On-machine scanning measurement and compensation method for workpiece easy to deform

Abstract

The invention relates to the technical field of aircraft manufacturing and spaceflight rocket manufacturing, and discloses an on-machine scanning measurement and compensation method for easily-deformed workpieces (aircraft fuselage skins, spaceflight rocket wallboards and the like), which comprises the steps of preprocessing the easily-deformed workpieces, obtaining point cloud data of the actual appearances of the easily-deformed workpieces, unifying coordinates, flattening curved surfaces, matching point cloud and compensating programming paths. And finally, a programming path adaptive to the actual workpiece state is generated. The method is high in measurement precision and high in scanning efficiency, the algorithm does not need to depend on third-party software, full-automatic on-machine compensation can be achieved, the method is suitable for mirror image milling of large workpieces prone to deformation, and the machining precision and the production efficiency are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of aircraft and rocket manufacturing technology, specifically to an in-machine scanning measurement and compensation method for easily deformable workpieces (aircraft fuselage skin, aerospace rocket panels, etc.). Background Technology

[0002] Deformable workpieces such as aircraft fuselage skins and rocket panels are characterized by their large size and weak rigidity. Traditional manufacturing processes, such as chemical milling or die bonding, often fail to meet the precision and efficiency requirements of modern aerospace manufacturing. Mirror milling is a novel machining process for large, deformable workpieces, but the large size and weak rigidity of these workpieces remain a challenge to overcome. When clamping large, deformable workpieces, the actual state of the workpiece differs significantly from the theoretical model due to clamping forces, gravity, and its own stress, directly affecting machining accuracy.

[0003] Therefore, an on-machine measurement method is needed to quickly complete the measurement of easily deformable workpieces and the process of programming path compensation. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this invention is to provide a high-precision, high-efficiency, and highly automated in-machine scanning measurement and compensation method for easily deformable workpieces. This method enables rapid in-machine measurement and precise compensation of programming paths for easily deformable workpieces such as aircraft fuselage skin and aerospace rocket panels, thereby improving processing efficiency and accuracy.

[0005] To achieve the above technical objectives, this application provides the following technical solution: a method for on-machine scanning measurement and compensation of easily deformable workpieces, comprising the following steps: S1: Pre-treatment of easily deformable workpieces: Opening directional control holes in the non-part area of ​​the easily deformable workpiece, forming an approximately isosceles triangle distribution with the two main positioning holes of the workpiece itself. S2: Obtain point cloud data of the actual shape of the easily deformable workpiece. Use a tracking 3D laser scanner to scan the shape of the machine body workpiece and the main positioning hole to complete the acquisition of the point cloud on the workpiece surface. S3: Unify the coordinate system. Using the machining coordinate system of the theoretical model as the reference, register the point cloud of the positioning hole in the actual point cloud obtained in step S2 with the positioning hole in the theoretical point cloud. Determine the registration direction by controlling the coordinates of the direction control hole. S4: Surface point cloud flattening, which flattens the point cloud of the theoretical surface and the point cloud of the actual surface through isometric mapping; S5: Surface matching, constructing the mapping relationship between theoretical surfaces and actual surface point clouds to generate matching point clouds; through the reverse algorithm of centroid coordinate interpolation, the planar matching point cloud is restored to a three-dimensional matching point cloud; S6: Programming path compensation. Analyze the theoretical programming path of the workpiece, project each theoretical programming point onto the theoretical surface matching point cloud mesh, connect the projected point with the four vertices of the mesh to form four small triangles, calculate the area ratio of each triangle (S1:S2:S3:S4), and obtain the relative coordinates of the projected point in the mesh; according to the 3D matching point lookup table, find the corresponding position in the actual surface mesh, calculate the compensated actual programming point coordinates (X real, Y real, Z real), and import them into the machine tool for processing.

[0006] According to the present invention, the tracking three-dimensional laser scanner further comprises a scanner for acquiring point cloud data of the surface of easily deformable workpieces and a tracker for tracking the spatial position of the scanner; when scanning the curved surface of easily deformable workpieces, the scanner is fixedly connected to the machine tool tilting head, the tracker is fixed at a certain fixed position of the machine tool, and the scanner and the tilting head move to complete the scanning of the entire curved surface shape and obtain point cloud data of the actual shape of the workpiece.

[0007] According to the present invention, the theoretical workpiece surface is further discretized at equal intervals in three-dimensional digital modeling software to obtain point cloud data of the theoretical surface, which serves as the reference for the point cloud data of the theoretical shape of the workpiece.

[0008] According to the present invention, step S4 further employs isometric mapping by minimizing distance deformation.

[0009] According to the present invention, the reverse algorithm for surface flattening in step S4 further includes the following steps: In the surface flattening stage, a mapping function from a 3D surface (X, Y, Z) to a 2D plane (U, V) is obtained, so that every point on the 3D surface can find a unique corresponding point on the 2D plane, thus completing the parameterization of the surface. In a 2D planar pattern, for a point P_uv = (u, v), determine the UV triangle it falls into, and find the position (α, β, γ) of the point inside the UV triangle by calculating the centroid coordinates, where α + β + γ = 1; Find the 3D mesh triangle corresponding to the UV triangle, and use the same centroid coordinates (α, β, γ) to interpolate on the 3D triangle to calculate the corresponding 3D coordinates P_xyz = α*A_xyz + β*B_xyz + γ*C_xyz.

[0010] According to the present invention, the tracking three-dimensional laser scanner has a maximum scanning accuracy of 0.025mm, a single sampling area of ​​800mm×700mm, and a maximum scanning rate of 6,000,000 times / second, which meets the requirements for rapid and high-precision measurement of large-sized and easily deformable workpieces.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a tracking 3D measuring instrument. When scanning the curved surface of a deformable workpiece, the scanner is fixedly connected to the machine tool's tilting head, and the tracker is fixedly connected in the non-moving area of ​​the machine tool. The scanner and tilting head move to complete the scanning of the entire curved surface shape, obtaining point cloud data of the actual shape of the deformable workpiece, thus achieving efficient on-machine measurement. This invention addresses the discrepancy between the theoretical model and the actual state of large, weakly rigid, deformable workpieces after clamping due to stress deformation, achieving efficient and accurate programming path compensation. A tracking 3D laser scanner rapidly scans the shape and positioning holes of the deformable workpiece. Then, through a point cloud coordinate system, equidistant surface mapping and flattening, theoretical and actual point cloud matching, and programming path compensation steps, coordinate unification is achieved through positioning hole registration combined with direction control hole correction. An equidistant mapping algorithm based on angle and distance optimization is used to flatten the curved surface. Point cloud mapping relationships are established using grid centroid coordinate interpolation, ultimately generating a programming path adapted to the actual state of the deformable workpiece. This invention features high measurement accuracy and fast scanning efficiency. The algorithm does not require third-party software and can achieve fully automated on-machine compensation. It is suitable for mirror milling of large, easily deformable workpieces, effectively improving machining accuracy and production efficiency. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 This is a schematic diagram of the theoretical surface point cloud of the present invention; Figure 3 This is a schematic diagram showing the distribution of the positioning holes and orientation control holes of the present invention; Figure 4a This is a schematic diagram of the theoretical surface mesh of the present invention; Figure 4b This is a schematic diagram of the actual curved surface mesh of the present invention; Detailed Implementation The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] like Figures 1 to 4b As shown, this application provides an in-machine scanning measurement and compensation method for easily deformable workpieces (aircraft fuselage skin, aerospace rocket panels, etc.). Taking the fuselage skin of the C919 aircraft as the experimental object, its dimensions are 6500mm×3200mm×2.5mm and the material is 7075 aluminum alloy. The implementation steps of this application embodiment are described in detail with specific equipment parameters and operating thresholds.

[0014] S1: Skin (panel) pretreatment, skin (panel) clamping, directional control holes are opened in the non-part area of ​​the skin (panel), forming an isosceles triangle distribution with the two main positioning holes of the skin (panel) itself; through the positioning holes and directional control holes distributed in the isosceles triangle, reverse deviation is effectively solved, ensuring the accuracy of the coordinate uniformity of large-size skin; S2: Acquire point cloud data of the actual shape of the skin (panel). A tracking 3D laser scanner is used to scan the machine body skin (panel), including scanning the shape of the skin (panel) and two positioning holes, completing the acquisition of the point cloud data of the skin (panel) surface. The tracking 3D laser scanner has a maximum scanning accuracy of 0.025mm, a single sampling area of ​​800mm×700mm, and a maximum scanning rate of 6,000,000 scans / second, meeting the requirements for rapid and high-precision measurement of large-size skins. The tracking 3D laser scanner includes a scanner for acquiring point cloud data of the skin (panel) surface and a tracker for tracking the spatial position of the scanner. When scanning the easily deformable curved surface of the skin (panel), the 3D laser scanner is fixedly connected to the machine tool's tilting head, and the tracker is fixed at a fixed position on the machine tool. The scanner and tilting head move to complete the scanning of the entire curved surface shape, obtaining the point cloud data of the actual shape of the skin (panel). Simultaneously, the theoretical skin (panel) surface is discretized at equal intervals in the 3D modeling software. The theoretical surface point cloud data is acquired. In this step, the 3D laser scanner has a built-in high-resolution CMOS sensor and a line laser emission module to emit laser beams and receive reflected signals from the skin (panel) surface. The point cloud coordinates are calculated using the triangulation principle. The tracker uses infrared optical tracking technology to capture reflective markers on the 3D laser scanner in real time and dynamically outputs their spatial position and attitude data in the global coordinate system, ensuring the accuracy of the point cloud data in the same coordinate system. The 3D laser scanner is fixedly connected to the machine tool tilting head through a fixture to ensure that the movement of the machine tool tilting head is synchronized with the scanner's attitude. The spatial tracker is fixed in the non-moving area of ​​the machine tool, no more than 7m away from the scanning area, to avoid the machine tool's moving parts from blocking the tracking optical path. During the scanning process, the spatial tracker updates the 3D laser scanner's position data in real time and merges it with the point cloud data acquired by the 3D laser scanner to generate complete point cloud data in the global coordinate system, effectively reducing the impact of workpiece deformation and equipment movement errors on the measurement results. S3: Unify the coordinate system. Using the machining coordinate system of the theoretical model as the reference, register the point cloud of the positioning hole in the actual point cloud with the positioning hole in the theoretical point cloud. The registration direction is determined by the coordinate of the direction control hole to avoid reverse deviation and complete the transformation of the actual point cloud to the machining coordinate system. S4: Surface Point Cloud Flattening. This involves flattening the point clouds of both the theoretical and actual curved surfaces using equidistant mapping. For the non-developable fuselage skin, equidistant mapping is performed by minimizing distance deformation. This involves dividing the skin surface into many small local regions, ensuring that the transformation of each local region approximates a rigid body transformation as closely as possible, and then iteratively optimizing for global consistency. Optionally, both the theoretical and actual surfaces are divided into 50mm × 50mm local regions, with 20 iterations and a distance deformation error controlled to ≤0.3%. The equidistant mapping process maintains all intrinsic distances on the surface unchanged; specifically, the geodesic distance between any two points on the surface equals the Euclidean distance between corresponding points on the mapped plane. This method minimizes distance deformation, reducing the distance deformation error of the non-developable surface and ensuring the flattening accuracy and consistency. S5: Surface matching establishes a mapping relationship between theoretical and actual surface point clouds, generating matching point clouds; matching points are generated and numbered on the flattened plane according to a set point spacing, with the optimal point spacing being 10mm, establishing a one-to-one correspondence; the planar matching point cloud is restored to a three-dimensional matching point cloud through a reverse algorithm of centroid coordinate interpolation; multiple uniform matching points are used to establish a mapping relationship, combined with the reverse algorithm of centroid coordinate interpolation, to achieve accurate matching between theoretical and actual point clouds, providing reliable data support for subsequent compensation; The basic process of the reverse algorithm for surface flattening is as follows: First, during the surface flattening stage, a mapping function from the 3D surface (X, Y, Z) to the 2D plane (U, V) has been found, so that every point on the 3D surface can find a unique corresponding point on the 2D plane, thus completing the parameterization of the surface; In a 2D planar pattern, for a point P_uv = (u, v), it is necessary to determine which UV triangle it falls within. The position (α, β, γ) of the point within the UV triangle is found by calculating the centroid coordinates, where α + β + γ = 1. Find the 3D mesh triangle corresponding to this UV triangle, and use the same centroid coordinates (α, β, γ) to interpolate on the 3D triangle to calculate the corresponding 3D coordinates P_xyz = α*A_xyz + β*B_xyz + γ*C_xyz; Similarly, normals and tangents can also be obtained by interpolating from 3D vertices using centroid coordinates, which will not be elaborated here; S6: Programming Path Compensation. This process analyzes the theoretical programming path of the fuselage skin in the C919, projects each theoretical programming point onto a theoretical surface matching point cloud mesh, connects the projected point to the four vertices of the mesh to form four small triangles, calculates the area ratio of each triangle (S1:S2:S3:S4), and obtains the relative coordinates of the projected point within the mesh. Based on a 3D matching point lookup table, the corresponding position is found in the actual surface mesh, and the compensated actual programming point coordinates (X_actual, Y_actual, Z_actual) are calculated and imported into the machine tool for processing. This programming path compensation method, based on mesh projection and area ratio calculation, accurately corrects the actual skin's shape deviation, improving the machining accuracy and efficiency of the fuselage skin.

[0015] This invention first uses a tracking 3D scanner to quickly measure the skin, and then combines it with a programming path compensation method for on-machine compensation, thereby narrowing the gap between the actual coordinates of the skin (panel) and the theoretical model and improving the compensation and correction efficiency.

[0016] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for on-machine scanning measurement and compensation of easily deformable workpieces, characterized in that, Includes the following steps, S1: Pre-treatment of easily deformable workpieces: Opening directional control holes in the non-part area of ​​the easily deformable workpiece, forming an isosceles triangle distribution with the two main positioning holes of the workpiece itself. S2: Obtain point cloud data of the actual shape of the easily deformable workpiece. Use a tracking 3D laser scanner to scan the workpiece shape and main positioning hole. The scanner and the tilting head motion complete the scanning of the entire curved surface shape to obtain point cloud data of the actual shape of the workpiece. S3: Unify the coordinate system. Using the machining coordinate system of the theoretical model as the reference, register the point cloud of the positioning hole in the actual point cloud obtained in step S2 with the positioning hole in the theoretical point cloud. Determine the registration direction by controlling the coordinates of the direction control hole. S4: Surface point cloud flattening, which flattens the point cloud of the theoretical surface and the point cloud of the actual surface through isometric mapping; S5: Surface matching, constructing the mapping relationship between theoretical surfaces and actual surface point clouds to generate matching point clouds; through the reverse algorithm of centroid coordinate interpolation, the planar matching point cloud is restored to a three-dimensional matching point cloud; S6: Programming path compensation. Analyze the theoretical programming path of easily deformable workpieces, project each theoretical programming point onto the theoretical surface matching point cloud mesh, connect the projected point with the four vertices of the mesh to form four small triangles, calculate the area ratio of each triangle (S1:S2:S3:S4), and obtain the relative coordinates of the projected point in the mesh; according to the 3D matching point reference table, find the corresponding position in the actual surface mesh, calculate the compensated actual programming point coordinates (X real, Y real, Z real), and import them into the machine tool for processing.

2. The method for on-machine scanning measurement and compensation of easily deformable workpieces as described in claim 1, characterized in that, The tracking 3D laser scanner includes a scanner for acquiring point cloud data of the surface of easily deformable workpieces and a tracker for tracking the spatial position of the scanner; when scanning the curved surface of the workpiece, the scanner is fixed to the machine tool tilting head, and the tracker is fixed at a fixed position on the machine tool.

3. The method for on-machine scanning measurement and compensation of easily deformable workpieces as described in claim 2, characterized in that, In 3D modeling software, the surface of the theoretical workpiece is discretized at equal intervals to obtain point cloud data of the theoretical surface, which serves as the benchmark for the point cloud data of the theoretical shape of the workpiece.

4. The method for on-machine scanning measurement and compensation of easily deformable workpieces as described in claim 1, characterized in that, Step S4 employs isometric mapping by minimizing distance deformation.

5. The method for on-machine scanning measurement and compensation of easily deformable workpieces as described in claim 1, characterized in that, The reverse algorithm for surface flattening in step S4 includes the following steps. In the surface flattening stage, a mapping function from a 3D surface (X, Y, Z) to a 2D plane (U, V) is obtained, so that every point on the 3D surface can find a unique corresponding point on the 2D plane, thus completing the parameterization of the surface. In a 2D planar pattern, for a point P_uv = (u, v), determine the UV triangle it falls into, and find the position (α, β, γ) of the point inside the UV triangle by calculating the centroid coordinates, where α + β + γ = 1; Find the 3D mesh triangle corresponding to the UV triangle, and use the same centroid coordinates (α, β, γ) to interpolate on the 3D triangle to calculate the corresponding 3D coordinates P_xyz = α*A_xyz + β*B_xyz + γ*C_xyz.

6. The method for on-machine scanning measurement and compensation of easily deformable workpieces as described in claim 1, characterized in that, The tracking 3D laser scanner has a maximum scanning accuracy of 0.025mm, a single sampling area of ​​800mm×700mm, and a maximum scanning rate of 6,000,000 times / second, meeting the needs for rapid and high-precision measurement of large-sized, easily deformable workpieces.

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