CN112986105A - Liquid drop counting and speed measuring method based on machine vision - Google Patents
Liquid drop counting and speed measuring method based on machine vision Download PDFInfo
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- 238000003384 imaging method Methods 0.000 claims abstract description 13
- 238000012545 processing Methods 0.000 claims abstract description 12
- 238000004448 titration Methods 0.000 claims abstract description 7
- 238000005516 engineering process Methods 0.000 claims description 6
- 238000004458 analytical method Methods 0.000 claims description 5
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- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/10—Investigating individual particles
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Abstract
The invention discloses a liquid drop counting and speed measuring method based on machine vision, which comprises the steps that firstly, a camera is aligned to a clear liquid drop imaging area and is kept fixed, continuous images for liquid drop titration are collected, a continuous signal F (t) with a sampling frequency band F is sampled, the time interval delta t between adjacent sampling points is less than or equal to 1/(2F), and the imaging frame rate used by the camera is at least twice of the dropping speed of liquid drops to be measured; then, selecting a specific area for droplet imaging; setting a threshold value to carry out binarization processing on the image, wherein the pixel point value larger than the threshold value is 1, and the pixel point value smaller than the threshold value is 0; secondly, counting the number of pixel point values in the ROI area as 1, wherein the pixel point values are used as the basis for judging liquid drops, and each frame can obtain one datum; and drawing a waveform diagram; then, the number of the liquid drops and the dropping speed are calculated, and finally closed-loop control is realized. The scheme can be used for dynamically monitoring a plurality of liquid drops in real time, has high accuracy and improves the efficiency and the automation degree of the automatic liquid treatment instrument.
Description
Technical Field
The invention belongs to the technical field of solvent constant volume, and particularly relates to a liquid drop counting and speed measuring method based on machine vision.
Background
The traditional method for measuring the flow rate of the liquid drops generally adopts (1) a mechanical weighing type (2) an infrared photoelectric type (3) a capacitance metering type. In an automatic liquid treatment instrument, the instrument needs to be used for replacing manual operation to realize processes of liquid separation, liquid adding or titration and the like, the requirements on the volume and the flow rate of liquid are high, and parameters such as the number of drops of the liquid, the speed of the drop generation and the like need to be accurately measured. The traditional liquid drop flow velocity measuring method is difficult to be applied to an automatic liquid processing instrument, and particularly, the common liquid drop flow velocity measuring method cannot be realized for simultaneously monitoring a plurality of liquid drops. At present, the technology for measuring the volume of the fast volatile solvent in the industry is not mature enough, and most of the technologies rely on complex measuring devices, so the existing measuring method still remains to be broken through.
Disclosure of Invention
The invention aims to provide a liquid drop counting and speed measuring method based on machine vision, which can be used for dynamically monitoring a plurality of liquid drops in real time, has high accuracy and improves the efficiency and the automation degree of an automatic liquid processing instrument.
In order to achieve the above purpose, the solution of the invention is: a machine vision based drop counting and velocity measurement method comprising the steps of:
s1 camera model selection and mode setting: the position of a camera is relatively static with a liquid drop port, the liquid drop is taken as a moving target, the camera is aligned to a clear imaging area of the liquid drop and is kept fixed, continuous images for titration of the liquid drop are collected, continuous signals F (t) with a sampling frequency band F are expressed by discrete sampling values F (t1), F (t1 +/-delta t), F (t1 +/-2 delta t), time intervals delta t between adjacent sampling points are less than or equal to 1/(2F), and the imaging frame rate used by the camera is at least twice of the dripping speed of the liquid drop to be measured;
s2 setting ROI: selecting a specific area for droplet imaging;
s3 binarization of image: setting a threshold value to carry out binarization processing on the image, wherein the pixel point value larger than the threshold value is 1, and the pixel point value smaller than the threshold value is 0;
s4 obtaining pixel points: after the ROI is set, the total pixel number in the ROI is determined, the total pixel number is fixed, the number of pixel point values in the ROI is counted to be 1, the pixel point values are used as the basis for judging liquid drops, and each frame can obtain one piece of data;
and S5 waveform drawing: performing oscillogram drawing on the data acquired in the step S4;
s6 calculating the number of droplets and the droplet velocity: setting a threshold value through a time domain analysis technology of digital signal processing, extracting the positions of the troughs or the crests in each periodic waveform, extracting the positions of the crests or the troughs, and setting ViRepresenting the position of the ith peak or trough, wherein the number of the peaks/troughs is the number n of the liquid drops; calculating the time difference between adjacent droplets, and setting f to represent the frame rate of image acquisition, so that the time difference T between adjacent droplets is (V)i+1-Vi) The drop velocity of the liquid drop is 1/T;
s7 closed-loop control: and repeating the step S2 in the next frame, and outputting a control signal according to the quantity of the liquid drops and the drop speed to realize the closed-loop control of the liquid drops.
Preferably, the camera frame rate is 25 fps.
After the scheme is adopted, compared with the prior art, the invention has the beneficial effects that:
the invention realizes the control of the processes of liquid adding, liquid separating, titration and the like based on a machine vision mode, compared with the traditional mechanical weighing type, infrared photoelectric type and capacitance type, the invention adopts completely different technical principles to realize the real-time monitoring of the liquid drop state, can realize the real-time dynamic monitoring of a plurality of liquid drops simultaneously, introduces a digital signal analysis and processing technology, combines the traditional image processing mode with a digital signal time domain analysis method to realize the accurate measurement of the quantity and the speed of the liquid drops, improves the efficiency and the automation degree of an automatic liquid processing instrument, greatly reduces the operation error and improves the efficiency compared with a manual operation mode, further, the invention can be used for the calibration and the calibration of the liquid titration process, can form negative feedback to input the quantity of the liquid drops and the liquid drop generation speed into a control system, the closed-loop control is formed, the accurate control of liquid drops is finally realized, the application requirements of various automatic liquid treatment instruments are met, the difficulty in structural realization is reduced, and as long as the frame rate of a camera/camera is high enough and the imaging is clear enough, the monitoring of the liquid drop states of a plurality of liquid drop openings can be completed by using one camera/camera.
Drawings
FIG. 1 is a block flow diagram of an embodiment of the present invention;
FIG. 2 is a distribution diagram of image binarization in the ROI area according to an embodiment of the present invention;
FIG. 3 shows an image before droplet formation has not begun; wherein, fig. 3-a shows an original image taken by a camera, and fig. 3-b shows a diagram of selecting a ROI area in fig. 3-a;
FIG. 4 shows an image after droplet formation; wherein, FIG. 4-a shows the original image taken by the camera, and FIG. 4-b shows the selection of the ROI area map in FIG. 4-a;
FIG. 5 shows an image of a drop about to exit a drop port; wherein, FIG. 5-a shows the original image taken by the camera, and FIG. 5-b shows the selection of the ROI area map in FIG. 5-a;
FIG. 6 shows a waveform of a liquid after treatment to produce droplets at a rate of 2 mL/min;
FIG. 7 shows a waveform of a liquid after treatment to produce droplets at a rate of 3 mL/min.
Detailed Description
The invention is described in detail below with reference to the accompanying drawings and specific embodiments. The present embodiment is described with respect to monitoring the generation of droplets by one of the droplet orifices.
The present invention provides a method for measuring drop count and velocity based on machine vision, please refer to fig. 1, fig. 1 is a complete flow chart of the system, including the following steps:
s1 camera model selection and mode setting: the position of the camera is relatively static with the liquid drop opening, the liquid drop is considered as a moving object, the camera is aligned to a liquid drop clearly imaging area and is kept fixed, continuous images for liquid drop titration are acquired, and according to the Nyquist sampling theorem: a continuous signal F (t) with a sampling frequency band F is represented by discrete sampling values F (t1), F (t1 ± Δ t), F (t1 ± 2 Δ t), and so long as the time interval Δ t between adjacent sampling points is less than or equal to 1/(2F), the original signal F (t) can be completely restored according to each sampling value. In the invention, each frame of the camera is a signal to be processed, and in order to realize accurate measurement of the number of the liquid drops, the imaging frame rate of the camera is at least twice of the dropping speed of the liquid drops to be measured. The drop velocity refers to the number of drops per unit time. The frame rate of the camera used in this embodiment is 25fps, the maximum drop velocity that can be measured is 12.5 drops/second, and if a higher drop velocity needs to be measured, a camera with a higher frame rate is used according to the sampling theorem. In the real-time example, the adopted liquid is transparent colorless liquid drops, so that the liquid drops can be imaged clearly, the dropping condition of the liquid drops is convenient to distinguish, the irradiation direction of a light source is adjusted, and the process of dropping the liquid drops can be shot clearly by a camera.
S2 sets ROI (region of interest): selecting a specific area for droplet imaging; as shown in fig. 3, 4, and 5, the photographs taken at the moment when the droplet is not generated and the droplet is generated until the droplet is separated from the droplet outlet are shown. The liquid drop is a gradually enlarging process from generation to dropping, after the liquid drop is generated, the liquid drop is gradually enlarged, the size of the liquid drop is related to parameters such as liquid capillarity, density, pipe orifice diameter and the like, after a critical condition is reached, the liquid drop is separated from the pipe orifice of the burette and drops from the pipe orifice, and whether the liquid drop in the image is the same liquid drop or not can be judged according to the liquid drop changing process.
S3 binarization of image: as shown in fig. 2, the number of each pixel value is set to be a threshold value, and the image is subjected to binarization processing, wherein the pixel value larger than the threshold value is 1, and the pixel value smaller than the threshold value is 0; the right images in each of fig. 3, 4, and 5 are images of the ROI region after the binarization process.
S4 obtaining pixel points: after the ROI is set, the total pixel number in the ROI area is determined, the total pixel number is fixed, the number of pixel point values in the ROI area which are 1 is counted and used as the basis of liquid drop judgment, and one piece of data can be obtained in each frame.
And S5 waveform drawing: as shown in fig. 6 and 7, the data acquired at S4 is plotted as a waveform diagram in which a periodically changing curve contains information on the number of droplets and the droplet velocity.
S6 calculating the number of droplets and the droplet velocity: according to the quantity information and the dropping speed information of the liquid drops S5, setting a threshold value through a time domain analysis technology of digital signal processing, extracting the positions of peaks or troughs in each periodic waveform, taking troughs as an example, extracting the positions of the troughs, and setting ViRepresenting the position of the ith wave trough, wherein the number of the wave troughs is the number n of the liquid drops; calculating the time difference between adjacent droplets, and setting f to represent the frame rate of image acquisition, so that the time difference T between adjacent droplets is (V)i+1-Vi) The drop velocity of the liquid drop is 1/T;
s7 closed-loop control: and repeating the step S2 in the next frame, and outputting a control signal according to the quantity of the liquid drops and the drop speed to realize the closed-loop control of the liquid drops.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the design of the present invention, and all equivalent changes made in the design key point of the present invention fall within the protection scope of the present invention.
Claims (2)
1. A method of drop counting and velocity measurement based on machine vision, comprising the steps of:
s1 camera model selection and mode setting: the position of a camera is relatively static with a liquid drop port, the liquid drop is taken as a moving target, the camera is aligned to a clear imaging area of the liquid drop and is kept fixed, continuous images for titration of the liquid drop are collected, continuous signals F (t) with a sampling frequency band F are expressed by discrete sampling values F (t1), F (t1 +/-delta t), F (t1 +/-2 delta t), time intervals delta t between adjacent sampling points are less than or equal to 1/(2F), and the imaging frame rate used by the camera is at least twice of the dripping speed of the liquid drop to be measured;
s2 setting ROI: selecting a specific area for droplet imaging;
s3 binarization of image: setting a threshold value to carry out binarization processing on the image, wherein the pixel point value larger than the threshold value is 1, and the pixel point value smaller than the threshold value is 0;
s4 obtaining pixel points: after the ROI is set, the total pixel number in the ROI is determined, the total pixel number is fixed, the number of pixel point values in the ROI is counted to be 1, the pixel point values are used as the basis for judging liquid drops, and each frame can obtain one piece of data;
and S5 waveform drawing: performing oscillogram drawing on the data acquired in the step S4;
s6 calculating the number of droplets and the droplet velocity: setting a threshold value through a time domain analysis technology of digital signal processing, extracting the positions of the troughs or the crests in each periodic waveform, extracting the positions of the crests or the troughs, and setting ViRepresenting the position of the ith peak or trough, wherein the number of the peaks or troughs is the number n of the liquid drops; calculating the time difference between adjacent droplets, and setting f to represent the frame rate of image acquisition, so that the time difference T between adjacent droplets is (V)i+1-Vi) The drop velocity of the liquid drop is 1/T;
s7 closed-loop control: and repeating the step S2 in the next frame, and outputting a control signal according to the quantity of the liquid drops and the drop speed to realize the closed-loop control of the liquid drops.
2. A machine vision based drop counting and velocity measurement method as claimed in claim 1, wherein: the camera frame rate is 25 fps.
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Application publication date: 20210618 |