Non-contact strain measurement method and system of rotating structure

Abstract

The invention discloses a non-contact strain measurement method and system for a rotating structure, and the method comprises the steps: obtaining a displacement estimation value and a rotation angle estimation value of a single first measurement point in a deformation image based on ring projection transformation; converting the displacement estimation value and the rotation angle estimation value, and obtaining a target deformation parameter through a local digital image correlation method; according to the target deformation parameter, acquiring local strain of the single first measuring point; acquiring initial displacements of a plurality of second measuring points; according to the initial displacement, obtaining displacement fields of the plurality of second measuring points through a global digital image correlation method; according to the displacement field, obtaining the distance change between the second measuring points; and obtaining the global strain of the plurality of second measuring points according to the distance change, and meeting the strain measurement requirement in small strain through local and global strain calculation. The method can improve the precision of strain measurement, and can be widely applied to the technical field of strain measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of strain measurement, and in particular to a non-contact strain measurement method and system for a rotating structure. Background Art

[0002] Rotating structures, such as wind turbine blades, aero-engine blades, etc., are subjected to complex alternating loads during high-speed rotation and are prone to failure due to fatigue, deformation, cracks, etc. It is necessary to monitor the strain in real time to evaluate the structural health status. Most of the existing strain measurements of rotating structures are mainly contact measurements. However, traditional contact strain measurements are difficult to apply due to complex installation and poor anti-interference ability. There are currently some non-contact measurement methods mainly based on vision measurement, but they have certain limitations on the rotational speed of the structure, usually limited to uniform rotation, and the rotational speed or rotation angle needs to be known, and they cannot cope with the surface strain measurement of structures with unknown rotation angles. Summary of the Invention

[0003] In view of this, the main purpose of the embodiments of the present invention is to provide a non-contact strain measurement method and system for a rotating structure, in order to solve at least one of the problems of the prior art. The present invention can improve the accuracy of strain measurement.

[0004] To achieve the above object, on the one hand, an embodiment of the present invention provides a non-contact strain measurement method for a rotating structure, the method comprising the following steps:

[0005] Based on ring projection transformation, obtain the displacement estimate value and the rotation angle estimate value of a single first measurement point in the deformed image;

[0006] Convert the displacement estimate value and the rotation angle estimate value, and obtain the target deformation parameter through the local digital image correlation method;

[0007] According to the target deformation parameter, obtain the local strain of a single first measurement point;

[0008] Obtain the initial displacements of a plurality of second measurement points;

[0009] According to the initial displacements, obtain the displacement fields of a plurality of second measurement points through the global digital image correlation method;

[0010] According to the displacement fields, obtain the distance changes between the second measurement points;

[0011] According to the distance changes, obtain the global strains of a plurality of second measurement points.

[0012] In some embodiments, the step of obtaining the displacement estimate value and the rotation angle estimate value of a single first measurement point in the deformed image based on ring projection transformation comprises the following steps:

[0013] In the template image, several radii of different sizes are selected to form a first ring centered on the first measurement point;

[0014] According to the first ring, the first image gray level is obtained, and the Fourier transform is performed on the first image gray level to obtain the first frequency component;

[0015] The pixel points in the deformed image are traversed, and radii of the same size are selected to form a second ring centered on each of the pixel points;

[0016] According to the second ring, the second image gray level is obtained, and the Fourier transform is performed on the second image gray level to obtain the second frequency component;

[0017] The first frequency component and the second frequency component are respectively encapsulated to obtain a first ring projection transformation vector and a second ring projection transformation vector;

[0018] According to the first ring projection transformation vector and the second ring projection transformation vector, a determination criterion is constructed;

[0019] According to the determination criterion, the displacement estimation value is obtained;

[0020] According to the first frequency component and the second frequency component, the rotation angle estimation value is obtained.

[0021] In some embodiments, the following steps are included in transforming the displacement estimation value and the rotation angle estimation value and obtaining the target deformation parameter by the local digital image correlation method:

[0022] The displacement estimation value and the rotation angle estimation value are transformed to obtain the initial deformation parameter;

[0023] According to the initial deformation parameter, the target deformation parameter of the first measurement point is obtained by the local digital image correlation method.

[0024] In some embodiments, before obtaining the local strain of a single first measurement point according to the target deformation parameter, the following steps are further included:

[0025] The first region of the first measurement point in the deformed image is obtained, and the second region of the first measurement point in the template image is obtained; wherein, the deformed image is obtained by deforming the template image;

[0026] According to the zero-mean normalization criterion, determine whether the first region matches the second region. If the first region does not match the second region, obtain the target deformation parameters of several adjacent first measurement points, and return the steps of obtaining the first region of the first measurement point in the deformed image and obtaining the second region of the first measurement point in the template image. If the first region matches the second region, obtain the local strain of a single first measurement point according to the target deformation parameters.

[0027] In some embodiments, the obtaining the initial displacements of multiple second measurement points includes the following steps:

[0028] Based on the circular projection transformation, obtain the initial displacement of each second measurement point in the deformed image.

[0029] In some embodiments, the obtaining the distance change between the second measurement points according to the displacement field includes the following steps:

[0030] Obtain the first distance between the second measurement points in the template image;

[0031] Obtain the second distance between the second measurement points in the deformed image;

[0032] According to the first distance and the second distance, obtain the distance change.

[0033] In some embodiments, the obtaining the global strain of multiple second measurement points according to the distance change includes the following steps:

[0034] Obtain the first angle between the direction vector between the second measurement points in the template image and the horizontal axis;

[0035] Construct a weight matrix according to the first distance between the second measurement points in the template image;

[0036] According to the distance change, the first angle, and the weight matrix, obtain the global strain by the least squares method.

[0037] To achieve the above object, another aspect of the embodiments of the present invention proposes a non-contact strain measurement system for a rotating structure, and the system includes:

[0038] A first module for obtaining an estimated displacement value and an estimated rotation angle value of a single first measurement point in a deformed image based on circular projection transformation;

[0039] A second module for transforming the estimated displacement value and the estimated rotation angle value, and obtaining target deformation parameters by the local digital image correlation method;

[0040] A third module, configured to obtain the local strain of a single said first measurement point according to the said target deformation parameter;

[0041] A fourth module, configured to obtain the initial displacements of a plurality of second measurement points;

[0042] A fifth module, configured to obtain the displacement fields of a plurality of said second measurement points by means of global digital image correlation according to the said initial displacements;

[0043] A sixth module, configured to obtain the distance changes between the said second measurement points according to the said displacement fields;

[0044] A seventh module, configured to obtain the global strains of a plurality of said second measurement points according to the said distance changes.

[0045] To achieve the above object, on the other hand, an embodiment of the present invention provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements the non-contact strain measurement method for a rotating structure described above.

[0046] To achieve the above object, on the other hand, an embodiment of the present invention provides a computer-readable storage medium, which stores a computer program, and when the computer program is executed by a processor, it implements the non-contact strain measurement method for a rotating structure described above.

[0047] To achieve the above object, on the other hand, an embodiment of the present invention provides a computer program product or a computer program. The computer program product or the computer program includes computer instructions, and the computer instructions are stored in a computer-readable storage medium. The processor of a computer device can read the computer instructions from the computer-readable storage medium, and when the processor executes the computer instructions, the computer device executes the non-contact strain measurement method for a rotating structure described above.

[0048] The embodiments of the present invention at least include the following beneficial effects: The present invention provides a non-contact strain measurement method and system for a rotating structure. This solution obtains the displacement estimation value and the rotation angle estimation value of a single first measurement point in the deformed image based on ring projection transformation; converts the displacement estimation value and the rotation angle estimation value, and obtains the target deformation parameter through the local digital image correlation method; obtains the local strain of a single first measurement point according to the target deformation parameter; obtains the initial displacements of multiple second measurement points; obtains the displacement fields of multiple second measurement points through the global digital image correlation method according to the initial displacements; obtains the distance change between the second measurement points according to the displacement fields; and obtains the global strain of multiple second measurement points according to the distance change. By satisfying the strain measurement requirements within small strains in both local and global strain calculations, the accuracy of strain measurement can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0050] Figure 1 is a flowchart of the non-contact strain measurement method for a rotating structure provided by an embodiment of the present invention;

[0051] Figure 2 is a schematic diagram of a template image and its corresponding deformed image provided by an embodiment of the present invention;

[0052] Figure 3 is a schematic diagram of the process of obtaining displacement estimation and rotation angle estimation provided by an embodiment of the present invention;

[0053] Figure 4 is a schematic diagram of the process of calculating local strain provided by an embodiment of the present invention;

[0054] Figure 5 is a schematic diagram of the positional relationship between two measurement points in the template image provided by an embodiment of the present invention;

[0055] Figure 6 is a schematic diagram of the process of calculating global strain provided by an embodiment of the present invention;

[0056] Figure 7 is a schematic diagram of the overall process of non-contact strain measurement of a rotating structure provided by an embodiment of the present invention;

[0057] Figure 8 is a schematic diagram of the hardware structure of an electronic device provided by an embodiment of the present invention. Detailed Implementation Manner

[0058] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the embodiments of the present invention. They are only examples of devices and methods consistent with some aspects of the embodiments of the present invention detailed in the appended claims.

[0059] It should be noted that although functional module division is performed in the system schematic diagram and the logical sequence is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order from the module division in the system or the sequence in the flowchart. The terms "first / S100" and "second / S200" in the specification, claims and the above-mentioned drawings can be used herein to describe various concepts, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of the present invention, the first information can also be called the second information, and similarly, the second information can also be called the first information. Depending on the context, the words "if" and "when" as used herein can be interpreted as "when...", "while...", or "in response to determining".

[0060] The terms "at least one", "a plurality of", "each", "any one", etc. used in the present invention, at least one includes one, two or more than two, a plurality of includes two or more than two, each refers to each of the corresponding plurality, and any one refers to any one of the plurality.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used herein are only for the purpose of describing the embodiments of the present invention and are not intended to limit the present invention.

[0062] Before the embodiments of the present invention are described in detail, some nouns and terms involved in the embodiments of the present invention will be described first. The nouns and terms involved in the embodiments of the present invention are applicable to the following explanations.

[0063] Digital image correlation (DIC) is a non-contact optical measurement technology that realizes precise quantification of object deformation through image analysis and is mainly used to analyze the displacement and strain of an object during the process of being stressed or deformed.

[0064] Ring projection transformation, which converts a two-dimensional image into a one-dimensional feature vector, is used for rotation-invariant feature extraction by integrating or projecting along a circular path. An initial integer-pixel translation estimate is obtained through amplitude correlation, and a rotation estimate is obtained through the rotation-related phase features of the ring.

[0065] Zero-normalized Cross-Correlation (ZNCC), a mathematical method for measuring the similarity between two signals or image regions, is commonly used in tasks such as template matching and stereo vision matching.

[0066] Green's strain, also known as Green-Lagrange strain, is a strain measurement method in continuum mechanics for describing the finite deformation (large deformation) of materials. It is commonly used in nonlinear elasticity, plasticity mechanics, and large deformation analysis.

[0067] Rotating structures are subjected to complex alternating loads during high-speed rotation and are prone to failure due to fatigue, deformation, cracks, etc. It is necessary to monitor the strain in real time to evaluate the structural health status. Most existing strain measurements of rotating structures are mainly contact measurements. These methods require sensors to be embedded in the structure in advance, which is difficult to deploy later, and the additional mass of the sensors may affect the dynamic characteristics of the structure. Traditional contact strain measurements are difficult to apply due to complex installation and poor anti-interference ability. There are currently some non-contact measurement methods mainly based on visual measurement, but they have certain limitations on the rotation speed of the structure, usually limited to uniform rotation, and the rotation speed or rotation angle needs to be known, and they cannot handle the surface strain measurement of structures with unknown rotation angles. Existing strain measurement methods cannot balance accuracy, speed, and environmental adaptability, etc. There are optical methods such as digital image correlation to achieve full-field strain measurement by tracking the displacement of speckles, but for large-displacement and large-deformation objects, a suitable initial estimate needs to be provided; Laser Doppler Vibrometry (LDV) has high sensitivity but is limited to single-point analysis; electromagnetic methods such as eddy current and microwave radar are applicable to metal or long-distance scenarios, but the accuracy is limited.

[0068] In view of this, as Figure 1 shown, an embodiment of the present invention provides a non-contact strain measurement method for a rotating structure, which may include but is not limited to steps S100 to S700:

[0069] Step S100, based on ring projection transformation, obtain the displacement estimate value and rotation angle estimate value of a single first measurement point in the deformed image;

[0070] Step S200, transform the displacement estimate value and the rotation angle estimate value, and obtain the target deformation parameter through the local digital image correlation method;

[0071] Step S300, obtain the local strain of a single first measurement point according to the target deformation parameter;

[0072] Step S400: Obtain the initial displacements of multiple second measurement points;

[0073] Step S500: According to the initial displacements, obtain the displacement fields of multiple second measurement points by means of the global digital image correlation method;

[0074] Step S600: According to the displacement fields, obtain the distance changes between the second measurement points;

[0075] Step S700: According to the distance changes, obtain the global strains of multiple second measurement points.

[0076] In steps S100 to S700 of some embodiments, the ring projection transformation algorithm is used to locate the positions of the measurement points (or measurement regions) before and after movement, and high-precision strain measurement of the measurement points (or measurement regions) is realized based on the digital image correlation method.

[0077] In some embodiments, step S100 may include but is not limited to steps S110 to S180:

[0078] Step S110: In the template image, select several radii of different sizes to form a first ring centered on the first measurement point;

[0079] Step S120: According to the first ring, obtain the first image gray level and perform Fourier transform on the first image gray level to obtain the first frequency component;

[0080] Step S130: Traverse the pixel points in the deformed image, select radii of the same size, and form a second ring centered on each pixel point;

[0081] Step S140: According to the second ring, obtain the second image gray level and perform Fourier transform on the second image gray level to obtain the second frequency component;

[0082] Step S150: Package the first frequency component and the second frequency component respectively to obtain a first ring projection transformation vector and a second ring projection transformation vector;

[0083] Step S160: Construct a judgment criterion according to the first ring projection transformation vector and the second ring projection transformation vector;

[0084] Step S170: Obtain the displacement estimated value according to the judgment criterion;

[0085] Step S180: Obtain the rotation angle estimated value according to the first frequency component and the second frequency component.

[0086] In steps S110 to S140 of some embodiments, in the template image, a first measurement point is selected. Taking the first measurement point as the center, a number of first rings with different radii r are selected. The first image grayscale is extracted along the first circular path, and the first frequency component F(k; r) can be obtained through Fourier transform. Similarly, by traversing all pixel points in the deformed image, for all pixel points, second rings with the same radius are selected. The second image grayscale is extracted along the second circular path, and the second frequency component G(k; r) can be obtained through Fourier transform. Among them, the formulas for the first frequency component and the second frequency component are as follows:

[0087]

[0088]

[0089] In the formula, F(k; r) represents the first frequency component, indicating the component with frequency k in the Fourier transform of the grayscale distribution on the first ring with the measurement point as the center and radius r in the template image; G(k; r) represents the second frequency component, indicating the component with frequency k in the Fourier transform of the grayscale distribution on the second ring with the measurement point as the center and radius r in the deformed image; f polar (r, α) represents the polar coordinate representation of the template image; g polar (r, α) represents the polar coordinate representation of the deformed image; e -ikα represents the phase shift caused by the rotation angle in the frequency domain.

[0090] In some embodiments, the template image can obtain the corresponding deformed figure through movement. For a template image that only undergoes pure rotation with a rotation angle of θ, such as Figure 2 the green ring shown, there is f polar (r, α) = g polar (r, α + θ), while the conventional rectangular window represented by the red ring cannot extract rotation-invariant features. Among them, Figure 2 part (a) in is the template image, Figure 2 part (b) in is the deformed image corresponding to the template image. After Fourier transform, there is f(k; r) = e ikθ G(k; r), then |F(k; r)| = |G(k; r)|, where conj(·) is the conjugate operator.

[0091] In step S150 of some embodiments, the information extracted on the rings with different radii r i (i = 1, 2, 3 …) is encapsulated to form a ring projection transform vector (RPT vector). Exemplarily, encapsulating the first frequency component to form the first ring projection transform vector, then there is:

[0092] ST (x0,y0; k) = [|F(k; r1)|; |F(k; r2)|;...; |F(k; r n )|]

[0093] In the formula, S T (x0,y0; k) represents the first-ring projection transformation vector, indicating the RPT vector at the center point (x0, y0) in the template image; F(k; r1), F(k; r2), … F(k; r n ) represents the first frequency components extracted from the first ring with different radii.

[0094] Encapsulate the second frequency components to form the second-ring projection transformation vector, then there is:

[0095] S I (x0 + u, y0 + v; k) = [|G(k; r1)|; |G(k; r2)|;...; |G(k; r n )|]

[0096] In the formula, S I (x0 + u, y0 + v; k) represents the second-ring projection transformation vector, indicating the RPT vector at the center point (x0 + u, y0 + v) in the deformed image; u and v respectively represent the horizontal and vertical displacements of the structural measurement points; G(k; r1), G(k; r2), … G(k; r n ) represents the second frequency components extracted from the second ring with different radii.

[0097] In steps S160 to S170 of some embodiments, according to the first-ring projection transformation vector and the second-ring projection transformation vector, introduce the decision criterion formula C RPT (u, v), and the formula is as follows:

[0098]

[0099] In the formula,

[0100] W = diag(N1, N2,..., N n )

[0101] Among them, is the set of circular frequencies used in the ring projection; (·) T is the transpose operation; W is the weight matrix; N j (j = 1, 2, …, n) represents the number of discrete points for calculating F(k; r) and G(k; r); 1 represents an n-dimensional column vector with all elements being 1; and respectively represent S T (x0, y0; k) and SI The mean value of (x0 + u, y0 + v; k).

[0102] By introducing the judgment criterion formula, calculate the integer pixel displacement (u0, v0) of the selected measurement point in the deformed image. Then, the formula for the integer pixel displacement, that is, the displacement estimate value (u0, v0), is

[0103] In step S180 of some embodiments, according to the first frequency component and the second frequency component, calculate the initial rotation angle estimate value θ0 of the selected measurement point in the deformed image. Then, there is the following calculation formula:

[0104]

[0105] In the formula, arg(·) represents the argument of a complex number.

[0106] In steps S110 to S180 of some embodiments, as Figure 3 shown, by obtaining the pixel distribution information on rings with different radii around the measurement point, and using the amplitude-phase correlation on the ring, the initial estimates of the structural translation and rotation can be obtained respectively.

[0107] In some embodiments, step S200 may include but is not limited to steps S210 to S220:

[0108] Step S210, transform the displacement estimate value and the rotation angle estimate value to obtain the initial deformation parameters;

[0109] Step S220, according to the initial deformation parameters, obtain the target deformation parameters of the first measurement point through the local digital image correlation method.

[0110] In step S210 of some embodiments, transform the rotation angle estimate value into the initial value of the first-order deformation parameter (u x0 , u y0 , v x0 , v y0 ). Combining with the displacement estimate value, the initial deformation parameters (u0, v0, u x0 , u y0 , v x0 , v y0 ) can be obtained. Exemplarily, let u x0 = v y0 = cosθ0 - 1, u y0 = -sinθ0, v x0 = sinθ0, then the initial value of the first-order deformation parameter (u x0 , u y0 , v x0 , v y0 ) can be obtained.

[0111] In some embodiments, when ignoring the existing minute deformations, the coordinate transformation between the deformed image subset and the template image subset can be established with different parameters, that is

[0112]

[0113] where (u, v) and (u ′ , v ′ ) are the local coordinates of the template image subset and the deformed image subset respectively, so the above equivalence can be made.

[0114] In step S220 of some embodiments, based on the local DIC algorithm, the first-order deformation of the selected measurement points is calculated, and accurate target deformation parameters (u, v, u x , u y , v x , v y ) can be obtained. Since the DIC algorithm can obtain accurate deformation parameters, when using the first-order deformation parameters to describe the image deformation, the motion (deformation) information of the structure including displacement, rotation, and deformation can be obtained.

[0115] Before step S300 of some embodiments, it further includes obtaining the first region of the first measurement point in the deformed image and obtaining the second region of the first measurement point in the template image; according to the zero-mean normalization criterion, determining whether the first region and the second region match. If the first region and the second region do not match, obtain the target deformation parameters of several adjacent first measurement points, and return to the step of obtaining the first region of the first measurement point in the deformed image and obtaining the second region of the first measurement point in the template image. If the first region and the second region match, according to the target deformation parameters, obtain the local strain of a single first measurement point.

[0116] Exemplarily, as Figure 4 shown, take the initially obtained deformation parameters after conversion as the initial values of the local DIC algorithm, calculate the first-order deformation of the selected measurement points based on the local DIC algorithm to obtain the target deformation parameters. Use the zero-mean normalized cross-correlation (ZNCC) criterion to determine whether the corresponding regions of the measurement points in the deformed image and the template image match. When the ZNCC value is greater than or equal to 0.8, it is considered a good match, and then proceed to the next step of calculating the Green strain of the measurement points. When the ZNCC value is less than 0.8, it is considered a match failure and the deformation parameter calculation is inaccurate. For the measurement points with match failure, obtain new initial deformation parameters by interpolating several adjacent measurement points with good matches, re-perform the local DIC calculation to obtain the target deformation parameters of several adjacent measurement points with good matches, and then perform the step of using the ZNCC criterion to determine whether the corresponding regions of the measurement points in the deformed image and the template image match.

[0117] Evaluating the rationality of the initial estimate through the ZNCC criterion can provide reasonable deformation parameters as the initial values for local / global digital image correlation algorithms.

[0118] In step S300 of some embodiments, according to the target deformation parameters, the Green strain of a single measurement point, that is, the local strain of the measurement point, can be calculated. Exemplarily, the formula for calculating the Green strain is:

[0119]

[0120]

[0121] γ xy = u y + v x + u x u y + v x v y

[0122] Then the local strain of a single first measurement point can be obtained as (ε x , ε y , γ xy ).

[0123] In step S400 of some embodiments, based on the ring projection transformation, the initial displacement of each second measurement point in the deformed image is obtained. Optionally, in the template image, for each second measurement point, several rings with different radii are selected with the second measurement point as the center, the image gray levels are extracted along the circular path, and the Fourier transform is performed to obtain the third frequency component; similarly, for all pixel points in the deformed image, rings with the same radius are selected, the image gray levels are extracted along the circular path, and the Fourier transform is performed to obtain the fourth frequency component; for each second measurement point, the third frequency components and the fourth frequency components extracted on the rings with different radii are respectively encapsulated to form each ring projection transformation vector; according to the ring projection transformation vector, the determination criterion formula is introduced to calculate the integer pixel displacement of each second measurement point in the deformed image, and thus the initial displacement of each second measurement point in the deformed image can be obtained.

[0124] In step S500 of some embodiments, using the global DIC algorithm, according to the initial displacement field, the exact displacement field (u1, v1, u2, v2,..., u n , v n ) of all grid nodes (i.e., all second measurement points) is calculated.

[0125] In some embodiments, step S600 may include but is not limited to steps S610 to S630:

[0126] Step S610: Obtain the first distance between the second measurement points in the template image;

[0127] Step S620: Obtain the second distance between the second measurement points in the deformed image;

[0128] Step S630: Obtain the distance change based on the first distance and the second distance.

[0129] In steps S610 to S630 of some embodiments, the global strain is calculated by calculating the distance changes between the second measurement points and multiple adjacent nodes. Exemplarily, as Figure 5 shown, obtain the distance l between the second measurement point O and one of the nodes i in the template image i , and obtain the distance l between the second measurement point O and the node i in the deformed image after the deformation of the template image i +d i , then the distance change d can be obtained i , and the included angle between the direction vector of the second measurement point O and the node i and the x-axis can also be obtained as

[0130] In some embodiments, step S700 may include but is not limited to steps S710 to S730:

[0131] Step S710: Obtain the first included angle between the direction vector between the second measurement points in the template image and the horizontal axis;

[0132] Step S720: Construct a weight matrix according to the first distance between the second measurement points in the template image;

[0133] Step S730: Obtain the global strain by the least squares method based on the distance change, the first included angle, and the weight matrix.

[0134] In step S710 of some embodiments, obtain the included angles between the second measurement point and multiple adjacent second measurement points in the template image. As Figure 5 shown, the included angle between the direction vector of the second measurement point O and one of the nodes i and the x-axis can be obtained as

[0135] In steps S720 to S730 of some embodiments, according to the first distance l between the second measurement points in the template image i , i = 1, 2,..., n, construct a weight matrix Based on the distance change and the first included angle, where, s iDenote the linear strain between node i and the second measurement point O. Considering multiple nodes around the second measurement point, combining the distance change, the first included angle, and the weight matrix, we have:

[0136]

[0137] Optionally, the global strain (ε x , ε y , γ xy ) of the second measurement point can be calculated by the least squares method.

[0138] In steps S400 to S700 of some embodiments, as Figure 6 shown, for the case of a large measurement area, multiple measurement points need to be arranged. The displacement / strain fields calculated independently for multiple measurement points are discontinuous. It is necessary to determine the initial displacement value for each measurement point and use the global DIC method to obtain the displacement field and the strain field.

[0139] In some embodiments, the overall process of non-contact strain measurement of a rotating structure is as follows:

[0140] Step 1: Collect the motion and deformation information of the structure by arranging cameras postnatally, and estimate the initial values of the motion (deformation) parameters based on the ring projection transformation. This process focuses on the measurement of small surface strains of the rotating structure, and the strain can be ignored compared to its spatial scale. The rotation-invariant characteristics can be used to estimate the motion parameters.

[0141] Step 2: Convert the motion parameters estimated in Step 1 into the initial values of the first-order deformation parameters, use them as the initial values of the DIC algorithm, calculate the accurate target deformation parameters of the selected measurement points, and calculate the Green strain, i.e., the local strain, of the measurement points using the first-order deformation parameters.

[0142] Step 3: Steps 1 and 2 are applicable to the strain measurement of a single measurement point. For the case of a large measurement area, multiple measurement points need to be arranged. The displacement / strain fields calculated independently for multiple measurement points are discontinuous. It is necessary to determine the initial displacement value for each measurement point and use the global DIC method to obtain the displacement field and the global strain.

[0143] In summary, the non-contact strain measurement method of the rotating structure in the embodiments of the present invention is as Figure 7As shown, the motion and deformation information of the structure is collected by arranging cameras later, and the image data is obtained. In local strain measurement, measurement points (or measurement areas) are selected. In global strain measurement, the grid size is selected, and measurement points (or measurement areas) are selected in the grid and the grid is divided. By obtaining the pixel distribution information on rings with different radii around the measurement points, and using the amplitude and phase correlation on the rings, the initial estimates of the structure translation and rotation are obtained respectively, and the ZNCC criterion is used to evaluate the rationality of the initial estimates, providing reasonable initial values for the local / global digital image correlation method. The strain at local points can be calculated by calculating the Green strain with local first-order deformation parameters; the global strain can be defined by the distance changes between the measurement points and the measurement points in their neighborhoods. The strains calculated by both can meet the requirements of strain measurement within small strains.

[0144] An embodiment of the present invention also provides a non-contact strain measurement system for a rotating structure, which can implement the non-contact strain measurement method for the rotating structure as described above. The system includes:

[0145] A first module for obtaining the displacement estimate value and the rotation angle estimate value of a single first measurement point in the deformed image based on ring projection transformation;

[0146] A second module for transforming the displacement estimate value and the rotation angle estimate value, and obtaining the target deformation parameters by the local digital image correlation method;

[0147] A third module for obtaining the local strain of a single first measurement point according to the target deformation parameters;

[0148] A fourth module for obtaining the initial displacements of multiple second measurement points;

[0149] A fifth module for obtaining the displacement fields of multiple second measurement points by the global digital image correlation method according to the initial displacements;

[0150] A sixth module for obtaining the distance changes between the second measurement points according to the displacement fields;

[0151] A seventh module for obtaining the global strains of multiple second measurement points according to the distance changes.

[0152] It can be understood that the content in the above method embodiments is applicable to the system embodiments of the present invention. The functions specifically implemented by the system embodiments of the present invention are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those of the above method embodiments.

[0153] An embodiment of the present invention also provides an electronic device, which includes a processor and a memory. The memory stores a computer program, and when the processor executes the computer program, the non-contact strain measurement method of the rotating structure described above is implemented. The electronic device can be any intelligent terminal including a tablet computer, an in-vehicle computer, etc.

[0154] It can be understood that the content in the above method embodiments is applicable to this device embodiment. The functions specifically implemented by this device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those of the above method embodiments.

[0155] Refer to Figure 8 , Figure 8 which schematically shows the hardware structure of an electronic device in another embodiment. The electronic device includes:

[0156] A processor 801, which can be implemented in ways such as a general-purpose CPU (Central Processing Unit), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided by the embodiments of the present invention;

[0157] A memory 802, which can be implemented in forms such as a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 802 can store an operating system and other application programs. When implementing the technical solutions provided in the embodiments of this specification through software or firmware, the relevant program codes are stored in the memory 802, and the processor 801 is called to execute the non-contact strain measurement method of the rotating structure in the embodiments of the present invention;

[0158] An input / output interface 803, which is used to implement information input and output;

[0159] A communication interface 804, which is used to implement communication interaction between this device and other devices, and can implement communication through a wired method (such as USB, network cable, etc.) or through a wireless method (such as a mobile network, WIFI, Bluetooth, etc.);

[0160] A bus 805, which transmits information between various components of the device (such as the processor 801, the memory 802, the input / output interface 803, and the communication interface 804);

[0161] Among them, the processor 801, the memory 802, the input / output interface 803, and the communication interface 804 are communicatively connected to each other inside the device through the bus 805.

[0162] An embodiment of the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the non-contact strain measurement method for a rotating structure described above.

[0163] It can be understood that the content in the above method embodiments is applicable to the present storage medium embodiment. The functions specifically implemented by the present storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those in the above method embodiments.

[0164] An embodiment of the present invention also provides a computer program product or a computer program, which includes computer instructions stored in a computer-readable storage medium. The processor of the computer device can read the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions to cause the computer device to execute the non-contact strain measurement method for the rotating structure described above.

[0165] In summary, a non-contact strain measurement method and system for a rotating structure according to an embodiment of the present invention have the following advantages:

[0166] 1. The embodiment of the present invention is based on a digital image correlation-based visual measurement method, and collects the motion and deformation information of the structure by arranging cameras afterwards, realizing non-destructive strain measurement of the structure.

[0167] 2. For the rotating structure, after selecting the measurement area, the embodiment of the present invention can self-locate the selected measurement position in the image after the motion occurs, providing an algorithm initial value for the gradient-based digital image correlation method, without the need to artificially determine the rotational speed or rotation angle of the structure, without artificial intervention and any other prior information, and can adaptively identify the structure motion and strain.

[0168] 3. The embodiment of the present invention realizes high-precision strain measurement of the measurement point (or measurement area) based on the digital image correlation method, can obtain a high-precision displacement field and strain field on the surface of the structure, and improves the accuracy of strain measurement.

[0169] In some alternative embodiments, the functions / operations recited in the block diagrams may not occur in the order presented in the operational illustrations. For example, depending on the functions / operations involved, two blocks shown in succession may actually be executed substantially concurrently or the blocks may sometimes be executed in reverse order. Further, the embodiments presented and described in the flowcharts of the present invention are provided by way of example for the purpose of providing a more thorough understanding of the technology. The disclosed methods are not limited to the operations and logical flows presented herein. Alternative embodiments are contemplated in which the order of various operations is altered and in which sub-operations described as part of a larger operation are executed independently.

[0170] Moreover, although the present invention has been described in the context of functional modules, it should be understood that unless otherwise stated to the contrary, one or more of the described functions and / or features may be integrated in a single physical device and / or software module, or one or more functions and / or features may be implemented in separate physical devices or software modules. It should also be understood that a detailed discussion of the actual implementation of each module is not necessary for an understanding of the present invention. Rather, given the attributes, functions, and internal relationships of the various functional modules in the devices disclosed herein, the actual implementation of the modules will be understood within the ordinary skill of an engineer. Accordingly, those of ordinary skill in the art will be able to implement the present invention as set forth in the claims without undue experimentation. It should also be understood that the particular concepts disclosed are illustrative only and are not intended to limit the scope of the present invention, which is determined by the full scope of the appended claims and their equivalents.

[0171] If the described functions are implemented in the form of software functional units and sold or used as independent products, they may be stored in a computer-readable storage medium. Based on such understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or a part of such technical solution, may be embodied in the form of a software product stored in a storage medium, including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The foregoing storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc.

[0172] The logic and / or steps represented in the flowchart or otherwise described herein can, for example, be considered as a definable sequence of executable instructions for implementing a logical function, and can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

[0173] More specific examples (a non-exhaustive list) of the computer-readable medium include the following: an electrical connection part (electronic device) having one or more wirings, a portable computer disk cartridge (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or otherwise processing as appropriate, and then stored in a computer memory.

[0174] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application-specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), and the like.

[0175] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0176] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

[0177] The above has specifically described the preferred embodiments of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art can also make various equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included within the scope defined by the claims of the present invention.

Claims

1. A non-contact strain measurement method for a rotating structure, characterized in that: The following steps are involved: Based on the ring projection transformation, a displacement estimation value and a rotation angle estimation value of a single first measuring point in the deformed image are obtained; The displacement estimation value and the rotation angle estimation value are transformed, and a target deformation parameter is obtained by using a local digital image correlation method; According to the target deformation parameter, obtaining a local strain of a single first measuring point; Obtaining initial displacements of multiple second measuring points; According to the initial displacement, obtaining the displacement fields of the plurality of second measuring points by a global digital image correlation method; acquiring a distance change between the second measuring points according to the displacement field; According to the distance change, the global strains of the plurality of second measuring points are obtained.

2. The non-contact strain measurement method of a rotating structure according to claim 1, characterized in that: The method of obtaining a displacement estimation value and a rotation angle estimation value of a single first measuring point in a deformed image based on a ring projection transformation comprises the following steps: In the template image, a plurality of radii of different sizes are selected to form a first ring with the first measuring point as the center; According to the first ring shape, a first image grayscale is acquired, and the first image grayscale is subjected to Fourier transform to obtain a first frequency component; Traversing the pixel points in the deformed image, selecting radii of the same size, and forming a second ring with each pixel point as the center; According to the second ring shape, a second image grayscale is acquired, and the second image grayscale is subjected to Fourier transformation to obtain a second frequency component; Encapsulating the first frequency component and the second frequency component respectively to obtain a first ring projection transformation vector and a second ring projection transformation vector; constructing a determination criterion according to the first ring projection transformation vector and the second ring projection transformation vector; According to the determination criterion, obtaining the displacement estimation value; The rotation angle estimation value is obtained according to the first frequency component and the second frequency component.

3. The non-contact strain measurement method of a rotating structure according to claim 1, characterized in that: The step of converting the displacement estimation value and the rotation angle estimation value and obtaining the target deformation parameter by using a local digital image correlation method comprises the following steps: Converting the displacement estimation value and the rotation angle estimation value to obtain initial deformation parameters; According to the initial deformation parameters, target deformation parameters of the first measuring point are obtained by using a local digital image correlation method.

4. The non-contact strain measurement method of a rotating structure according to claim 1, characterized in that: Before obtaining the local strain of a single first measuring point according to the target deformation parameter, the following steps are also included: Acquire the first measuring point in a first area of ​​the deformed image, and acquire the first measuring point in a second area of ​​the template image; wherein the deformed image is obtained by deforming the template image; According to the zero mean normalization criterion, it is determined whether the first region matches the second region. If the first region does not match the second region, target deformation parameters of a plurality of adjacent first measuring points are obtained, and the process returns to the step of obtaining the first measuring point in the first region of the deformed image and obtaining the first measuring point in the second region of the template image. If the first region matches the second region, local strain of a single first measuring point is obtained according to the target deformation parameter.

5. The non-contact strain measurement method of a rotating structure according to claim 1, characterized in that: The step of obtaining the initial displacements of the plurality of second measuring points comprises the following steps: Based on the ring projection transformation, the initial displacement of each second measuring point in the deformed image is obtained.

6. The non-contact strain measurement method of a rotating structure according to claim 1, characterized in that: The step of obtaining the distance change between the second measuring points according to the displacement field comprises the following steps: Acquire a first distance between the second measuring points in the template image; Acquire a second distance between the second measuring points in the deformed image; The distance change is obtained according to the first distance and the second distance.

7. The non-contact strain measurement method of a rotating structure according to claim 1, characterized in that: The step of obtaining the global strain of the plurality of second measuring points according to the distance change comprises the following steps: Acquire a first angle between a direction vector between the second measuring points in the template image and the horizontal axis; constructing a weight matrix according to the first distance between the second measuring points in the template image; The global strain is obtained according to the distance change, the first angle and the weight matrix through a least squares method.

8. A non-contact strain measurement system for a rotating structure, characterized in that: include: The first module is used to obtain a displacement estimation value and a rotation angle estimation value of a single first measuring point in a deformed image based on a ring projection transformation; The second module is used to transform the displacement estimation value and the rotation angle estimation value, and obtain the target deformation parameter by using the local digital image correlation method; A third module is used to obtain a local strain of a single first measuring point according to the target deformation parameter; A fourth module is used to obtain initial displacements of multiple second measuring points; A fifth module is used to obtain the displacement fields of the plurality of second measuring points according to the initial displacement by using a global digital image correlation method; A sixth module is used to obtain a distance change between the second measuring points according to the displacement field; The seventh module is used to obtain the global strain of multiple second measuring points according to the distance change.

9. An electronic device, characterized in that: including a processor and a memory; The memory is used to store programs; The processor executes the program to implement the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: The storage medium stores a program, and the program is executed by a processor to implement the method according to any one of claims 1 to 7.

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