A vector approximation iterative measurement method for aeroengine blades

Abstract

The present invention relates to an aero-engine blade vector approximation iterative measurement method, and belongs to the field of aero-engine blade calibration. As a typical complex free-form surface part, the blade has the problem of complex blade profile measurement and poor consistency of parameter evaluation results. In order to improve the accuracy of blade profile measurement, the present invention uses the normal vector of the theoretical model surface as the initial measurement guide, obtains the measured compensation data of the blade section, performs B-spline surface fitting with several adjacent blade section data, calculates the normal vector of the measured data point, and uses the measured point coordinates and the obtained normal vector as the nominal value input for the next measurement. The measurement process is circulated until the iteration termination condition is reached, and the result is used as the final measured data of the blade section. The present invention is suitable for fields such as aero-engines, and can accurately measure the profiles of parts such as blades with complex free-form surfaces.

Description

Technical Field

[0001] The invention relates to a method for measuring an aero-engine blade, in particular to a method for vector approximation and iteration measurement of an aero-engine blade, and belongs to the field of aero-engine blade calibration. Background Art

[0002] As the core component of an aero-engine, blades have a decisive influence on the performance of the engine, so accurate blade calibration plays a pivotal role in the field of aero-engine testing and research. The key to the accuracy of complex surface measurement of blades is to measure based on the vector direction and compensate according to the vector direction, thereby reducing the surface coordinate measurement error caused by the probe radius compensation error.

[0003] At present, in the measurement of engine blades, the vector direction of the touch measurement is mainly obtained from the point cloud data on the theoretical model. However, since the model is the theoretical ideal state of the blade, there is a situation where the normal direction of the actual processed surface of the blade is inconsistent with that of the theoretical surface, making it difficult to achieve accurate measurement of the blade surface. Summary of the invention

[0004] In view of the problem that there is a deviation between the normal vectors of the theoretical model and the actual blade in the current blade measurement method, which results in the contact normal vector being not the actual normal vector of the blade, the purpose of the present invention is to provide an aero-engine blade vector approximation iterative measurement method, which obtains a normal vector that is closer to the actual blade in the measurement, thereby obtaining a more accurate blade surface measurement result.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The invention discloses an aero-engine blade vector approximation iterative measurement method. The method uses the normal vector of the aero-engine blade theoretical model surface as an initial measurement guide, obtains measured compensation data of a blade section, performs B-spline surface fitting with a number of adjacent blade section data, calculates the normal vector of the measured data point, uses the measured point coordinates and the obtained normal vector as the nominal value input for the next measurement, and loops the measurement process until an iterative termination condition is reached. The result is used as the final measured data of the blade section.

[0007] The invention discloses an aero-engine blade vector approximation iterative measurement method, comprising the following steps:

[0008] Step 1: Preparation for measurement implementation;

[0009] The measurement preparation includes calibration of the probe and the turntable, importing the theoretical CAD model, workpiece installation and positioning, and establishing the measurement coordinate system;

[0010] Step 2: On the theoretical model of the aircraft engine blade, intercept the section line whose height needs to be measured and generate the nominal point cloud coordinate value (x n ,y n ,z n ,i n ,j n ,k n ), as a guiding input for initial measurement;

[0011] Step 3: Scan and measure the blade detection section;

[0012] Set the scanning angle, speed and other measurement parameters, and use the multi-link motion control system of the measurement system to scan the blade section. Make the probe measure the blade basin, blade back, leading edge and trailing edge in the development motion mode, and ensure that the probe touch direction vector is always along the three-dimensional normal direction of the surface, so as to obtain the compensation data of the blade section profile after the i-th measurement.

[0013] Step 4: Perform B-spline surface modeling on the blade profile measurement data of the measured height and its adjacent sections.

[0014] The B-spline surface modeling process includes the determination of the surface u-direction and v-direction parameter times, the parameterization of blade profile detection data points, the determination of node vectors and the calculation of surface control points.

[0015] Step 5: Calculate the three-dimensional normal vector of the data point of the blade section in step 4 on the fitting surface;

[0016] The three-dimensional normal vector is obtained by the cross product operation of the partial derivative vectors of the blade section data points in the u-direction and v-direction of the fitting surface.

[0017]

[0018] U, V are node vectors

[0019] Step 6: The data set (x a ,y a ,z a ,i a ,j a ,k a ), as the nominal value input for the i+1th iteration measurement;

[0020] Step 7: Repeat steps 3 to 6 until the iterative measurement termination condition is reached, and the final measurement data is used as the actual value of the blade profile.

[0021] The iteration termination condition is set as the change in the sum of the contour deviations between the current touch point and the last touch point in the least squares fitting alignment state and the square root of the sum of the squares of the vector deviations.

[0022]

[0023] E k Mean square sum of contour deviations; p i Indicates the value point; q i represents the control vertex of the surface mesh; R represents the rational basis function determined by the data points; N is the number of blade section points; T represents the position change before and after the best fit.

[0024] When the change in the sum of the profile deviations is not greater than the judgment threshold ε, it indicates that the blade cross-section profile measurement is close to the true state and the measurement is terminated.

[0025] Step 8: According to the number of designed cross-section inspections of the blade, follow the above steps 1 to 7 to complete the output of all cross-section inspection data, that is, to achieve high-precision measurement of aircraft engine blade vector approximation iteration.

[0026] Beneficial effects:

[0027] 1. The present invention discloses an aero-engine blade vector approximation iterative measurement method, which combines theoretical and actual measured point cloud coordinate values ​​and takes the profile standard deviation in the blade parameters as an evaluation and judgment criterion, and can effectively achieve iterative convergence. After completing multiple iterations, the actual measured point cloud coordinates of the blade profile cross-section line are obtained, effectively improving the accuracy of blade surface measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the overall measurement flow chart of the vector approximation method involved in the present invention;

[0029] Figure 2 is a schematic diagram of a fixed height cross-section line involved in the present invention;

[0030] Figure 3 is a schematic diagram of the normal vector points of the blade cross section involved in the present invention;

[0031] Figure 4 This is an example of point cloud data deviation after three iterations involved in the present invention. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. The technical problems solved by the technical solution of the present invention and the beneficial effects are also described. It should be noted that the described embodiments are only intended to facilitate the understanding of the present invention and do not have any limiting effect on it.

[0033] like Figure 1As shown, the present embodiment discloses a method for iterative measurement of aero-engine blade vector approximation, and the measurement steps for a blade of a certain specification are as follows:

[0034] Step 1: Measurement preparation.

[0035] Before measurement, complete the calibration of the probe and turntable; import the theoretical CAD model into the software; prepare the blade, including checking that the blade surface is clean and free of contamination; install and position the workpiece; establish the measurement coordinate system; and make preparations for measurement.

[0036] Step 2: On the theoretical model, cut the section line whose height needs to be measured (such as Figure 2 The nominal value of the point cloud coordinates (x n ,y n ,z n ,i n ,j n ,k n ), as the coordinate value of the initial measurement;

[0037] Step 3: Scan and measure the blade inspection section.

[0038] Set the scanning angle, speed and other measurement parameters, and use the multi-link motion control system of the measurement system to scan the blade section. Make the probe measure in the unfolded motion mode relative to the blade basin, blade back, leading edge and trailing edge, and ensure that the probe touch direction vector is always along the three-dimensional normal direction of the surface (such as Figure 3 As shown), the compensation data of the measured cross-section profile of the blade after the i-th measurement is obtained;

[0039] Step 4: Perform B-spline surface modeling on the blade profile measurement data of the measured height and its adjacent sections.

[0040] The measured section line and the adjacent section line with a height distance of (+0.1, -0.1) mm from the section line are measured, and the B-spline surface modeling is performed after the blade profile measurement point cloud data within this height is obtained;

[0041] The B-spline surface modeling process includes the determination of the surface u-direction and v-direction parameter times, the parameterization of the blade profile detection data points, the determination of the node vectors and the calculation of the surface control points;

[0042] Step 5: Calculate the three-dimensional normal vector of the blade section data point in step 4 on the fitting surface.

[0043] The three-dimensional normal vector is obtained by the cross product operation of the partial derivative vectors of the blade section data points in the u-direction and v-direction of the fitting surface;

[0044]

[0045] Step 6: The data set (x a ,y a ,z a ,i a ,j a ,k a ), as the nominal value input for the i+1th iteration measurement;

[0046] Step 7: Repeat steps 3 to 6 until the iterative measurement termination condition is reached, and the final measurement data is used as the actual value of the blade profile;

[0047] The iteration termination condition is set as the change in the sum of the contour deviations between the current touch point and the last touch point in the least squares fitting alignment state and the square root of the sum of the squares of the vector deviations.

[0048]

[0049] E k Mean square sum of contour deviations; p i Indicates the value point; q i represents the control vertex of the surface mesh; R represents the rational basis function determined by the data points; N is the number of blade section points; T represents the position change before and after the best fit.

[0050] When the change in the sum of the profile deviations is not greater than the judgment threshold of 0.02, it indicates that the blade cross-section profile measurement is close to the true state and the measurement is terminated.

[0051] Step 8: Based on the number of blade design section inspections, follow the above plan to complete the output of all section inspection data.

[0052] The measurement deviation is the difference between the actual point cloud and the theoretical point cloud obtained by each measurement of the blade. In this embodiment, the number of iterations is set to 3. After three iterations of measuring the blade cross section, the second and third measurement deviations are significantly reduced (e.g. Figure 4 As shown in the figure, iterative convergence is effectively achieved. Compared with the point cloud data obtained directly from the theoretical model and the measurement results of the touch test, the blade surface point cloud obtained in this embodiment after convergence is closer to the measurement results of the blade on a higher precision device, so as to achieve the purpose of obtaining a blade surface closer to the actual blade surface by changing the measurement method and improve the measurement accuracy.

[0053] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A vector approximation iterative measurement method for aircraft engine blades, characterized by: The following steps are included: Step 1: Preparation for measurement implementation; Step 2: On the theoretical model of the aircraft engine blade, intercept the section line whose height needs to be measured and generate the nominal point cloud coordinate value of the detection section line that can describe the blade shape by controlling the sampling point density, which serves as the guiding input for the initial measurement; Step 3: Scan and measure the blade detection section; Step 4: Perform B-spline surface modeling on the blade profile measurement data of the measured height and its adjacent sections; Step 5: Calculate the three-dimensional normal vector of the data point of the blade section in step 4 on the fitting surface; Step 6: The data set consisting of the coordinate points of the i-th blade profile detection section and the normal vector obtained in step 5 is input as the nominal value of the i+1-th iteration measurement; Step 7: Repeat steps 3 to 6 until the iterative measurement termination condition is reached, and the final measurement data is used as the actual value of the blade profile; Step 8: According to the number of blade design section inspections, follow the above steps 1 to 7 to complete the output of all section inspection data, that is, to achieve high-precision measurement of aero-engine blades by vector approximation iteration; The implementation method of step 7 is: The iteration termination condition is set as the change in the sum of the contour deviations and the square root of the sum of the squares of the vector deviations in the least squares fitting alignment state between the current touch point and the last touch point; E k Mean square sum of contour deviations; p i Indicates the value point; q i represents the control vertex of the surface mesh; R represents the rational basis function determined by the data points; N is the number of blade section points; T represents the position change before and after the best fit; When the change in the sum of the profile deviations is not greater than the judgment threshold ε, it indicates that the blade cross-section profile measurement is close to the true state and the measurement is terminated.

2. The method for iterative measurement of aeroengine blade vector approximation according to claim 1, characterized in that: The implementation method of step 1 is: It includes calibration of the probe and turntable, importing theoretical CAD models, installing and positioning the workpiece, and establishing a measurement coordinate system.

3. The method for iterative measurement of aeroengine blade vector approximation according to claim 1, characterized in that: The implementation method of step 3 is: The measurement parameters are set, including scanning angle and speed, and the blade profile section is scanned by using the multi-link motion control system of the measurement system; the probe is made to measure the unfolded motion mode relative to the blade basin, blade back, leading edge and trailing edge, and it is ensured that the probe touch direction vector is always along the three-dimensional normal direction of the surface, so as to obtain the compensation data of the measured section profile line of the blade after the i-th measurement.

4. The method for iterative measurement of aeroengine blade vector approximation according to claim 1, characterized in that: The implementation method of step 4 is: The B-spline surface modeling process includes the determination of the surface u-direction and v-direction parameter times, the parameterization of blade profile detection data points, the determination of node vectors and the calculation of surface control points.

5. The method for iterative measurement of aeroengine blade vector approximation according to claim 1, characterized in that: The implementation method of step 5 is: The three-dimensional normal vector is obtained by the cross product operation of the partial derivative vectors of the blade section data points in the u-direction and v-direction of the fitting surface; U, V are node vectors.

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