimination module is used to use the PSF point spread function half wavelength value χ est Calculate the defocus distance z of the droplet being measured, use the maximum gradient method to eliminate unreasonable defocus distance z, and obtain the true defocus distance z′ of the droplet: Get the half-wavelength value of the PSF point spread function χ est , according to χ est =f1(z) to obtain the defocus distance z; f1() represents χ est and the fitting relationship of the defocus distance z; Where f is the focal length of the camera, l represents the distance between the measured droplet and the lens; According to the maximum gradient of the droplet being measured, the focus parameter lnf of the droplet being measured is obtained. L3 : in, Indicates the maximum gradient of the measured droplet; d ei is the diameter of the droplet being measured; I max is the maximum gray level of the measured droplet; I min is the minimum gray level of the measured droplet; According to lnf Lq =f2(z,d ei ) respectively obtain the focal parameters lnf corresponding to z1 and z2 L1 and the intra-focus parameter lnf L2 ; f2() represents the focus parameter lnf Lq With z, d ei The fitting relationship of According to lnf L1 、lnf L2 and lnf L3 Based on the relationship between the two, we can exclude the unreasonable situation of the defocus distance z and determine the actual defocus distance z′ of the measured droplet to be z1 or z2: The feature matching module is used to use the position and shape features of the droplets in each spray image to match the corresponding droplets in two adjacent spray images based on the two factors of features and close distance, and calculate the movement speed of the droplets by V=L / t, where L represents the movement distance of the same droplet in two adjacent images, and t represents the interval time between the capture of two adjacent images.

2. The single-camera PTV device for measuring spray particle size and three-dimensional velocity according to claim 1, characterized in that: The processor (12) further includes a droplet labeling module; The droplet labeling module is connected to the adaptive threshold cutting module, and the droplet labeling module marks and labels the droplets identified by the adaptive threshold cutting module.

3. The single-camera PTV device for measuring spray particle size and three-dimensional velocity according to claim 2, characterized in that: The processor (12) also includes a calculation result visualization display and storage module for displaying and storing the processing results of the image import and preprocessing module, the adaptive threshold cutting module, the droplet labeling module, the droplet defocus distance ambiguity elimination module and the feature matching module.

4. The single-camera PTV device for measuring spray particle size and three-dimensional velocity according to claim 1, characterized in that: The PTV device further comprises a controller (11) for adjusting the operating frequencies of the laser emitter (8) and the high-speed camera (1).

5. The single-camera PTV device for measuring spray particle size and three-dimensional velocity according to claim 1, characterized in that: The controller (11) adjusts the laser emitter (8) and the high-speed camera (1) to the same operating frequency.

6. The single-camera PTV device for measuring spray particle size and three-dimensional velocity according to claim 1, characterized in that: The PTV device further comprises an optical fiber (7); The laser emitter (8) is connected to the laser beam expander (6) via an optical fiber (7) and is used for directionally transmitting the laser light generated by the laser emitter (8) to the laser beam expander (6).

7. The single-camera PTV device for measuring spray particle size and three-dimensional velocity according to claim 6, characterized in that: The PTV device further comprises a fixing frame (9); The laser beam expander (6) and the laser emitter (8) are simultaneously mounted on the fixing frame (9) and fixed as one body. The light emitting direction of the laser beam expander (6) can be adjusted according to the placement of the fixing frame (9) to ensure that the observation area (4) is illuminated.

8. The single-camera PTV device for measuring spray particle size and three-dimensional velocity according to claim 1, characterized in that: The laser emitter (8) and the high-speed camera (1) are arranged on both sides of the observation area and are arranged opposite to each other.

9. The single-camera PTV device for measuring spray particle size and three-dimensional velocity according to claim 1, characterized in that: The PTV device further comprises a micro-displacement platform (3), on which a nozzle for emitting a spray is mounted, providing angular displacement for the nozzle.

Images