Large thin-wall part non-uniform allowance tool path adaptability generation method

Abstract

The invention belongs to the field of precision manufacturing of aerospace parts, and relates to an adaptive generation method for a non-uniform allowance tool path of a large thin-wall part, in particular to an adaptive generation method for a non-uniform allowance tool path of a large thin-wall part. The method comprises the following steps: firstly, analyzing the elastic deformation of a large thin-wall cabin sample piece during horizontal installation, and solving the actual offset of a local bracket characteristic installation surface of the cabin under different stations; after an ideal tool path is generated by using CAM software, pose mapping is carried out on the tool path generated by the theoretical model, and it is ensured that the tool path on the support mounting surface is accurately adjusted. And performing array layout and optimization on the mapped tool path, and quickly and accurately generating the tool path adaptive to the non-uniform machining allowance. According to the method, the thickness of each layer of removed material in the actual machining process is accurately controlled, the machining error of the mounting surface of the support of the large thin-walled part caused by elastic deformation resilience under different stations is reduced, and the overall machining quality and machining precision of the large thin-walled part are improved.

Description

Technical Field

[0001] The invention belongs to the field of precision manufacturing of aerospace parts, and relates to a method for adaptively generating a non-uniform margin tool path for large thin-walled parts. Background Art

[0002] As a key component of a spacecraft, large thin-walled spacecraft cabin parts provide the overall configuration of the spacecraft and directly affect the service performance of the spacecraft. It consists of a thin-walled cabin body and more than a hundred brackets installed on it. The thin-walled cabin body is large in size and low in rigidity, and is a typical large thin-walled shell part. The mounting surface of the outboard bracket provides an installation interface for outboard loads such as space manipulators and solar wings. In order to ensure the strict geometric tolerance requirements between the installation interfaces of the outboard loads, extremely high precision requirements are placed on the design dimensions of the outboard bracket mounting surface. For the high-precision machining tasks of large cabin outboard brackets, the traditional split repair and manufacturing model has low production efficiency and is difficult to ensure the stability of machining quality. The manufacturing model based on the gantry machining center has high production costs and limited process methods. In response to these manufacturing problems, robot in-situ integrated machining provides a feasible solution for the high-precision manufacturing of cabin bracket mounting surfaces.

[0003] However, due to its large size and low rigidity, the spacecraft cabin is prone to overall elastic deformation during machining. In addition, due to the overall manufacturing tolerance of the cabin and the bracket installation error, there is a difference between the actual machining allowance and the designed machining allowance, which will cause more problems. Machining based only on theoretical models and unified design allowances may lead to unstable machining, and the accuracy of the bracket after machining may not meet the design standard. Therefore, when performing robotic in-situ integrated machining of such large spacecraft cabins, accurate tool path planning for the local bracket features of the cabin plays a key role in ensuring the final machining accuracy of the bracket installation surface.

[0004] Patent publication number CN116117597B of Feng Changxi et al., "A method for online measurement and compensation processing of spacecraft thin-walled cabin lightening grooves", this patent performs online measurement of spacecraft thin-walled cabin lightening grooves, calculates compensation values ​​based on contour and thickness data, and finally performs processing by calling compensation values, thereby improving the degree of automation of measurement and processing. However, this method mainly focuses on the calculation of compensation values ​​to ensure the dimensional accuracy of the lightening groove thickness, and the compensation value calling method has limitations when processing multi-layer and multi-pass removal processing of complex structural features. The document "A technology framework for robotic profiling of blade edges based on model reconstruction and trajectory replanning", Journal of Manufacturing Processes, 2023, 94, 214-227 by Dazhuang Tian et al., adopts the method of blade model reconstruction and trajectory replanning to generate a blade edge profiling processing trajectory suitable for robot measurement-processing integrated manufacturing. However, this method ensures the accuracy of model reconstruction through complex operations such as point cloud reconstruction and registration. The calculation process is complex and time-consuming, and has certain limitations. Summary of the invention

[0005] In view of the defects of the prior art, the present invention invents a method for adaptively generating tool paths for non-uniform allowances of large thin-walled parts. The method first analyzes the elastic deformation of a large thin-walled cabin sample during horizontal installation to solve the actual offset of the cabin local bracket feature installation surface at different workstations; then, after generating an ideal tool path using CAM software, the tool path generated by the theoretical model is subjected to posture mapping to ensure that the tool path on the bracket installation surface is accurately adjusted to compensate for the deviation caused by elastic deformation; the spatial position of the blank surface is solved by actual measuring point data to determine the spatial distribution of the actual machining allowance; finally, the mapped tool path is arrayed and optimized to quickly and accurately generate a tool path that adapts to non-uniform machining allowances, so as to be suitable for in-situ integrated machining of the local bracket features of large thin-walled cabins, thereby avoiding complex allowance modeling, thereby ensuring that the machining accuracy of the local bracket installation surface of the large thin-walled cabin can meet the design requirements under the condition of considering elastic deformation and manufacturing errors.

[0006] The technical solution adopted by the present invention is a method for adaptively generating tool paths for non-uniform allowances of large thin-walled parts, which is characterized in that the method solves the actual offset of the installation surface of the local bracket feature of the cabin at different workstations by analyzing the elastic deformation of the large thin-walled cabin sample during horizontal installation; after generating the ideal tool path using CAM software, the tool path generated by the theoretical model is subjected to posture mapping to ensure accurate adjustment of the tool path on the bracket installation surface; the spatial position of the blank surface is solved by actual measuring point data to determine the spatial distribution of the actual machining allowance; finally, the mapped tool path is arrayed and optimized to quickly and accurately generate a tool path that adapts to the non-uniform machining allowance, so as to be suitable for the in-situ integrated machining of the local bracket features of the large thin-walled cabin, and ensure that the machining accuracy of the local bracket installation surface of the large thin-walled cabin can meet the design requirements while considering the elastic deformation and manufacturing errors.

[0007] The specific steps of the method are as follows:

[0008] Step 1: Calculate the actual offset of the characteristic mounting surface of the local support of the cabin at different workstations.

[0009] The thin-walled cabin of a spacecraft is a typical thin-walled shell structure made of aluminum alloy plates, on which relatively rigid bracket features are installed. During the integrated processing, the cabin will undergo elastic deformation due to the clamping force and gravity. Although the local bracket components are rigid, they will change their position in the global coordinate system due to the elastic deformation of the entire cabin.

[0010] First, finite element analysis is used to solve the deformation of the cabin under the action of clamping force and gravity. Then, a local coordinate system is established on the bracket installation surface. The position change of the bracket feature is defined in the local coordinate system, and the spatial position change of the bracket installation surface is accurately described by rotation transformation and translation transformation. Based on the finite element solution results, the singular value decomposition method is used to analyze the coordinates of multiple nodes on the installation surface before and after the cabin deformation in order to calculate the offset of the bracket installation surface. First, the coordinates of the nodes on the bracket installation surface before and after the cabin deformation are extracted, and the node coordinate difference ΔP is calculated i :

[0011] ΔP i =P i '-P i (1)

[0012] Among them, P i and P i ' are the coordinates of the i-th node before and after deformation.

[0013] Furthermore, the center point of the coordinate difference vector of the bracket mounting surface node before and after deformation is calculated as follows:

[0014]

[0015] Where n represents the total number of mesh nodes on the mounting surface.

[0016] Then, the covariance matrix H is constructed for singular value decomposition.

[0017]

[0018] H=UΣV T (4)

[0019] Among them, U and V are the left singular vector and the right singular vector obtained by singular value decomposition.

[0020] The rotation transformation and translation transformation of the local coordinate system of the bracket installation surface before and after the cabin deformation are calculated as follows:

[0021]

[0022] Among them, O L and O' L are the coordinates of the origin of the local coordinate system before and after the cabin is deformed.

[0023] Through the above calculation, the posture transformation of the bracket installation surface can be determined, providing accurate bracket installation surface offset data for the subsequent posture mapping in the tool path generation.

[0024] Step 2: Generate the ideal tool path and pose mapping for the local bracket mounting surface of the cabin.

[0025] In order to reduce the machining error of the bracket installation surface caused by the elastic deformation of the spacecraft cabin, after the ideal tool path is generated by CAM software, it is necessary to perform pose mapping on the tool path generated by the theoretical model to ensure accurate adjustment of the tool path on the bracket installation surface. The tool path pose mapping process can be described as follows:

[0026]

[0027] Among them, {CL} actual Indicates the actual installation surface tool path generated after posture mapping, cl jG and cl' jG They are the ideal tool path of the j-th bracket mounting surface in the global coordinate system and the tool path after pose mapping. jn and S ja They represent the ideal mounting surface and the actual mounting surface of the j-th bracket, respectively, where j = 1, 2, ..., N, and N is the total number of brackets. The f function is used to map the ideal tool path to the actual tool path.

[0028] Using CAM software, a local machining coordinate system is established on the bracket mounting surface, and an ideal tool path is generated in this coordinate system based on the theoretical model. L In this local machining coordinate system, the tool contact point coordinates and tool axis vector of the ideal tool path are as follows:

[0029]

[0030] Among them, P L is the tool contact point coordinate data set in the local support coordinate system, x i ,y i 、z i are the x, y, and z coordinates of the i-th knife contact point, V L is the tool axis vector in the local support coordinate system, V x 、V y 、V z They are the tool axis vector components in three directions.

[0031] The rotation and translation components from the local coordinate system to the global coordinate system are denoted as G R L and G D L In the global coordinate system, the tool contact point coordinates and tool axis vector are expressed as follows:

[0032]

[0033] Since the bracket is a local rigid body, the pose mapping of the ideal tool path on the bracket installation surface can be realized in the global coordinate system by performing pose transformation on the local machining coordinate system. The rotation and translation components of the local machining coordinate system caused by the elastic deformation of the entire cabin are R Trans and D Trans After the cabin body undergoes elastic deformation, the rotation matrix and translation vector obtained from the global coordinate system to the local coordinate system are as follows:

[0034]

[0035] The mapped tool path is composed of the tool contact point coordinates P in the global coordinate system. G ' and the tool axis vector V G '. In addition, in the plane feature end milling process, the tool axis vector remains unchanged. Therefore, the tool contact point coordinates and tool axis vector after posture mapping are calculated as follows:

[0036]

[0037] Combining formulas (7) to (10), the theoretical tool path {CL} from the bracket mounting surface can be derived: faceTo the actual tool path after offset {CL'} face The mapping relationship.

[0038]

[0039] By solving the offset of the bracket mounting surface caused by the overall deformation of the cabin, and obtaining the rotation component R of the local coordinate system Trans and translation component D Trans , which can complete the theoretical tool path generated based on the ideal design model {CL} face The actual tool path of the bracket installation surface after the overall deformation of the cabin {CL'} face 's mapping.

[0040] Step 3, solve the actual spatial position of the characteristic blank surface of the local support of the cabin.

[0041] Due to the overall machining error of the spacecraft cabin and the installation error of the bracket, there is a deviation between the actual machining allowance of the bracket feature and the design allowance during the in-situ integrated machining of the cabin. To solve this problem, the actual blank surface of the bracket feature is first scanned and measured using structured light measurement technology to accurately determine the spatial position of the blank surface.

[0042] In order to match the coordinate system of the ideal machining trajectory with the actual measured point cloud data, the coordinate data Q of the measured points on the surface of the bracket blank in the global coordinate system are firstly G (x i ,y i ,z i ) is converted to the actual local processing coordinate system to obtain the measuring point coordinate data Q in the local processing coordinate system L .

[0043] Q L =( G R L ) -1 (Q G - G D L ) (12)

[0044] Then, define the plane equation of the bracket blank surface in space as:

[0045] z=ax+by+c (13)

[0046] Among them, a, b, and c are parameters of the bracket blank plane equation to be determined.

[0047] In actual measurement operations, the collected measurement point data may be affected by measurement errors. In order to accurately determine the optimal plane position of the blank surface, the least squares method is used to fit and solve the measurement point data. Specifically, for the measurement point coordinate data Q on the bracket blank surface L , construct the following objective function for plane fitting:

[0048]

[0049] Taking partial derivatives of a, b, and c respectively, and setting these partial derivatives equal to zero, we get:

[0050]

[0051] Rewrite the above equation into matrix form:

[0052]

[0053] By solving the above matrix equation, the optimal values ​​of a, b and c can be obtained, and then the optimal position of the actual blank surface of the bracket can be determined. For the actual bracket feature, the enveloping space of the target surface and the blank surface in the local bracket coordinate system is the actual machining allowance space. This method ensures the accuracy of the blank surface positioning and provides a reliable basis for subsequent tool path planning.

[0054] Step 4: Adaptively generate the tool path for the non-uniform allowance of the local support features of the cabin.

[0055] Furthermore, in view of the unevenly distributed machining allowances on the spacecraft cabin bracket, an adaptive tool path generation strategy was developed to control the removal thickness and ensure that the robot machining system can accurately remove the actual allowances on the bracket mounting surface. The specific steps are:

[0056] 1) Construct the coordinate array of the knife contact points on the bracket mounting surface.

[0057] Calculate the surface measurement data Q of the bracket blank L The maximum distance H between the actual installation surface after pose mapping max , and use it as the maximum spacing of the tool path array copy. Since the surface of the bracket blank is a plane and the tool axis vector is parallel to the Z axis of the local machining coordinate system, H max Corresponds to the maximum Z coordinate value in the blank surface measurement data.

[0058] H max =max(z i ) (17)

[0059] Then, the single-layer removal thickness h of the bracket mounting surface finishing is used as the step length, and the coordinates of the knife contact points on the bracket mounting surface are arrayed along the Z direction of the local processing coordinate system.

[0060] P ij =P 0 +i·(0 0 h) T (18)

[0061] Where i represents the serial number of each layer in the tool path array, i = 1, 2, ..., n, j represents the processing layer number, j = 1, 2, ..., H max / h. ij Represents the coordinates of the knife contact point after the array.

[0062] 2) Filter valid knife contact point coordinates from the knife contact point coordinates after the array.

[0063] For each array, the knife contact point coordinates P ij , its positional relationship relative to the blank surface B and the target surface T must be calculated to determine whether the tool contact point is located between the two surfaces. The tool contact point position is determined by the following formula:

[0064] f effective =(B(P ij )≤0)∩(T(P ij )≥0) (19)

[0065] Among them, B(P ij ) represents the coordinates of the knife contact point P ij The directed distance to the blank surface B (if B (P ij )≤0, then the knife contact P ij Located on the surface of the blank or below), T(P ij ) represents the coordinates of the knife contact point P ij The directed distance to the target surface T (if T(P ij )≥0, then the knife contact P ij located on or above the target surface).

[0066] Based on the judgment of formula (19), the effective tool positions can be filtered into the set {CL} body middle:

[0067] {CL} body = {P ij ∣f effective} (20)

[0068] This ensures that the final generated tool path contains only those tool contact points that are between the stock surface and the target surface, thereby improving machining accuracy and efficiency.

[0069] 3) Tool contact connection and tool path generation

[0070] Sort the effective tool contact point coordinates of each processing layer in ascending order and connect them in sequence. Then insert appropriate transition points between each layer to form a continuous tool path that can adapt to the actual non-uniform machining allowance of the bracket. Through the above operations, a tool path that can fully cover the non-uniform allowance can be generated.

[0071] The significant effect and benefit of the present invention is that the method is aimed at the problem of inconsistency between the actual machining allowance and the reserved design allowance caused by the overall manufacturing error of the cabin and the installation error of the bracket feature during the actual integrated processing of the local bracket feature of the large thin-walled cabin. The method first analyzes the elastic deformation of the large thin-walled cabin sample during horizontal installation to solve the actual offset of the installation surface of the local bracket feature of the cabin at different stations. After the ideal tool path is generated by CAM software, the tool path generated by the theoretical model is mapped to ensure accurate adjustment of the tool path on the bracket installation surface. The mapped tool path is arrayed and optimized to quickly and accurately generate a tool path that adapts to non-uniform machining allowances. The method accurately controls the thickness of each layer of material removed during the actual processing process, reduces the processing error of the bracket installation surface of large thin-walled parts caused by elastic deformation rebound at different stations, and improves the processing stability and the overall processing quality and processing accuracy of large thin-walled parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 —Overall flow chart of the method.

[0073] Figure 2 —Scene diagram of robot in-situ integrated processing of large thin-walled cabin parts, in which: 1—large thin-walled cabin, 2—mobile robot measurement and processing integrated system, 3—support device, 4—rotating fixture.

[0074] Figure 3 —Diagram of the integrated system of mobile robot measurement and processing, in which: 5—industrial robot, 6—high-speed electric spindle, 7—line laser scanner, 8—mobile platform.

[0075] Figure 4 —Actual machining allowance distribution diagram of a typical bracket and its mounting surface.

[0076] Figure 5 —Result diagram of tool path of typical bracket mounting surface generated according to theoretical design allowance.

[0077] Figure 6 —Result diagram of tool path of typical bracket mounting surface generated according to actual machining allowance.

[0078] Figure 7—Generate the deviation distribution diagram of the typical bracket installation surface obtained by machining the theoretical tool path according to the design model.

[0079] Figure 8 —Deviation distribution diagram of a typical bracket mounting surface obtained by machining with the tool path obtained after pose mapping.

[0080] Fig. 9 —Comparison of absolute value of dimensional error of bracket mounting surface obtained by different processing methods. DETAILED DESCRIPTION

[0081] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention more clear, the specific implementation methods of the present invention will be described in detail below in combination with the technical solutions and the accompanying drawings.

[0082] Due to its large size and low rigidity, the spacecraft cabin is prone to overall elastic deformation during machining. In addition, due to the overall manufacturing tolerance of the cabin and the bracket installation error, there is a difference between the actual machining allowance and the designed machining allowance, which will cause more problems. Machining based only on theoretical models and unified design allowances may lead to unstable machining, and the accuracy of the bracket after machining may not meet the design standard. In order to overcome the above problems, a method for adaptive generation of non-uniform allowance tool paths for large thin-walled parts was invented. The overall process is shown in the attached figure. Figure 1 shown.

[0083] Taking the robot in-situ integrated processing of a 7075 aluminum alloy thin-wall cabin sample with an outer diameter of 3600mm and a length of 6200mm as an example, the implementation process of the present invention is described in detail. Figure 2 In the scenario of robot in-situ integrated processing of large thin-walled cabin parts, the large thin-walled cabin parts are stably mounted on the supporting device 3, and the circumferential rotational displacement of the cabin parts is realized with the help of the rotating fixture 4. The scanning and processing of the actual blank surface of the local support feature of the cabin are further completed through the mobile robot measurement and processing integrated system 2.

[0084] First, according to the attached Figure 2 The actual clamping layout and standard gravity load are shown, and the thin-walled cabin is subjected to static analysis using ANSYS software. The material elastic modulus of the large thin-walled cabin is E = 71.7 GPa, Poisson's ratio ν = 0.33, and density ρ = 2.81 g / cm 2 , define the mesh unit type as tetrahedral unit, the unit mesh size as 5mm, and obtain the topological relationship between the finite element mesh, unit, and node of the large thin-walled cabin body through post-processing, as well as the coordinate values ​​and deformation displacement vectors of the finite element mesh nodes before and after the elastic deformation of the large thin-walled cabin body under gravity and clamping. According to equations (1)-(5), the rotation component R of the local processing coordinate system caused by the elastic deformation of the cabin body as a whole is calculated. Trans and the translation component D Trans .

[0085] Secondly, taking four typical local bracket features as an example, UG software was used to plan the machining path for the local bracket feature target surface of the design model cabin. During machining, the spindle speed was 5000r / min, the feed speed was 200mm / min, and the theoretical tool path generated according to the ideal design model was obtained through post-processing {CL} face According to equations (7)-(11), the theoretical tool path {CL} generated based on the ideal design model is completed. face The actual tool path of the bracket installation surface after the overall deformation of the cabin {CL'} face 's mapping.

[0086] Then, use the following Figure 3 The mobile robot measurement and processing integrated system shown in the figure scans and measures the blank surface of the local bracket feature of the large thin-walled cabin in the horizontal installation state, obtains the actual blank surface point cloud data of the local bracket feature of the cabin, and converts it to the actual local processing coordinate system. According to equations (13)-(16), the actual spatial position of the bracket blank surface is solved. According to the spatial position of the bracket installation surface and the actual blank surface after posture mapping, the actual processing allowance distribution of four typical local bracket features is obtained as shown in the attached figure. Figure 4 As shown in the figure, the machining allowance reserved for the local bracket feature during the design process is a uniformly distributed 5mm equal thickness removal. However, the actual machining allowance of the local bracket feature is different from the ideal allowance state, and its thickness distribution is uneven. It is necessary to generate a targeted machining path for its actual non-uniform allowance.

[0087] Combined with the actual tool path of the bracket installation surface after posture mapping and the calculation results of the actual blank surface obtained in the above process, the machining path of the actual non-uniform allowance of the cabin bracket feature is calculated and generated according to equations (17)-(20). Finally, through post-processing, the processing file that can be recognized by the robot is output to realize the adaptive planning of the machining path of the actual non-uniform allowance of the local bracket feature of large thin-walled cabin parts, and achieve stable machining of local features while ensuring machining accuracy.

[0088] In order to verify the effectiveness of the proposed method in controlling the thickness of single-layer material removal, the machining paths obtained by planning according to the theoretical design allowance and the machining paths generated by the proposed method were compared with each other, as shown in the attached figure. Figure 5 and attached Figure 6 As shown. Figure 5It can be seen that the machining paths directly planned according to the ideal reserved 5mm equal thickness machining allowance are all three-layer machining paths. The number of machining paths is insufficient, and the thickness of the material to be removed between the first layer machining path and the actual blank surface is large. When machining according to this path, the material removal thickness varies significantly, and the actual maximum removal thickness even exceeds 5mm. Therefore, the typical bracket installation surface tool path generated according to the theoretical design allowance cannot be directly used for robot machining system machining operations. Figure 6 It can be seen that the machining path generated by this method can generate a machining path layer by layer with equal thickness between the actual blank surface and the target installation surface, which can effectively fill all the excess space and ensure that the thickness of a single layer of material removed during the actual machining process does not exceed 2 mm, which can effectively ensure the stable and controllable removal of the actual excess.

[0089] At the same time, in order to verify the effectiveness of the method in improving machining accuracy, four typical bracket samples were used as the objects, and the results of the tool paths generated by the theoretical design model and the tool paths planned by the proposed method were compared. The actual deviation distribution of the mounting surfaces of the four typical brackets obtained by different machining methods was calculated, and the absolute value of the final dimensional error of the bracket mounting surface was used as the judgment standard for the machining results. Among them, the deviation value distribution of the bracket mounting surface obtained by machining according to the tool path generated by the theoretical design model is shown in the attached figure. Figure 7 As shown in the figure; according to the tool path planned by the proposed method, the obtained bracket installation surface deviation value distribution is shown in the attached figure. Figure 8 As shown. Figure 7 and attached Figure 8 From the deviation value distribution results, it can be seen that when the tool path generated by the theoretical design model is used for processing, the minimum deviation of the four typical bracket mounting surfaces is greater than 0.9mm, and the maximum value can even reach more than 1.6mm; while the absolute values ​​of the deviation values ​​of the four typical bracket mounting surfaces processed by the proposed method are all below 0.15mm, indicating that the proposed method can effectively reduce the processing deviation of the bracket mounting surface.

[0090] In order to further evaluate the machining accuracy of different methods, the absolute value of the final dimensional error of the bracket mounting surface obtained by machining was calculated. The absolute value of the final dimensional error is shown in the attached figure. Fig. 9 Attached Fig. 9 The calculation results show that the absolute value of the final dimensional error of the bracket mounting surface is significantly reduced when the tool path planned by the proposed method is used for processing. Compared with the processing directly using the tool path planned by the theoretical design model, the absolute values ​​of the dimensional errors of the four typical bracket samples are reduced by more than 90%.

[0091] The comparison results show that the adaptive generation method of non-uniform allowance tool paths for large thin-walled parts of the present invention can accurately control the thickness of material removed in each layer during the actual processing, while reducing the processing error of the mounting surface of the bracket of large thin-walled parts caused by elastic deformation and springback at different workstations, thereby improving the overall processing quality and processing accuracy of large thin-walled parts, and playing an important guiding role in the in-situ integrated processing of large thin-walled components in actual engineering.

Claims

1. A method for adaptively generating tool paths for non-uniform allowances of large thin-walled parts, characterized in that: The method analyzes the elastic deformation of the large thin-walled cabin sample during horizontal installation, and solves the actual offset of the cabin local bracket feature installation surface at different workstations; after generating the ideal tool path using CAM software, the tool path generated by the theoretical model is mapped to ensure accurate adjustment of the tool path on the bracket installation surface; the spatial position of the blank surface is solved by the actual measuring point data, and the spatial distribution of the actual machining allowance is determined; finally, the mapped tool path is arrayed and optimized, and a tool path that adapts to non-uniform machining allowance is quickly and accurately generated, so as to be suitable for the in-situ integrated processing of the local bracket features of the large thin-walled cabin, and ensure that the processing accuracy of the local bracket installation surface of the large thin-walled cabin can meet the design requirements under the condition of considering elastic deformation and manufacturing errors; the specific steps of the method are as follows: Step 1, solving the actual offset of the characteristic mounting surface of the local support of the cabin at different workstations; The thin-walled cabin of a spacecraft is a typical thin-walled shell structure made of aluminum alloy plates, on which relatively rigid bracket features are installed. During the integrated processing, the cabin will undergo elastic deformation due to the clamping force and gravity. Although the local bracket components are rigid, they will change their position in the global coordinate system due to the elastic deformation of the entire cabin. Firstly, finite element analysis is used to solve the deformation of the cabin under the action of clamping force and gravity. Then, a local coordinate system is established on the bracket installation surface. The position and posture changes of the bracket features are defined in the local coordinate system, and the spatial position and posture changes of the bracket installation surface are accurately described by rotation transformation and translation transformation. Based on the finite element solution results, the singular value decomposition method is used to analyze the coordinates of multiple nodes on the installation surface before and after the cabin deformation in order to calculate the offset of the bracket installation surface. Firstly, the coordinates of the nodes on the bracket installation surface before and after the cabin deformation are extracted, and the node coordinate difference ΔP is calculated. i : ΔP i =P i '-P i (1) Among them, P i and P i ' are the coordinates of the i-th node before and after deformation; Furthermore, the center point of the coordinate difference vector of the bracket mounting surface node before and after deformation is calculated as follows: Where n represents the total number of mesh nodes on the mounting surface; Then, the covariance matrix H is constructed for singular value decomposition; H=UΣV T (4) Among them, U and V are the left singular vector and right singular vector obtained by singular value decomposition; The rotation transformation and translation transformation of the local coordinate system of the bracket installation surface before and after the cabin deformation are calculated as follows: Among them, O L and O' L are the coordinates of the origin of the local coordinate system before and after the cabin deformation; Through the above calculation, the posture transformation of the bracket installation surface can be determined, providing accurate bracket installation surface offset data for the subsequent posture mapping in the tool path generation; Step 2: ideal tool path generation and pose mapping of the local bracket mounting surface of the cabin; In order to reduce the machining error of the bracket installation surface caused by the elastic deformation of the spacecraft cabin, after the ideal tool path is generated by CAM software, it is necessary to perform pose mapping on the tool path generated by the theoretical model to ensure accurate adjustment of the tool path on the bracket installation surface; the tool path pose mapping process can be described as follows: Among them, {CL} actual Indicates the actual installation surface tool path generated after posture mapping, cl jG and cl' jG They are the ideal tool path of the j-th bracket mounting surface in the global coordinate system and the tool path after pose mapping; S jn and S ja represent the ideal mounting surface and the actual mounting surface of the j-th bracket, respectively, where j = 1, 2, ..., N, N is the total number of brackets; the f function is used to map the ideal tool path to the actual tool path; Using CAM software, a local machining coordinate system is established on the bracket mounting surface, and an ideal tool path is generated in this coordinate system based on the theoretical model. L ; In this local machining coordinate system, the tool contact point coordinates and tool axis vector of the ideal tool path are as follows: Among them, P L is the tool contact point coordinate data set in the local support coordinate system, x i ,y i 、z i are the x, y, and z coordinates of the i-th knife contact point, V L is the tool axis vector in the local support coordinate system, V x 、V y 、V z They are the tool axis vector components in three directions; The rotation and translation components from the local coordinate system to the global coordinate system are denoted as G R L and G D L ; In the global coordinate system, the tool contact point coordinates and tool axis vector are expressed as follows: Since the bracket is a local rigid body, the pose mapping of the ideal tool path on the bracket installation surface can be realized in the global coordinate system by performing pose transformation on the local machining coordinate system. The rotation and translation components of the local machining coordinate system caused by the overall elastic deformation of the cabin are R Trans and D Trans ; After the cabin body undergoes elastic deformation as a whole, the rotation matrix and translation vector obtained from the global coordinate system to the local coordinate system are as follows: The mapped tool path is represented by the tool contact point coordinates P′ in the global coordinate system. G and tool axis vector V′ G In addition, in the plane feature end milling process, the tool axis vector remains unchanged. Therefore, the tool contact point coordinates and tool axis vector after posture mapping are calculated as follows: Combining formulas (7) to (10), the theoretical tool path {CL} from the bracket mounting surface can be derived: face To the actual tool path after offset {CL'} face The mapping relationship of By solving the offset of the bracket mounting surface caused by the overall deformation of the cabin, and obtaining the rotation component R of the local coordinate system Trans and the translation component D Trans , which can complete the theoretical tool path generated based on the ideal design model {CL} face The actual tool path of the bracket installation surface after the overall deformation of the cabin {CL'} face The mapping of Step 3, solving the actual spatial position of the characteristic blank surface of the local support of the cabin; Due to the overall machining error of the spacecraft cabin and the installation error of the bracket, there is a deviation between the actual machining allowance of the bracket feature and the design allowance during the in-situ integrated machining of the cabin. To solve this problem, the actual blank surface of the bracket feature is scanned and measured using structured light measurement technology to accurately determine the spatial position of the blank surface. In order to match the coordinate system of the ideal machining trajectory with the actual measured point cloud data, the measured point coordinate data Q on the surface of the bracket blank in the global coordinate system is first G (x i ,y i ,z i ) is converted to the actual local processing coordinate system to obtain the measuring point coordinate data Q in the local processing coordinate system L ; Q L =( G R L ) -1 (Q G - G D L ) (12) Then, define the plane equation of the bracket blank surface in space as: z=ax+by+c (13) Among them, a, b, and c are the parameters of the plane equation of the bracket blank to be determined; In actual measurement operations, the collected measurement point data may be affected by measurement errors. In order to accurately determine the optimal plane position of the blank surface, the least squares method is used to fit and solve the measurement point data. Specifically, for the measurement point coordinate data Q on the bracket blank surface, L , construct the following objective function for plane fitting: Taking partial derivatives of a, b, and c respectively, and setting these partial derivatives equal to zero, we get: Rewrite the above equation into matrix form: By solving the above matrix equation, the optimal values ​​of a, b and c can be obtained, and then the optimal position of the actual blank surface of the bracket can be determined; for the actual bracket features, the enveloping space of the target surface and the blank surface in the local bracket coordinate system is the actual machining allowance space; this method ensures the accuracy of the blank surface positioning and provides a reliable basis for subsequent tool path planning; Step 4, adaptive generation of tool path for non-uniform allowance of local support features of cabin; Furthermore, in view of the unevenly distributed machining allowance on the spacecraft cabin bracket, an adaptive tool path generation strategy was developed to control the removal thickness and ensure that the robot machining system can accurately remove the actual allowance on the bracket mounting surface; the specific steps are as follows: 1) constructing a knife contact point coordinate array of the bracket mounting surface; Calculate the surface measurement data Q of the bracket blank L The maximum distance H between the actual installation surface after pose mapping max , and use it as the maximum spacing of the tool path array copy; since the surface of the bracket blank is a plane, and the tool axis vector is parallel to the Z axis of the local machining coordinate system, H max Corresponding to the maximum Z coordinate value in the blank surface measurement data; H max =max(z i ) (17) Then, the single-layer removal thickness h of the bracket mounting surface finishing is used as the step length, and the coordinates of the knife contact points on the bracket mounting surface are arrayed along the Z direction of the local processing coordinate system; P ij =P0+i·(0 0 h) T (18) Where i represents the serial number of each layer in the tool path array, i = 1, 2, ..., n, j represents the processing layer number, j = 1, 2, ..., H max / h; P ij Represents the coordinates of the knife contact point after the array; 2) selecting effective knife contact point coordinates from the knife contact point coordinates after the array; For each array, the knife contact point coordinates P ij , its positional relationship relative to the blank surface B and the target surface T must be calculated to determine whether the tool contact point is located between the two surfaces; the tool contact point position is determined by the following formula: f effective =(B(P ij )≤0)∩(T(P ij )≥0) (19) Among them, B(P ij ) represents the coordinates of the knife contact point P ij The directed distance to the blank surface B (if B (P ij )≤0, then the knife contact P ij Located on the surface of the blank or below), T(P ij ) represents the coordinates of the knife contact point P ij The directed distance to the target surface T (if T(P ij )≥0, then the knife contact P ij located on or above the target surface); Based on the judgment of formula (19), the effective tool positions can be filtered into the set {CL} body middle: {CL} body = {P ij ∣f effective } (20) This ensures that the final generated tool path only contains those tool contact points located between the blank surface and the target surface, thereby improving machining accuracy and efficiency; 3) Tool contact connection and tool path generation The effective tool contact point coordinates of each processing layer are sorted in ascending order and connected in sequence; then appropriate transition points are inserted between the layers to form a continuous tool path so that it can adapt to the actual non-uniform processing allowance of the bracket; through the above operations, a tool path that can completely cover the non-uniform allowance can be generated.

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