Digital assembling method for helicopter fairing

Abstract

The embodiment of the invention discloses a digitalized assembling method of a helicopter fairing, which comprises the following steps of: 1, scanning the surface of the fairing and the surface of a helicopter body structure, and acquiring a three-dimensional contour model of the surface of the fairing and the surface of the helicopter body structure according to scanning data; 2, generating a visual assembly correction scheme by comparing the three-dimensional contour model with a design model imported into a controller; 3, in the fairing assembly process, a visual assembly correction scheme is projected through laser, non-contact hole making and polishing guiding are achieved, and digital assembly of the fairing is implemented; and 4, in the fairing assembling process, dynamic position information of the fairing and all the positioning targets on the aircraft body structure is obtained, the moving track of the fairing in the assembling process is solved, automatic alarming is conducted when the fairing is out of tolerance, and laser projection is frozen. The problems that an existing fairing assembling mode is low in assembling efficiency and precision, and the production efficiency and the assembling requirement of a helicopter are difficult to meet are solved.

Description

Technical Field

[0001] This invention relates to, but is not limited to, the field of helicopter assembly technology, and particularly to a digital assembly method for a helicopter fairing. Background Technology

[0002] The helicopter fairing is an important component of the helicopter's external structure. Its main functions include optimizing the aerodynamic shape to reduce flight drag, protecting internal mechanical components (such as the transmission system and engine) from external environmental corrosion, reducing aerodynamic noise and vibration, and facilitating quick disassembly for maintenance.

[0003] During the final assembly stage, helicopter fairings typically employ a modular design, composed of multiple complex curved surface components made of composite materials. Traditionally, helicopter fairings are assembled manually by operators, who must repeatedly calibrate the mating gaps between components and the differences in the shapes of adjacent parts to ensure the continuity and sealing of the aerodynamic shape. Furthermore, traditional assembly methods for helicopter fairings usually require specialized tooling, whose main function is to support the fairing during assembly and assist the operator in positioning. While this can improve assembly efficiency to some extent, it results in a high dependence on tooling, and the need to prepare specialized tooling increases assembly costs. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems. This invention provides a digital assembly method for helicopter fairings, which solves the problems of traditional helicopter fairing assembly methods, such as high dependence on tooling, increased assembly costs due to tooling preparation, and significant influence of subjective factors such as the operator's skill level on the assembly process, resulting in low assembly efficiency, low precision, and difficulty in meeting production efficiency and helicopter assembly requirements.

[0005] The technical solution of the present invention: An embodiment of the present invention provides a digital assembly method for a helicopter fairing, comprising: Step 1: Use a laser 3D scanner to scan the surface of the fairing and the fuselage structure, and obtain a 3D contour model of the surface of the fairing and the fuselage structure based on the scanning data. Step 2: By comparing the 3D contour model obtained in Step 1 with the design model imported into the controller, a visual assembly correction scheme is generated. Step 3: Based on the three-dimensional contour model, the visual assembly correction scheme of Step 2 is projected by laser during the fairing assembly process to achieve non-contact hole making and grinding guidance, and to implement digital assembly of the fairing. Step 4: During the fairing assembly process, the dynamic position information of each positioning target on the fairing and the body structure is acquired, and the movement trajectory of the fairing during the assembly process is calculated. If the deviation exceeds the tolerance, an automatic alarm is triggered and the laser projection is frozen.

[0006] Optionally, in the digital assembly method for the helicopter fairing as described above, step 1 includes: Step 11: A laser 3D scanner is used to project a laser grating onto the surface of the fairing and the fuselage structure, and a camera is used to capture grating images along the changes in the morphology of the fairing and the fuselage structure. Step 12: Calculate the three-dimensional spatial coordinates of each pixel in the raster image, acquire point cloud data of the fairing and body structure surface in real time, and convert the point cloud data into a three-dimensional contour model of the fairing and body structure through real-time processing.

[0007] Optionally, in the digital assembly method for helicopter fairings described above, step 2, the method for generating a visual assembly correction scheme is as follows: By automatically aligning the 3D contour model obtained in step 1 with the design model imported into the controller, manufacturing errors and assembly deviations are identified, interference risks after fairing assembly are predicted, areas requiring rework are marked, and a visual assembly correction plan is generated to guide operators in completing the adjustment assembly.

[0008] Optionally, in the digital assembly method for the helicopter fairing as described above, step 3 includes: During the fairing assembly process, the six-degree-of-freedom pose of the fairing and the fuselage structure is tracked in real time using an optical infrared tracker. Combined with the three-dimensional contour model obtained in step 1, a visual assembly correction scheme is projected using spatial laser to achieve non-contact hole making and grinding guidance.

[0009] Optionally, in the digital assembly method for the helicopter fairing as described above, step 4 includes: An optical infrared tracker is used to scan the positioning targets on the fairing and the body structure to obtain the dynamic position information of each positioning target. The dynamic spatial coordinate calculation algorithm inside the controller calculates the movement trajectory of the fairing during the assembly process. The dynamic deviation trend chart of the fairing assembly is displayed in real time, and an alarm is automatically triggered when the deviation exceeds the limit and the laser projection is frozen.

[0010] Optionally, in the digital assembly method for the helicopter fairing as described above, the optical infrared tracker includes: an infrared tracker, a positioning target, and a laser projection device; The optical infrared tracker is used to detect and measure spatial coordinates by using infrared light emitted by the infrared tracker, establish a global coordinate system for the assembly scene, and track the six-degree-of-freedom pose of the fairing and the body structure in real time using infrared light; it uses positioning targets installed on the fairing and the body structure as spatial reference markers to construct a dynamic measurement reference system; and it uses a laser projection device to convert the issued assembly instructions into spatial light projection to achieve non-contact hole making and grinding guidance.

[0011] Optionally, in the digital assembly method for the helicopter fairing described above, the positioning target includes: an active target, a passive target, and a target adapter; The active and passive targets are mounted on the fairing and airframe structure via target adapters to keep the normal vector of each target aligned with the optical axis of the infrared tracker. The active target has a built-in infrared LED array and IMU sensor to emit coded infrared signals, which are combined with fused inertial measurement data to improve tracking stability. The passive target uses a magnetic base coated with retroreflective material to reflect infrared light emitted by the infrared tracker.

[0012] Optionally, in the digital assembly method for helicopter fairings described above, step 3, which involves digitally assembling the fairing, includes: S1, for grinding the amount to be removed in the visual assembly correction scheme, including: the controller controls the optical infrared tracker to generate a grinding path on the fairing and guides the grinding machine to move along the path; the optical infrared tracker monitors the movement trajectory of the grinding tool on the fairing in real time and displays it in the controller; when the deviation exceeds the deviation threshold, it automatically pauses and alarms. S2, for hole making in the visualization assembly correction scheme, the optical infrared tracker projects the virtual hole center position on the fairing to guide the operator to make the hole. When the overlap between the tip of the hole making tool and the virtual hole center is less than the hole making deviation value, the controller prompts that drilling is allowed.

[0013] Optionally, in the digital assembly method for the helicopter fairing as described above, before step 1, the method further includes: Step a: Import the helicopter design model into the controller and parse the product structure and size information in the design model; Step b: Establish a three-dimensional coordinate system for the design model in the controller and align it with the helicopter body coordinate system; Step c: Calibrate the laser 3D scanner, calibrate the optical infrared tracker, and calibrate the tool center point of the electric grinder and hole-making equipment.

[0014] The beneficial effects of this invention: The digital assembly method for helicopter fairings provided in this embodiment of the invention uses a laser 3D scanner to scan the surfaces of the fairing and fuselage structure, and obtains a 3D contour model of the fairing and fuselage structure surfaces based on the scanning data. By comparing the 3D contour model with the design model imported into the controller, a visual assembly correction scheme is generated. Based on the 3D contour model, the visual assembly correction scheme is projected during the fairing assembly process, achieving non-contact hole making and grinding guidance. During the fairing assembly process, the dynamic position information of each positioning target on the fairing and fuselage structure is obtained, and the movement trajectory of the fairing during the assembly process is calculated. Automatic alarms are triggered for out-of-tolerance conditions, and the laser projection is frozen. The technical solution provided in this embodiment of the invention adopts a closed-loop technology of "multi-sensor fusion + intelligent decision-making + precise execution," systematically solving the difficulties in helicopter fairing assembly and achieving breakthroughs in accuracy, efficiency, and cost. The solution provided by this invention has the following beneficial effects: First, high-precision digital twin matching: the actual shape of the fairing is obtained by a handheld laser scanner (accuracy ±0.05mm), and a full-size comparison is performed with the CATIA design model to generate a three-dimensional deviation heat map and automatically mark the out-of-tolerance areas; in practical applications, the installation gap control accuracy can be improved to ±0.2mm, and the step difference fluctuation range can be compressed to ±0.3mm.

[0015] Second, dynamic pose monitoring: The optical infrared tracker monitors the six-degree-of-freedom pose of the fairing and the fuselage structure in real time (position accuracy ±0.1mm, angle accuracy ±0.05°), and displays the deviation vector in real time, allowing operators to make quick adjustments based on the guidance.

[0016] Third, intelligent margin calculation: After comparing the laser scanning data with the design model, the controller automatically generates a three-dimensional grinding navigation map (i.e., a visual assembly correction scheme), marks the areas to be removed (highlighted in red) and the areas to be retained (green), and calculates the optimal grinding amount (accuracy ±0.1mm).

[0017] Fourth, laser projection positioning: The actual coordinates of the mounting holes on the body structure are obtained by an optical infrared tracker. The laser equipment directly projects the hole contour (including the normal reference line) onto the surface of the fairing. The hole positioning accuracy reaches ±0.15mm and the normal angle deviation is ≤0.3°.

[0018] Fifth, reverse matching technology: automatically calculate the reverse matching path based on the scan data, first locate the structural holes of the body → reverse calculate the theoretical hole position of the fairing → dynamically compensate for manufacturing errors.

[0019] Sixth, interference prediction technology: Virtual assembly simulation is performed by scanning the fairing model and the point cloud of the airframe structure (acquired by laser scanning). Based on the physics engine, the minimum gap is detected (accuracy 0.1mm), high-risk interference areas are marked in advance, and more than 90% of interference problems are predicted and resolved before installation. Attached Figure Description

[0020] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0021] Figure 1 This is a flowchart illustrating a digital assembly method for a helicopter fairing provided in an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

[0023] As explained in the background section, the traditional assembly method for helicopter fairings is highly dependent on tooling. Tooling preparation increases assembly costs, and the assembly process is greatly affected by subjective factors such as the operator's skill level. This results in low assembly efficiency and low precision, making it difficult to meet production efficiency and helicopter assembly requirements.

[0024] In addition to the main problems mentioned above, the current fairing assembly also has the following issues: (1) The acceptance criteria after installation are difficult to guarantee: In the acceptance criteria after the installation of a certain helicopter fuselage structure, the clearance around the fairing is generally required to be between 0.5 and 2 mm, and the difference in shape between the fairing and adjacent components is generally required to be no more than ±2 mm. For large-sized, complex curved irregular parts like helicopter fairings, it is difficult to guarantee the accuracy by relying on manual experience and tooling positioning.

[0025] (2) The grinding process is complicated: the fairing of advanced helicopters is made of composite materials. Due to the properties of composite materials, they will deform during molding. Considering the uncertainty of installation, a certain margin will be left during the molding of the fairing. Therefore, the outer ring is usually larger than the theoretical size. Before formal installation, the operator will visually compare and grind it. In order to prevent excessive grinding from causing product scrap, multiple comparison grinding is usually required.

[0026] (3) Difficulty in matching mounting holes: Due to the limitations of manufacturing process precision and the uncertainty of cumulative error in the body structure, some fairings are not drilled during molding, but are matched through the mounting holes of the structure during assembly. The fairing covers the outer surface of the body structure, and since the mounting holes on the structure cannot be seen during matching, it is difficult to ensure the accuracy of the hole position.

[0027] (4) Interference with the fuselage structure after installation: Generally, the fairing is installed by the final assembly workshop after the fuselage structure is riveted. Due to the accumulation of structural tolerances, interference with the fuselage structure, such as firewalls, often occurs after the fairing is installed. It is difficult to determine the cause of the problem through conventional measurement methods.

[0028] To address the aforementioned problems, this invention provides a digital assembly method for helicopter fairings, which solves various issues arising from the high dependence of existing helicopter fairing assembly methods on tooling and the significant influence of subjective factors such as the operator's skill level on the assembly process. It also solves four major challenges in the assembly process of helicopter fairings: difficulty in ensuring acceptance criteria, cumbersome grinding procedures, difficulty in matching mounting holes, and interference with the airframe structure.

[0029] The present invention provides the following specific embodiments, which can be combined with each other. For the same or similar concepts or processes, they may not be described again in some embodiments.

[0030] Figure 1 This is a flowchart illustrating a digital assembly method for a helicopter fairing provided in an embodiment of the present invention. Figure 1 As shown, the digital assembly method for helicopter fairings provided by the present invention includes the following steps: Step 1: Use a laser 3D scanner to scan the surface of the fairing and the fuselage structure, and obtain a 3D contour model of the surface of the fairing and the fuselage structure based on the scanning data. Step 2: By comparing the 3D contour model obtained in Step 1 with the design model imported into the controller, a visual assembly correction scheme is generated. Step 3: Based on the three-dimensional contour model, the visual assembly correction scheme of Step 2 is projected by laser during the fairing assembly process to achieve non-contact hole making and grinding guidance, and to implement digital assembly of the fairing. Step 4: During the fairing assembly process, the dynamic position information of each positioning target on the fairing and the body structure is acquired, and the movement trajectory of the fairing during the assembly process is calculated. If the deviation exceeds the tolerance, an automatic alarm is triggered and the laser projection is frozen.

[0031] In one implementation of this invention, the process of step 1 described above may include: Step 11: A laser 3D scanner is used to project a laser grating onto the surface of the fairing and the fuselage structure, and a camera is used to capture grating images along the changes in the morphology of the fairing and the fuselage structure. Step 12: Calculate the three-dimensional spatial coordinates of each pixel in the raster image, acquire point cloud data of the fairing and body structure surface in real time, and convert the point cloud data into a three-dimensional contour model of the fairing and body structure through real-time processing.

[0032] In one implementation of this invention, step 2 above, the method for generating the visual assembly correction scheme is as follows: By automatically aligning the 3D contour model obtained in step 1 with the design model imported into the controller, manufacturing errors and assembly deviations are identified, interference risks after fairing assembly are predicted, areas requiring rework are marked, and a visual assembly correction plan is generated to guide operators in completing the adjustment assembly.

[0033] In one implementation of this invention, step 3 is carried out as follows: During the fairing assembly process, the six-degree-of-freedom pose of the fairing and the fuselage structure is tracked in real time using an optical infrared tracker. Combined with the three-dimensional contour model obtained in step 1, a visual assembly correction scheme is projected using spatial laser, enabling non-contact hole making and grinding guidance. In one implementation of this invention, step 4 is carried out as follows: An optical infrared tracker is used to scan the positioning targets on the fairing and the body structure to obtain the dynamic position information of each positioning target. The dynamic spatial coordinate calculation algorithm inside the controller calculates the movement trajectory of the fairing during the assembly process. The dynamic deviation trend chart of the fairing assembly is displayed in real time, and an alarm is automatically triggered when the deviation exceeds the limit and the laser projection is frozen.

[0034] The digital assembly method for helicopter fairings provided by this invention utilizes a handheld laser 3D scanner, an optical infrared tracker, and a controller during implementation. The following describes the aforementioned devices used to execute the digital assembly method provided in this embodiment of the invention: (a) Laser 3D Scanner: In this embodiment of the invention, a handheld laser 3D scanner can be used. The scanner adopts photogrammetric 3D scanning technology and utilizes the principle of structured light 3D measurement to project a laser grating onto the surface of the fairing and the fuselage structure. Two cameras are used to capture grating images along the changes in the shape of the fairing and the fuselage structure. The coordinates of each pixel in the grating image in three-dimensional space, i.e., point cloud data, are calculated to obtain the three-dimensional contour of the surface of the fairing and the fuselage structure.

[0035] The handheld laser 3D scanner in this embodiment of the invention mainly consists of a laser emitting and receiving unit, a positioning and attitude sensing unit, and a data transmission unit.

[0036] 1. Laser transmitting and receiving unit: This unit uses a high-precision laser beam to perform non-contact scanning of the fairing and fuselage structure surfaces, capturing their three-dimensional shape data. This unit can penetrate dark composite materials (such as carbon fiber) to accurately identify surface curvature, bolt hole locations, and mating gaps, providing raw data support for virtual pre-assembly. This unit includes: ① Multi-frequency laser emitter: emits dual-band structured light in blue (450nm) and infrared (850nm). Blue light is used in high reflectivity areas (such as metal edges), while infrared light penetrates the surface of dark composite materials to avoid scanning blind spots and ensure full coverage of the fairing surface.

[0037] ② High dynamic range (HDR) optical lens, equipped with adaptive filter and multi-level exposure CMOS sensor, to suppress strong light interference in the workshop, clean and capture details such as fairing probes and narrow slits (such as bolt holes with a diameter of <3mm), and prevent data loss.

[0038] ③ The point cloud preprocessing module removes environmental noise (such as dust and reflective spots) in real time and extracts effective feature points to ensure that the error between the scanned data and the real curved surface is <0.02mm.

[0039] 2. Positioning and attitude sensing unit: This unit tracks the spatial position and motion trajectory of the handheld laser 3D scanner in real time, ensuring seamless stitching of multi-view scan data. This unit includes: ① The inertial navigation module (IMU) integrates a six-axis gyroscope and accelerometer to update the scanner pose data at a frequency of 200Hz, dynamically compensate for operation jitter, and prevent model distortion caused by hand shaking during the scanning process.

[0040] ② The optical marker identification system uses pre-laid coded markers (accuracy ±0.1mm) to automatically align multi-station scanning data, solving the problem of cumulative error during fairing splicing.

[0041] ③ Temperature compensation sensor monitors changes in ambient temperature and dynamically corrects scanning data based on the thermal expansion coefficient of composite materials (e.g., fairing expands by 0.1 mm / m at high temperatures) to avoid assembly errors caused by thermal deformation.

[0042] 3. Data transmission unit: adopts a dual-mode transmission module to encrypt the scanned data before transmitting it to the controller.

[0043] (ii) Optical infrared tracker: During fairing assembly, an optical infrared tracker continuously scans the positioning targets on the fairing and fuselage structure to obtain the dynamic position information of each target. The controller then uses its internal dynamic spatial coordinate calculation algorithm to calculate the fairing's movement trajectory during assembly. Additionally, the optical infrared tracker tracks the fairing's six degrees of freedom (6DoF) pose in real time, and combined with the three-dimensional contour model obtained in step 1, enables non-contact hole drilling and grinding guidance during assembly.

[0044] The optical infrared tracker in this embodiment of the invention mainly consists of an infrared tracker, a positioning target, and a laser projection device.

[0045] 1. Infrared tracker: This tracker uses infrared light to measure spatial coordinates, establishes a global coordinate system for the assembly scene, and tracks the six-degree-of-freedom pose of the fairing and airframe structure in real time using infrared light. The airframe structure includes the following main components: ① An infrared camera array, equipped with a high frame rate (200Hz+) global shutter CMOS sensor, captures the infrared reflection / emission signals of the positioning target and calculates the spatial coordinates through multi-view visual triangulation.

[0046] ② Dynamic calibration module, with built-in checkerboard calibration plate and temperature compensation algorithm, automatically calibrates lens distortion and compensates for measurement drift caused by ambient temperature and humidity (accuracy ±0.01mm / m).

[0047] ③ Synchronization controller, integrating IEEE 1588 precision clock protocol, coordinates the time synchronization of multiple trackers (synchronization error <1μs), and eliminates jitter in moving target measurement.

[0048] 2. The positioning target, serving as a space reference marker, is installed on the fairing and fuselage structure to establish a dynamic measurement reference system. This positioning target includes the following main components: ① Active target, with built-in infrared LED array and IMU sensor, used to emit coded infrared signals (wavelength 850nm), and integrate inertial measurement data to improve tracking stability.

[0049] ② Passive target, using a magnetic base coated with retroreflective material to reflect the infrared light emitted by the infrared tracker.

[0050] ③ The target adapter is set as a variable curvature vacuum adsorption structure to adapt to the complex curved surface of the fairing and keep the target normal vector aligned with the optical axis of the infrared tracker.

[0051] 3. Laser projection equipment, used to convert assembly instructions into spatial light projection, enabling non-contact hole making and grinding guidance. This laser projection equipment includes the following main components: ① The laser emitter uses a nanometer-level green semiconductor laser module to project a cross-shaped positioning mark and generate a hole center projection on the curved surface.

[0052] ② Dynamic focusing module, equipped with motorized zoom lens and distance sensor, automatically adjusts the spot size to adapt to projection onto surfaces with different curvatures.

[0053] ③ The path planner integrates anti-collision algorithms and energy density control algorithms to optimize the laser scanning path and avoid thermal deformation of materials caused by continuous projection.

[0054] 4. Data transmission unit: adopts a dual-mode transmission module to encrypt the scanned data before transmitting it to the controller.

[0055] (iii) Controller: This controller integrates reverse modeling, tolerance analysis, and assembly guidance functions. It automatically compares the 3D contour model obtained through scanning in step 1 with the CATIA design model imported into the controller using AI algorithms, generating a visual assembly correction scheme (such as bolt hole compensation values). The controller then controls the laser projection device in the optical infrared tracker to project information onto the fairing entity to guide drilling and grinding operations. The controller mainly consists of a 3D scanning data acquisition module, a reverse modeling engine, an AI assembly deviation analysis module, a laser positioning control unit, and a real-time monitoring module.

[0056] 1. The 3D scanning data acquisition module communicates with the laser 3D scanner and acquires point cloud data of the fairing and body structure surface in real time based on the 3D spatial coordinates of each pixel in the raster image calculated in step 1.

[0057] 2. Reverse modeling engine: This engine processes point cloud data in real time, converting it into a 3D contour model of the fairing and fuselage structure. The reverse modeling engine mainly comprises the following components: ①FPGA acceleration chip, based on hardware-accelerated phase calculation algorithm, converts raster images into point cloud data in a processing time of ≤0.5 seconds / frame, supporting real-time 3D reconstruction.

[0058] ② Supports multi-terminal collaborative analysis (such as synchronous parameter adjustment at the design and process ends) to achieve fully digital management of the assembly process.

[0059] ③ The embedded multi-core processor adopts a GPU parallel computing architecture to complete point cloud noise reduction, triangulation and 3D model reconstruction in real time with a processing latency of <50ms, which meets the continuous operation requirements of the final assembly line.

[0060] 3. The AI ​​assembly deviation analysis module automatically aligns the 3D contour model with the CATIA design model inside the controller, identifies manufacturing errors and assembly deviations (such as surface curvature deviation, gap deviation, and hole position offset), predicts interference risks after fairing assembly (such as bolt hole misalignment > 0.3mm), marks areas requiring rework, and generates a visual assembly correction plan. This plan, for example, is a 3D grinding navigation map, including: offset adjustment amount, shim thickness suggestions, etc., to guide operators to complete the adjustment assembly.

[0061] 4. Laser positioning and control unit, integrating optical calibration and compensation algorithms, converts theoretical hole-making coordinates into the actual machining coordinate system through dual closed-loop control. This unit is used to achieve the following positioning functions: ① Coarse positioning: Determine the reference hole group based on feature matching of the three-dimensional contour model.

[0062] ② Precise positioning: The hole center coordinates are calibrated using sub-pixel level image processing technology.

[0063] ③ The laser projection device is controlled to perform spatial coordinate mapping based on the center coordinates of the hole, thereby realizing the blind hole guidance function.

[0064] The principle is the same for grinding boundary markings.

[0065] 5. Real-time monitoring module: Based on the dynamic position information of each positioning target obtained by scanning in step 2, the module uses a dynamic spatial coordinate calculation algorithm to calculate the movement trajectory of the fairing during the assembly process, and displays the dynamic deviation trend chart of fairing assembly in real time (X / Y / Z axis separate display). Automatic alarm for exceeding the tolerance and freezing of laser projection.

[0066] The following describes the specific implementation process of the digital assembly method for helicopter fairings provided in the embodiments of the present invention.

[0067] Phase 1: Equipment Preparation and Debugging (1) Import the helicopter CATIA design model into the controller, including: fairing theoretical model, airframe structure model and mounting hole coordinate set, etc.

[0068] (2) Analyze the PMI (Product Manufacturing Information, including product structure and dimensions) in the CATIA design model, extract key dimensional tolerances, surface profile requirements, etc.; enter the acceptance criteria, including gap requirements, step difference requirements, etc.

[0069] (3) Convert the CATIA design model into a lightweight format, optimize the display performance of the model, and establish a three-dimensional coordinate system of the CATIA design model in the controller, aligning it with the helicopter body coordinate system.

[0070] (4) Calibration of handheld laser 3D scanner: Use a standard ball plate for calibration to ensure that the point cloud fitting error is ≤0.02mm and set the vibration threshold (the compensation algorithm is triggered when the acceleration is >0.5g).

[0071] (5) Calibration of optical infrared tracker: Measure the three-dimensional coordinates of the target ball, generate a coordinate system in the controller, and verify that the positioning repeatability error is ≤0.03mm.

[0072] (6) Calibrate the tool center point of the electric grinder and hole-making equipment: record at least 6 pose data, and the controller automatically calculates the TCP offset.

[0073] Phase Two: Digital Assembly (7) The operator moves a handheld laser 3D scanner along the surface of the fairing, the scanning path follows a “Z” trajectory, and the scanning distance is kept at 300±50mm; the same method is used to scan the installation structure of the fairing on the body.

[0074] (8) The controller automatically stitches together point cloud data to generate a three-dimensional contour model of the fairing and body structure surface, with a point cloud density of ≥10 points / mm².

[0075] (9) By extracting 5 feature sections, compare the deviation between the 3D contour model obtained based on point cloud data and the design model. If the local deviation is >0.5mm, trigger a rescan prompt.

[0076] (10) The controller performs “best fit alignment” to match the three-dimensional contour model with the CATIA design model in 6 degrees of freedom and minimize the overall deviation.

[0077] (11) The controller generates a three-dimensional deviation chromatogram (i.e., a three-dimensional polishing navigation map): - Green area: Deviation within ±0.1mm; - Yellow area: Deviation ±0.1~0.5mm, requires grinding and adjustment; -Red area: Deviation > 0.5mm, manual verification required; (12) The controller generates process instructions: calculates the amount of material to be removed based on the deviation, and outputs the hole position correction value based on the theoretical coordinates of the mounting hole.

[0078] (13) Load the three-dimensional contour model (including fairing and fuselage structure) in the controller and load the fastener model in the design model (in order to verify the matching degree between the scanned model and the actual assembly fastener); set physical simulation parameters, such as contact stiffness, friction system, etc.; simulate the assembly process of the fairing on the fuselage structure through simulation software, check the interference of the assembly process, and verify the bolt preload, etc.

[0079] (14) Grinding for the amount removed in (12): The controller controls the optical infrared tracker to generate a grinding path on the fairing and guides the grinder to move along the path; the optical infrared tracker monitors the movement trajectory of the grinding tool on the fairing in real time and displays it in the controller. When the deviation exceeds 0.5mm, the system automatically pauses and alarms.

[0080] (15) For the hole making in (12), the optical infrared tracker projects the virtual hole center position on the fairing. The operator holds the hole making tool close to the target hole position. When the overlap between the tool tip and the virtual hole center is <0.1mm, the controller prompts that drilling is allowed.

[0081] (16) After the fairing is installed, the fairing and surrounding body structure are scanned in full size by a handheld laser 3D scanner. By comparing the RMS error between the final model and the design model, an inspection report is generated.

[0082] Based on the digital assembly method for helicopter fairings provided in the above embodiments of the present invention, the accompanying digital assembly system for helicopter fairings includes: a handheld laser 3D scanner for panoramic mobile scanning of the fairing's shape, fuselage structure, fairing mounting point on the fuselage, and fairing mounting on the fuselage; an optical infrared tracker for guiding hole drilling on the fairing and guiding grinding of the fairing's outer ring; and a controller integrating measurement, analysis, and control functions to achieve closed-loop management of the assembly process. This digital assembly system is particularly suitable for flexible assembly scenarios of complex curved surface fairings for helicopters, effectively solving the pain points of high dependence on traditional tooling and large workload of manual repair, and has significant technological advancement and industrial application value.

[0083] This invention provides a digital assembly method for helicopter fairings. The method employs a laser 3D scanner to scan the surfaces of the fairing and fuselage structure, obtaining 3D contour models of these surfaces based on the scan data. By comparing the 3D contour models with the design models imported into the controller, a visual assembly correction scheme is generated. Based on the 3D contour models, the visual assembly correction scheme is projected during fairing assembly, enabling non-contact hole making and grinding guidance. During fairing assembly, the dynamic position information of various positioning targets on the fairing and fuselage structure is acquired, and the fairing's movement trajectory during assembly is calculated. Automatic alarms are triggered for out-of-tolerance conditions, and the laser projection is frozen. The technical solution provided by this invention employs a closed-loop technology of "multi-sensor fusion + intelligent decision-making + precise execution," systematically solving the difficulties in helicopter fairing assembly and achieving breakthroughs in accuracy, efficiency, and cost. The solution provided by this invention has the following beneficial effects: First, high-precision digital twin matching: the actual shape of the fairing is obtained by a handheld laser scanner (accuracy ±0.05mm), and a full-size comparison is performed with the CATIA design model to generate a three-dimensional deviation heat map and automatically mark the out-of-tolerance areas; in practical applications, the installation gap control accuracy can be improved to ±0.2mm, and the step difference fluctuation range can be compressed to ±0.3mm.

[0084] Second, dynamic pose monitoring: The optical infrared tracker monitors the six-degree-of-freedom pose of the fairing and the fuselage structure in real time (position accuracy ±0.1mm, angle accuracy ±0.05°), and displays the deviation vector in real time, allowing operators to make quick adjustments based on the guidance.

[0085] Third, intelligent margin calculation: After comparing the laser scanning data with the design model, the controller automatically generates a three-dimensional grinding navigation map (i.e., a visual assembly correction scheme), marks the areas to be removed (highlighted in red) and the areas to be retained (green), and calculates the optimal grinding amount (accuracy ±0.1mm).

[0086] Fourth, laser projection positioning: The actual coordinates of the mounting holes on the body structure are obtained by an optical infrared tracker. The laser equipment directly projects the hole contour (including the normal reference line) onto the surface of the fairing. The hole positioning accuracy reaches ±0.15mm and the normal angle deviation is ≤0.3°.

[0087] Fifth, reverse matching technology: automatically calculate the reverse matching path based on the scan data, first locate the structural holes of the body → reverse calculate the theoretical hole position of the fairing → dynamically compensate for manufacturing errors.

[0088] Sixth, interference prediction technology: Virtual assembly simulation is performed by scanning the fairing model and the point cloud of the airframe structure (acquired by laser scanning). Based on the physics engine, the minimum gap is detected (accuracy 0.1mm), high-risk interference areas are marked in advance, and more than 90% of interference problems are predicted and resolved before installation.

[0089] The following specific embodiments illustrate the implementation of the digital assembly method for helicopter fairings provided in this invention.

[0090] Example 1: Intelligent Assembly Method for Helicopter Intermediate Gearbox Fairing The fairing of the intermediate gearbox of a certain type of helicopter is made of carbon fiber composite material. It has fairings at both the front and rear of its mounting position on the aircraft, thus requiring matching through trial fitting. One end along the flight direction is a non-grindable curved structure, while the other end requires grinding to adjust the mounting dimensions. Traditional assembly presents two major challenges: 1. Dimensional control contradiction: While ensuring the geometric accuracy of the non-grindable end, the other end needs to be ground to meet the requirements of peripheral gap (0.5~2mm) and step difference (±2mm); 2. Risk of hole making accuracy: Φ6mm mounting holes need to be made in curved areas with a radius of curvature ≤150mm. Manual positioning deviation often exceeds ±0.5mm, resulting in uneven stress distribution in the bolt group.

[0091] The implementation process of this embodiment using the digital assembly method provided by the present invention includes the following steps: Step 1: Assembly Data Preparation Download the CATIA design model of the helicopter's intermediate gearbox area, including: fairing theoretical model, airframe structural model, and mounting hole coordinate set; Establish an assembly process database in the controller, import the design model, and set acceptance criteria, including: —Contour tolerance of non-grindable end: ±0.15mm; —Grinding end fitting allowance: 0.2-1.5mm; —Mounting hole position tolerance: ±0.2mm.

[0092] Step 2: Equipment Networking and Calibration Establish a multi-sensor collaborative measurement network, including: —Connect the handheld laser 3D scanner to the controller; —Deploy optical infrared trackers, installing 3 optical infrared trackers on top of the assembly station; Perform system calibration, including: —Laser 3D scanner: Standard sphere center-to-center calibration method (50mm diameter ceramic spheres, 200mm spacing), calibration error <0.01mm; —Optical infrared tracker: Multi-view joint calibration is completed through a V-shaped target to establish a global coordinate system (overlap error with CATIA model coordinate system ≤ 0.05mm).

[0093] Step 3: Target Placement and Data Acquisition The non-grindable end of the target is configured as follows: —Attach 6 active IMU targets (temperature resistant -40~120℃) at equal intervals in the curved area, with a spacing of 150mm; —The angle between the target normal vector and the tangent plane of the curved surface is ≤10° to ensure omnidirectional coverage of the infrared signal; The data acquisition method for the polishable end is as follows: —Use a handheld laser scanner to perform a spiral scan along the flight path (scanning interval 2mm) to obtain an actual model of the fairing; —Perform a local scan of the mounting surface of the aircraft structure (key areas: 4 reference mounting bases) to generate a structural point cloud model.

[0094] Step 4: Surface Matching and Deviation Analysis Performing multi-level matching in intelligent software includes: — Coarse matching: Based on the algorithm, the feature lines of the fairing bend are extracted and initially aligned with the design model (error tolerance ±1mm). —Precise matching: The ICP algorithm is used to perform rigid registration on the non-grindable end (iteration count > 1000 times) to lock the bend reference; —Dynamic compensation: Based on the end positioning results, calculate the theoretical fit amount Δh = H0 - (H1 + δ) of the grindable end, where H0 is the design height, H1 is the measured height, and δ is the assembly gap compensation amount (0.3mm). Generate a 3D deviation contour plot, including the following display content: —Red area: Material to be removed > 0.5mm; —Yellow area: 0.2-0.5mm needs to be removed; —Green area: Remain unchanged.

[0095] Step 5: Guided Precision Repair The operator uses abrasive tools to remove the material, including: —Coarse grinding: 80-grit grinding wheel, removal amount 0.3-0.8mm; —Fine grinding: 240-grit sandpaper belt, removal amount 0.1-0.3mm.

[0096] Step 6: Hole-making scheme generation and simulation Reverse calculation of hole position: —Based on the scanned point cloud of the body structure, extract the coordinate set of the actual mounting hole center; —The theoretical aperture positions of the fairing are calculated by fitting the aperture group distribution pattern using the least squares method; —Add manufacturing error compensation (0.1mm) to generate the final hole coordinate set; Process simulation verification: —Simulate the drill bit path (6mm diameter, 3000rpm) in a virtual environment to detect the risk of interference with the internal structure; —Optimize the hole-making sequence: prioritize machining the reference hole, and then complete the remaining holes using a spiral path.

[0097] Step 7: Optical-guided precision hole making The infrared tracker monitors the fairing's position and attitude in real time (frequency 200Hz) and drives the laser projection equipment to perform the following: —Coarse positioning: Project a Φ10mm green light ring to guide the drill bit into the working area (positioning error ±0.3mm); —Precise positioning: Switch to Φ6mm red crosshair to display the normal angle (accuracy ±0.1°).

[0098] Step 8: Assembly quality closed-loop verification Pre-installation checks include: —Perform a full-size remeasurement of the repaired fairing (scanning interval of 0.5mm for key areas); —Perform virtual assembly simulation: Import the fairing model and the fuselage model into the physics engine and detect the minimum gap (threshold 0.5mm). Step 9: Final Assembly During installation, the gap changes are monitored in real time (laser displacement sensor sampling rate 1kHz), and an automatic alarm is triggered if the gap exceeds the tolerance.

[0099] Step 10: Redundant checks Remove and return the equipment to its proper place, and check that there are no extra items in the installation area on the machine.

[0100] Example 2: After the engine cowling of a certain type of helicopter was installed, the clearance between the cowling and the firewall exceeded the tolerance. After the engine cowling of a certain type of helicopter was installed, the gap between the cowling and the firewall exceeded the tolerance (the design requirement is 0.5-3mm, but the actual measured gap is 4.5mm in some areas). Traditional laser trackers can only measure discrete points and cannot fully analyze the root cause of the deviation.

[0101] The implementation process of this embodiment using the digital assembly method provided by the present invention includes the following steps: Step 1: Assembly Data Preparation Download the CATIA model of the power compartment, including: the theoretical model of the fairing, the design model of the firewall, and the coordinate set of the installation points; Establish an assembly process database in the controller, import the design model, and set acceptance criteria, including: —Fairing-firewall gap: 0.5-2mm; —Installation point position tolerance: ±0.3mm (relative to the reference axis).

[0102] Step 2: Equipment Networking and Calibration Establish a multi-sensor collaborative measurement network, including: —Connect the handheld laser 3D scanner to the control host; —Deploy optical infrared trackers, installing 3 infrared trackers on top of the assembly station; Perform system calibration, including: —Laser 3D scanner: Standard sphere center-to-center calibration method (50mm diameter ceramic spheres, 200mm spacing), calibration error <0.01mm; —Optical infrared tracker: Multi-view joint calibration is completed through a V-shaped target to establish a global coordinate system (overlap error with CATIA model coordinate system ≤ 0.05mm).

[0103] Step 3: Target Placement and Data Acquisition The target configuration method is as follows: —Attach 8 active IMU targets at equal intervals along the edge of the fairing, with a spacing of 200mm; — Install four passive targets at critical structural points of the firewall to form a global measurement benchmark network.

[0104] The implementation method of 3D scanning is as follows: —Fairing scanning: Perform a spiral scan along the circumference (line spacing 1mm), focusing on the installation flange area (scanning density increased to 0.5mm); —Firewall Scan: Use a laser scanner to perform a partitioned scan of the firewall (5×5 grid) to obtain the actual model; simultaneously record the ambient temperature and humidity for thermal expansion compensation.

[0105] Step 4: Multi-source data fusion and deviation analysis The data preprocessing method is as follows: —Denoising M2 / M3 point clouds (bilateral filtering algorithm) and hole repair (Poisson surface reconstruction); — Rigidly register M2 / M3 with M0 / M1 using the ICP algorithm (iteration error < 0.01 mm).

[0106] Gap calculation, including: —Perform adaptive gap analysis in intelligent software; — Generate 5,000 sets of measurement lines (10mm interval) along the normal direction; —Calculate the minimum distance matrix D(i,j) between the fairing and the firewall.

[0107] Source tracing of out-of-tolerance issues: Establish a tolerance transfer model to identify the main causes of out-of-tolerance issues, including: —Installation point offset analysis: Compare the actual installation point coordinates C1 with the theoretical value C0, and calculate the cumulative error ΔC=Σ|C1i-C0i|; —Structural deformation analysis: Extract the rate of change of curvature δk of the firewall skin (design value k0=0.15m) -1 The measured value of k1 is 0.21m. -1 ); Step 5: Generation of dynamic compensation and repair schemes Intelligent decision-making: The system recommends repair strategies based on the type of deviation, including: —Mounting point offset is the primary factor: compensation is achieved using shims (thickness calculation accuracy ±0.02mm); —Structural deformation is the main factor: localized grinding of firewalls (maximum removal amount ≤ 0.3mm).

[0108] Gasket optimization design, including: —Stress distribution of gaskets with different thicknesses (0.1-0.5 mm) was calculated based on finite element analysis (FEA); —Select a combination of washers that results in bolt preload fluctuation of <5% (e.g., 0.2mm + 0.1mm stack).

[0109] Step 6: Repair and closed-loop, including: —Addition of gaskets; —Firewall repair.

[0110] Step 7: Redundant checks Remove and return the equipment to its proper place, and check that there are no extra items in the installation area on the machine.

[0111] While the embodiments disclosed in this invention are as described above, they are merely illustrative of the embodiments to facilitate understanding of the invention and are not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method of digitally assembling a helicopter fairing, characterized in that, The method comprises the following steps: Step 1: scanning the surface of the fairing and the body structure by using a laser three-dimensional scanner, and obtaining a three-dimensional profile model of the surface of the fairing and the body structure according to the scanning data; Step 2: generating a visual assembly correction scheme by comparing the three-dimensional profile model obtained in step 1 with a design model imported into a controller; Step 3: based on the three-dimensional profile model, projecting the visual assembly correction scheme of step 2 by laser during the assembly process of the fairing to realize non-contact hole drilling and polishing guidance, and implementing digital assembly of the fairing; Step 4: during the assembly process of the fairing, the dynamic position information of each positioning target on the fairing and the body structure is obtained, and the movement trajectory of the fairing during the assembly process is calculated, and the laser projection is automatically frozen and alarmed when the error exceeds the tolerance.

2. The method for digital assembly of a helicopter fairing according to claim 1, characterized in that, The step 1 comprises: Step 11: projecting a laser grating on the surface of the fairing and the body structure by using a laser three-dimensional scanner, and shooting the grating image along the change of the surface of the fairing and the body structure by using a camera; Step 12: calculating the three-dimensional space coordinates of each pixel point in the grating image, obtaining the point cloud data of the surface of the fairing and the body structure in real time, and converting the point cloud data into the three-dimensional profile model of the fairing and the body structure by processing the point cloud data in real time.

3. The method for digital assembly of a helicopter fairing according to claim 1, characterized in that, In the step 2, the visual assembly correction scheme is generated in the following manner: The three-dimensional profile model obtained in step 1 is automatically aligned with the design model imported into the controller, the manufacturing error and the assembly deviation are identified, the interference risk after the assembly of the fairing is predicted, the rework area is marked, and the visual assembly correction scheme is generated to guide the operator to complete the adjustment and assembly.

4. The method of digitally assembling a helicopter fairing of claim 1, wherein, The step 3 comprises: During the assembly process of the fairing, the six-degree-of-freedom pose of the fairing and the body structure is tracked in real time by using an optical infrared tracker, and the visual assembly correction scheme is projected by space laser in combination with the three-dimensional profile model obtained in step 1 to realize non-contact hole drilling and polishing guidance.

5. The method of digitally assembling a helicopter fairing of claim 1, wherein, The step 4 comprises: The positioning targets on the fairing and the body structure are scanned by using an optical infrared tracker to obtain the dynamic position information of each positioning target, and the movement trajectory of the fairing during the assembly process is calculated by a dynamic space coordinate calculation algorithm in the controller; and a dynamic deviation trend chart of the fairing assembly is displayed in real time, and the laser projection is automatically frozen and alarmed when the error exceeds the tolerance.

6. The method for digital assembly of a helicopter fairing according to claim 5, characterized in that, The optical infrared tracker comprises an infrared tracker, positioning targets and a laser projection device. The optical infrared tracker is used for detecting by infrared light emitted by the infrared tracker to realize space coordinate measurement, establishing a global coordinate system of the assembly scene, and tracking the six-degree-of-freedom pose of the fairing and the body structure in real time by infrared light; the positioning targets installed on the fairing and the body structure are used as space reference markers to construct a dynamic measurement reference system; and the assembly instructions issued are converted into space light projection by the laser projection device to realize non-contact hole drilling and polishing guidance.

7. The method for digital assembly of a helicopter fairing according to claim 6, characterized in that, The positioning targets comprise active targets, passive targets and target adapters. The active targets and the passive targets are installed on the fairing and the body structure through the target adapters, and the normal vectors of the targets are aligned with the optical axis of the infrared tracker. The active target, built-in infrared LED array and IMU sensor, is used to emit coded infrared signals, combined with fusion inertial measurement data to improve tracking stability. The passive target, a magnetic base coated with retroreflective material, is used to reflect infrared light emitted by the infrared tracker.

8. The method for digital assembly of a fairing of a helicopter according to any one of claims 1 to 7, characterized in that, In step 3, digital assembly of the fairing is implemented, including: S1, polishing for the removal amount in the visual assembly correction scheme, including: the controller controls the optical infrared tracker to generate a polishing path on the fairing, guiding the polishing machine to move along the path; the optical infrared tracking device monitors the movement trajectory of the polishing tool on the fairing in real time and displays it in the controller, and automatically pauses and alarms when the deviation exceeds the deviation threshold; S2, for the virtual hole center position projected by the optical infrared tracker on the fairing to guide the operator to drill holes, when the coincidence degree between the tip of the drilling tool and the virtual hole center is less than the drilling deviation value, the controller prompts to allow drilling.

9. The method for digital assembly of a fairing of a helicopter according to any one of claims 1 to 7, characterized in that, Before step 1, it also includes: Step a, importing the design model of the helicopter into the controller, and analyzing the product structure and size information in the design model; Step b, establishing a three-dimensional coordinate system of the design model in the controller, and aligning it with the helicopter body coordinate system; Step c, calibrating the laser three-dimensional scanner, calibrating the optical infrared tracker, and tool center point calibration for the electric polisher and hole drilling equipment.

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