CN113970311A - Aero-engine blade vector approximation iterative measurement method - Google Patents
Aero-engine blade vector approximation iterative measurement method Download PDFInfo
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Abstract
The invention relates to an aircraft engine blade vector approximation iterative measurement method, and belongs to the field of aircraft engine blade calibration. The blade serving as a typical complex free-form surface part has the problems of complex blade profile measurement and poor parameter evaluation result consistency. In order to improve the accuracy of blade profile measurement, the method takes the normal vector of a theoretical model curved surface as initial measurement guidance, after actual measurement compensation data of the blade profile section is obtained, B-spline surface fitting is carried out on a plurality of adjacent blade profile section data, the normal vector of an actual measurement data point is calculated, the coordinates of an actual measurement point and the obtained normal vector are used as the nominal value of the next measurement to be input, the measurement process is circulated until an iteration termination condition is reached, and the result is used as the final actual measurement data of the blade profile section. The invention is suitable for the fields of aeroengines and the like, and is used for accurately measuring the molded surfaces of parts such as blades with complex free-form surfaces.
Description
Technical Field
The invention relates to a measuring method of an aircraft engine blade, in particular to an aircraft engine blade vector approximation iterative measuring method, and belongs to the field of aircraft engine blade calibration.
Background
The blade is used as a core part of the aeroengine and has decisive influence on the performance of the engine, so that the blade can be accurately calibrated, and the blade has a great significance in the field of aeroengine test research. The measurement accuracy of the complex curved surfaces of the blades is characterized in that the measurement is based on the touch measurement in the vector direction and the compensation is carried out according to the vector direction, so that the measurement error of the coordinates of the curved surfaces caused by the radius compensation error of the measuring head is reduced.
In the existing measurement of the engine blade, the vector direction of touch measurement is mainly obtained by point cloud data on a theoretical model, but because the model is in a theoretical ideal state of the blade, the condition that the normal vector direction of an actual processing curved surface of the blade is inconsistent with the normal vector direction of the theoretical curved surface exists, and therefore the accurate measurement of the profile of the blade is difficult to realize.
Disclosure of Invention
Aiming at the problem that the contact normal vector is not the actual normal vector of the blade due to the fact that the deviation exists between the theoretical model and the normal vector of the actual blade in the conventional blade measuring method, the invention aims to provide an aero-engine blade vector approximation iterative measuring method, and the normal vector which is closer to the actual blade is obtained in the measurement, so that a more accurate blade curved surface measuring result is obtained.
The purpose of the invention is realized by the following technical scheme:
the invention discloses an aircraft engine blade vector approximation iterative measurement method, which takes a normal vector of a theoretical model curved surface of an aircraft engine blade as initial measurement guidance, performs B-spline surface fitting on a plurality of adjacent blade section data after acquiring actually measured compensation data of a blade section, calculates a normal vector of an actually measured data point, inputs the coordinates of an actually measured point and the obtained normal vector as a nominal value of the next measurement, circulates the measurement process until an iteration termination condition is reached, and takes the result as final actually measured data of the blade section.
The invention discloses an aircraft engine blade vector approximation iterative measurement method, which comprises the following steps:
step 1: preparing for measurement implementation;
the measurement implementation preparation comprises the calibration of a measuring needle and a rotary table, the introduction of a theoretical CAD model, the installation and the positioning of a workpiece, and the establishment of a measurement coordinate system;
step 2: on a theoretical model of an aircraft engine blade, intercepting a section line of which the height needs to be measured and generating a nominal point cloud coordinate value (x) of a detection section line capable of describing the shape of the blade profile by controlling the density of sampling pointsn,yn,zn,in,jn,kn) As a guide input for initial measurements;
and step 3: scanning and measuring the blade detection section;
and setting measurement parameters such as scanning angle, speed and the like, and scanning the blade profile section by using a multi-linkage motion control system of the measurement system. And the measuring head is enabled to measure relative to the generating motion mode of the blade basin, the blade back, the front edge and the rear edge of the blade, and the vector of the measuring head touch direction is ensured to be always along the three-dimensional normal vector direction of the curved surface, so that the compensation data after the ith measurement of the profile of the section to be measured of the blade is obtained.
And 4, step 4: and B spline surface modeling is carried out on the measured height and the blade profile measurement data of the adjacent sections.
The B spline surface modeling process comprises the steps of determining the times of u-direction and v-direction parameters of the surface, parameterizing leaf profile detection data points, determining node vectors and resolving surface control points.
And 5: calculating a three-dimensional normal vector of the data points of the leaf-shaped section on the fitting curved surface in the step 4;
the three-dimensional normal vector is obtained through the cross product operation of the partial derivative vectors of the leaf section data points in the u direction and the v direction of the fitting curved surface.
U, V are node vectors
Step 6: forming a data set (x) by the coordinate point of the ith leaf profile detection section and the normal vector obtained in the step 5a,ya,za,ia,ja,ka) Inputting as a nominal value of the (i + 1) th iteration measurement;
and 7: and repeating the steps 3 to 6 until an iterative measurement termination condition is reached, and taking the final measurement data as an actual value of the blade profile.
The iteration termination condition is set as the variance of the contour deviation sum and the square value of the vector deviation sum in the least square fitting alignment state of the current touch point and the last touch point.
EkThe sum of the mean square deviations of the contours; p is a radical ofiRepresenting a type value point; q. q.siRepresenting a curved surface mesh control vertex; r represents a rational basis function determined from the data points; n is the number of the blade profile cross-sectional points; t represents the amount of positional change before and after the best fit.
And when the variation of the profile deviation sum is not greater than the judgment threshold epsilon, the measurement of the profile line of the blade section approaches the real state, and the measurement is terminated.
And 8: and (4) according to the designed section detection number of the blades and the steps 1 to 7, finishing the output of all section detection data, namely realizing the vector approximation iteration high-precision measurement of the blades of the aero-engine.
Has the advantages that:
1. according to the method for the vector approximation iterative measurement of the blade of the aircraft engine, disclosed by the invention, the theory and the actual measurement point cloud coordinate value are combined, the profile standard deviation in the blade parameter is taken as an evaluation judgment standard, iterative convergence can be effectively realized, the actual measurement point cloud coordinate of the section line of the blade profile is obtained after multiple iterations are completed, and the measurement accuracy of the blade curved surface is effectively improved.
Drawings
FIG. 1 is a flow chart of the overall measurement of the vector approximation method according to the present invention;
FIG. 2 is a cross-sectional line view of a fixed height in accordance with the present invention;
FIG. 3 is a schematic view of a blade cross-sectional normal vector point in accordance with the present invention;
FIG. 4 is an example of a point cloud data deviation after three iterations in accordance with the present invention.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and examples. The technical problems and the advantages solved by the technical solutions of the present invention are also described, and 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.
As shown in fig. 1, the vector approximation iterative measurement method for the blade of the aircraft engine disclosed in the present embodiment includes the following measurement steps:
step 1: and (4) preparing for measurement.
Before measurement, completing calibration of the measuring needle and the rotary table; importing a theoretical CAD model in software; preparing the blade, including checking the blade surface to be clean and pollution-free; installing and positioning a workpiece; establishing a measurement coordinate system; and preparing for measurement.
Step 2: on the theoretical model, a section line (as shown in fig. 2) of the height to be measured is intercepted, and a point cloud coordinate nominal value (x) of blade measurement is obtained through the theoretical modeln,yn,zn,in,jn,kn) As the coordinate value of the primary measurement;
and step 3: and scanning and measuring the blade detection section.
And setting measurement parameters such as scanning angle, speed and the like, and scanning the blade profile section by using a multi-linkage motion control system of the measurement system. Measuring a generating motion mode of a measuring head relative to a blade basin, a blade back, a front edge and a rear edge of the blade, and ensuring that a vector of a measuring head touch direction is always along a curved surface three-dimensional normal vector direction (as shown in figure 3), so as to obtain compensation data after the ith measurement of the profile of the section to be measured of the blade;
and 4, step 4: and B spline surface modeling is carried out on the measured height and the blade profile measurement data of the adjacent sections.
B spline surface modeling is carried out after a measured section line and an adjacent section line with the height distance (+ 0.1-0.1) mm from the measured section line are measured, and the obtained leaf profile measuring point cloud data in the height;
the B spline surface modeling process comprises the steps of determining the times of u-direction and v-direction parameters of a surface, parameterizing leaf profile detection data points, determining node vectors and resolving curved surface control points;
and 5: and 4, calculating the three-dimensional normal vector of the leaf-shaped section data point on the fitting curved surface in the step 4.
The three-dimensional normal vector is obtained through the cross product operation of the partial derivative vectors of the leaf section data points in the u direction and the v direction of the fitting curved surface;
step 6: forming a data set (x) by the coordinate point of the ith leaf profile detection section and the normal vector obtained in the step 5a,ya,za,ia,ja,ka) Inputting as a nominal value of the (i + 1) th iteration measurement;
and 7: repeating the step 3 to the step 6 until an iterative measurement termination condition is reached, and taking final measurement data as an actual value of the profile of the blade profile;
the iteration termination condition is set as the variance of the contour deviation sum and the square value of the vector deviation sum in the least square fitting alignment state of the current touch point and the last touch point.
EkThe sum of the mean square deviations of the contours; p is a radical ofiRepresenting a type value point; q. q.siRepresenting a curved surface mesh control vertex; r represents a rational basis function determined from the data points; n is the number of the blade profile cross-sectional points; t represents the amount of positional change before and after the best fit.
And when the variation of the profile deviation sum is not greater than 0.02 of the judgment threshold, indicating that the measurement of the profile line of the blade section approaches the real state, and terminating the measurement.
And 8: and according to the designed section detection number of the blades, finishing the output of all section detection data according to the scheme.
The measurement deviation is the difference between the actual point cloud and the theoretical point cloud obtained by each measurement of the blade. The present embodiment sets the number of iterations to 3. After three times of iterative measurement of the blade section, the deviation between the second measurement and the third measurement is obviously reduced (as shown in fig. 4), and iterative convergence is effectively realized. Compared with the measurement result of the point cloud obtained from the theoretical model and subjected to touch measurement, the point cloud data obtained after convergence is closer to the measurement result of the blade on higher-precision equipment, so that the aim of obtaining a curve closer to the actual blade by changing the measurement method is fulfilled, and the measurement precision is improved.
The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. An aircraft engine blade vector approximation iterative measurement method is characterized by comprising the following steps: comprises the following steps of (a) carrying out,
step 1: preparing for measurement implementation;
step 2: intercepting a section line of which the height needs to be measured on an aircraft engine blade theoretical model, and generating a nominal point cloud coordinate value of a detection section line capable of describing the shape of a blade profile as a guide input of initial measurement by controlling the density of sampling points;
and step 3: scanning and measuring the blade detection section;
and 4, step 4: b spline surface modeling is carried out on the measured height and the blade profile measurement data of the adjacent section;
and 5: calculating a three-dimensional normal vector of the data points of the leaf-shaped section on the fitting curved surface in the step 4;
step 6: inputting a data set consisting of the ith leaf profile detection cross-section coordinate point and the normal vector obtained in the step 5 as a nominal value of the (i + 1) th iterative measurement;
and 7: repeating the step 3 to the step 6 until an iterative measurement termination condition is reached, and taking final measurement data as an actual value of the profile of the blade profile;
and 8: and (4) according to the designed section detection number of the blades and the steps 1 to 7, finishing the output of all section detection data, namely realizing the vector approximation iteration high-precision measurement of the blades of the aero-engine.
2. The iterative vector approximation measurement method for the aircraft engine blade according to claim 1, characterized in that: the implementation method of the step 1 is that,
the method comprises the steps of calibrating a measuring probe and a rotary table, importing a theoretical CAD model, installing and positioning a workpiece, and establishing a measuring coordinate system.
3. The iterative vector approximation measurement method for the aircraft engine blade according to claim 1, characterized in that: the implementation method of the step 3 is that,
setting measurement parameters including scanning angle and speed, and scanning the blade profile section by using a multi-linkage motion control system of a measurement system; and the measuring head is enabled to measure relative to the generating motion mode of the blade basin, the blade back, the front edge and the rear edge of the blade, and the vector of the measuring head touch direction is ensured to be always along the three-dimensional normal vector direction of the curved surface, so that the compensation data after the ith measurement of the profile of the section to be measured of the blade is obtained.
4. The iterative vector approximation measurement method for the aircraft engine blade according to claim 1, characterized in that: the implementation method of the step 4 is that,
the B spline surface modeling process comprises the steps of determining the times of u-direction and v-direction parameters of the surface, parameterizing leaf profile detection data points, determining node vectors and resolving surface control points.
5. The iterative vector approximation measurement method for the aircraft engine blade according to claim 1, characterized in that: the implementation method of the step 5 is that,
the three-dimensional normal vector is obtained through the cross product operation of the partial derivative vectors of the leaf section data points in the u direction and the v direction of the fitting curved surface;
u and V are node vectors.
6. The iterative vector approximation measurement method for the aircraft engine blade according to claim 1, characterized in that: the implementation method of the step 7 is that,
the iteration termination condition is set as the variance of the contour deviation sum and the square value of the vector deviation sum in the least square fitting alignment state of the current touch point and the last touch point;
Ekthe sum of the mean square deviations of the contours; p is a radical ofiRepresenting a type value point; q. q.siRepresenting a curved surface mesh control vertex; r represents a rational basis function determined from the data points; n is the number of the blade profile cross-sectional points; t represents the amount of positional change before and after the best fit;
and when the variation of the profile deviation sum is not greater than the judgment threshold epsilon, the measurement of the profile line of the blade section approaches the real state, and the measurement is terminated.
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