Method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo

Abstract

The invention discloses a measurement method for in-vivo measurement of deformation and pressure distribution characteristics of an elastic fabric, and relates to the technical field of in-vivo pressure measurement of the elastic fabric, and the method comprises the following steps: S1, building a three-dimensional image correlation method measurement system, and respectively obtaining an image of a non-pressure state and an image of an in-vivo wearing state of the elastic fabric; s2, calculating the global deformation of the elastic fabric, and constructing the three-dimensional geometrical morphology of the human body surface to obtain the global curvature; and S3, carrying out global pressure measurement on the elastic fabric. According to the measurement method for in-vivo measurement of the deformation and pressure distribution characteristics of the elastic fabric, global accurate pressure measurement is realized when a human body part wears the elastic fabric, and the measurement efficiency and the spatial resolution of a measurement result are remarkably improved; and a reliable data support and a decision optimization direction are provided for a development scheme of the medical health-care elastic fabric.

Description

Technical Field

[0001] The invention relates to the technical field of elastic fabric on-body pressure measurement, and in particular to a method for measuring deformation and pressure distribution characteristics of elastic fabric on-body. Background Art

[0002] With the development of economic level and the improvement of national health awareness, medical and health care elastic fabrics are playing an increasingly important role in people's lives. Effective measurement of the medical and health care effects of elastic fabrics is of great significance to safeguarding national health. On the one hand, medical elastic fabrics are the most widely used means of treating and preventing lower extremity venous diseases. On the other hand, they also have excellent effects on beauty and body shaping and improving athletes' sports performance. The decisive factors affecting the medical and health care effects of elastic fabrics are the size of the pressure value applied at a specific position and the distribution of the pressure gradient. Due to differences in region, living habits, race, etc., there are large individual differences in the morphology of parts in the population. The lack of compliance of existing elastic fabric users is mainly due to inaccurate pressure measurement. Excessive pressure leads to insufficient comfort for users, and uneven skin pressure along the cross-section of human body parts, such as excessive or peak local pressure, has caused side effects, while too low pressure at the part leads to weak medical and health care effects. This puts forward an urgent need for refined pressure measurement of elastic fabrics.

[0003] The pressure measurement of elastic fabrics is complex. The diversity of local morphology of human body parts, the difficulty in accurately measuring the geometric parameters of the human body surface, and the insufficient spatial resolution of the pressure measurement results make accurate global pressure measurement a great challenge. The existing technology has the following problems:

[0004] 1) There are great individual differences in the morphology of human body parts. The protrusions of bones and the irregularities of muscles make the pressure distribution of elastic fabrics extremely complex.

[0005] 2) It is difficult to obtain the geometric parameters of the surface of human body parts, such as circumference and curvature. Existing methods such as 3D scanning equipment are expensive and require high technical level of personnel.

[0006] 3) The deformation of elastic fabric after wearing has a decisive influence on the final applied pressure. Existing methods all assume that the deformation distribution is uniform on the cross-section of the human body, and lack effective deformation measurement methods.

[0007] 4) The fitting range selection of human body part curvature data mostly relies on manual selection of the range, lacking effective error measurement and automated calculation process.

[0008] 5) The existing elastic fabric pressure measurement methods have insufficient spatial resolution, and most of them only involve scattered data from limited points, making it impossible to obtain global pressure measurement results.

[0009] As a new type of vision-based measurement method, the three-dimensional image correlation method has the advantages of less interference with the measurement target, being able to measure the deformation information of the elastic body, and having high measurement spatial resolution. It is an ideal tool for measuring the deformation of elastic fabrics.

[0010] In summary, due to the high individual differences in the morphology of human body parts, the insufficient spatial resolution and accuracy of obtaining the geometric parameters of the human body surface, and the difficulty in measuring the deformation of elastic fabrics, there are still great challenges in the measurement of the global pressure of elastic fabrics used in medical care. The current pressure measurement methods for elastic fabrics have not met the existing measurement needs, and cannot effectively improve the compliance of users and effectively guarantee the expected effects of elastic fabrics. Summary of the invention

[0011] The purpose of the present invention is to provide a method for measuring the deformation and pressure distribution characteristics of elastic fabrics on the body, so as to solve the problems raised in the above-mentioned background technology, and to efficiently, comprehensively and accurately acquire the geometric data of the human body surface, collect the deformation data of the elastic fabric and measure the global pressure, so as to provide accurate and reliable results for users and healthcare practitioners, and provide solid data support and decision-making guidance for optimizing and customizing personalized pressure application schemes.

[0012] To achieve the above object, the present invention provides a method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo, comprising the following steps:

[0013] Step S1, building a three-dimensional image correlation method measurement system, and obtaining images of the elastic fabric in a stress-free state and an image of the elastic fabric in a wearing state;

[0014] Step S2, calculating the global deformation of the elastic fabric, and constructing the three-dimensional geometric morphology of the human body surface to obtain the global curvature;

[0015] Step S3: measuring the global pressure of the elastic fabric.

[0016] Preferably, the specific steps of step S1 are as follows:

[0017] Step S11, select two industrial cameras with fixed-focus lenses and two diffuse reflection fill lights, fix the two industrial cameras on an optical platform according to a predetermined target distance, inter-camera distance and solid angle, turn on the diffuse reflection fill lights, and perform a calibration procedure;

[0018] Step S12, making washable speckles on the surface of the elastic fabric by spray painting, and putting the elastic fabric on the human body-shaped tube to obtain an initial image of the elastic fabric in a pressure-free state;

[0019] Step S13, putting the elastic fabric with the washable spot patch in step S12 on a part of the human body to obtain a deformation image of the elastic fabric in the wearing state.

[0020] Preferably, the specific steps of step S2 are as follows:

[0021] Step S21, setting the sub-area size and step length of the three-dimensional image correlation method measurement in the calculation, and starting to calculate the global deformation value of the elastic fabric in the wearing state and the three-dimensional coordinates of the surface of the wearing part of the human body;

[0022] Step S22: Based on the three-dimensional morphology of the human body surface, a spherical area with a continuously iterative radius is used to perform three-dimensional surface fitting, and the calculation results of the fitting curvature radius before and after the iteration are compared. When the result error meets the error requirement, the iteration is terminated to obtain the final curvature calculation result.

[0023] Preferably, the fitting function of the three-dimensional surface fitting in step S22 is as follows:

[0025] z=f(x,y)=a 0 +a 1 x+a 2 y+a 3 x 2 +a 4 y 2 ;

[0026] Among them, a0 represents the constant term coefficient, a1 represents the linear term coefficient of x, a2 represents the linear term coefficient of y, a3 represents the quadratic term coefficient of x, a4 represents the quadratic term coefficient of y, x represents the x-axis coordinate of the data point, and y represents the y-axis coordinate of the data point.

[0027] Preferably, step S3 uses Laplace's law in combination with mechanical parameters of the elastic fabric, global deformation of the elastic fabric and curvature of a human body part to perform global pressure measurement.

[0028] Preferably, in step S3, the calculation formula for obtaining the pressure measurement value is as follows:

[0029]

[0030] Wherein, t is the thickness of the elastic fabric, E is the elastic modulus of the elastic fabric, ε is the deformation of the elastic fabric surface, and R is the radius of curvature.

[0031] Therefore, the present invention adopts the above-mentioned method for measuring the deformation and pressure distribution characteristics of elastic fabrics on the body to achieve global accurate pressure measurement when the human body wears elastic fabrics, which significantly improves the measurement efficiency and the spatial resolution of the measurement results, and provides reliable data support and decision-making optimization direction for the development of medical and health care elastic fabrics.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a three-dimensional image correlation method measurement system of an embodiment of a method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo according to the present invention;

[0034] Figure 2 It is a schematic diagram of an image of an elastic fabric under a near-zero and negligible pressure state measured by using a hollow elastic model imitating a human body part in a method for measuring deformation and pressure distribution characteristics of an elastic fabric in vivo according to the present invention;

[0035] Figure 3 A schematic diagram of an iterative calculation model of geometric parameters of a human body part of a method for measuring deformation and pressure distribution characteristics of elastic fabric in the body according to the present invention;

[0036] Figure numerals: 1. computer; 2. diffuse reflection fill light; 3. industrial camera; 4. elastic fabric; 5. undeformed elastic fabric; 6. air pump; 7. uninflated deformable human body-shaping cylinder; 8. elastic fabric in the initial state without pressure; 9. inflated human body-shaping cylinder. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0038] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0039] Example

[0040] See also Figure 1-3 The present invention provides a method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo, comprising the following steps:

[0041] Step S1, build a three-dimensional image correlation measurement system, and obtain images of the elastic fabric 4 in a stress-free state and in a wearing state. The three-dimensional image correlation measurement system can capture the three-dimensional geometric information of the surface of the elastic fabric 4 through two industrial cameras 3 based on the principle of binocular vision, thereby calculating high-precision geometric parameters of human body parts such as the radius of curvature and deformation information of the elastic fabric 4 when worn. The steps are as follows:

[0042] Step S11, select two industrial cameras 3 with fixed focus lenses and two diffuse reflection fill lights 2, fix the two industrial cameras 3 on the optical platform according to the predetermined target distance, distance between cameras and solid angle, turn on the diffuse reflection fill lights 2, and perform the calibration procedure. Figure 1 The specific steps are as follows:

[0043] Fix two industrial cameras 3 on a solid tripod with a horizontal calibrator and a vertical calibrator. In order to calculate the results accurately, the lens fixing system needs to have enough degrees of freedom to accurately adjust the position and posture of the camera / lens. After determining the final position, target distance, distance between cameras and posture that meets the target solid angle, lock all adjustable parts on the lens fixing system, such as the focus ring, aperture adjustment ring and zoom knob.

[0044] Turn on the diffuse fill light 2 and observe whether the contrast of the collected image meets the requirements. There should be no overexposure or underexposure in the target area, and there should be no glare. Use the zero-mean normalized error square sum correlation function to determine the appropriate contrast parameter.

[0045] Connect the industrial camera 3 to a computer 1 with computing software installed, set the image acquisition frame rate and camera synchronization settings, and perform the calibration procedure. Turn on the camera and set it to the target frame rate, allowing it to warm up to a stable operating temperature. The time required for the camera to warm up to a stable temperature depends on the camera, the laboratory environment, and the image acquisition frame rate. The warm-up time usually varies from a few minutes to a few hours. Before using a new camera, the camera temperature should be monitored during the warm-up period in the expected (or similar) laboratory environment at the desired image acquisition rate, and the time required for the temperature to stabilize should be recorded.

[0046] After the above-mentioned devices and programs are set up, open the synchronization setting in the computer 1 installed with the three-dimensional image correlation method calculation software to ensure that the synchronization setting of the two industrial cameras 3 is correct. Then carry out the calibration procedure, select the calibration plate that matches the field of view range, and perform static, rotation, tilt and translation operations as needed to complete the requirements of the calibration procedure. Note that the feature point spacing of the calibration plate here should be accurate to within 0.1 pixels. Sufficient high-quality calibration images should be collected here, and the calibration images should be input into the calculation software to complete the calibration calculation. After calibration, perform parameter checks to ensure the correctness of the calibration results. The main calibration results to be checked should include the lens focal length and image center in the internal parameters, as well as the angle and distance between the two cameras in the external parameters.

[0047] Step S12: a washable speckle patch of suitable size is made on the surface of the elastic fabric 4 by spray painting, and the elastic fabric 4 is put on the inflatable human body imitation tube to obtain the initial image of the elastic fabric 4 in a pressure-free state. The operation process is as follows: Figure 2 As shown, the specific steps are as follows:

[0048] A washable speckle patch of suitable size is made on the surface of the elastic fabric 4 by spray painting. First, in order to attach the speckle required by the three-dimensional image correlation method to the surface of the elastic fabric 4, a washable speckle patch with good adhesion is used for spraying. The predetermined speckle size accounts for 3-5 pixels in the image, and in order to ensure the accuracy of the calculation results, the speckle is randomly optimized to ensure the uniqueness of the speckle characteristics in different areas and can be firmly attached to the surface of the elastic fabric 4. After the speckle is made, the undeformed elastic fabric 5 is put into the uninflated deformable human body imitation tube 7, and the human body imitation tube is slowly inflated by the air pump 6 so that the human body imitation tube expands to form an inflated human body imitation tube 9, which can just stretch the elastic fabric 4. The elastic fabric 4 is an elastic fabric 8 in the initial state without pressure. In this embodiment, it is considered that the elastic fabric 4 is in the initial state without tension (i.e., zero pressure or negligible pressure state). The three-dimensional image correlation method calculation software is opened, and the image of the elastic fabric 4 at this time is captured and saved as the initial control image.

[0049] Step S13, the elastic fabric 4 sprayed with the washable speckle sticker in step S12 is put on a real human body part to obtain a deformation image of the elastic fabric 4 in the wearing state. The specific process is to first remove the elastic fabric 4 with speckles from the elastic model of the simulated human body part, directly wear it on the human body part, and after wearing, open the three-dimensional image correlation method calculation software to capture the image at this time as the target image for deformation calculation. Note that the ambient light conditions and the parameters of the three-dimensional image correlation method measurement system at this time should be completely consistent with those in step S12.

[0050] Step S2, calculate the global deformation of the elastic fabric 4, and automatically construct the three-dimensional geometric shape of the human body surface to obtain the global curvature. The steps are as follows:

[0051] Step S21, in the calculation, set the sub-area size and step length measured by the three-dimensional image correlation method, and start calculating the global deformation value of the elastic fabric 4 in the wearing state and the three-dimensional coordinates of the surface of the wearing part of the human body. The sub-area size is a relatively important user-defined parameter in the three-dimensional image correlation method. The size of a sub-area should be large enough to contain sufficient information to distinguish the sub-area from other sub-areas. The standard selected in this embodiment is that a sub-area must contain at least three speckles. The ideal speckle size is 3-5 pixels and the density of the speckle is about 50%, so the sub-area size is about 15*15 square pixels. In order to improve practicality, this embodiment uses a sub-area size of 21*21 square pixels.

[0052] The step size controls the density of data points calculated by the three-dimensional image correlation method and affects the spatial resolution of the measurement to a certain extent. Generally, it is recommended that the step size be selected between one-third and one-half of the sub-area size so that adjacent sub-areas partially overlap, and the step size can vary according to the specific application. In this embodiment, one-half of the sub-area size is selected as the step size. After selecting the sub-area size and step size, the remaining parameters are kept at the default values, and the reference image taken in step S1 and the calculated target image are used to calculate the global deformation value of the elastic fabric 4 in the wearing state and the three-dimensional coordinate value of the surface of the human body part.

[0053] Step S22: Based on the three-dimensional morphology of the human body surface, a spherical area with a continuously iterated radius is used to perform three-dimensional surface fitting, and the calculation results of the fitting curvature radius before and after the iteration are compared. When the result error meets the error requirement, the iteration is terminated to obtain the final curvature calculation result. The calculation process is as follows: Figure 3 shown.

[0054] Generally, the three-dimensional surface data directly obtained are stored in a specific data format in the form of a large number of discrete points, and the curvature of the human body parts needs to be defined in a continuous curve or surface. It is impossible to obtain it by directly calculating the discrete points. It is necessary to make the large number of scattered points continuous, that is, to fit them to form a surface to represent the original data. The least squares method is a basic calculation method for solving optimization problems. This embodiment adopts the principle of the least squares method to perform surface fitting. In order to achieve efficient calculation and convenient parameter adjustment, a quadratic function is used as the function form of surface fitting. First, the properties of the quadratic function are relatively simple, which can simplify the calculation of curvature and is conducive to the efficient processing of large amounts of data. Secondly, the surface fitting performed in this embodiment is within a local range and can be dynamically iterated and adjusted according to the error, which can ensure the accuracy of the final calculation result. The fitting function form used is as follows:

[0056] z=f(x,y)=a 0 +a 1 x+a 2 y+a 3 x 2 +a 4 y 2 ;

[0057] Among them, a0 represents the constant term coefficient, a1 represents the linear term coefficient of x, a2 represents the linear term coefficient of y, a3 represents the quadratic term coefficient of x, a4 represents the quadratic term coefficient of y, x represents the x-axis coordinate of the data point, and y represents the y-axis coordinate of the data point.

[0058] For the selection of the adjacent points in the fitting range, this embodiment establishes a circle with the target point as the center and the radius as the initial value r. 0 The spherical value range of , and the data points within this value range are used to calculate the fitting function.

[0059] This embodiment uses errors to control the selection of neighboring points. Specifically, first select an error threshold, then perform surface fitting, and calculate the fitting error. If the calculated error is greater than the error threshold, gradually increase the radius of the fitting area. Then perform fitting and error calculation for new points, and repeat this process recursively until the error is less than the error threshold. In this way, a relatively accurate local fitting surface with an error less than the error threshold is obtained, and the circumference C and curvature radius R of the leg surface can be calculated.

[0060] Step S3, use Laplace's law to combine the mechanical parameters of the elastic fabric 4 and the curvature of the human body to perform global pressure measurement. Specifically, firstly, the thickness t of the elastic fabric 4 and the elastic modulus E of the elastic fabric 4 are obtained through a simple mechanical stretching test, and then the pressure measurement value of each point of the elastic fabric 4 on the surface of the human body is obtained by combining the deformation ε and the curvature radius R of the elastic fabric 4 surface obtained in the above steps. The specific formula is as follows:

[0061]

[0062] Therefore, the present invention adopts the above-mentioned method for measuring the deformation and pressure distribution characteristics of elastic fabrics on the body to achieve global accurate pressure measurement when the human body wears elastic fabrics, which significantly improves the measurement efficiency and the spatial resolution of the measurement results, and provides reliable data support and decision-making optimization direction for the development of medical and health care elastic fabrics.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for measuring deformation and pressure distribution characteristics of elastic fabric on body, characterized in that: The following steps are involved: Step S1, building a three-dimensional image correlation method measurement system, and obtaining images of the elastic fabric in a stress-free state and an image of the elastic fabric in a wearing state; Step S2, calculating the global deformation of the elastic fabric, and constructing the three-dimensional geometric morphology of the human body surface to obtain the global curvature; Step S3: measuring the global pressure of the elastic fabric.

2. The method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo according to claim 1, characterized in that: The specific steps of step S1 are as follows: Step S11, select two industrial cameras with fixed-focus lenses and two diffuse reflection fill lights, fix the two industrial cameras on an optical platform according to a predetermined target distance, inter-camera distance and solid angle, turn on the diffuse reflection fill lights, and perform a calibration procedure; Step S12, making washable speckles on the surface of the elastic fabric by spray painting, and putting the elastic fabric on the human body-shaped tube to obtain an initial image of the elastic fabric in a pressure-free state; Step S13, putting the elastic fabric with the washable spot patch in step S12 on a part of the human body to obtain a deformation image of the elastic fabric in a wearing state.

3. The method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo according to claim 2, characterized in that: The specific steps of step S2 are as follows: Step S21, setting the sub-area size and step length of the three-dimensional image correlation method measurement in the calculation, and starting to calculate the global deformation value of the elastic fabric in the wearing state and the three-dimensional coordinates of the surface of the wearing part of the human body; Step S22: Based on the three-dimensional morphology of the human body surface, a spherical area with a continuously iterative radius is used to perform three-dimensional surface fitting, and the calculation results of the fitting curvature radius before and after the iteration are compared. When the result error meets the error requirement, the iteration is terminated to obtain the final curvature calculation result.

4. The method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo according to claim 3, characterized in that: The fitting function of the three-dimensional surface fitting in step S22 is as follows: z=f(x,y)=a0+a1x+a2y+a3x 2 +a4y 2 ; Among them, a0 represents the constant term coefficient, a1 represents the linear term coefficient of x, a2 represents the linear term coefficient of y, a3 represents the quadratic term coefficient of x, a4 represents the quadratic term coefficient of y, x represents the x-axis coordinate of the data point, and y represents the y-axis coordinate of the data point.

5. The method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo according to claim 4, characterized in that: The step S3 uses Laplace's law in combination with the mechanical parameters of the elastic fabric, the global deformation of the elastic fabric and the curvature of the human body to perform global pressure measurement.

6. The method for measuring deformation and pressure distribution characteristics of elastic fabric in vivo according to claim 5, characterized in that: In step S3, the calculation formula for obtaining the pressure measurement value is as follows: Wherein, t is the thickness of the elastic fabric, E is the elastic modulus of the elastic fabric, ε is the deformation of the elastic fabric surface, and R is the radius of curvature.

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