Blade wall thickness measuring method

Abstract

The invention relates to the technical field of engine blade detection, in particular to a blade wall thickness measuring method which comprises the following steps: acquiring a blade model file and blade CT image data after linear array scanning reconstruction; acquiring blade model data and wall thickness measuring point positions from the blade model file; performing matching operation on the blade CT image data and the blade model data to obtain coordinate conversion parameters from the blade model data to the blade CT image data; according to the coordinate conversion parameter, converting the position of a wall thickness measurement point in the blade model data into blade CT image data to obtain a CT image wall thickness measurement point; and carrying out wall thickness measurement operation at the wall thickness measurement point of the CT image in the normal direction of the edge of the CT image. According to the invention, the wall thickness of the closed cavity of the blade can be measured. And the problems of low efficiency and inaccurate measurement value caused by the fact that the blade wall thickness measurement on the CT image is realized through manual operation are solved.

Description

Technical Field

[0001] The invention relates to the technical field of engine blade detection, and in particular to a blade wall thickness measurement method. Background Art

[0002] Engine blades are one of the core components of an engine, and their quality directly determines the quality and safety of the engine. Wall thickness is one of the important indicators for measuring blade quality. Accurate wall thickness measurement can ensure that the blades meet the design requirements during the manufacturing process and prevent quality problems and safety hazards caused by uneven or excessive wall thickness. Modern aircraft engines are increasingly using hollow blade designs to improve heat dissipation and flow guidance. The internal structure of hollow blades is complex, including concave and convex curves and serrated interlaced mesh types, which increases the difficulty of wall thickness measurement. However, accurate wall thickness measurement is crucial to evaluating the heat dissipation performance and structural strength of hollow blades, which helps optimize blade design and improve engine efficiency.

[0003] The CT system can measure the wall thickness of the blade without destroying the blade structure. Therefore, the CT system has become a key device for blade quality inspection. At present, the CT system's measurement of blades is mostly achieved through manual measurement of CT images. Manual measurement is inefficient and the standards cannot be unified. Therefore, automatic measurement of blade wall thickness based on CT images has become an urgent need.

[0004] Prior art CN201711091649 discloses a portable aero-engine blade tenon cavity wall thickness measuring device, which directly measures the wall thickness mainly through a built-in measuring foot extending into the tenon cavity and an external measuring foot with a tenon tooth bottom contact measuring cone. This invention can only measure the thickness of the tenon open cavity wall, but cannot measure the thickness of the closed cavity wall inside the blade.

[0005] Prior art CN201711248629 discloses that a caliper gauge and a positioning measuring plate are used to measure the wall thickness of an engine blade. This method can measure the wall thickness of a specific blade without disassembling the engine. However, this invention can only measure the wall thickness of an open cavity, and cannot measure the wall thickness of a closed cavity inside a blade.

[0006] Therefore, a blade wall thickness measurement method is urgently needed, which can realize the wall thickness measurement of the blade closed cavity, and solve the problem of low efficiency and inaccurate measurement value caused by manual operation to realize the blade wall thickness measurement on CT images. Summary of the invention

[0007] The object of the present invention is to provide a blade wall thickness measurement method which can solve the above-mentioned problem.

[0008] In order to achieve the above object, a blade wall thickness measurement method is provided, comprising the following steps:

[0009] Obtain blade model files and blade CT image data reconstructed by linear array scanning;

[0010] Obtain blade model data and wall thickness measurement point positions from the blade model file;

[0011] Perform matching operation on the blade CT image data and the blade model data to obtain coordinate conversion parameters from the blade model data to the blade CT image data;

[0012] The wall thickness measurement point position in the blade model data is converted to the blade CT image data according to the coordinate conversion parameters to obtain the CT image wall thickness measurement point;

[0013] The wall thickness measurement operation is performed at the wall thickness measurement point of the CT image in the direction of the normal line of the CT image edge.

[0014] Furthermore, the steps of matching the blade CT image data with the blade model data to obtain coordinate transformation parameters are as follows:

[0015] Obtain edge data of the blade CT image data and fill it into a point cloud image to obtain a blade CT point cloud image;

[0016] The blade model data is converted into edge data and filled into a point cloud image to obtain a blade model point cloud image;

[0017] The center of the blade CT point cloud image and the center of the blade model point cloud image are obtained through a circular fitting operation;

[0018] The conversion parameters in the horizontal and vertical directions are obtained through the centroid deviation between the blade CT point cloud image and the blade model point cloud image;

[0019] The rotation angle parameter is obtained by the difference between the angle between the centroid of the blade CT point cloud image and its center and the angle between the centroid of the blade model point cloud image and its center;

[0020] The horizontal and vertical transformation parameters and the rotation angle parameters are combined into coordinate transformation parameters.

[0021] Furthermore, the circular fitting operation is a least squares method.

[0022] Further, the calculation formula of the conversion parameter is as follows:

[0023] OffX=CTCentroid_X-ModelCentroid_X

[0024] OffY=CTCentroid_Y-ModelCentroid_Y

[0025] The calculation formula of the rotation angle parameter is as follows:

[0026]

[0027] Among them, the center of the leaf CT point cloud image (CTCircle_X, CTCircle_Y);

[0028] The center of the blade model point cloud image (ModelCircle_X, ModelCircle_Y);

[0029] The centroid of the leaf CT point cloud image (CTCentroid_X, CTCentroid_Y);

[0030] The centroid of the blade model point cloud image (ModelCentroid_X, ModelCentroid_Y).

[0031] Furthermore, the wall thickness measurement operation specifically includes the following steps:

[0032] Obtain a CT edge point group in the area near the wall thickness measurement point, and perform polynomial fitting on the edge point group;

[0033] Obtain the normal line of the polynomial at the wall thickness measurement point;

[0034] A gray point group is obtained by interpolation operation along the normal direction on the CT image with a single pixel length as a step length;

[0035] Polynomial fitting is performed on the grayscale point group to obtain the grayscale curve, and the half-height position on both sides of the grayscale curve is obtained to achieve wall thickness length measurement.

[0036] Principles and advantages:

[0037] 1. This solution determines the wall thickness measurement point on the CT image through automatic matching operation between the blade design model and the CT image. Then, the normal direction is obtained through the wall thickness measurement point and the CT edge image as the wall thickness measurement line, and the CT image gray point group is collected on this line to form a gray curve through fitting. Then, the wall thickness value is accurately calculated by the half-height method.

[0038] 2. This solution uses a non-contact measurement method to measure the wall thickness of the blade closed cavity. At the same time, it solves the problem of low efficiency and inaccurate measurement value when manually measuring the blade wall thickness on CT images. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flowchart of a blade wall thickness measurement method according to an embodiment of the present invention;

[0040] Figure 2It is a partial enlarged schematic diagram of the blade design model and wall thickness measurement points;

[0041] Figure 3 It is a schematic diagram for obtaining the fitting circle center and mass center in the point cloud image;

[0042] Figure 4 Schematic diagram of wall thickness measurement based on grayscale profile line. DETAILED DESCRIPTION

[0043] The following is further described in detail through specific implementation methods:

[0044] Example

[0045] A method for measuring blade wall thickness is basically as follows Figure 1 As shown, the following steps are included:

[0046] S1, obtaining a blade model file and blade CT image data reconstructed by linear scanning; in this embodiment, obtaining a blade model file refers to obtaining the design model data of the blade measurement slice, which includes the blade design model slice data and the measurement point data, such as Figure 2 As shown, the file format is usually DXF.

[0047] S2, obtaining blade model data and wall thickness measurement point positions from the blade model file;

[0048] S3, matching the blade CT image data with the blade model data to obtain the coordinate conversion parameters from the blade model data to the blade CT image data; the steps of matching the blade CT image data with the blade model data to obtain the coordinate conversion parameters in step S3 are as follows:

[0049] S301, obtaining edge data of the blade CT image data and filling it into a point cloud image to obtain a blade CT point cloud image;

[0050] S302, converting the blade model data into edge data and filling it into a point cloud image to obtain a blade model point cloud image;

[0051] S303, obtaining the center of the blade CT point cloud image and the center of the blade model point cloud image through circular fitting operation; the center of the blade CT point cloud image (CTCircle_X, CTCircle_Y); the center of the blade model point cloud image (ModelCircle_X, ModelCircle_Y); wherein the circular line formula is x 2 +y 2 =R 2 ,See Figure 3 As shown;

[0052] S304, obtain the horizontal and vertical conversion parameters through the centroid deviation between the blade CT point cloud image and the blade model point cloud image; obtain the centroid (CTCentroid_X, CTCentroid_Y) of the blade CT point cloud image through centroid calculation; the centroid (ModelCentroid_X, ModelCentroid_Y) of the blade model point cloud image, such as Figure 3 As shown; the calculation formula of the conversion parameter is as follows:

[0053] OffX=CTCentroid_X-ModelCentroid_X

[0054] OffY=CTCentroid_Y-ModelCentroid_Y

[0055] S305, obtaining a rotation angle parameter through the difference between the angle between the centroid of the blade CT point cloud image and its center and the angle between the centroid of the blade model point cloud image and its center;

[0056] The calculation formula of the rotation angle parameter is as follows:

[0057]

[0058] S4, converting the wall thickness measurement point position in the blade model data into the blade CT image data according to the coordinate conversion parameters to obtain the CT image wall thickness measurement point;

[0059] S5. Perform wall thickness measurement calculation at the wall thickness measurement point of the CT image in the direction of the normal line of the CT image edge, such as Figure 4 The step S5 comprises the following steps:

[0060] S501, obtain the CT edge point group in the area near the wall thickness measurement point (x∈[Measure_X-50,Measure_X+50], y∈[Measure_Y-50,Measure_Y+50]), and perform polynomial fitting on the edge point group (n=4, the polynomial is y=F(x)=a n x n +...+a4x 4 +a3x 3 +a2x 2 +a1x+a0); where a n ,a n-1 ,...,a2,a1,a0 are constant coefficients, x is a variable, n is the highest degree of the polynomial, and in this embodiment, n is 4.

[0061] S502, obtaining the normal line y=k at the wall thickness measurement point (Measure_X, Measure_Y) of the polynomial n x+b n ;

[0062] S503, obtaining a gray point group by interpolation operation along the normal direction on the CT image with a single pixel length as a step length;

[0063] S504, perform polynomial fitting on the gray point group (polynomial is F(x)=a n x n +..+a5x 5 +a4x 4 +a3x 3 +a2x 2 +a1x+a0, where a n ,a n-1 ,...,a2,a1,a0 are constant coefficients, y is the grayscale value of a single pixel, x is the number of single pixels from the starting point to the end point of the normal line, n is the highest degree of the polynomial, and n is 5 in this embodiment), the grayscale curve is obtained, and the half-height position on both sides of the grayscale curve is obtained to realize the wall thickness length measurement.

[0064] 1. This solution determines the wall thickness measurement point on the CT image through automatic matching operation between the blade design model and the CT image. Then, the normal direction is obtained through the wall thickness measurement point and the CT edge image as the wall thickness measurement line, and the CT image gray point group is collected on this line to form a gray curve through fitting. Then, the wall thickness value is accurately calculated by the half-height method.

[0065] 2. This solution uses a non-contact measurement method to measure the wall thickness of the blade closed cavity. At the same time, it solves the problem of low efficiency and inaccurate measurement value when manually measuring the blade wall thickness on CT images.

[0066] The above is only an embodiment of the present invention. The common sense such as the known specific structure and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for measuring blade wall thickness, characterized in that: The following steps are involved: Obtain blade model files and blade CT image data reconstructed by linear array scanning; Obtain blade model data and wall thickness measurement point positions from the blade model file; Perform matching operation on the blade CT image data and the blade model data to obtain coordinate conversion parameters from the blade model data to the blade CT image data; The wall thickness measurement point position in the blade model data is converted to the blade CT image data according to the coordinate conversion parameters to obtain the CT image wall thickness measurement point; The wall thickness measurement operation is performed at the wall thickness measurement point of the CT image in the direction of the normal line of the CT image edge.

2. A blade wall thickness measurement method according to claim 1, characterized in that: The steps of matching the blade CT image data with the blade model data to obtain the coordinate conversion parameters are as follows: Obtain edge data of the blade CT image data and fill it into a point cloud image to obtain a blade CT point cloud image; The blade model data is converted into edge data and filled into a point cloud image to obtain a blade model point cloud image; The center of the blade CT point cloud image and the center of the blade model point cloud image are obtained through a circular fitting operation; The conversion parameters in the horizontal and vertical directions are obtained through the centroid deviation between the blade CT point cloud image and the blade model point cloud image; The rotation angle parameter is obtained by the difference between the angle between the centroid of the blade CT point cloud image and its center and the angle between the centroid of the blade model point cloud image and its center; The horizontal and vertical transformation parameters and the rotation angle parameters are combined into coordinate transformation parameters.

3. A blade wall thickness measurement method according to claim 2, characterized in that: The circle fitting operation is the least squares method.

4. A blade wall thickness measurement method according to claim 2, characterized in that: The calculation formula of the conversion parameter is as follows: OffX=CTCentroid_X-ModelCentroid_X OffY=CTCentroid_Y-ModelCentroid_Y The calculation formula of the rotation angle parameter is as follows: Among them, the center of the leaf CT point cloud image (CTCircle_X, CTCircle_Y); The center of the blade model point cloud image (ModelCircle_X, ModelCircle_Y); The centroid of the leaf CT point cloud image (CTCentroid_X, CTCentroid_Y); The centroid of the blade model point cloud image (ModelCentroid_X, ModelCentroid_Y).

5. A blade wall thickness measurement method according to claim 2, characterized in that: The wall thickness measurement operation specifically includes the following steps: Obtain a CT edge point group in the area near the wall thickness measurement point, and perform polynomial fitting on the edge point group; Obtain the normal line of the polynomial at the wall thickness measurement point; A gray point group is obtained by interpolation operation along the normal direction on the CT image with a single pixel length as a step length; Polynomial fitting is performed on the grayscale point group to obtain the grayscale curve, and the half-height position on both sides of the grayscale curve is obtained to achieve wall thickness length measurement.

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