A Visualization Method for Mask Sealing Test and Evaluation

Abstract

The present invention discloses a method for visualizing mask seal testing and evaluation. The mouth and nose of a human head model are connected to a respiratory simulator to simulate human exhalation. On the premise that the respiratory simulation parameters remain unchanged, after collecting exhalation schlieren images, image processing and analysis are carried out to obtain the schlieren area S1 of the side exhalation schlieren image of the human head model without wearing a mask, the schlieren area S2 of the side exhalation schlieren image of the mask worn normally, the schlieren area S2' of the front exhalation schlieren image of the mask worn normally, the schlieren area S3 of the side exhalation schlieren image of the mask worn with a seal, and the schlieren area S3' of the front exhalation schlieren image of the mask worn with a seal. The leakage rate P is calculated using a formula, and the mask seal is rated according to the value of P. The testing and evaluation method of the present invention can visually observe the leakage of air flow inside the mask at different positions and determine the mask seal level according to the grading threshold.

Description

Technical Field

[0001] The present invention belongs to the technical field of mask detection methods, and relates to a method for visual mask seal test and evaluation. Background Art

[0002] GB 19083-2010 "Medical protective masks" stipulates that the fit factor is used to evaluate the sealing degree of masks, that is, during the process of simulating the operation of wearing a mask by a human body, the ratio of the concentration of the external test agent of the mask to the concentration leaking into the interior is quantitatively measured. For the mask seal test, the data results are greatly affected by the body shape, age, and race of the subjects, and the data differences are obvious.

[0003] Under the existing technology, the testing instruments and methods are relatively complex, including qualitative detection and quantitative detection. Qualitative detection requires the tester to wear a mask and be exposed to a test agent aerosol at a certain concentration. When performing various predefined activity exercises, if the tester feels the taste of the test agent, it fails. If the tester does not feel the taste of the test agent, it passes. Finally, the tester needs to deliberately damage the mask seal and still be able to feel the taste of the test agent to eliminate the influence of personal factors on the experiment. Quantitative detection is to install a special device on the mask so that it can detect the concentration of the test agent inside the mask. After the tester wears the mask and makes specified movements, during which the mask cannot be adjusted, the fit factor is obtained by continuously measuring and comparing the ratio of the concentration of the external test agent of the mask to the concentration inside, for evaluating the seal. Such methods cannot determine the specific leakage location of the mask, and the results can only reflect whether the mask seal index is qualified, and it is difficult to guide the adjustment of mask wearing.

[0004] Patent CN 114001876 A discloses a mask seal multi-point monitoring system and method, by setting multiple particulate matter collection points on a head mold, and each particulate matter collection point corresponds to an aerosol concentration detection device to reflect the specific situation of the mask edge seal. Although this method can quantitatively display the seal indexes of multiple parts, the test time is long, the instrument is complex, and the image of the air flow at the mask edge cannot be actually observed.

[0005] Patent CN 212228332 U discloses a detection device for the air tightness of a mask and a breathing valve, by using an air flow sensor to detect the flow rate difference on both sides of the mask and the breathing valve, so as to calculate its air tightness. However, this device does not consider the specific wearing situation, only tests the mask product, and cannot accurately locate the leakage part of the mask.

[0006] Patent CN 212748206 U discloses a tester for quickly detecting the wearing safety of respiratory protection equipment. It uses the principle of infrared thermal imaging to detect the airtightness of masks, and realizes the visualization of the leaked air flow of masks by utilizing the temperature difference between the exhaled gas and the surrounding external temperature. However, the required equipment has high sensitivity, the exhaled air flow of the human body is relatively close to the body temperature, the observation effect of the air flow is not obvious, and the air flow leakage amount cannot be quantitatively characterized.

[0007] Patent CN 113865791 A discloses a method for testing the airtightness of a mask nose clip. By using a camera to photograph the edge contour of the mask at the nose bridge, the gap area at the nose bridge of the mask under different wearing methods is calculated, so as to calculate the airtightness of the mask. This method only focuses on the sealing degree of the mask at the nose bridge, ignores the mask gaps at the chin and both sides of the cheeks, and ignores the influence of the human exhalation flow rate on the mask edge gaps.

[0008] The literature (Influence of wearing masks on exhaled air aerodynamics) uses single-sided schlieren imaging to evaluate the distance of the exhaled gas of 10 respirators worn by real people, and takes the side and front schlieren images of the coughing action with an N95 mask. According to the size of the exhaled air area in different directions defined by the two-dimensional Cartesian coordinate system, the proportion of the exhaled air volume in different directions is calculated. However, the thermal plume of real people has a great influence on the experiment, and there are also certain individual differences when real people exhale.

[0009] The literature (Effectiveness of different types of mask in aerosol dispersionin SARS-CoV-2infection) uses single-sided schlieren imaging to compare the effects of different types of masks in restricting the diffusion of coughing air, and calculates the contaminated area during coughing under different masks. The shortcoming of this study is that it only conducts research from the side, ignores the observation of air flow leakage from the front, only focuses on the coughing state, and does not study normal breathing.

[0010] Therefore, it is of great significance to establish a rapid and convenient visualization method for testing and evaluating the mask airtightness. For this reason, we propose a method for testing the mask airtightness by combining schlieren imaging technology, which can visualize the air flow, not only observe the airtightness of masks at different parts, but also quantitatively characterize the air flow leakage rate, evaluate the airtightness performance of masks, and guide actual wearing. Summary of the Invention

[0011] The purpose of the present invention is to solve the problems existing in the prior art and provide a visualization method for testing and evaluating the mask airtightness.

[0012] To achieve the above object, the technical solution of the present invention is as follows:

[0013] A method for visualizing mask sealability testing and evaluation, in which the mouth and nose of a human head model are connected to a breathing simulator through a hose to simulate human exhalation. On the premise that the breathing simulation parameters remain unchanged, after collecting exhalation schlieren images, image processing and analysis are carried out to obtain the schlieren area S1 of the side exhalation schlieren image of the human head model without wearing a mask, the schlieren area S2 of the side exhalation schlieren image of the mask worn normally, the schlieren area S2' of the front exhalation schlieren image of the mask worn normally, the schlieren area S3 of the side exhalation schlieren image of the mask worn with sealing, and the schlieren area S3' of the front exhalation schlieren image of the mask worn with sealing. The leakage rate P is calculated using a formula, and the mask sealability is rated according to the value of P;

[0014] Among them, the schlieren of the side exhalation schlieren image is the airflow schlieren at the bridge of the nose and the chin, and the schlieren of the front exhalation schlieren image is the airflow schlieren at both cheeks;

[0015] Wearing the mask with sealing means that on the basis of wearing the mask normally, the edge part of the mask in contact with the human head model is sealed with tape;

[0016] The formula is as follows:

[0017]

[0018] S4 = (S2 + S2') - (S3 + S3');

[0019] In the formula, (S2 + S2') is the airflow leakage area between the mask edge and the mask protection layer when wearing the mask normally, (S3 + S3') is the airflow leakage area between the mask protection layers when wearing the mask normally, S4 is the airflow leakage area through the mask edge, that is, the mask leakage area. The larger the mask leakage area, the more serious the airflow leakage degree;

[0020] The corresponding relationship between the P value and the mask sealability level is: when P value ≤ 1%, the mask sealability is A level, and the sealability is excellent; when 1% < P value ≤ 10%, the mask sealability is B level, and the sealability is good; when 10% < P value ≤ 15%, the mask sealability is C level, and the sealability is moderate; when P value > 15%, the mask sealability is D level, and the sealability is poor.

[0021] As a preferred technical solution:

[0022] As described above, in a method for visualizing mask fit testing and evaluation, the gas temperature, gas humidity, and gas flow rate of the breathing simulator can vary, and it can simulate the breathing cycle of the human body under different states. The gas temperature change range of the breathing simulator is 25 - 37 °C, the gas relative humidity change range is 65% - 90%, and the gas flow rate change range is 10 - 30 L / min.

[0023] As described above, in a method for visualizing mask fit testing and evaluation, a schlieren imaging system is used to collect exhaled schlieren images. The schlieren imaging system includes a first guide rail, a second guide rail, a first point light source, a first blade, a first high-speed camera, a second point light source, a second blade, a second high-speed camera, first to sixth lifting brackets, a computer, a first concave mirror, and a second concave mirror;

[0024] The first guide rail is parallel to the left - right direction, the second guide rail is parallel to the front - back direction, and the middle parts of the first guide rail and the second guide rail are connected;

[0025] The first point light source, the first blade, and the first high - speed camera are arranged at intervals above the first guide rail, and are arranged in sequence from the middle part to the right end of the first guide rail. The first point light source, the first blade, and the first high - speed camera are respectively connected to the slider of the first guide rail through the first lifting bracket, the second lifting bracket, and the third lifting bracket;

[0026] The second point light source, the second blade, and the second high - speed camera are arranged at intervals above the second guide rail, and are arranged in sequence from the middle part to the front end of the second guide rail. The second point light source, the second blade, and the second high - speed camera are respectively connected to the slider of the second guide rail through the fourth lifting bracket, the fifth lifting bracket, and the sixth lifting bracket;

[0027] Both the first high - speed camera and the second high - speed camera are connected to the computer;

[0028] The first concave mirror is fixed above the first guide rail and near its left end; the second concave mirror is fixed above the second guide rail and near its rear end;

[0029] The human head model is installed above the middle part of the second guide rail and faces the second point light source.

[0030] As described above, in a method for visualizing mask fit testing and evaluation, the bulb diameters of the first point light source and the second point light source are not greater than 3 mm.

[0031] As described above, in a method for visualizing mask fit testing and evaluation, the diameters of the first concave mirror and the second concave mirror are not less than 200 mm.

[0032] As described above, in a method for visualizing mask seal test and evaluation, the shooting angles and magnification factors of the first high-speed camera and the second high-speed camera are variable, the range of shooting angle variation is 42° - 45°, and the range of magnification factor variation is 1 - 20.

[0033] As described above, in a method for visualizing mask seal test and evaluation, the steps of image processing and analysis are as follows:

[0034] S1. Set the exhalation schlieren image to a unified scale specification, use a straight line tool to draw the diameter of the concave mirror in the exhalation schlieren image, and set the length of this diameter as the actual size of the concave mirror; when the exhalation schlieren image is a side exhalation schlieren image, the concave mirror is the first concave mirror, and when the exhalation schlieren image is a front exhalation schlieren image, the concave mirror is the second concave mirror;

[0035] S2. Sharpen the exhalation schlieren image, and at the same time increase the contrast, brightness, and saturation, so that the diffusion air flow with alternating light and dark and the boundary line of uniform air in the schlieren image are prominent, and the contour line is clearly visible;

[0036] S3. Select the outer contour of the diffusion air flow in the above-mentioned exhalation schlieren image;

[0037] S4. Automatically calculate the area of this region, and convert according to the pixel size and scale specification of the exhalation schlieren image to obtain the actual schlieren area of the exhalation schlieren image.

[0038] Beneficial effects:

[0039] The present invention can directly observe the air leakage situation inside the mask at different positions. At the same time, quantitative calculations of two indicators, the leakage area and the leakage rate, are realized, and mask seal level evaluation is carried out. A non-contact and fast visual mask seal detection and evaluation method is proposed. Compared with the existing test and evaluation methods, no harm is caused to the subjects during the test, there is no risk of cross-infection, and the result error caused by individual differences is avoided. Moreover, the specific leakage positions of the mask can be determined. On the one hand, it can guide medical workers to wear masks, and on the other hand, it can guide mask product optimization for production enterprises. Description of the drawings

[0040] Figure 1 It is a flow schematic diagram of a method for visualizing mask seal test and evaluation of the present invention;

[0041] Figure 2 It is a mask schlieren image in a method for visualizing mask seal test and evaluation of the present invention, where (a) is the sharpened exhalation schlieren image, and (b) is the exhalation schlieren image with the outer contour of the diffusion air flow selected;

[0042] Figure 3Simplified structural schematic diagram of the device used in a visualization method for testing and evaluating the tightness of a mask according to the present invention;

[0043] Figure 4 External overall three-dimensional schematic diagram of the device used in a visualization method for testing and evaluating the tightness of a mask according to the present invention;

[0044] Figure 5 First perspective three-dimensional schematic diagram of the device used in a visualization method for testing and evaluating the tightness of a mask according to the present invention;

[0045] Among them, 1 - first guide rail, 2 - second guide rail, 3 - first point light source, 4 - second point light source, 5 - first concave mirror, 6 - second concave mirror, 7 - first high-speed camera, 8 - second high-speed camera, 9 - first blade, 10 - second blade, 11 - breathing simulator, 12 - human head model, 13 - hose, 14 - first lifting bracket, 15 - second lifting bracket, 16 - third lifting bracket, 17 - fourth lifting bracket, 18 - fifth lifting bracket, 19 - sixth lifting bracket, 20 - computer. Detailed implementation manners

[0046] The present invention will be further described below in conjunction with specific implementation manners. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0047] A visualization method for testing and evaluating the tightness of a mask, the specific steps are as follows:

[0048] (1) As shown in Figure 3 , connect the mouth and nose of the human head model 12 to the breathing simulator 11 through the hose 13 to simulate human exhalation; among them, the gas temperature change range of the breathing simulator 11 is 25 - 37 °C, the gas relative humidity change range is 65% - 90%, and the gas flow rate change range is 10 - 30 L / min;

[0049] (2) On the premise that the breathing simulation parameters remain unchanged, after collecting the exhalation schlieren images and performing image processing and analysis, obtain the schlieren area S1 of the side exhalation schlieren image of the human head model 12 without wearing a mask, the schlieren area S2 of the side exhalation schlieren image of the normally worn mask, the schlieren area S2' of the front exhalation schlieren image of the normally worn mask, the schlieren area S3 of the side exhalation schlieren image of the airtight worn mask, and the schlieren area S3' of the front exhalation schlieren image of the airtight worn mask. Use the formula to calculate the leakage rate P, and classify the tightness of the mask according to the value of P;

[0050] Among them, as Figures 3 to 5 shown, the schlieren imaging system is adopted to collect the exhalation schlieren image. The schlieren imaging system includes a first guide rail 1, a second guide rail 2, a first point light source 3, a first blade 9, a first high-speed camera 7, a second point light source 4, a second blade 10, a second high-speed camera 8, first to sixth lifting brackets, a computer 20, a first concave mirror 5 and a second concave mirror 6; the bulb diameters of the first point light source 3 and the second point light source 4 are not greater than 3 mm; the diameters of the first concave mirror 5 and the second concave mirror 6 are not less than 200 mm;

[0051] The first guide rail 1 is parallel to the left-right direction, the second guide rail 2 is parallel to the front-back direction, and the middle parts of the first guide rail 1 and the second guide rail 2 are connected;

[0052] The first point light source 3, the first blade 9 and the first high-speed camera 7 are arranged at intervals above the first guide rail 1, and are arranged in sequence from the middle part to the right end of the first guide rail 1. The first point light source 3, the first blade 9 and the first high-speed camera 7 are respectively connected to the slider of the first guide rail 1 through the first lifting bracket 14, the second lifting bracket 15 and the third lifting bracket 16;

[0053] The second point light source 4, the second blade 10 and the second high-speed camera 8 are arranged at intervals above the second guide rail 2, and are arranged in sequence from the middle part to the front end of the second guide rail 2. The second point light source 4, the second blade 10 and the second high-speed camera 8 are respectively connected to the slider of the second guide rail 2 through the fourth lifting bracket 17, the fifth lifting bracket 18 and the sixth lifting bracket 19;

[0054] Both the first high-speed camera 7 and the second high-speed camera 8 are connected to the computer 20; the shooting angle variation range of the first high-speed camera 7 and the second high-speed camera 8 is 42° - 45°, and the magnification variation range is 1 - 20;

[0055] The first concave mirror 5 is fixed above the first guide rail 1 and near its left end; the second concave mirror 6 is fixed above the second guide rail 2 and near its rear end;

[0056] The human head mold 12 is installed above the middle part of the second guide rail 2 and faces the second point light source 4;

[0057] Among them, the steps of image processing and analysis are as follows:

[0058] S1. Set the exhalation schlieren image to a unified scale specification, use a straight line tool to draw the diameter of the concave mirror in the exhalation schlieren image, and set the length of this diameter as the actual size of the concave mirror; when the exhalation schlieren image is a side exhalation schlieren image, the concave mirror is the first concave mirror 5, and when the exhalation schlieren image is a front exhalation schlieren image, the concave mirror is the second concave mirror 6;

[0059] S2. Sharpen the exhalation schlieren image, and at the same time increase the contrast, brightness, and saturation, making the boundary between the diffused air flow with alternating light and dark and the uniform air in the schlieren image prominent, and the contour line clearly visible, as Figure 2 (a) shown;

[0060] S3. Select the outer contour of the diffused air flow in the above exhalation schlieren image, as Figure 2 (b) shown;

[0061] S4. Automatically calculate the area of this region, and convert according to the pixel size and scale specification of the exhalation schlieren image to obtain the actual schlieren area of the exhalation schlieren image;

[0062] Among them, the schlieren in the side exhalation schlieren image is the air flow schlieren at the nose bridge and chin, and the schlieren in the front exhalation schlieren image is the air flow schlieren at both cheeks; wearing a mask with a seal means that on the basis of wearing a mask normally, use tape to seal the edge part where the mask contacts the human head mold 12;

[0063] The formula is as follows:

[0064]

[0065] S4 = (S2 + S2′) - (S3 + S3′);

[0066] The corresponding relationship between the P value and the mask fit level is: when the P value ≤ 1%, the mask fit is Class A, with excellent fit; when 1% < P value ≤ 10%, the mask fit is Class B, with good fit; when 10% < P value ≤ 15%, the mask fit is Class C, with moderate fit; when the P value > 15%, the mask fit is Class D, with poor fit.

[0067] Now, a specific case is combined to illustrate the visualization mask fit test and evaluation method of the present invention.

[0068] Example 1

[0069] A visualization mask fit test and evaluation method, as Figures 1 to 5 shown, the specific steps are as follows:

[0070] S1. Select a human head mold 12 that conforms to the head and face dimensions of a male and place it at the centers of the first concave mirror 5 and the second concave mirror 6. Independently build a schlieren imaging system for the front and side angles of the human head mold 12 respectively. Fix the first concave mirror 5 on the connecting rod of the first guide rail 1, and fix the second concave mirror 6 on the connecting rod of the second guide rail 2. The specifications of the first concave mirror 5 and the second concave mirror 6 are: diameter of 203 mm and focal length of 750 mm. Then connect the first lifting bracket 14 with the first point light source 3, and connect the fourth lifting bracket 17 with the second point light source 4. The first lifting bracket 14 is located in the chute of the first guide rail 1, and the fourth lifting bracket 17 is located in the chute of the second guide rail 2. The first point light source 3 and the second point light source 4 use LED light sources, and the diameter of the used light bulbs is 2 mm. Then, by adjusting the first lifting bracket 14, move the first point light source 3 up and down in the vertical direction to the center of the first concave mirror 5, and adjust the fourth lifting bracket 17 to move the second point light source 4 up and down in the vertical direction to the center of the second concave mirror 6. Subsequently, move the first point light source 3 back and forth along the direction of the first guide rail 1 so that the distance between the first concave mirror 5 and the first point light source 3 is at twice the focal length (1.5 m). Move the second point light source 4 back and forth along the direction of the second guide rail 2 so that the distance between the second concave mirror 6 and the second point light source 4 is at twice the focal length (1.5 m). Then, adjust the front and back distance of the first blade 9 along the direction of the first guide rail 1 so that a clear and equal-sized image of the first point light source 3 can be found at the blade part of the first blade 9. Then, adjust the height of the first blade 9 through the second lifting bracket 15 so that the above-mentioned clear and equal-sized image is just cut by half of its area. Then, adjust the front and back distance of the second blade 10 along the direction of the second guide rail 2 so that a clear and equal-sized image of the second point light source 4 can be found at the blade part of the second blade 10. Then, adjust the height of the second blade 10 through the fifth lifting bracket 18 so that the above-mentioned clear and equal-sized image is just cut by half of its area. Then, by adjusting the height of the third lifting 16, the light rays cut by the first blade 9 can be received in the lens of the first high-speed camera 7 connected to its upper surface. Then, by adjusting the height of the sixth lifting bracket 19, the light rays cut by the second blade 10 can be received in the lens of the second high-speed camera 8 connected to its upper surface. The frame rates of the first high-speed camera 7 and the second high-speed camera 8 are 2000 FPS / s. The first high-speed camera 7 focuses on the airflow schlieren at the bridge of the nose and the chin, and the second high-speed camera 8 focuses on the airflow schlieren at both cheeks;

[0071] S2. Set the temperature of the breathing simulator 11 to 37 °C, the relative humidity to 65%, and the air flow rate to 25 L / min, and conduct a simulation of normal human exhalation;

[0072] S3. Adjust the shooting angles of the first high-speed camera 7 and the second high-speed camera 8 to be between 42° and 45°, and the magnification to 3 times. Use the first high-speed camera 7 to collect the side schlieren images of the head mold without wearing a mask and transmit them to the computer 20;

[0073] S4. Properly wear a disposable mask of a certain brand on the human head mold 12, pinch the nose clip of the mask, and conduct an exhalation simulation under the same breathing simulation parameters. The first high-speed camera 7 and the second high-speed camera 8 respectively collect side and front schlieren images and transmit them to the computer 20;

[0074] S5. Use tape to seal the edge part of the disposable mask in contact with the human head mold 12, conduct an exhalation simulation under the same breathing simulation parameters. The first high-speed camera 7 and the second high-speed camera 8 respectively collect side and front schlieren images and transmit them to the computer 20;

[0075] S6. The computer 20 performs image processing and analysis; the specific process is as follows: Import the exhalation schlieren picture without wearing a mask into the image processing software; Set the scale, the diameter of the concave mirror field of view is 203, unit mm; Sharpen the image to increase the brightness and contrast, making the boundary between the interlaced diffusion airflow and the uniform air in the image significant and the contour line clearly visible; Select the outer contour of the diffusion airflow of the above exhalation schlieren; Automatically calculate the area of this area, and convert the actual schlieren area of the exhalation schlieren image according to the pixel size and scale specification of the exhalation schlieren image, and obtain the schlieren area S1 of the side exhalation image without wearing a mask = 111.14 cm 2 ; Repeating the above operations can successively obtain the schlieren areas S2 = 36.43 cm of the side and front exhalation images when wearing the disposable mask correctly 2 、S2' = 28.56 cm 2 ; After the mask edge is sealed, the schlieren areas S3 = 14.09 cm of the side and front exhalation images of the mask 2 、S3' = 8.45 cm 2 ;

[0076] S7. Calculate the sum of S2 and S2', which is the airflow leakage area between the mask edge and the mask protection layer when wearing the mask correctly; Calculate the sum of S3 and S3', which is the leakage airflow area between the mask protection layers when wearing the mask correctly; Calculate the difference between the two, which is the airflow area leaking through the mask edge, denoted as the mask leakage area S4, that is:

[0077] S4 = (S2 + S2′) - (S3 + S3′) = 42.45 cm 2 ;

[0078] S8. Calculate the ratio of the disposable mask edge leakage area S4 to the total exhalation area S1 when not wearing a mask, denoted as the leakage rate P, that is:

[0079]

[0080] S9. Rate and classify the airtightness of disposable masks according to the P value. The specific grades are shown in the following table:

[0081] Air tightness level Grade A Grade B Grade C Grade D Leakage rate P / % ≤1 ≤10 ≤15 ＞15 Degree of fit Excellent fit Good fit Moderate fit Poor fit

[0082] S10. For male wearers, the airtightness level of this disposable mask is D under normal human exhalation, and the airtightness is poor.

[0083] In addition, by recruiting volunteers (male, 33 years old, 175 cm tall, 73 kg in weight), using the test and evaluation method in GB 19083-2010 "Technical Requirements for Medical Protective Masks", the fit factor during normal breathing was tested. The result was 2.752, that is, the ratio of the external particulate matter concentration to the internal concentration of the mask was 2.752. The leakage rate P measured by this method was 38.20%, and the converted fit factor was 2.618. The results were relatively consistent.

[0084] Example 2

[0085] A method for visualizing the test and evaluation of mask airtightness is as Figures 1 to 5 shown. The specific steps are as follows:

[0086] S1. Select a human head mold 12 that matches the size of a woman's head and face, and place it at the centers of the first concave mirror 5 and the second concave mirror 6. Independently build a schlieren imaging system for the front and side angles of the human head mold 12. Fix the first concave mirror 5 on the connecting rod of the first guide rail 1, and fix the second concave mirror 6 on the connecting rod of the second guide rail 2. The specifications of the first concave mirror 5 and the second concave mirror 6 are: diameter of 500 mm and focal length of 550 mm. Connect the first lifting bracket 14 to the first point light source 3, and connect the fourth lifting bracket 17 to the second point light source 4. The first lifting bracket 14 is located in the chute of the first guide rail 1, and the fourth lifting bracket 17 is located in the chute of the second guide rail 2. The first point light source 3 and the second point light source 4 use LED light sources, and the diameter of the used light bulbs should be 2 mm. Then, adjust the first lifting bracket 14 to move the first point light source 3 up and down vertically to the center of the first concave mirror 5, and adjust the fourth lifting bracket 17 to move the second point light source 4 up and down vertically to the center of the second concave mirror 6. Subsequently, move the first point light source 3 back and forth along the direction of the first guide rail 1 so that the distance between the first concave mirror 5 and the first point light source 3 is at twice the focal length (1.1 m). Move the second point light source 4 back and forth along the direction of the second guide rail 2 so that the distance between the second concave mirror 6 and the second point light source 4 is at twice the focal length (1.1 m). Then, adjust the front and back distance of the first blade 9 along the direction of the first guide rail 1 so that a clear and equal-sized image of the first point light source 3 can be found at the blade part of the first blade 9. Then, adjust the height of the first blade 9 through the second lifting bracket 15 so that the above-mentioned clear and equal-sized image is just cut by half of its area. Then, adjust the front and back distance of the second blade 10 along the direction of the second guide rail 2 so that a clear and equal-sized image of the second point light source 4 can be found at the blade part of the second blade 10. Then, adjust the height of the second blade 10 through the fifth lifting bracket 18 so that the above-mentioned clear and equal-sized image is just cut by half of its area. Then, adjust the height of the third lift 16 so that the light rays cut by the first blade 9 can be received by the lens of the first high-speed camera 7 connected to its upper surface. Then, adjust the height of the sixth lifting bracket 19 so that the light rays cut by the second blade 10 can be received by the lens of the second high-speed camera 8 connected to its upper surface. The frame rates of the first high-speed camera 7 and the second high-speed camera 8 are 2000 FPS / s. The first high-speed camera 7 focuses on the airflow schlieren at the bridge of the nose and the chin, and the second high-speed camera 8 focuses on the airflow schlieren at both cheeks;

[0087] S2. Set the temperature of the breathing simulator 11 to 37 °C, the relative humidity to 75%, and the air flow rate to 30 L / min to simulate the exhalation condition when a human speaks;

[0088] S3. Adjust the shooting angles of the first high-speed camera 7 and the second high-speed camera 8 to be between 42° and 45°, and the magnification to 3 times. Use the first high-speed camera 7 to collect the side schlieren images of the head mold without wearing a mask and transmit them to the computer 20;

[0089] S4. Correctly wear a certain brand of N95 mask on the human head mold 12, pinch the nose clip of the mask, and conduct an exhalation simulation under the same breathing simulation parameters. The first high-speed camera 7 and the second high-speed camera 8 respectively collect the side and front schlieren images and transmit them to the computer 20;

[0090] S5. Seal the edge part where the N95 mask contacts the human head mold 12 with tape, conduct an exhalation simulation under the same breathing simulation parameters. The first high-speed camera 7 and the second high-speed camera 8 respectively collect the side and front schlieren images and transmit them to the computer 20;

[0091] S6. The computer 20 performs image processing and analysis. The specific process is as follows: Import the exhalation schlieren picture without wearing a mask into the image processing software; Set the scale, the diameter of the concave mirror field of view is 500, unit mm; Sharpen the image to increase the brightness and contrast, making the boundary between the interlaced diffusion airflow and the uniform air in the image significant and the contour line clearly visible; Select the outer contour of the diffusion airflow of the above-mentioned exhalation schlieren; Automatically calculate the area of this area, and convert the actual schlieren area of the exhalation schlieren image according to the pixel size and scale specification of the exhalation schlieren image, and obtain the schlieren area S1 of the side exhalation image without wearing a mask = 123.25 cm 2 ; Repeat the above operations to successively obtain the schlieren areas S2 = 18.67 cm of the side and front exhalation images when wearing the N95 mask correctly 2 、S2' = 11.94 cm 2 ; After the mask edge is sealed, the schlieren areas S3 = 11.45 cm of the side and front exhalation images of the mask 2 、S3' = 7.58 cm 2 ; The computer performs image processing and analysis, and calculates the schlieren areas S3 and S3' of the side and front exhalation images of the mask after the mask edge is sealed;

[0092] S7. Calculate the sum of S2 and S2', which is the airflow leakage area between the mask edge and the mask protection layer when wearing the mask correctly; Calculate the sum of S3 and S3', which is the leakage airflow area between the mask protection layers when wearing the mask correctly; Calculate the difference between the two, which is the airflow area leaked through the mask edge, denoted as the mask leakage area S4, that is:

[0093] S4 = (S2 + S2′) - (S3 + S3′) = 11.58 cm 2 ;

[0094] S8. Calculate the ratio of the N95 mask edge leakage area S4 to the total exhalation area S1 when not wearing a mask, denoted as the leakage rate P, that is:

[0095]

[0096] S9. Rate and classify the airtightness of disposable masks according to the P value. The specific grades are shown in the following table:

[0097]

[0098]

[0099] S10. For female wearers, the airtightness level of this N95 mask is grade B and the airtightness is good when the human body is participating in activities.

[0100] In addition, by recruiting volunteers (aged 29, height 165 cm, weight 61 kg), using the test and evaluation methods in GB 19083-2010 "Technical Requirements for Medical Protective Masks", the fit factor during the speaking action was tested separately, and the result was 10.387, that is, the ratio of the external particulate matter concentration to the internal concentration of the mask was 10.387. The leakage rate P measured by this method was 9.40%, and the converted fit factor was 10.638, and the results were relatively consistent.

Claims

1. A method for visualizing mask seal testing and evaluation, characterized in that, Connect the mouth and nose of the human head model to the breathing simulator to conduct human exhalation simulation. On the premise that the breathing simulation parameters remain unchanged, after collecting the exhalation schlieren images, perform image processing and analysis to obtain the schlieren area S1 of the side exhalation schlieren image of the human head model without wearing a mask, the schlieren area S2 of the side exhalation schlieren image of wearing a mask normally, the schlieren area S2' of the front exhalation schlieren image of wearing a mask normally, the schlieren area S3 of the side exhalation schlieren image of wearing a mask sealed, and the schlieren area S3' of the front exhalation schlieren image of wearing a mask sealed. Use the formula to calculate the leakage rate P, and classify the mask sealability according to the size of the P value; Among them, the schlieren of the side exhalation schlieren image is the airflow schlieren at the bridge of the nose and the chin, and the schlieren of the front exhalation schlieren image is the airflow schlieren at both cheeks; Sealed wearing of the mask means that on the basis of normal wearing of the mask, use tape to seal the edge part where the mask contacts the human head model; The formula is as follows: S4 = (S2 + S2′) - (S3 + S3′); The corresponding relationship between the P value and the mask sealability level is: when the P value ≤ 1%, the mask sealability is Class A, and the sealability is excellent; 1% < P value ≤ 10%, the mask sealability is Class B, and the sealability is good; 10% < P value ≤ 15%, the mask sealability is Class C, and the sealability is moderate; P value > 15%, the mask sealability is Class D, and the sealability is poor.

2. The visualization mask seal test and evaluation method according to claim 1, wherein The gas temperature change range of the breathing simulator is 25 - 37 °C, the gas relative humidity change range is 65% - 90%, and the gas flow rate change range is 10 - 30 L / min.

3. A method for visualizing mask seal test and evaluation according to claim 1, characterized in that, The exhalation schlieren image is collected by a schlieren imaging system. The schlieren imaging system includes a first guide rail (1), a second guide rail (2), a first point light source (3), a first blade (9), a first high-speed camera (7), a second point light source (4), a second blade (10), a second high-speed camera (8), the first to sixth lifting brackets, a computer (20), a first concave mirror (5) and a second concave mirror (6); The first guide rail (1) is parallel to the left - right direction, the second guide rail (2) is parallel to the front - back direction, and the middle parts of the first guide rail (1) and the second guide rail (2) are connected; The first point light source (3), the first blade (9), and the first high-speed camera (7) are arranged at intervals above the first guide rail (1), and are arranged in sequence from the middle of the first guide rail (1) to the right end. The first point light source (3), the first blade (9), and the first high-speed camera (7) are respectively connected to the slider of the first guide rail (1) through the first lifting bracket (14), the second lifting bracket (15), and the third lifting bracket (16); The second point light source (4), the second blade (10), and the second high-speed camera (8) are arranged at intervals above the second guide rail (2), and are arranged in sequence from the middle of the second guide rail (2) to the front end. The second point light source (4), the second blade (10), and the second high-speed camera (8) are respectively connected to the slider of the second guide rail (2) through the fourth lifting bracket (17), the fifth lifting bracket (18), and the sixth lifting bracket (19); Both the first high-speed camera (7) and the second high-speed camera (8) are connected to the computer (20); The first concave mirror (5) is fixed above the first guide rail (1) and near its left end; the second concave mirror (6) is fixed above the second guide rail (2) and near its rear end; The human head phantom is installed above the middle of the second guide rail (2) and faces the second point light source (4).

4. A method for visualizing mask seal test and evaluation according to claim 3, characterized in that The bulb diameters of the first point light source (3) and the second point light source (4) are not greater than 3 mm.

5. A method for visualizing mask seal test and evaluation according to claim 3, characterized in that, The diameters of the first concave mirror (5) and the second concave mirror (6) are not less than 200 mm.

6. The visualization mask seal test and evaluation method according to claim 3, characterized in that, The shooting angle change ranges of the first high-speed camera (7) and the second high-speed camera (8) are 42° to 45°, and the magnification change ranges are 1 to 20.

7. A method for visualizing mask seal test and evaluation according to claim 3, characterized in that, The steps of image processing and analysis are as follows: S1. Set the exhalation schlieren image to a unified scale specification. Use the straight line tool to draw the diameter of the concave mirror in the exhalation schlieren image, and set the length of this diameter as the actual size of the concave mirror; when the exhalation schlieren image is a side exhalation schlieren image, the concave mirror is the first concave mirror (5), and when the exhalation schlieren image is a front exhalation schlieren image, the concave mirror is the second concave mirror (6); S2. Sharpen the exhalation schlieren image, and at the same time increase the contrast, brightness, and saturation to make the boundary between the diffused air flow with alternating light and dark and the uniform air in the schlieren image prominent and the contour line clearly visible; S3. Select the outer contour of the diffused air flow in the above-mentioned exhalation schlieren image; S4. Automatically calculate the area of this area, and convert the actual schlieren area of the exhalation schlieren image according to the pixel size and scale specification of the exhalation schlieren image.

Images