Rapid measurement system for aviation blades based on four-line structured light sensor

Abstract

The present application relates to the field of measurement technology, and in particular to a rapid measurement system for aviation blades based on a four-line structured light sensor, wherein the measurement system comprises: four line structured light sensors and a calculation processing module mounted on a three-dimensional coordinate measuring machine; determining the equation of the laser plane in the camera coordinate system based on a target; solving the three-dimensional coordinates of the target point on the intersection of the laser plane and the blade in the camera coordinate system based on the equation; establishing a transformation relationship between the camera coordinate system and the machine coordinate system of the three-dimensional coordinate measuring machine, converting the target point to the machine coordinate system, and realizing three-dimensional scanning measurement; obtaining the point cloud data of the standard sphere in the sensor external parameter calibration module, fitting and outputting a point cloud sphere; using the center of the point cloud sphere as the measurement reference, combining the measurement data of multiple line structured light sensors to obtain the measurement result. Through the present application, only one-dimensional movement along the Z axis of the three-dimensional coordinate measuring machine is required to complete the measurement, thereby improving the measurement efficiency.

Description

Technical Field

[0001] The present application relates to the field of measurement technology, and in particular to a rapid measurement system for aviation blades based on a four-line structured light sensor. Background Art

[0002] During the manufacturing process of blade components (such as wind turbine blades and aircraft engine turbine blades), ensuring that their contour accuracy and geometric parameters meet design requirements is crucial for improving overall machine efficiency and safety. Existing inspection methods primarily rely on contact-type coordinate measuring machines (CMMs) or laser scanning measurement systems. While these systems offer high measurement accuracy, they commonly suffer from the following issues:

[0003] First, traditional three-dimensional coordinate measurement systems typically require complex multi-axis path planning, resulting in a time-consuming measurement process that struggles to meet the real-time inspection requirements of production lines. This limits their application in large-scale blade manufacturing, especially as the demand for full inspection grows, where inspection efficiency becomes a bottleneck.

[0004] Secondly, most existing non-contact measurement solutions use single-view laser scanning or structured light technology. The light source is arranged at an angle to the leading and trailing edges of the blade, making it impossible to accurately image areas with smaller R angles. This causes point cloud data to be missing or distorted in these key surface areas, thereby affecting the accuracy of profile curvature analysis and defect identification.

[0005] In addition, when traditional systems obtain measurement data in multiple directions, they usually need to manually set coordinate transformation relationships or later splice point cloud data. This not only increases the complexity of the operation, but also easily introduces errors, affecting the consistency and repeatability of the measurement results. Summary of the Invention

[0006] The embodiments of the present application provide a rapid measurement system for aircraft blades based on a four-line structured light sensor, so as to at least solve the problem of poor consistency of measurement results in the related art.

[0007] To achieve the above objectives, the present invention provides a rapid measurement system for aircraft blades based on a four-line structured light sensor, comprising:

[0008] Four line structured light sensors are symmetrically mounted on the three-dimensional coordinate measuring machine, with the Z axis of the three-dimensional coordinate measuring machine as the center. The blade to be measured is mounted on the three-dimensional coordinate measuring machine. During measurement, the blade to be measured moves along the Z axis, and the four line structured light sensors perform a three-dimensional scan of the blade. The four line structured light sensors are respectively used to measure the leading edge, trailing edge, blade basin, and blade back of the blade to be measured. The line structured light sensor includes a camera and a line laser. The laser plane direction is perpendicular to the Z axis, and the laser plane intersects the leading edge and trailing edge of the blade approximately perpendicularly. The high-resolution camera of the camera can clearly capture very small R angles and obtain sufficient point cloud data to describe the contours of the leading and trailing edges of the blade.

[0009] The computing and processing module is configured to include:

[0010] A sensor intrinsic parameter calibration module, which calibrates the intrinsic parameters of the line structured light sensor based on an equation that determines the laser plane in the camera coordinate system based on a target, and solves the three-dimensional coordinates of the target point on the intersection of the laser plane and the blade in the camera coordinate system based on the equation;

[0011] The sensor extrinsic parameter calibration module calibrates the extrinsic parameters of the linear structured light sensor based on a standard sphere, establishes the transformation relationship between the camera coordinate system and the machine coordinate system of the three-dimensional coordinate measuring machine, converts the target point into the machine coordinate system, and realizes three-dimensional scanning measurement;

[0012] The data stitching module obtains the point cloud data of the standard sphere in the sensor extrinsic parameter calibration module, fits and outputs a point cloud sphere, and stitches the measurement data of multiple line structured light sensors using the center of the point cloud sphere as the measurement reference.

[0013] In some embodiments, the sensor intrinsic parameter calibration module is configured to:

[0014] A target is determined, and based on the target, a homography relationship is established from the image plane to the target plane in each line structured light sensor. The center of the target is set as a black strip area, and multiple annular coding points are symmetrically distributed on both sides of the black strip area in an array. The coordinates of a point on the target are calibrated as ,make is 0, and the homography relationship between the image plane and the target plane is expressed as:

[0015]

[0016] Set up the first The homography relationship between the image plane of a line structured light sensor and the target plane is expressed as:

[0017]

[0018] Projecting a laser plane onto a black strip area on the target, changing the target position and posture, repeatedly capturing multiple sets of target images using a camera, wherein the target images include multiple coded point areas and laser light strips, and extracting the center of each coded area and laser light strip;

[0019] Calibrate the intrinsic parameters, radial distortion coefficient and extrinsic parameters of the camera based on the center of the encoding area using the Zhang Zhengyou calibration method, where the extrinsic parameters are the rotation vector and translation vector from the target coordinate system to the camera coordinate system;

[0020] Based on the internal parameters 、 、 、 , radial distortion coefficient 、 and external parameters 、 Solve for the coefficients in the homography relationship .

[0021] Determine the points on the laser strip at different positions based on the homography relationship Coordinates in the target coordinate system Then, based on the following expression, it is converted to the camera coordinate system to obtain the point Coordinates in the camera coordinate system :

[0022] ;

[0023] By changing the target position, we can get an intersection line between the laser plane and the target at different positions. Based on the above process, we can transform the coordinates of the points on the intersection line into the camera coordinate system, and use the least squares method to fit the plane to get the equation of the laser plane in the camera coordinate system. .

[0024] In some embodiments, the sensor extrinsic parameter calibration module is configured to:

[0025] Calibration of the translation vector of each line structured light sensor based on the reading value of the grating ruler of the three-dimensional coordinate measuring machine .

[0026] In some embodiments, the sensor extrinsic parameter calibration module is configured to:

[0027] Projecting the laser plane of the line structured light sensor onto the spherical surface of a standard sphere, measuring multiple arcs obtained at different heights, fitting multiple circles based on the multiple arcs, and calculating the linear relationship between the movement amount along the Z-axis and the distance between the laser plane and the center of the standard sphere based on the positions of the centers of the multiple circles from the center of the standard sphere;

[0028] A fixed point O in the measurement space is determined based on a linear relationship between the amount of movement along the Z axis and the distance between the laser planes. At least one conjugate pair is determined based on the fixed point O, and then the X-axis and Y-axis of the coordinate measuring machine are moved to obtain multiple sets of conjugate pairs.

[0029] Solve the rotation vector of the calibration line structured light sensor based on multiple sets of the conjugate pairs .

[0030] In some embodiments, the data stitching module is further configured to:

[0031] The point cloud data of the line structured light sensor is converted into the machine coordinate system based on the three-dimensional rigid body transformation, and the center coordinates of the point cloud sphere are obtained using the least squares fitting method. and radius ;

[0032] Calculate the distance between the coordinates of each point in the point cloud data and the fitting sphere, and set the sum of all distances as the fitness function;

[0033] Based on the rotation vector Set the parameter range of each particle in the particle swarm algorithm, and adjust the rotation vector based on the fitness function. Perform iterative optimization until the iteration termination condition is met.

[0034] In some embodiments, the fitness function is represented by the following computational model:

[0035] .

[0036] in, The number of points of each line structured light sensor, For the coordinates of each point in the point cloud data, this function traverses all points and calculates the coordinates of each point to the center of the sphere The distance between the point and the fitting sphere is calculated and compared with the radius of the sphere to obtain the deviation distance as the distance from the point to the fitting sphere. Finally, all the deviation distances are summed up. By minimizing this function, that is, minimizing the sum of the distances from all points to the fitting sphere, the coordinates of the sphere center and the radius can be optimized, thereby improving the accuracy of fitting the point cloud data to the sphere.

[0037] Compared with the related art, the rapid measurement system for aviation blades based on four-line structured light sensors provided in the embodiment of the present application has the same reference for measurement data in four directions after the internal parameter calibration and external parameter calibration processes, and can be automatically spliced ​​together, avoiding manual splicing of measurement data and improving measurement efficiency. Using the rapid measurement system of the embodiment of the present application, only one-dimensional movement along the Z axis of the three-coordinate measuring machine is required to complete the measurement, and real-time online measurement is realized. It can be flexibly inserted into the intermediate links of blade production and manufacturing to achieve full inspection of all blades.

[0038] The details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0040] Figure 1 This is a structural diagram of the rapid measurement system of this application;

[0041] Figure 2 It is a structural diagram of the rapid measurement system of this application;

[0042] Figure 3 It is a schematic diagram of the model of the structured light sensor of the present application;

[0043] Figure 4 This is a schematic diagram of the transformation relationship between the structured light sensor of the present application and the machine coordinate system;

[0044] Figure 5 This is a schematic diagram of the coordinate relationship of points on the laser light strip in the target coordinate system of this application;

[0045] Figure 6 This is a schematic diagram of the coordinate relationship of points on the laser light strip in the camera coordinate system of this application;

[0046] Figure 7 This is a schematic diagram of the positional relationship between the four camera coordinate systems and the three-coordinate measuring machine of this application;

[0047] Figure 8 is a schematic diagram of the standard ball of this application;

[0048] Figure 9 This is a schematic diagram of the effect of the intersection of the laser plane of the present application and the spherical surface of the standard ball;

[0049] Figure 10 This is a schematic diagram of the accuracy of the point cloud sphere fitted in this application;

[0050] Figure 11 This is a schematic diagram of the accuracy of the point cloud sphere fitted in another embodiment of the present application;

[0051] Figure 12 This is a physical picture of the blade 1 used for verification of this application;

[0052] Figure 13 This is the point cloud data of blade 1 output by the rapid measurement system of this application;

[0053] Figure 14 This is a rendering of the point cloud data of blade 1 output by the rapid measurement system of this application;

[0054] Figure 15 It is the cross-sectional profile of the blade data taken along the height direction of the blade;

[0055] Figure 16 This is a physical picture of the second blade used for verification of this application;

[0056] Figure 17 This is the point cloud data of blade 2 output by the rapid measurement system of this application;

[0057] Figure 18 This is a rendering of the point cloud data of blade 2 output by the rapid measurement system of this application;

[0058] Figure 19 It is the cross-sectional profile of the blade data taken along the second height direction of the blade. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative efforts are within the scope of protection of this application.

[0060] Obviously, the drawings described below are merely examples or embodiments of the present application. Those skilled in the art can, without inventive effort, apply the present application to other similar scenarios based on these drawings. Furthermore, it is also understood that, although the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, changes in design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as an insufficiency of the content disclosed in this application.

[0061] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments unless there is a conflict.

[0062] A line structured light sensor is a high-precision 3D measurement device based on the principle of active optical triangulation. It consists of a line laser and a camera. The laser projects a bright, linear light strip onto the surface of an object, while the camera captures the deformed light stripes from an oblique angle. Using calibrated camera intrinsic parameters (focal length, distortion, etc.) and the laser plane equation (extrinsic parameters), and leveraging the geometric relationship between pixel offset and object height, it can calculate 3D coordinates to submillimeter resolution.

[0063] refer to Figure 1-Figure 2 As shown, the embodiment of the present application provides a rapid measurement system for aircraft blades based on a four-line structured light sensor, comprising:

[0064] Four line structured light sensors are symmetrically installed on the three-dimensional coordinate measuring machine with the Z axis of the three-dimensional coordinate measuring machine as the center. The blade to be measured is installed on the three-dimensional coordinate measuring machine. During measurement, the blade to be measured moves along the Z axis, and the four line structured light sensors perform a three-dimensional scan on the blade. The four line structured light sensors are used to measure the leading edge, trailing edge, blade basin, and blade back of the blade to be measured respectively. The line structured light sensor includes a camera and a line laser. The laser plane direction is perpendicular to the Z axis, and the laser plane intersects the leading edge and trailing edge of the blade approximately perpendicularly. The high-resolution camera of the camera can clearly capture a very small R angle and obtain enough point cloud data to describe the contours of the leading and trailing edges of the blade, such as Figure 2 As shown, the camera receives only the laser wavelength (e.g., 650nm) through a filter to eliminate ambient light interference, while the polarizer suppresses mirror flare, ultimately obtaining a high-contrast laser stripe image.

[0065] The computing and processing module is configured to include:

[0066] A sensor intrinsic parameter calibration module, which calibrates the intrinsic parameters of the line structured light sensor based on an equation that determines the laser plane in the camera coordinate system based on a target, and solves the three-dimensional coordinates of the target point on the intersection of the laser plane and the blade in the camera coordinate system based on the equation;

[0067] The sensor extrinsic parameter calibration module calibrates the extrinsic parameters of the linear structured light sensor based on a standard sphere, establishes the transformation relationship between the camera coordinate system and the machine coordinate system of the three-dimensional coordinate measuring machine, converts the target point into the machine coordinate system, and realizes three-dimensional scanning measurement;

[0068] The data stitching module obtains the point cloud data of the standard sphere in the sensor extrinsic parameter calibration module, fits and outputs a point cloud sphere, and stitches the measurement data of multiple line structured light sensors using the center of the point cloud sphere as the measurement reference.

[0069] Because the line structured light sensors are oriented in different directions, the four sensors have different references after calibration, and the measurement data cannot be combined. Therefore, after calibration, the point cloud data of the measurement standard sphere is used to fit the sphere. The coordinates of the sphere center are then subtracted from the measurement results of the line structured light sensors. In this way, the center of the standard sphere is used as the measurement reference for all four sensors, and the measurement results from different directions can be combined.

[0070] In order to facilitate the calibration of the sensor's intrinsic parameters, the intrinsic parameter model of a single line structured light sensor is first established as follows.

[0071] Figure 3 is a schematic diagram of a model of a line structured light sensor according to an embodiment of the present application, with reference to Figure 3 As shown, is the camera coordinate system, is the optical center of the camera, is the world coordinate system, is the image coordinate system, is the image plane coordinate system of the camera, is the intersection of the optical axis and the image plane, is the focal length of the camera. P is the point where the laser plane intersects the object, and the projection coordinates of point P on the image plane are , the image coordinates corresponding to point P are ,According to the pinhole imaging principle, the relationship between point P from the world coordinate system to the image coordinate system can be expressed as follows:

[0072]

[0073] in, is the scale factor, is the camera internal parameter equation, are the rotation vector and translation vector from the world coordinate system to the camera coordinate system, respectively, and are expressed as the following formulas:

[0074]

[0075] In the above formula, is the image center coordinate, and The camera edge Axis and The focal length in the axial direction can be based on the focal length Calculation yields:

[0076]

[0077] in, and It is the number of pixels per millimeter in the width and height directions of the camera image plane.

[0078] Among them, the rotation vector , the translation vector .

[0079] Based on the above expression, the camera model can be obtained as follows:

[0080]

[0081] The equation for constructing the laser plane in the camera coordinate system is: , combined with the projection coordinates of point P on the image plane: You have to start from the center of light and pass through The ray equation is:

[0082]

[0083] in, , , then the three-dimensional coordinates of the intersection of the ray in the laser plane are obtained by combining the equation of the laser plane in the camera coordinate system and the ray equation. The coordinates of the intersection are in the camera coordinate system, which means that a line structured light sensor is used to measure a laser line on the object. The calibration of the internal parameters of the line structured light sensor is mainly to calibrate the equation of the laser plane in the camera coordinate system.

[0084] In order to facilitate the calibration of sensor extrinsic parameters, the embodiment of the present application establishes extrinsic parameter models of four line structured light sensors as follows.

[0085] In the embodiment of the present application, the coordinates of the points on the laser plane detected by the line structured light sensor are marked as , the corresponding camera coordinate system is recorded as , , The point is transformed into the machine coordinate system through three-dimensional rigid body transformation to obtain its coordinates in the machine coordinate system ,refer to Figure 4 As shown, the point on the laser plane detected by the first line structured light sensor is recorded as , and its camera coordinate system is recorded as , the point on the laser plane detected by the second line structured light sensor is recorded as , and its camera coordinate system is recorded as , the point on the laser plane detected by the third line structured light sensor is recorded as , and its camera coordinate system is recorded as , the point on the laser plane detected by the fourth line structured light sensor is recorded as , and its camera coordinate system is recorded as .

[0086] Among them, the three-dimensional rigid body transformation is expressed as:

[0087] .

[0088] Based on the above intrinsic parameter model, the sensor intrinsic parameter calibration module is configured as follows:

[0089] Identify a target, such as Figure 5 As shown, based on the target, a homography relationship is established from the image plane to the target plane in each line structured light sensor. The middle of the target is set as a black strip area. There are multiple ring-shaped coding points symmetrically distributed on both sides of the black strip area and arranged in an array. The coordinates of a point on the target are calibrated as ,make is 0, and the homography relationship between the image plane and the target plane is expressed as:

[0090]

[0091] Set up the first Image plane of a line structured light sensor The homography relationship with the target plane is expressed as:

[0092]

[0093] Projecting a laser plane onto a black strip area on the target, adjusting the exposure time of the camera to ensure that the coding point and the laser light strip at the intersection of the black strip area and the laser plane can be clearly captured, changing the target position and posture, and repeatedly capturing multiple sets of target images through the camera. The target image includes multiple coding point areas and laser light strips. The coding point area is used to calibrate the camera, and the laser light strip area is used to calibrate the laser plane. The image is segmented using an image processing method to extract the center of each coding area and the laser light strip;

[0094] Based on the center of the encoding area, the intrinsic parameters, radial distortion coefficient and extrinsic parameters of the camera are calibrated by the Zhang Zhengyou calibration method. The extrinsic parameters are the rotation vector and translation vector from the target coordinate system to the camera coordinate system. The Zhang Zhengyou calibration method is a mature method in this field, so its specific implementation is not detailed here.

[0095] Based on the internal parameters 、 、 、 , radial distortion coefficient 、 and external parameters 、 Solve for the coefficients in the homography relationship .

[0096] Determine the points on the laser strip at different positions based on the homography relationship Coordinates in the target coordinate system Then, based on the following expression, it is converted to the camera coordinate system to obtain the point Coordinates in the camera coordinate system :

[0097] ;

[0098] By changing the target position, we can get an intersection line between the laser plane and the target at different positions. Based on the above process, we can transform the coordinates of the points on the intersection line into the camera coordinate system, and use the least squares method to fit the plane to get the equation of the laser plane in the camera coordinate system. .like Figure 6 As shown in the figure The laser light strips are at four different positions of the target. The points of the laser strips on the targets at four different positions are represented in the camera coordinate system. Based on the four laser strips in the example, the least squares method is used to fit the plane, and the coefficients of the equation are solved as follows:

[0099] 、 、 、 .

[0100] The calibration of the external parameters of the line structured light sensor is to determine the coordinates of each camera to the machine coordinate system The rotation vector , translation vector , the rotation vector Unchanged during the measurement process. During the measurement process of a three-dimensional coordinate measuring machine, as the reading value of the grating ruler changes, the coordinate value of any point at the end of the Z axis of the three-dimensional coordinate measuring machine can be considered as the current coordinate value. During the movement of the measuring machine, the current coordinate value changes continuously relative to the world coordinate system.

[0101] In the above formula, , , , .

[0102] refer to Figure 7 As shown, in the embodiment of the present application, the line structured light sensor is fixed on the three-dimensional coordinate measuring machine. When the blade to be measured is driven by the Z axis of the three-dimensional coordinate measuring machine, since the movement is relative, the line structured light sensor can be considered to be fixed to the Z axis, that is, the origin of the four camera coordinate systems is fixed to the Z axis. In other words, although the origin positions of the four line structured light sensors are different, when the three-dimensional coordinate measuring machine moves, the four line structured light sensors have the same amount of movement and the same amount of translation. In the embodiment of the present application, the negative value of the reading value of the three-dimensional coordinate measuring machine grating scale is regarded as the origin of the camera coordinate system in the machine coordinate system. The coordinates below.

[0103] Assume that the reading of the grating ruler is ,but .

[0104] Based on this, the sensor external parameter calibration module is configured to calibrate the translation vector of each line structured light sensor based on the reading value of the three-coordinate measuring machine grating ruler .

[0105] Then, rotate the vector calibration process.

[0106] Based on the above rotation vector , translation vector The expression of the four line structured light sensors to the coordinate system of the three-coordinate measuring machine can be obtained as follows:

[0107]

[0108]

[0109]

[0110]

[0111] Based on the above analysis, the coordinate of the Z axis is the origin of the four camera coordinate systems relative to the machine coordinate system. Therefore, the origins of the four camera coordinate systems have the same coordinates, namely:

[0112] , .

[0113] In order to solve the transformation relationship between the above four line structured light sensors and the coordinate measuring machine, taking the transformation relationship of the first line structured light sensor as an example, the solution of the 12 unknown quantities in the formula needs to be based on four groups and conjugate pair, while maintaining In other words, it is necessary to ensure that the points measured by the line structured light sensor at different positions are the same fixed point in space. In principle, a set of equations containing 12 unknown quantities can be established using 4 sets of conjugate pairs. However, the solution is greatly affected by the accuracy of the conjugate pairs, making it unstable. In order to overcome this shortcoming, the solution is used. Conjugate pairs are used to establish a system of equations so that the number of equations is greater than the number of unknowns. In this way, solving the system of equations for the transformation relationship from the line structured light sensor to the coordinate measuring machine coordinate system becomes a least squares problem:

[0114] , .

[0115] The internal parameters of a multi-structure sensor system can be calibrated by calibrating each linear structured light sensor individually before installing them together. External parameter calibration is performed after the four linear structured light sensors are installed and secured. This requires the calibration equipment used to calibrate all four linear structured light sensors. Because the standard sphere can measure from any direction, it can meet the requirements of calibrating all four linear structured light sensors simultaneously.

[0116] In order to ensure that the line structured light sensor accurately measures the same fixed point in space, the present application provides a standard ball, such as Figure 8 As shown, the center of the standard sphere is regarded as a fixed point in space, such as Figure 8 As shown, assuming that the standard ball is fixed, the Z axis of the three-dimensional coordinate measuring machine drives the linear structured light sensor to move, and the X axis and Y axis of the three-dimensional coordinate measuring machine are fixed. When the laser plane is projected onto the spherical surface, a series of arcs are obtained by intersecting. Figure 9 As shown, when the Z axis of the coordinate measuring machine is located at When the laser plane and the standard sphere intersect to form an arc, the points on the arc are fitted to obtain Figure 9 The circle with A as the center has a radius of , and the radius of the standard sphere is R, so the following relationship is obtained:

[0117]

[0118] Based on this, the distance OA from the laser plane to the center of the sphere can be determined based on the radius of the arc where the laser plane intersects the spherical surface of the standard sphere.

[0119] Similarly, when the Z axis is at When the laser plane intersects the standard sphere, the arc is fitted to form a circle with B as the center, and its radius is , the distance OB from the laser plane to the center of the sphere is:

[0120] ,

[0121] Similarly, when the Z axis is at When the laser plane intersects the standard sphere, the arc is fitted to form a circle with C as the center, and its radius is , the distance OC from the laser plane to the center of the sphere is:

[0122] .

[0123] Therefore, there is a linear relationship between the distance between any two circles and the difference in the Z-axis coordinates of the coordinate measuring machine when measuring the circles:

[0124] ,in, is the proportional coefficient, which remains unchanged when the probe direction remains unchanged.

[0125] Based on the above linear relationship, let the Z-axis coordinate be When the laser plane passes through the center of the standard sphere, that is:

[0126]

[0127] Thus, the Z-axis coordinate of the coordinate measuring machine when the laser plane passes through the center of the standard sphere can be calculated and determined, and the measuring machine only needs to be controlled to move to this coordinate.

[0128] At this time, the sphere center O is set as a point on the laser plane, and its coordinate value in the camera coordinate system is obtained by fitting the circle where the laser plane and the standard sphere intersect, so as to achieve the purpose of measuring the fixed point O in space, and also determine the conjugate pair. and By changing the X-axis and Y-axis coordinates of the three-dimensional coordinate measuring machine, and using different areas of the laser plane to obtain multiple sets of conjugate pairs using the same method, the accuracy of the extrinsic parameter calibration can be improved. The extrinsic parameters of the other three line structured light sensors were calibrated using the same method, and the extrinsic parameter calibration results were obtained as shown below:

[0129]

[0130]

[0131]

[0132] .

[0133] As mentioned above, in the process of calibrating the external parameters of the four line structured light sensors, it is considered that the origins of the four camera coordinate systems are They have the same machine coordinates, but are actually distributed in different positions relative to the origin of the machine coordinate system of the coordinate measuring machine. The coordinates of the measuring machine are different. In the calibration process of the external parameters, they are considered to have the same machine coordinates, but are only relative to the origin of the machine coordinate system of the measuring machine. Just the same amount of exercise.

[0134] Based on the above embodiment, the sensor external parameter calibration module of the present application is configured as follows:

[0135] Projecting the laser plane of the line structured light sensor onto the spherical surface of a standard sphere, measuring multiple arcs obtained at different heights, fitting multiple circles based on the multiple arcs, and calculating the linear relationship between the movement amount along the Z-axis and the distance between the laser plane and the center of the standard sphere based on the positions of the centers of the multiple circles from the center of the standard sphere;

[0136] A fixed point O in the measurement space is determined based on a linear relationship between the amount of movement along the Z axis and the distance between the laser planes. At least one conjugate pair is determined based on the fixed point O, and then the X-axis and Y-axis of the coordinate measuring machine are moved to obtain multiple sets of conjugate pairs.

[0137] Solve the rotation vector of the calibration line structured light sensor based on multiple sets of the conjugate pairs .

[0138] In another embodiment, Figure 10 This is a schematic diagram of point dribbling obtained by fitting the point cloud data of a standard ball obtained by four line structured light sensors during calibration, as shown in Figure 10 As shown, with the center of the sphere as the measurement reference, the accuracy of measuring the standard sphere in this application is approximately ±0.04mm. Since the four line structured light sensors obtain local data on the spherical surface from four directions respectively, the diameter and center coordinates of the point cloud sphere obtained by fitting the sphere using these data cannot be accurately obtained.

[0139] Therefore, in order to further improve the accuracy of the external parameters, the embodiment of the present application also uses the particle swarm algorithm suitable for solving the optimal solution of the multivariable function to simultaneously optimize the rotation vectors of the four line structured light sensors. To achieve this goal, the data splicing module is further configured to:

[0140] The point cloud data of the line structured light sensor is converted into the machine coordinate system based on the three-dimensional rigid body transformation, and the center coordinates of the point cloud sphere are obtained using the least squares fitting method. and radius ;

[0141] Calculate the distance from the coordinates of each point in the point cloud data to the fitting sphere, and set the sum of all distances as the fitness function. The fitness function is expressed as the following calculation model:

[0142] .

[0143] in, The number of points of each line structured light sensor, For the coordinates of each point in the point cloud data, this function traverses all points and calculates the coordinates of each point to the center of the sphere The distance is calculated and compared with the sphere radius to obtain the deviation distance as the distance from the point to the fitting sphere. Finally, all the deviation distances are summed up. By minimizing this function, that is, minimizing the sum of the distances from all points to the fitting sphere, the coordinates of the sphere center and the radius can be optimized, thereby improving the accuracy of fitting the point cloud data to the sphere.

[0144] Based on the rotation vector Set the parameter range of each particle in the particle swarm algorithm, and adjust the rotation vector based on the fitness function. Perform iterative optimization until the iteration termination condition is met.

[0145] In order to ensure the orthogonality of the rotation vector parameters, the initial rotation vector in the particle swarm algorithm is converted into the ZXY direction Euler angle, and the Euler angle is set The initial value is ±1°, the dimension is 12, and the particle field attraction strategy is set to the global topology strategy. The overall particle size is 34, the particle swarm iteration step range is 5, the target maximum number of iterations is set to 2000, and the required iteration termination value is 0.1.

[0146] After testing, such as Figure 11 As shown, using the optimized rotation vector The data stitching module was re-run, and four line structured light sensors were used to measure the standard sphere with the center of the sphere as the reference. The fitting accuracy of the obtained point cloud sphere was improved to ±0.018mm.

[0147] Using particle swarm optimization to calculate the rotation vector After optimization, the difference between the radius of the fitting sphere and the true radius of the standard sphere is 0.0045 mm; the distance from the discrete point to the fitting sphere surface is ±0.018 mm. Therefore, the measurement system of the present application can have a high overall measurement accuracy when measuring from four different directions at the same time.

[0148] In the verification experiment, in order to illustrate the measurement effect of the present application, blade 1 and blade 2 were measured based on the measurement system of the present application.

[0149] like Figures 12 to 15 As shown in the figure, the blade height is about 110mm, the width is about 40mm, the leading edge radius is 1.25mm, and the trailing edge radius is 0.55mm. The laser line interval for scanning measurement is 0.1mm, the scanning speed is 5mm / s, the actual measurement time is about 22 seconds, and the total number of points obtained in the four directions is 4092876. The point cloud data is processed using Imageware, and the cross-sectional profile of the blade data is intercepted at any position along the blade height direction. Figure 14 As can be seen in the figure, the data on the leading and trailing edges of the blade are complete and well spliced ​​with the data between the blade base and the blade back.

[0150] like Figures 16 to 19As shown in the figure, blade 2 has a height of approximately 55 mm, a width of approximately 35 mm, a leading edge radius of 0.5 mm, and a trailing edge radius of 0.2 mm. The laser line interval for the scanning measurement was 0.1 mm, and the scanning speed was 5 mm / s. The actual measurement time was approximately 11 seconds, and a total of 1,846,532 points were acquired in four directions. Imageware was used to process the point cloud data, and a cross-sectional profile of the blade data was captured at any position along the blade height. As can be seen from the figure, sufficient data was obtained for both the leading and trailing edges, even with very small R angles, to characterize their profiles. The leading and trailing edge measurement data was well integrated with the energy data between the blade base and blade back.

[0151] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A rapid measurement system for aviation blades based on a four-line structured light sensor, characterized in that: include: Four line structured light sensors are symmetrically mounted on the three-dimensional coordinate measuring machine, with the Z axis of the three-dimensional coordinate measuring machine as the center. The blade to be measured is mounted on the three-dimensional coordinate measuring machine. During measurement, the blade to be measured moves along the Z axis, and the four line structured light sensors perform a three-dimensional scan of the blade. The computing and processing module is configured to include: A sensor intrinsic parameter calibration module, which calibrates the intrinsic parameters of the line structured light sensor based on an equation that determines the laser plane in the camera coordinate system based on a target, and solves the three-dimensional coordinates of the target point on the intersection of the laser plane and the blade in the camera coordinate system based on the equation; The sensor extrinsic parameter calibration module calibrates the extrinsic parameters of the linear structured light sensor based on a standard sphere, establishes the transformation relationship between the camera coordinate system and the machine coordinate system of the three-dimensional coordinate measuring machine, converts the target point into the machine coordinate system, and realizes three-dimensional scanning measurement; The data stitching module obtains the point cloud data of the standard sphere in the sensor extrinsic parameter calibration module and fits and outputs a point cloud sphere. The center of the point cloud sphere is used as the measurement reference to stitch the measurement data of multiple line structured light sensors to obtain the measurement results.

2. The rapid measurement system for aircraft blades based on a four-line structured light sensor according to claim 1 is characterized in that: The sensor internal parameter calibration module is configured as follows: A target is determined, and based on the target, a homography relationship is established between the image plane and the target plane in each line structured light sensor, wherein the center of the target is set as a black strip area, and a plurality of annular coding points are symmetrically distributed and arranged in an array on both sides of the black strip area; Projecting a laser plane onto a black strip area on the target, changing the target position and posture, repeatedly capturing multiple sets of target images using a camera, wherein the target images include multiple coded point areas and laser light strips, and extracting the center of each coded point area and the laser light strip; Determine the points on the laser strip at different positions based on the homography relationship Coordinates in the target coordinate system After that, convert it to the camera coordinate system and get point Coordinates in the camera coordinate system ; Use the least squares method to fit the plane and get the equation of the laser plane in the camera coordinate system .

3. The rapid measurement system for aviation blades based on a four-line structured light sensor according to claim 1 or 2, characterized in that: The sensor external parameter calibration module is configured as follows: Calibration of the translation vector of each line structured light sensor based on the reading value of the grating ruler of the three-dimensional coordinate measuring machine .

4. The rapid measurement system for aircraft blades based on a four-line structured light sensor according to claim 3 is characterized in that: The sensor external parameter calibration module is configured as follows: Projecting the laser plane of the line structured light sensor onto the spherical surface of a standard sphere, measuring multiple arcs obtained at different heights, fitting multiple circles based on the multiple arcs, and calculating the linear relationship between the movement amount along the Z-axis and the distance between the laser plane and the center of the standard sphere based on the positions of the centers of the multiple circles from the center of the standard sphere; A fixed point O in the measurement space is determined based on a linear relationship between the amount of movement along the Z axis and the distance between the laser planes. At least one conjugate pair is determined based on the fixed point O, and then the X-axis and Y-axis of the coordinate measuring machine are moved to obtain multiple sets of conjugate pairs. Solve the rotation vector of the calibration line structured light sensor based on multiple sets of the conjugate pairs .

5. The rapid measurement system for aircraft blades based on a four-line structured light sensor according to claim 4, characterized in that: The data splicing module is further configured to: The point cloud data of the line structured light sensor is converted into the machine coordinate system based on the three-dimensional rigid body transformation, and the center coordinates of the point cloud sphere are obtained using the least squares fitting method. and radius ; Calculate the distance between the coordinates of each point in the point cloud data and the fitting sphere, and set the sum of all distances as the fitness function; Based on the rotation vector Set the parameter range of each particle in the particle swarm algorithm, and adjust the rotation vector based on the fitness function. Perform iterative optimization until the iteration termination condition is met.

6. The rapid measurement system for aircraft blades based on a four-line structured light sensor according to claim 5, characterized in that: The fitness function is expressed as the following calculation model: ， in, The number of points of each line structured light sensor, is the coordinate of each point in the point cloud data.

7. The rapid measurement system for aircraft blades based on a four-line structured light sensor according to claim 3, characterized in that: The translation vector Expressed as: ， in, is the reading value of the grating ruler.

8. The rapid measurement system for aircraft blades based on a four-line structured light sensor according to claim 2, characterized in that: No. The homography relationship between the image plane of a line structured light sensor and the target plane is expressed as: in, is the scale factor, is the coordinate of the midpoint of the image plane, is the coordinate on the target plane, are the coefficients in the homography relationship.

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