In-situ robotic machining method and system for large spherical shell members

Abstract

The large spherical shell component robot in-situ processing method and system solve the problem of how to realize high-efficiency and high-precision processing of large spherical shell assembly multi-specification hole system, and belong to the high-precision installation technical field of flange parts. The present application determines the optimal robot processing station set on the basis of the existing in-situ robot processing equipment, determines the overall structure size of the arch-shaped moving platform according to the optimal robot processing station set, and completes the manufacturing and installation; finds the installation position on the installed arch-shaped moving platform, and fixes the cantilever fixed platform on the installation position; tracks the outer public point of the ball, the inner public point of the ball and the auxiliary measuring point on the cantilever fixed platform by using a laser tracker multi-station measuring network, and obtains the conversion relationship between the robot base coordinate system and the to-be-processed hole workpiece coordinate system; according to the processing sequence and the obtained conversion relationship, robot error modeling and compensation are carried out, and the robot is processed by using the compensated processing program.

Description

Technical Field

[0001] This invention relates to a robotic in-situ machining method and system for large spherical shell components, belonging to the field of high-precision installation technology for flange parts. Background Technology

[0002] In the field of major scientific and technological equipment, increasingly complex and ultra-large components are being used as the main structure. Due to their large size and weight, these components are difficult to move and transport, making their manufacturing a significant challenge. On-site, in-situ machining using mobile equipment is a reasonable solution. Industrial robots, with their low cost, high flexibility, and versatility, are being widely applied in the on-site, in-situ machining of ultra-large components. However, existing technologies lack effective methods for machining multi-specification hole systems in large spherical shells.

[0003] Existing technologies already contain relevant solutions. Invention patent publication number CN107138762A proposes a method for machining large spherical shells with multiple holes, utilizing a robot and a combined mobile support for drilling holes in the sphere. Invention patent publication numbers CN120619438A and CN108908376A both propose machining schemes using an arched rotary platform and a robotic machining system, with an external laser tracker guiding the robot to complete the drilling of large spherical shell components, and statistically analyzing the drilling patterns of the large spherical shell components for overall machining planning. However, the above solutions, relying solely on an external laser tracker to guide the robot to complete the machining, still have the following problems:

[0004] First, the robot's position was not optimized and was arranged based on experience, which may result in some holes being unreachable or requiring multiple disassembly and reassembly of the platform, thus reducing processing efficiency.

[0005] Second, the lack of precise calibration of the robot's base coordinate system and a systematic transformation method with the workpiece coordinate system means that the robot's absolute positioning error directly affects the hole-opening accuracy.

[0006] Third, the measurement network is simple to construct, relying only on a single external tracker for station transfer, making it difficult to unify internal and external measurement benchmarks, which leads to the accumulation of coordinate system transmission errors;

[0007] Fourth, the lack of a compensation mechanism for robot machining errors makes it impossible to meet the machining requirements of high-precision flange holes.

[0008] Therefore, there is an urgent need for a field processing method that can systematically solve the problems of robot positioning planning, precise installation, multi-station measurement network construction, coordinate system unification, and error compensation, so as to achieve efficient and high-precision processing of multi-specification hole systems for large spherical shell components. Summary of the Invention

[0009] To address the problem of how to achieve efficient and high-precision machining of multi-specification hole systems in large spherical shell components, this invention provides a robotic in-situ machining method and system for large spherical shell components.

[0010] The present invention provides a method for in-situ robotic machining of large spherical shell components, characterized in that the method is based on in-situ robotic machining equipment, which includes a load-bearing mechanism, an arched moving platform, a cantilevered fixed platform, a robotic milling system, and a multi-station measurement network of a laser tracker.

[0011] The load-bearing mechanism is fixed in the foundation, the arched moving platform can rotate around the axis of the load-bearing mechanism, and the cantilevered fixed platform is used to fix itself on the arched moving platform and support the robot milling system; the processing method includes:

[0012] S1. Determine the processing sequence and processing location of large spherical shell components;

[0013] S2. Based on the features to be processed at each processing location, extract the set of key limit points that can characterize its spatial range and processing accessibility requirements; with the goal of ensuring that the set of key limit points of all processing features can be covered by the workspace of the robot milling system and minimizing the total number of processing stations required to cover all processing features, establish and solve the station optimization model to obtain the optimal set of robot processing stations in the spherical coordinate system.

[0014] Based on the optimal set of robot processing stations and the fixed interface dimensions of the cantilever fixed platform, the overall structural dimensions of the arched mobile platform are determined, and manufacturing and installation are completed.

[0015] S3. Locate the installation position on the already installed arched mobile platform and fix the cantilever fixed platform at the installation position;

[0016] S4. Using a multi-station measurement network of a laser tracker, track the common point outside the sphere, the common point inside the sphere, and the auxiliary measurement points on the cantilever fixed platform to obtain the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed.

[0017] S5. Based on the machining sequence of the large spherical shell component and the transformation relationship between the robot's base coordinate system and the workpiece coordinate system of the hole to be machined, perform robot error modeling and compensation, and use the compensated machining program to machine the large spherical shell component by robot.

[0018] Preferably, S2 includes:

[0019] S21. Establish a sphere center coordinate system and a workpiece coordinate system for each feature to be processed; for each feature to be processed, construct an envelope space based on its geometric dimensions, and extract a set of key limit points that can characterize its spatial range and processing accessibility requirements in the envelope space. Establish feature verification point coordinate systems with the extracted key limit points as the origin. The feature verification point coordinate systems are aligned with the corresponding workpiece coordinate systems for the holes to be processed.

[0020] S22. Based on the workspace of the robot milling system, the set of candidate robot processing stations corresponding to each feature to be processed is determined with the criterion that the origin of the coordinate system of all feature verification points of each feature to be processed can be covered by the workspace.

[0021] S23. Select robot processing stations from the discrete set of all candidate robot processing stations, and establish an optimization model with the objective of minimizing the number of selected robot processing stations and the constraint of covering all features to be processed.

[0022] S24. Solve the optimization model to obtain a set of preliminary feasible robot processing positions;

[0023] S25. For each initially feasible robot processing station, define the coordinate system of its corresponding feature verification point as the robot end coordinate system. Calculate the joint angles through the robot kinematics inverse solution. If all joint angles are within the preset limit range, the corresponding station is confirmed to meet the feasibility requirements. Otherwise, the corresponding station is removed and the optimization model is re-solved until all stations meet the joint angle constraints, thus obtaining the optimal set of robot processing stations.

[0024] S26. Based on the position of the optimal robot processing station in the spherical coordinate system and the fixed interface size of the cantilever fixed platform, determine the overall structural size of the arched mobile platform to ensure that all optimal robot processing stations can be installed on the arched mobile platform.

[0025] Preferably, in step S3, at least three marking reference points of the cantilever fixed platform obtained during flat ground measurement are combined with the optimal station set, and the coordinates of the at least three marking reference points in the spherical coordinate system are calculated through coordinate transformation. These coordinates serve as the positioning reference points of the cantilever fixed platform on the arched moving platform. Based on these positioning reference points, the installation position is found on the already installed arched moving platform, and the cantilever fixed platform is fixed at the installation position.

[0026] Preferably, S3 includes:

[0027] S31. Temporarily place the cantilever platform equipped with the robot on the ground, establish the robot's base coordinate system at this time, and measure and record the coordinates of at least three non-collinear scribing reference points on the back plate of the cantilever platform under the base coordinate system.

[0028] S32. Based on the base coordinate system of the robot positions in the optimal robot processing station set, calculate the coordinates of the at least three non-collinear scribing reference points in the sphere-centered coordinate system, and calculate the distance between the sphere center and each scribing reference point in the sphere-centered coordinate system.

[0029] S33. On the installed arched bearing platform, measure the pre-arranged common points using a multi-station measurement network of a laser tracker to reproduce the sphere center coordinate system;

[0030] S34. In the sphere-centered coordinate system, measure the mounting plane on the arched bearing platform used to install the cantilever platform, and fit the plane equation of the mounting plane.

[0031] S35. In the sphere-centered coordinate system, with the origin of the sphere-centered coordinate system as the sphere center, construct spatial spheres with the distance between the sphere center and each scribed reference point in the sphere-centered coordinate system as the radius, solve for the intersection points of each spatial sphere with the plane equation, and obtain a set of spatial point coordinates on the installation plane, which serve as the positioning reference points of the cantilever fixed platform on the arched mobile platform.

[0032] S36. In the sphere center coordinate system, using the pointing function of the multi-station measurement network of the laser tracker, find the installation position on the installed arched moving platform according to the positioning reference point;

[0033] S37. Based on the installation location, install a support structure on the arched bearing platform, and hoist the cantilever platform onto the support structure for fixation.

[0034] Preferably, S4 includes:

[0035] S41. Measure the common points inside the sphere that are preset on the inner surface of the large spherical shell component, fit the center of the sphere, establish the coordinate system of the sphere center, and realize the unification of the measurement network inside and outside the sphere through the light guide hole on the large spherical shell component.

[0036] S42. Using the multi-station measurement network of the laser tracker, measure the common point outside the sphere preset on site to obtain the transformation relationship between the laser tracker measurement coordinate system and the sphere center coordinate system. ;

[0037] S43. Based on the design parameters of the hole to be machined, establish a corresponding workpiece coordinate system for the hole to be machined in the sphere-centered coordinate system, and obtain the transformation relationship between the sphere-centered coordinate system and the workpiece coordinate system for the hole to be machined. ;

[0038] S44. Measure the auxiliary measurement points on the cantilevered fixed platform, establish the robot base coordinate system at the current position under the laser tracker measurement coordinate system, and obtain the transformation relationship between the laser tracker measurement coordinate system and the robot base coordinate system at the current position. ;

[0039] S45. Combining the transformation relationships obtained from S42 to S44, calculate the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed.

[0040] As a preferred embodiment, S5 includes:

[0041] S51. Based on the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed, generate the initial sampling point measurement program, the no-load running program, and the processing program;

[0042] S52. Run the sampling point measurement program, measure the actual pose of the robot at each preset sampling point using a laser tracker, and compare it with the theoretical pose to obtain the positioning error at each sampling point.

[0043] S53. Based on the positioning error of the sampling points and their theoretical coordinate values, establish a robot positioning error prediction model;

[0044] S54. Based on the robot positioning error prediction model, compensate the empty running program and the machining program to generate compensated empty running program and machining program.

[0045] S55. Run the compensated no-load program, measure the actual running trajectory of the robot through the multi-station measurement network of the laser tracker, and calculate the position error and centering error of the trajectory relative to the theoretical trajectory of the hole to be processed based on the measurement data;

[0046] S56. Determine whether the position error and alignment error meet the preset machining accuracy requirements:

[0047] If the requirements are met, the hole to be machined is machined using the compensated machining program;

[0048] If the requirements are not met, return to S52 and re-measure the sampling points until the requirements are met.

[0049] Preferably, the method for compensating the empty run program and the processing program includes:

[0050] The robot positioning error prediction model optimizes the sampling point interval, the first The and the first The optimal interval between sampling points is obtained by the following formula:

[0051]

[0052] in, The distance between sampling points For the first Coordinates of each sampling point, This is the predicted value of the sampling point positioning error. This refers to the robot's positioning error before compensation at the target point. Measurement error in multi-station measurement network for laser tracker; To improve robot positioning accuracy; , These represent the lower and upper limits of the machining space for the trajectory points of the holes to be machined, respectively.

[0053] As a preferred option, in S56, a segmented roughing strategy is adopted to process the hole to be processed:

[0054] Depending on the machining depth, two different overhang lengths of end mills are provided, with overhang lengths of 100 mm and 140 mm respectively;

[0055] Use a milling cutter with an overhang of 100 mm to machine workpieces with a thickness of 0~80 mm and a cutting depth of 1 mm;

[0056] The workpiece with the remaining thickness was machined using a milling cutter with an overhang of 140 mm and a depth of cut of 0.5 mm.

[0057] Preferably, the common points outside the sphere are evenly distributed at a certain distance from the axis of the circular foundation, with two points arranged in a staggered pattern at different heights. Four common points outside the sphere are fixed on each concrete column, and the common points inside the sphere are arranged on the inner surface of the sphere shell and avoid the area of ​​the hole to be processed.

[0058] The beneficial effects of this invention are as follows: the invention designs the optimal robot position based on all processing features of the spherical shell component, and further designs the structural dimensions of the arched platform. Based on the calibration of the arched platform using laser tracking, it can ensure that the cantilevered fixed platform can be accurately installed in the designated position. Furthermore, the invention provides a robot processing solution using laser tracking and error compensation technology, enabling efficient and high-precision processing of multi-specification hole systems in large spherical shell components. Attached Figure Description

[0059] Figure 1 Schematic diagram of in-situ robotic processing equipment;

[0060] Figure 2 A schematic diagram of the flange hole envelope space and its eight corner points;

[0061] Figure 3 A schematic diagram illustrating the feasibility of robot positioning for processing using a simplified spatial design;

[0062] Figure 4 This is a schematic diagram of an arched mobile platform;

[0063] Figure 5 A schematic diagram of the network setup process for the tracking device measurement network;

[0064] Figure 6 A schematic diagram of the sampling point data for the processing trajectory;

[0065] Figure 7 A schematic diagram of the measurement data for a circular hole;

[0066] Figure 8 This is a schematic diagram of the measurement data for a rectangular hole.

[0067] Figure 9 This is a schematic diagram of the guide rail structure;

[0068] Figure 10 A schematic diagram is provided for establishing the coordinate system of the cantilevered fixed robot platform. Detailed Implementation

[0069] 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.

[0070] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0071] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0072] The in-situ robotic machining method for large spherical shell components in this embodiment is based on in-situ robotic machining equipment, which includes a load-bearing mechanism 8, an arched moving platform 2, a cantilevered fixed platform 4, a robotic milling system 3, and a laser tracker multi-station measurement network 5.

[0073] The load-bearing mechanism 8 is fixed in the foundation, the arched mobile platform 2 can rotate around the axis of the load-bearing mechanism 8, and the cantilever fixed platform 4 is used to fix on the arched mobile platform 2 and support the robot milling system 3. Specifically, the load-bearing mechanism 8 is embedded in reinforced concrete and consists of a circular frame beam, a fixed arched platform device, a radial positioning device and a guide rail. The processing stability of the arched mobile platform is achieved through five evenly distributed crossbeams.

[0074] The arched mobile platform 2 is composed of four arched beams and a circular frame beam connected by bolts. The circular frame beam is adapted to the guide rail of the load-bearing mechanism 8 and can rotate circumferentially around the axis of the load-bearing mechanism. The cantilevered fixed platform 4 is welded and fixed to the arched mobile platform 2 via positioning blocks and is used to support the robotic milling system. The multi-station laser tracker measurement network includes at least two laser trackers, an external common point 7, and several internal common points. The external common points 7 are evenly distributed at a certain distance from the axis of the circular foundation, with two points arranged in a staggered pattern. Four external common points 7 are fixed on each concrete column. The internal common points are arranged on the inner surface of the spherical shell and avoid the area of ​​the hole to be processed. The robotic milling system consists of a robot body, an electric spindle system, a PLC control system, and a monitoring system, and is configured and communicated via a fieldbus. The processing method of this embodiment includes:

[0075] Step 1: Determine the processing sequence and processing locations of large spherical shell components;

[0076] Determine the machining sequence of the flange holes on the large spherical shell, and determine the specific location of the holes to be machined in the sphere's center coordinate system. Check if the robot is operating normally and check if the cutting tools are damaged.

[0077] Step 2: Based on the features to be processed at each location, extract the set of key limit points that can characterize its spatial range and processing accessibility requirements; with the goal of ensuring that the set of key limit points of all features to be processed can be covered by the workspace of the robot milling system 3 and minimizing the total number of processing stations required to cover all features to be processed, establish and solve the station optimization model to obtain the optimal set of robot processing stations in the spherical coordinate system.

[0078] Based on the optimal set of robot processing stations and the fixed interface dimensions of the cantilever fixed platform 4, the overall structural dimensions of the arched mobile platform 2 are determined, and manufacturing and installation are completed.

[0079] Specifically, taking the machining of flange holes as an example, the robot station design is based on the principles of ensuring the machinability of all features and minimizing the number of robot disassemblies and reassemblies. It is divided into several steps: first, quickly selecting robot stations based on simplified space; second, aiming to cover all eight corner points of the holes to be machined with the fewest possible stations; and finally, precisely verifying the accessibility of the selected robot stations using eight verification points for each flange hole. Specifically: Step 21, establish the sphere center coordinate system {Q} and the flange hole coordinate system {WF}. For example... Figure 2 As shown, the cubic envelope space of N flange holes on the spherical shell is calculated. Under the coordinate system {WFi} of the verification point of the i-th flange hole, the coordinate system {WFi} of the verification point of the flange hole is established with the 8 corner points of the envelope space as the origin. }, { The coordinate system} is aligned with the coordinate system {WFi}. , ;

[0080] Step 22, as follows Figure 3 As shown, the workspace of the robot machining system is drawn, using the flange hole verification point coordinate system { The criteria for determining whether each flange hole falls within the robot's workspace are the set of robot machining stations corresponding to each flange hole. The set contains at most Each robot is positioned.

[0081] Step 23: To reduce the number of robot machining stations, it is necessary to merge robot machining stations to reduce the transportation and installation time of the cantilever fixed platform. The robot machining station planning problem is transformed into starting from a set of discrete machining stations. The problem of selecting the minimum number of processing stations, i.e., this discrete set of stations. We select a set of machining stations with the fewest possible numbers to minimize the number of disassemblies the robot makes on the arched platform, while ensuring that all flange hole machining tasks can be completed. Therefore, the optimization model for the robot machining station planning problem is:

[0082]

[0083] in, This is the set of 8 corner points of all holes to be machined. It is related to the robot processing station The corresponding position variables (in the sphere-centered coordinate system). It is related to the robot processing station The set of 8 corner points corresponding to the lower hole. When the position... If selected as a processing station, then The robot is at the processing station The set of all processable objects.

[0084] Step 24: Solve the optimization model to obtain a set of preliminary feasible robot processing positions;

[0085] Step 25: For each initially feasible robot processing station, the k-th robot station is known. The base coordinate system {B k}, and will Flange hole verification point coordinate system {Y i，j} is defined as the robot end-effector coordinate system. The joint angles are solved by inverse kinematics of the robot. If the joint angles are within the limit range of robot joint angles, it proves that the selected station meets the feasibility requirements. If there is no solution or the limit range is exceeded, the robot station is re-selected until the requirements are met, and the optimal set of robot processing stations is obtained.

[0086] Step 26, as follows Figure 4 As shown, based on the position of the optimal robot processing station in the spherical coordinate system and combined with the fixed interface size of the cantilever fixed platform 4, the overall structural size of the arched mobile platform 2 is determined to ensure that all optimal robot processing station sets can be installed on the arched mobile platform 2.

[0087] Step 3: Locate the installation position on the installed arched mobile platform 2 and fix the cantilever fixed platform 4 at that position. Using at least three marking reference points obtained during flat ground measurement, combined with the optimal station set, calculate the coordinates of the at least three marking reference points in the spherical coordinate system through coordinate transformation. These coordinates serve as the positioning reference points for the cantilever fixed platform 4 on the arched mobile platform 2. Based on these positioning reference points, locate the installation position on the installed arched mobile platform 2 and fix the cantilever fixed platform 4 at that position. Specifically, this includes:

[0088] Step 31: Install the cantilever fixed platform with the robot on the ground, obtain the robot's base coordinate system, and measure and record the three scribing reference points on the bottom edge of the cantilever platform's back plate in this coordinate system. ;

[0089] Step 32: Based on the optimal set of robot processing stations, the k-th robot station is known. The base coordinate system {B k} Calculate the three points marked on the sphere in the coordinate system. Calculate the center of the sphere and The distances between them are used to obtain d1, d2, and d3;

[0090]

[0091] This represents the transformation relationship between the robot's base coordinate system and the sphere-centered coordinate system.

[0092] Step 33: On the installed arched bearing platform 2, measure the pre-arranged common points through the laser tracker multi-station measurement network 5 to reproduce the sphere center coordinate system;

[0093] Step 34: In the spherical coordinate system, use the laser tracker multi-station measurement network 5 to measure the mounting plane on the arched bearing platform 2 for mounting the cantilever platform 4, and fit the plane equation D of the mounting plane. g .

[0094] Step 35: In the spherical coordinate system, construct spatial spheres with radii d1, d2, and d3 respectively, and solve for the equations D of each spatial sphere and the plane. gThe intersection points are used to obtain a set of spatial point coordinates on the mounting plane, which serve as the positioning reference points for the cantilever fixed platform 4 on the arched mobile platform 2. ;

[0095] Step 36: Using the pointing function of the multi-station measurement network 5 of the laser tracker, mark the intersection point on the installed arched mobile platform 2 according to the positioning reference point. coordinate;

[0096] Step 37: Based on the markings on the arched platform Support legs are welded onto the platform, and a crane is used to place the cantilever fixed platform onto the support legs. The cantilever fixed platform is then fixed onto the arched platform through welding.

[0097] Step 4: Use the laser tracker multi-station measurement network 5 to track the common point 7 outside the sphere, the common point inside the sphere, and the auxiliary measurement points on the cantilever fixed platform 4 to obtain the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed;

[0098] Due to the large size of the spherical shell and the fact that flange holes are distributed throughout the surface of the shell, a laser tracker is needed to guide the machining robot to the designated position. Single-station measurement by the laser tracker is insufficient to meet the measurement requirements of flange hole machining. Therefore, the laser tracker needs to be deployed at the flange hole machining site, and a measurement network needs to be constructed based on the common point data measured by each measurement station to achieve multi-station network measurement of the laser tracker.

[0099] The necessary condition for constructing a measurement network is the need to arrange several common points at the large spherical shell processing site. The principles for arranging these common points mainly include: uniform distribution, measurement accessibility, coverage of the measurement area, and the long-term stability of the mounting base for the common point targets. To minimize the impact of environmental factors, concrete columns with a low coefficient of thermal expansion are selected as the mounting base for the common measurement points outside the sphere, satisfying the principle of long-term stability of the base. Four common points 7 are arranged on each concrete column. To improve the measurement accuracy of the measurement network, 24 common point 7 targets are evenly arranged at a distance of 5500mm from the axis of the circular foundation, with two targets forming a group, to ensure that the common points 7 are spatially staggered, satisfying the principles of uniform distribution and coverage of the measurement area. After the common points 7 are arranged and installed, laser trackers at different stations are used to measure the common points 7 and save the data, satisfying the principle of measurement accessibility. During the processing and manufacturing of the flange holes of the large spherical shell, measurement data can be retrieved as needed. When no abnormalities occur, there is no need to repeat the measurement.

[0100] To obtain the pose relationship between the robot's base coordinate system and the workpiece coordinate system of the flange hole to be processed, and to guide the cantilevered fixed robot to the flange hole, a multi-station measurement network using an external spherical tracker needs to be constructed. Laser trackers are sequentially installed at appropriate positions, and the external common point 7 is measured, ensuring that each common point is measured by at least two laser trackers. The data from each laser tracker's measurement station are then fused into a single measurement network to form the external spherical measurement network. The main hardware required to construct the external spherical measurement network includes laser trackers and the external common point 7.

[0101] In addition to the external measurement network, a laser tracker is also needed to perform measurements inside the sphere to construct an internal measurement network. The internal measurement network mainly serves the following purposes:

[0102] (a) Measure the common points on the inner surface of the large spherical shell, fit the sphere, and establish the sphere center coordinate system;

[0103] (b) Determine the position of the flange hole to be processed in the sphere coordinate system, scribing with a laser tracker, and welding the welding joints of the plate to fix it;

[0104] (c) Use an in-sphere laser tracker to measure the completed flange holes to determine whether the flange hole machining accuracy meets the requirements;

[0105] (d) Provide measurement data for subsequent flange installation and adjustment.

[0106] After the large spherical shell is welded and formed, several common points inside the sphere need to be arranged on the inner surface of the shell, such as... Figure 5 As shown. The arrangement of common points inside the sphere needs to avoid the flange hole location to facilitate measurement by the laser tracker inside the sphere. Due to the obstruction of the large spherical shell, light guide holes are pre-machined at the flange holes of larger sizes, and the laser tracker is installed near the light guide holes so that it can simultaneously measure the common points inside the sphere and the common measurement points outside the sphere on the concrete column, thereby unifying the measurement network inside and outside the sphere.

[0107] Step 4 specifically includes:

[0108] Step 41: Measure the common points inside the sphere that are preset on the inner surface of the large spherical shell component, fit the center of the sphere, establish the coordinate system of the sphere center, and realize the unification of the measurement network inside and outside the sphere through the light guide hole on the large spherical shell component;

[0109] Step 42: Measure the pre-set common point 7 outside the sphere on site using the laser tracker multi-station measurement network 5, and obtain the transformation relationship between the laser tracker measurement coordinate system and the sphere center coordinate system. ;

[0110] According to the design requirements, the positional relationship between each flange hole and the sphere center coordinate system can be obtained. Therefore, it is necessary to establish an accurate sphere center coordinate system to determine the positional orientation of the flange holes and guide the flange hole machining.

[0111] To establish a sphere-centered coordinate system, a common point needs to be fixed on the inner surface of the sphere shell. This common point should be installed over a large area and should not be installed in the area of ​​the hole to be machined. After the common point is installed, a laser tracker is used to measure it. Using the data from this common point, sphere fitting is performed to determine the center of the sphere shell, which is then used as the origin of the sphere-centered coordinate system. Using the normal to the horizontal plane built into the laser tracker as the Z-axis of the sphere-centered coordinate system and the X-axis of the global coordinate system as the X-axis helps ensure the accuracy and repeatability of subsequent measurements. By establishing the sphere-centered coordinate system, the location of the flange hole to be machined can be determined.

[0112] Step 43: Based on the design parameters of the hole to be machined, establish the corresponding workpiece coordinate system of the hole to be machined in the spherical coordinate system, and obtain the transformation relationship between the spherical coordinate system and the workpiece coordinate system of the hole to be machined. ;

[0113] The design parameters for a flange hole mainly include the flange hole size and the latitude and longitude of the hole center in a spherical coordinate system. The workpiece coordinate system can be determined based on these parameters. The origin of the workpiece coordinate system is set at the intersection of the hole's central axis and the outer surface of the spherical shell. The Z-axis of the workpiece coordinate system points from the center of the sphere to the origin, while the X-axis runs along the latitude of the large spherical shell.

[0114] Step 44: Measure the auxiliary measurement points on the cantilevered fixed platform 4, establish the robot base coordinate system at the current position under the laser tracker measurement coordinate system, and obtain the transformation relationship between the laser tracker measurement coordinate system and the robot base coordinate system at the current position. ;

[0115] The origin of the robot's base coordinate system is located at the center of the robot's base, with the Z-axis pointing vertically upwards, the X-axis pointing directly forward, and the Y-axis determined according to the right-hand rule. The robot's base coordinate system can be established by sequentially rotating the robot's joints 1 and 2 along their axes.

[0116] Step 45: Combining the transformation relationships obtained in steps 42 to 44, calculate the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed.

[0117] The robot's base coordinate system {B} and the laser tracker's measuring coordinate system {L} are movable coordinate systems, while the sphere-centered coordinate system {Q} and the workpiece coordinate system {W} are fixed coordinate systems. A connection is established in the sphere-centered coordinate system by measuring the common point 7 outside the sphere using the laser tracker. Simultaneously, auxiliary measuring points on the cantilever platform are measured, establishing a connection in the base coordinate system. The connection between the base coordinate system and the workpiece coordinate system can be determined using the following formula:

[0118]

[0119] in, This defines the transformation relationship between the robot's base coordinate system and the workpiece coordinate system of the hole to be machined. The transformation relationship between the robot's base coordinate system and the laser tracker's measurement coordinate system is obtained by measuring auxiliary measurement points on the cantilevered fixed platform using the tracker. The transformation relationship between the laser tracker's coordinate system and the sphere's central coordinate system is obtained by measuring the common point 7 outside the sphere using the tracker. The transformation relationship between the sphere's center coordinate system and the workpiece coordinate system of the hole to be machined is calculated from the latitude and longitude of the hole and the radius of the sphere's shell.

[0120] Step 5: Based on the machining sequence of the large spherical shell component and the transformation relationship between the robot's base coordinate system and the workpiece coordinate system of the hole to be machined, perform robot error modeling and compensation, and then use the compensated machining program to machine the large spherical shell component using the robot. Specifically, this includes:

[0121] Step 51: Based on the dimensions of the flange hole to be processed, and according to the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed, generate the initial sampling point measurement program, the no-load running program, and the processing program.

[0122] Step 52: Run the sampling point measurement program, measure the actual pose of the robot at each preset sampling point using a laser tracker, and compare it with the theoretical pose to obtain the positioning error at each sampling point;

[0123] Step 53: Based on the positioning error of the sampling points and their theoretical coordinate values, establish a robot positioning error prediction model;

[0124] Step 54: Based on the robot positioning error prediction model, compensate the empty running program and the machining program to generate compensated empty running program and machining program;

[0125] Step 55: Run the compensated empty run program, measure the actual running trajectory of the robot through the multi-station measurement network 5 of the laser tracker, and calculate the position error and centering error of the trajectory relative to the theoretical trajectory of the hole to be processed based on the measurement data;

[0126] Step 56: Determine whether the position error and alignment error meet the preset machining accuracy requirements:

[0127] If the requirements are met, the hole to be machined is machined using the compensated machining program;

[0128] If the requirements are not met, return to step 52 and repeat the sampling point measurement until the requirements are met.

[0129] The establishment of a robot positioning error prediction model includes two steps: measuring the robot positioning error at sampling points and modeling the positioning error. The robot positioning error prediction model is established based on the errors at sampling points along the machining trajectory. Sampling points include... Figure 6 As shown, a robot positioning error prediction model is established using the measured sampling point errors and the theoretical coordinates of the sampling points. This model predicts the machining trajectory point errors and compensates for them. Theoretically, as the number of sampling points increases, the established error prediction model becomes more accurate, and the prediction precision improves. However, when the number of sampling points increases to a certain extent, the improvement in the prediction precision of the error prediction model is not very significant. Therefore, more sampling points are not necessarily better. More sampling points lead to longer measurement time and lower measurement efficiency, while fewer sampling points result in lower model prediction precision. To improve the sampling point measurement efficiency while maintaining model prediction precision, the sampling point interval needs to be optimized. Since the prediction is of the robot's systematic error, the compensated robot positioning precision will not exceed its repeatability accuracy.

[0130] The main factors affecting the sampling point interval are robot positioning error and sampling point measurement error. The robot positioning error primarily affects the sampling point interval by requiring more sampling points for larger errors and fewer sampling points for smaller intervals. The sampling point measurement error mainly affects the distance between the laser tracker and the sampling point; the greater the measurement distance, the greater the measurement error. Smaller sampling point intervals result in larger measurement errors between adjacent sampling points, thus affecting the prediction accuracy of the robot positioning error prediction model. In practical engineering applications, a reasonable sampling point interval should be designed based on the robot positioning accuracy requirements to improve measurement efficiency and meet the required prediction accuracy.

[0131] Optimizing the sampling point interval for robot positioning error compensation aims to minimize the residual error after compensation. While ensuring the residual error meets accuracy requirements, the number of sampling points should be reduced as much as possible to improve sampling efficiency. Based on the above analysis, optimizing the interval between sampling points must satisfy the following characteristics:

[0132] (1) Minimize the number of sampling points: that is, maximize the distance between adjacent sampling points, which can effectively reduce the measurement time and improve the measurement efficiency.

[0133] (2) The robot positioning error predicted by the sampling points meets the processing accuracy requirements: A robot positioning error prediction model is established based on the measured sampling point data. The final requirement is that the robot positioning accuracy after compensation meets the processing accuracy requirements.

[0134] (3) Sampling points based on the processing trajectory: Select sampling points according to the shape and characteristics of the trajectory to be processed to ensure coverage of the entire processing area, thereby ensuring prediction accuracy.

[0135] Taking all the above characteristics into account, in order to improve the efficiency of on-site measurement, the sampling point interval is optimized by combining the robot positioning error model. The optimal interval between the v-th and v-1-th sampling points is obtained by the following formula:

[0136]

[0137] The distance between sampling points Sampling point coordinates Predicted value of sampling point positioning error. The robot's positioning error before target point compensation Laser tracker measurement error; Robot positioning accuracy; The lower and upper limits of the machining space for the flange hole trajectory points are not specified.

[0138] In-situ measurement and accuracy inspection of the flange hole inner surface. For the machined flange hole 6, an in-spherical laser tracker is used to measure the inner surface of the flange hole. Data fitting is performed on the measured inner surface of the flange hole to determine the flange hole position and alignment error. If the accuracy requirements are met, the next hole is machined. If the accuracy requirements are not met, comprehensive compensation is applied to the flange hole position and alignment error until the flange hole position and alignment accuracy meet the requirements.

[0139] The processing method, in-situ robotic processing equipment, and actuator of this application can also form a large spherical shell component robotic in-situ processing system, with the actuator implementing the steps of the above processing method based on a processor.

[0140] Example: To improve the efficiency of flange hole milling, a strategy of segmented roughing of flange holes with a wall thickness of 100 mm was adopted. Two different lengths of milling cutters were used, with cutter lengths of 160 mm and 200 mm, respectively, a clamping depth of 60 mm, and overhang lengths of 100 mm and 140 mm, respectively. First, a 160 mm milling cutter was used to rough-machine the workpiece with a thickness of 0-80 mm, with a depth of cut of 1 mm. Then, a 200 mm milling cutter was used to rough-machine the workpiece with a thickness of 0-80 mm, with a depth of cut of 0.5 mm. Compressed air was used for cooling and chip removal during the machining process. After the hole machining was completed, the weld overlap was removed, and the plate material in the center of the hole was cleared to prepare for subsequent finishing. A 200 mm milling cutter was used to finish-machine the inner surface of the hole to eliminate the machining allowance left during roughing, thereby improving the machining accuracy of the flange hole's inner surface. The three-tooth indexable end mill used for machining has a tip diameter of 40 mm and a shank diameter of 32 mm. The inserts are special inserts for aluminum alloy machining. This tool provides a 4 mm clearance on each side to prevent the shank from scraping against the workpiece sidewall and affecting the machining quality of the flange hole. The roughing and finishing process parameters for the flange hole are shown in Table 1.

[0141] Table 1 Machining process parameters for flange holes in large spherical shells

[0142]

[0143] After determining the milling strategy for the flange holes, a robot machining program is generated and error compensation is performed. The tool holder is then mounted to the end of the robot's electric spindle, ensuring the tool is securely and correctly installed. The compensated machining program is imported into the robot control cabinet. Before importing the program, a virtual simulation test is performed using simulation software to verify its correctness. Simulation testing can identify potential problems and prevent unexpected situations from occurring during the machining process.

[0144] After the holes are machined, a laser tracker is installed at the center of the large spherical shell to measure the inner surface of the machined flange holes. Figure 7 and Figure 8 The table shows the measurement data for circular and rectangular holes, respectively. After processing the measurement points, the flange hole positions and alignment errors are shown in Table 2.

[0145] Table 2 Flange Hole Locations and Alignment Errors for Large Spherical Shells

[0146]

[0147] As shown in Table 2, the in-situ robotic machining equipment and method developed in the patent are highly effective in improving the flange hole alignment error. The flange hole alignment error was reduced from 25.393 mm before compensation to 4.241 mm after compensation, and the flange hole position error was reduced from (3.454, 2.123) mm before compensation to (0.134, 0.352) mm after compensation. The position errors of the other two rectangular flange holes were (-0.385, 0.426) mm and (0.441, 0.325) mm, respectively, and the alignment errors were 4.323 mm and 4.755 mm, respectively, proving the effectiveness of the proposed error prediction and compensation method.

[0148] Since the flange hole needs to be installed on the hole after machining, the dimensional error of the hole has a significant impact on the machining quality. Table 2 shows that robot trajectory error compensation reduced the radius error of the hole. For smooth flange installation, the single-sided clearance was 1.6 mm. Before compensation, the diameter error of the circular flange hole was 1.831 mm, and after error prediction compensation, the flange hole diameter error was 0.089 mm.

[0149] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for in-situ robotic machining of large spherical shell components, characterized in that, The method is based on in-situ robotic machining equipment, which includes a load-bearing mechanism, an arched mobile platform, a cantilevered fixed platform, a robotic milling system, and a multi-station measurement network of a laser tracker. The load-bearing mechanism is fixed in the foundation, the arched moving platform can rotate around the axis of the load-bearing mechanism, and the cantilevered fixed platform is used to fix itself on the arched moving platform and support the robot milling system; the processing method includes: S1. Determine the processing sequence and processing location of large spherical shell components; S2. Based on the features to be processed at each processing location, extract the set of key limit points that can characterize its spatial range and processing accessibility requirements; with the goal of ensuring that the set of key limit points of all processing features can be covered by the workspace of the robot milling system and minimizing the total number of processing stations required to cover all processing features, establish and solve the station optimization model to obtain the optimal set of robot processing stations in the spherical coordinate system. Based on the optimal set of robot processing stations and the fixed interface dimensions of the cantilever fixed platform, the overall structural dimensions of the arched mobile platform are determined, and manufacturing and installation are completed. S3. Locate the installation position on the already installed arched mobile platform and fix the cantilever fixed platform at the installation position. S4. Using a multi-station measurement network of a laser tracker, track the common point outside the sphere, the common point inside the sphere, and the auxiliary measurement points on the cantilever fixed platform to obtain the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed. S5. Based on the machining sequence of the large spherical shell component and the transformation relationship between the robot's base coordinate system and the workpiece coordinate system of the hole to be machined, perform robot error modeling and compensation, and use the compensated machining program to machine the large spherical shell component by robot.

2. The method for in-situ robotic processing of large spherical shell components according to claim 1, characterized in that, S2 includes: S21. Establish a sphere center coordinate system and a workpiece coordinate system for each feature to be processed; for each feature to be processed, construct an envelope space based on its geometric dimensions, and extract a set of key limit points that can characterize its spatial range and processing accessibility requirements in the envelope space. Establish feature verification point coordinate systems with the extracted key limit points as the origin. The feature verification point coordinate systems are aligned with the corresponding workpiece coordinate systems for the holes to be processed. S22. Based on the workspace of the robot milling system, the set of candidate robot processing stations corresponding to each feature to be processed is determined with the criterion that the origin of the coordinate system of all feature verification points of each feature to be processed can be covered by the workspace. S23. Select robot processing stations from the discrete set of all candidate robot processing stations, and establish an optimization model with the objective of minimizing the number of selected robot processing stations and the constraint of covering all features to be processed. S24. Solve the optimization model to obtain a set of preliminary feasible robot processing positions; S25. For each initially feasible robot processing station, define the coordinate system of its corresponding feature verification point as the robot end coordinate system. Calculate the joint angles through the robot kinematics inverse solution. If all joint angles are within the preset limit range, the corresponding station is confirmed to meet the feasibility requirements. Otherwise, the corresponding station is removed and the optimization model is re-solved until all stations meet the joint angle constraints, thus obtaining the optimal set of robot processing stations. S26. Based on the position of the optimal robot processing station in the spherical coordinate system and the fixed interface size of the cantilever fixed platform, determine the overall structural size of the arched mobile platform to ensure that all optimal robot processing stations can be installed on the arched mobile platform.

3. The method for in-situ robotic processing of large spherical shell components according to claim 1, characterized in that, In step S3, at least three scribing reference points of the cantilever fixed platform obtained during flat ground measurement are combined with the optimal robot processing station set, and the coordinates of the at least three scribing reference points in the spherical coordinate system are calculated through coordinate transformation. These coordinates serve as the positioning reference points of the cantilever fixed platform on the arched moving platform. Based on these positioning reference points, the installation position is found on the already installed arched moving platform, and the cantilever fixed platform is fixed at the installation position.

4. The method for in-situ robotic machining of large spherical shell components according to claim 3, characterized in that, S3 include: S31. Temporarily place the cantilever fixed platform on the ground with the robot, establish the robot's base coordinate system at this time, and measure and record the coordinates of at least three non-collinear scribing reference points on the back plate of the cantilever fixed platform under the base coordinate system. S32. Based on the base coordinate system of the robot positions in the optimal robot processing station set, calculate the coordinates of the at least three non-collinear scribing reference points in the sphere-centered coordinate system, and calculate the distance between the sphere center and each scribing reference point in the sphere-centered coordinate system. S33. On the installed arched mobile platform, measure the pre-arranged common points using a multi-station measurement network of a laser tracker to reproduce the sphere center coordinate system; S34. In the sphere-centered coordinate system, measure the mounting plane on the arched moving platform used to install the cantilever fixed platform, and fit the plane equation of the mounting plane. S35. In the sphere-centered coordinate system, with the origin of the sphere-centered coordinate system as the sphere center, construct spatial spheres with the distance between the sphere center and each scribed reference point in the sphere-centered coordinate system as the radius, solve for the intersection points of each spatial sphere with the plane equation, and obtain a set of spatial point coordinates on the installation plane, which serve as the positioning reference points of the cantilever fixed platform on the arched mobile platform. S36. In the sphere center coordinate system, using the pointing function of the multi-station measurement network of the laser tracker, find the installation position on the installed arched moving platform according to the positioning reference point; S37. Based on the installation location, install a support structure on the arched mobile platform, and hoist the cantilever fixed platform onto the support structure for fixation.

5. The method for in-situ robotic machining of large spherical shell components according to claim 1, characterized in that, S4 includes: S41. Measure the common points inside the sphere that are preset on the inner surface of the large spherical shell component, fit the center of the sphere, establish the coordinate system of the sphere center, and realize the unification of the measurement network inside and outside the sphere through the light guide hole on the large spherical shell component. S42. Using the multi-station measurement network of the laser tracker, measure the common point outside the sphere preset on site to obtain the transformation relationship between the laser tracker measurement coordinate system and the sphere center coordinate system. ; S43. Based on the design parameters of the hole to be machined, establish a corresponding workpiece coordinate system for the hole to be machined in the sphere-centered coordinate system, and obtain the transformation relationship between the sphere-centered coordinate system and the workpiece coordinate system for the hole to be machined. ; S44. Measure the auxiliary measurement points on the cantilevered fixed platform, establish the robot base coordinate system at the current position under the laser tracker measurement coordinate system, and obtain the transformation relationship between the laser tracker measurement coordinate system and the robot base coordinate system at the current position. ; S45. Combining the transformation relationships obtained from S42 to S44, calculate the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed.

6. The method for in-situ robotic machining of large spherical shell components according to claim 1, characterized in that, S5 include: S51. Based on the transformation relationship between the robot base coordinate system and the workpiece coordinate system of the hole to be processed, generate the initial sampling point measurement program, the no-load running program, and the processing program; S52. Run the sampling point measurement program, measure the actual pose of the robot at each preset sampling point using a laser tracker, and compare it with the theoretical pose to obtain the positioning error at each sampling point. S53. Based on the positioning error of the sampling points and their theoretical coordinate values, establish a robot positioning error prediction model; S54. Based on the robot positioning error prediction model, compensate the empty running program and the machining program to generate compensated empty running program and machining program. S55. Run the compensated no-load program, measure the actual running trajectory of the robot through the multi-station measurement network of the laser tracker, and calculate the position error and centering error of the trajectory relative to the theoretical trajectory of the hole to be processed based on the measurement data; S56. Determine whether the position error and alignment error meet the preset machining accuracy requirements: If the requirements are met, the hole to be machined is machined using the compensated machining program; If the requirements are not met, return to S52 and re-measure the sampling points until the requirements are met.

7. The method for in-situ robotic processing of large spherical shell components according to claim 6, characterized in that, The methods for compensating the empty run program and the processing program include: The robot positioning error prediction model optimizes the sampling point interval, the first The and the first The optimal interval between sampling points is obtained by the following formula: ； in, The distance between sampling points For the first Coordinates of each sampling point, This is the predicted value of the sampling point positioning error. This refers to the robot's positioning error before compensation at the target point. Measurement error in multi-station measurement network for laser tracker; To improve robot positioning accuracy; , These represent the lower and upper limits of the machining space for the trajectory points of the holes to be machined, respectively.

8. The method for in-situ robotic processing of large spherical shell components according to claim 6, characterized in that, In S56, a segmented roughing strategy is used to machine the hole to be machined: Depending on the machining depth, two different overhang lengths of end mills are provided, with overhang lengths of 100 mm and 140 mm respectively; Use a milling cutter with an overhang of 100 mm to machine workpieces with a thickness of 0~80 mm and a cutting depth of 1 mm; The remaining thickness of the workpiece was machined using a milling cutter with an overhang of 140 mm and a depth of cut of 0.5 mm.

9. The method for in-situ robotic processing of large spherical shell components according to claim 1, characterized in that, The common points outside the sphere are evenly distributed at a certain distance from the axis of the circular foundation, with two points arranged in a staggered pattern. Four common points outside the sphere are fixed on each concrete column. The common points inside the sphere are arranged on the inner surface of the sphere shell and avoid the area of ​​the hole to be processed.

10. A robotic in-situ machining system for large spherical shell components, characterized in that, It includes the in-situ robotic machining equipment and the actuator, the actuator being based on a processor to implement the steps of the in-situ robotic machining method for large spherical shell components as described in any one of claims 1 to 7.

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