A measuring device and method based on roller conveyor pipeline large field scanning

Abstract

The application discloses a kind of measurement device and method based on roller conveyor pipeline large field scanning, it is related to automatic detection technical field, to solve one of the problems that existing measurement device is difficult to simultaneously consider large field coverage and high-precision measurement in roller conveyor pipeline, poor universality.The measurement device of the present application includes roller conveying assembly, visual acquisition component and calibration reference component;The roller conveying assembly is used to transport workpiece;The visual acquisition component is arranged above and side of the roller conveying assembly, for collecting workpiece surface profile information;The calibration reference component is used to provide calibration reference.The present application can realize high-precision dynamic measurement in large field range without blocking production process, and compatible with online detection of multiple types of workpieces, effectively consider large field coverage and measurement accuracy, improve the universality of device.

Description

Technical Field

[0001] This invention relates to the field of automatic inspection technology, and in particular to a measuring device and method based on large field-of-view scanning of a roller conveyor line. Background Technology

[0002] Roller conveyor lines are widely used in the processing and manufacturing of metal sheets, bars, pipes, H-beams, wheel rings, and castings. Precise online measurement of workpieces is crucial for ensuring yield, product quality, and assembly accuracy. Traditional manual measurement suffers from low accuracy, low efficiency, high labor intensity, and safety hazards associated with high-temperature workpieces, failing to meet the quality and efficiency requirements of modern industrial production.

[0003] Existing technologies have been used to conduct non-contact measurement research on specific workpieces: for metal sheets, laser triangulation measurement systems are used, but the accuracy and coverage data are unclear; for pipes, a combination of multiple laser sources and CCD cameras is used, which has high accuracy but is only suitable for experimental platforms; for bars, H-beams, wheel rings, and irregularly shaped parts, laser scanning, multi-camera stitching, and visual measurement are used respectively, some of which have achieved high accuracy, while others have only completed simulation and feasibility verification.

[0004] However, existing technologies still have common drawbacks: camera-based measurement methods are limited by sensor size and pixel accuracy, making it difficult to maintain high accuracy in a large field of view; most systems are custom-designed for specific workpieces and cannot be compatible with the measurement of multiple types of workpieces; some solutions require the insertion of independent inspection stations in the production line, which slows down the production cycle and lacks adaptability and practicality, and cannot truly meet the online measurement needs of roller conveyor lines for multiple varieties, large field of view, high efficiency, and high accuracy.

[0005] Therefore, there is an urgent need for a large field-of-view scanning measurement device and method for roller conveyor lines that can achieve both large field-of-view coverage and high-precision measurement, be compatible with various workpiece shapes on roller conveyor lines, and adapt to complex industrial environments without interrupting the production process or adding independent inspection stations. Summary of the Invention

[0006] In view of the above analysis, the present invention aims to provide a measurement device and method based on large field-of-view scanning of roller conveyor lines, so as to solve one of the problems of existing measurement devices in roller conveyor lines, which are difficult to simultaneously achieve large field-of-view coverage and high-precision measurement, and have poor versatility.

[0007] The objective of this invention is mainly achieved through the following technical solutions: A measurement device based on a large field-of-view scanning of a roller conveyor line includes a roller conveyor assembly, a vision acquisition assembly, and a calibration reference assembly; the roller conveyor assembly is used to transport workpieces; the vision acquisition assembly is disposed above and to the side of the roller conveyor assembly, and is used to acquire contour information of the workpiece surface; the calibration reference assembly is used to provide a calibration benchmark.

[0008] Furthermore, the visual acquisition component includes a first-line laser camera, a second-line laser camera, and a third-line laser camera.

[0009] Furthermore, the first and third line laser cameras are installed upright, while the second line laser camera is installed upside down.

[0010] Furthermore, the visual acquisition component also includes an adjustable camera mount, which includes a tilt angle adjuster and a pitch angle adjuster.

[0011] Furthermore, the adjustable camera mount also includes a translation stage and a rotary stage.

[0012] Furthermore, the calibration reference component includes a calibration mechanism and a calibration ring.

[0013] Furthermore, the measuring device also includes a drive calculation component, which is connected to the roller conveyor component and the vision acquisition component. The drive calculation component is used to control the conveying, trigger acquisition, and process data.

[0014] Furthermore, the driving computing component includes a grating rotary encoder and a multi-channel signal distribution card, the multi-channel signal distribution card being connected to the grating rotary encoder and the vision acquisition component respectively.

[0015] Furthermore, the roller conveyor assembly also includes a drive belt, which connects the servo motor of the roller conveyor assembly to the roller conveyor.

[0016] On the other hand, the present invention provides a measurement method based on large field-of-view scanning of a roller conveyor line, employing the aforementioned measurement device, and including the following steps: S1 system initialization and parameter configuration; S2 coarse calibration and initial estimation of external parameters; S3 fine calibration and joint parameter optimization; S4 Dynamic Measurement and Point Cloud Solving.

[0017] Furthermore, the first and third line laser cameras are mounted upright on the lower crossbeam of the camera bracket of the roller conveyor assembly, while the second line laser camera is mounted upside down below the upper crossbeam of the camera bracket, forming a spatially spaced and opposite shooting relationship.

[0018] Furthermore, the calibration ring is a ring-shaped structure, and the outer cylindrical sidewall of the calibration ring is set as an inclined wall structure. A groove is opened in the middle part along the circumference, and the groove is provided with ring through holes at equal intervals along the circumference. The ring through holes are used as a non-perfect rotational symmetry feature to break symmetry constraints in calibration optimization.

[0019] Furthermore, the grating rotary encoder is connected to the shaft of the servo motor via a coupling, used to detect the rotational angular displacement of the motor shaft in real time and generate differential pulse signals; the input end of the multi-channel signal distribution card is connected to the signal output end of the grating rotary encoder, and the output end of the multi-channel signal distribution card is connected to the trigger signal interfaces of the first line laser camera, the second line laser camera and the third line laser camera respectively, used to distribute encoder pulses to each camera as synchronous trigger signals, realizing hardware-level synchronization between camera acquisition and workpiece displacement.

[0020] Furthermore, S2 includes: adjusting the laser planes of each line laser camera to be coplanar; establishing a common coordinate system with a calibration mechanism, and obtaining a coarse extrinsic transformation matrix from each camera coordinate system to the common coordinate system by fitting plane, cylindrical, and spherical geometric elements; for cameras that cannot observe all features simultaneously, moving the calibration mechanism step by step along the motion direction, and using the displacement matrix to achieve preliminary stitching of point clouds at different positions to obtain the initial solution for fine calibration.

[0021] Furthermore, S3 includes: establishing a precise calibration reference coordinate system using a calibration ring, introducing a correction amount of the pulse displacement scaling factor to compensate for axial scale deviation; constructing a joint geometric constraint optimization model, the model including the radial residual of the cylindrical surface, the end face distance residual, the distance residual of the non-perfect rotational symmetry feature, and the consistency residual of the spacing between adjacent contour lines; and using nonlinear least squares iteration to update the precise extrinsic parameters of each camera to the reference coordinate system and the corrected scaling factor.

[0022] The technical solution of this invention can achieve at least one of the following effects: (1) By setting up roller conveyor components, vision acquisition components, and calibration reference components, and adopting a multi-camera distributed layout to cover the workpiece measurement area, this invention solves the problem that existing measuring devices have a small field of view and cannot adapt to large-sized workpieces. It realizes the full-area contour acquisition of various types of workpieces such as plates, bars, and wheel rings on the roller conveyor line, and improves the applicability and measurement integrity of the device.

[0023] (2) The present invention solves the problem of blind spots in single-camera shooting and difficulty in stitching multi-view data by using a combination of upright and inverted spatial distribution of the first-line laser camera, the second-line laser camera and the third-line laser camera, thereby realizing multi-directional synchronous scanning of the workpiece from top to bottom and side, reducing measurement dead angles and improving the integrity of three-dimensional reconstruction.

[0024] (3) By setting an adjustable camera mounting base, the present invention integrates tilt angle adjustment, pitch angle adjustment, translation and rotation adjustment functions, which solves the problem of fixed camera posture and difficulty in aligning laser plane, realizes rapid coplanar calibration of laser plane of multiple cameras, simplifies the on-site debugging process, and improves system calibration efficiency and measurement consistency.

[0025] (4) By setting the calibration ring as a ring structure and setting the inclined wall structure, circumferential groove and ring through hole on the outer cylindrical surface, the present invention reduces laser diffuse reflection interference by using the inclined wall structure, and improves the point cloud acquisition quality and data stability under high temperature and high reflectivity conditions. On the other hand, the ring through hole forms a non-complete rotational symmetry feature, which solves the problem of equivalent solutions around the axis and optimization non-convergence that are easy to occur in the calibration process of rotating bodies, realizes the breaking of symmetry constraints, ensures the stability and reliability of the fine calibration process, and improves the system calibration accuracy and measurement repeatability.

[0026] (5) This invention achieves hardware-level synchronous triggering of displacement signal and camera acquisition through a hardware structure that directly connects the grating rotary encoder to the servo motor shaft and synchronously distributes pulses through a multi-channel signal distribution card. This solves the problems of point cloud stretching and axial dimension distortion caused by transmission gap, speed fluctuation and signal delay in dynamic production line measurement. It enables high-precision three-dimensional contour data to be obtained even when the workpiece is in continuous conveying state, and realizes online measurement that does not stop the machine, does not position and does not interrupt production.

[0027] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0028] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0029] Figure 1 This is a schematic diagram of the overall structure of the measuring device for large field-of-view scanning of a roller conveyor line according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the adjustable camera mounting base of the measuring device for large field-of-view scanning of a roller conveyor line according to Embodiment 1 of the present invention. Figure 3 This is a schematic diagram of the calibration mechanism of the measuring device for large field-of-view scanning of a roller conveyor line according to Embodiment 1 of the present invention; Figure 4This is a schematic diagram of the calibration ring of the measuring device for large field-of-view scanning of the roller conveyor line according to Embodiment 1 of the present invention; Figure 5 for Figure 4 A cross-sectional view along line AA; Figure 6 This is a schematic diagram of the drive and calculation component of the measuring device for large field-of-view scanning of a roller conveyor line according to Embodiment 1 of the present invention. Figure 7 This is a schematic diagram of the grating rotary encoder and coupling of the measuring device for large field-of-view scanning of a roller conveyor line according to Embodiment 1 of the present invention. Figure 8 This is a schematic diagram of the multi-view scanning point cloud fusion effect in Embodiment 2 of the present invention; Figure 9 This is a schematic diagram of the point cloud reconstruction and stitching effect of the calibration ring scanning device in Embodiment 2 of the present invention.

[0030] Figure label: 1-Roller conveyor assembly; 11-Roller conveyor; 12-Roller conveyor frame; 13-Servo motor; 14-Motor control box; 15-Camera bracket; 16-Drive belt; 2-Visual acquisition component; 21-First-line laser camera; 22-Second-line laser camera; 23-Third-line laser camera; 24-Adjustable camera mount; 241-Camera mounting plate; 242-Tilt angle adjuster; 243-Pitch angle adjuster; 244-Translation stage; 245-Rotation stage; 246-Plate base; 3-Calibration reference component; 31-Calibration mechanism; 311-Aluminum profile base; 312-Connecting bend plate; 313-Magnetic base; 314-Calibration ball; 32-Calibration ring; 321-Ring through hole; 4-Drive computing component; 41-Raster rotary encoder; 42-Power supply; 43-Multi-channel signal distribution card; 44-Coupling; 45-Industrial computer; 46-Power cord; 47-Display screen. Detailed Implementation

[0031] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0032] Example 1 This embodiment aims to provide a measurement device based on a large field-of-view scanning of a roller conveyor line, in order to solve one of the problems of existing measurement devices in roller conveyor lines, which are difficult to simultaneously achieve large field-of-view coverage and high-precision measurement, and have poor versatility.

[0033] like Figure 1 , Figure 4 and Figure 6 As shown, the measuring device includes a roller conveyor assembly 1, a vision acquisition assembly 2, a calibration reference assembly 3, and a drive and calculation assembly 4. The roller conveyor assembly 1 is used to carry and transport the workpiece to be measured; the vision acquisition assembly 2 is located above and to the side of the roller conveyor assembly 1 and is used to acquire the surface contour information of the workpiece to be measured; the calibration reference assembly 3 is used to provide a reference with known geometric features during the calibration process; the drive and calculation assembly 4 is connected to the roller conveyor assembly 1 and the vision acquisition assembly 2 respectively, and is used to control the workpiece transport, trigger image acquisition, and process and analyze the acquired data.

[0034] Specifically, the roller conveyor assembly 1 includes rollers 11, roller frame 12, servo motors 13, and motor control box 14. The roller frame 12 provides the foundation support for the entire device. Multiple rollers 11 are arranged axially parallel and rotatably connected to the roller frame 12. The servo motor 13 is fixedly connected to the end of the roller frame 12, and the motor control box 14 is connected to the servo motor 13 via a multi-pin interface and is powered by an external power source. The output shaft of the servo motor 13 is connected to the end roller 11, driving the end roller 11 to rotate, thereby causing all rollers 11 to rotate synchronously, enabling the workpieces placed on the rollers 11 to move at a uniform speed along the conveyor line direction. The motor control box 14 has a built-in control circuit for adjusting the start / stop, speed, and direction of the servo motor 13, achieving stability and controllability of the workpiece conveying speed.

[0035] The roller conveyor assembly 1 also includes a camera bracket 15 and a drive belt 16. The camera bracket 15 is fixed to both sides of the roller frame 12 and extends upward to form a crossbeam structure. The camera bracket 15 is used to provide mounting support for the vision acquisition assembly 2. The drive belt 16 is sleeved between the output shaft of the servo motor 13 and the drive wheel of the roller 11 at the end, realizing synchronous transmission between the servo motor 13 and the roller 11.

[0036] To address the limited field of view of a single camera, the visual acquisition component 2 employs a multi-camera distributed layout. The visual acquisition component 2 includes a first-line laser camera 21, a second-line laser camera 22, a third-line laser camera 23, and an adjustable camera mount 24.

[0037] Preferably, the first-line laser camera 21 and the third-line laser camera 23 are mounted upright on the lower crossbeam of the camera bracket 15 via an adjustable camera mounting base 24, while the second-line laser camera 22 is mounted upside down below the upper crossbeam of the camera bracket 15 via the adjustable camera mounting base 24. The horizontal height of the second-line laser camera 22 is higher than that of the first-line laser camera 21 and the third-line laser camera 23, forming a spatially spaced and relatively opposite shooting relationship, so that the scanning fields of view of the three cameras are spatially complementary and connected, covering a wider scanning range. The first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23 are used to project laser lines onto the surface of the workpiece being measured and to acquire laser contour images modulated by the workpiece surface.

[0038] To achieve precise adjustment of the camera's pose, such as Figure 2 As shown, the adjustable camera mount 24 includes a camera mounting plate 241, a tilt angle adjuster 242, and a pitch angle adjuster 243. The camera mounting plate 241 is fixedly connected to the back of the first line laser camera 21, the second line laser camera 22, and the third line laser camera 23, and is used to fix the first line laser camera 21, the second line laser camera 22, and the third line laser camera 23. The tilt angle adjuster 242 is connected below the camera mounting plate 241, and is used to adjust the tilt angle of the first line laser camera 21, the second line laser camera 22, and the third line laser camera 23 around the Y-axis. The pitch angle adjuster 243 is connected below the tilt angle adjuster 242, and is used to adjust the pitch angle of the first line laser camera 21, the second line laser camera 22, and the third line laser camera 23 around the X-axis.

[0039] Furthermore, the adjustable camera mount 24 also includes a translation stage 244, a rotary stage 245, and a flat base 246. The translation stage 244 is connected below the pitch angle adjuster 243 and is used to adjust the linear displacement of the camera in the horizontal plane. The rotary stage 245 is connected below the translation stage 244 and is used to adjust the horizontal rotation angle of the camera around the Z-axis. The flat base 246 is located at the bottom of the rotary stage 245 and is fixed to the camera bracket 15. Through the adjustable camera mount 24, the spatial position and attitude of the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23 can be finely adjusted, enabling the laser planes of multiple cameras to be spatially aligned to be coplanar, providing a basis for subsequent calibration and measurement.

[0040] To achieve high-precision calibration of the system, the calibration reference component 3 includes a calibration mechanism 31 and a calibration ring 32. The calibration mechanism 31 is used to establish a common coordinate system during the coarse calibration stage, providing constraints for various geometric elements such as planes, cylindrical surfaces, and spheres. The calibration ring 32 is used for high-precision correction during the fine calibration stage, and it has high-precision cylindrical surface and end face features.

[0041] Specifically, such as Figure 3 As shown, the calibration mechanism 31 includes an aluminum profile base 311, a connecting bend plate 312, a magnetic base 313, and a calibration ball 314. The aluminum profile base 311 forms the supporting body of the calibration mechanism 31. The connecting bend plate 312 is fixed to the aluminum profile base 311 and connects the aluminum profile base 311 to the magnetic base 313. The magnetic base 313 is attached to the connecting bend plate 312, and its position can be adjusted along the connecting bend plate 312. The calibration ball 314 is fixed to the magnetic base 313, providing a spherical feature, and is used for coarse calibration initialization or rapid consistency checks. The calibration mechanism 31 is movably placed on the roller conveyor 11 and is simultaneously photographed by multiple cameras during calibration.

[0042] Preferably, such as Figure 4 and Figure 5 As shown, the calibration ring 32 has a ring-shaped structure. The outer cylindrical sidewall of the calibration ring 32 is designed as an inclined wall structure, and a groove is formed around the middle part along the circumference. Three ring-shaped through holes 321 are formed at equal intervals along the circumference within the groove. The inclined wall structure helps to reduce laser diffuse reflection and improve the quality of point cloud acquisition. The ring-shaped through holes 321 can be used as a non-perfect rotational symmetry feature to break symmetry constraints in calibration optimization and achieve stable convergence. During fine calibration, the calibration ring 32 is placed on the roller conveyor 11, moves with the roller conveyor 11, and is scanned by the camera.

[0043] To achieve system drive, synchronization, and data processing, the drive computing component 4 includes a grating rotary encoder 41, a power supply 42, a multi-channel signal distribution card 43, a coupling 44, an industrial computer 45, a power cord 46, and a display screen 47. For example... Figure 7 As shown, the grating rotary encoder 41 is connected to the shaft of the servo motor 13 via a coupling 44. The grating rotary encoder 41 is used to detect the rotational angular displacement of the motor shaft in real time and generate differential pulse signals. Figure 6As shown, the signal lines A+, A-, B+, and B- of the grating rotary encoder 41 are respectively connected to the A+, A-, B+, and B- input interfaces of the multi-channel signal distribution card 43, transmitting the differential pulse signals generated by the encoder to the multi-channel signal distribution card 43. The power supply 42 provides the required voltage to each electrical component. The multi-channel signal distribution card 43 is powered by the power supply 42, and its A+, A-, B+, and B- output interfaces are respectively connected to the trigger signal interfaces of the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23. The multi-channel signal distribution card 43 distributes the encoder pulses to each camera as synchronous trigger signals.

[0044] Furthermore, the industrial control computer 45 is connected to the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23 via network cables. The industrial control computer 45 is used to receive the point cloud data acquired by the cameras and run calibration and measurement algorithms for data processing. One end of the power cord 46 is connected to the power supply 42, and the other end is connected to the power supply interface of each camera, providing 24V DC power to the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23. The display screen 47 is connected to the industrial control computer 45 via an HDMI interface and is used to display the measurement interface, point cloud images, and processing results. The grating rotary encoder 41 rotates synchronously with the shaft of the servo motor 13, generating a pulse for each rotation angle. This pulse is simultaneously triggered by the multi-channel signal distribution card 43 to acquire one line of contour data from the three cameras, achieving hardware-level synchronization between camera acquisition and workpiece displacement.

[0045] This embodiment constructs a measurement platform with multi-sensor collaboration, hardware synchronous triggering, and high-precision calibration through the above structure. The roller conveyor assembly 1 achieves uniform and stable workpiece transport; the vision acquisition assembly 2 covers a large field of view through a multi-camera layout combining forward and reverse views; the adjustable camera mount 24 provides fine adjustment capabilities for camera attitude; the calibration reference assembly 3 provides a high-precision spatial reference for the system; and the drive and calculation assembly 4 realizes synchronous control of acquisition and motion, as well as data processing. The collaborative work of these components provides a reliable hardware foundation for subsequent dynamic measurement methods, solving the problems of existing devices struggling to achieve both field of view coverage and measurement accuracy in roller conveyor lines, and exhibiting poor versatility.

[0046] Example 2 This embodiment provides a measurement method based on large field-of-view scanning on a roller conveyor line, addressing one of the problems of existing measurement methods in achieving both large field-of-view coverage and high-precision measurement on dynamic conveyor lines, and their inability to adapt to online inspection of various workpieces. This method employs the measurement device described in Embodiment 1 and includes the following steps: S1 System Initialization and Parameter Configuration: Before measurement, the mechanical structure is adjusted and the hardware parameters are initialized and configured. S2 Coarse Calibration and Initial Estimation of Extrinsic Parameters: Constructing initial system constraints and estimating initial values ​​of camera extrinsic parameters; S3 Fine Calibration and Joint Parameter Optimization: Joint optimization of coarse calibration results based on high-precision calibration components; S4 Dynamic Measurement and Point Cloud Solving: Performs dynamic scanning, point cloud fusion, registration, and deviation analysis on the workpiece.

[0047] The following is a detailed explanation of each step: S1 system initialization and parameter configuration specifically include the following steps: S11, Roller Horizontal Adjustment: Adjust the flatness and tilt angle between multiple roller conveyors 11 to make the entire roller conveyor system coplanar in the horizontal direction.

[0048] S12. Transmission synchronization check: Check the fixed position of the transmission belt 16 and the roller conveyor 11 to confirm that there is no obvious sliding friction between the transmission belt 16 and the roller conveyor 11.

[0049] S13. Adjusting the connecting roller conveyor: Adjust the roller conveyor frame 12 and the camera bracket 15 to keep the roller conveyor assembly 1 coplanar and prevent misalignment.

[0050] S14. Camera installation: Install the first line laser camera 21, the second line laser camera 22, and the third line laser camera 23 onto their respective adjustable camera mounts 24, and fix the adjustable camera mounts 24 onto the camera bracket 15.

[0051] S15, Field of view coverage adjustment: By adjusting the tilt angle adjuster 242 and the pitch angle adjuster 243 on the adjustable camera mount 24, the shooting range of the first line laser camera 21, the second line laser camera 22 and the third line laser camera 23 can cover the entire area to be measured of the workpiece.

[0052] S16. Coplanar Adjustment of Laser Planes: Place the first-line laser camera 21 and the third-line laser camera 23 on a horizontal surface using the flat base 246. Place the second-line laser camera 22 upside down below the crossbeam on the camera bracket 15. Place a whiteboard between the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23. Turn on the free acquisition mode of the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23. Adjust the tilt angle adjuster 242 to rotate the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23 through a preset angle. Adjust the pitch angle adjuster 243, the translation stage 244, and the rotation stage 245 to make the three laser lines coincide on the whiteboard. Adjust the height of the whiteboard and repeat the adjustment until the projections of the three laser lines basically coincide at each height, establishing the coplanar prior of the laser planes of the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23.

[0053] S17. Kinematic parameter setting: During the calibration and measurement phase, the servo motor 13 is controlled to rotate at a uniformly set constant speed to ensure that the kinematic boundary conditions of the calibration conditions and the actual measurement conditions are consistent.

[0054] S18. Communication and Trigger Check: Power on the industrial control computer 45, the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23. Check the communication status of the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23 in the acquisition and control software, and verify whether the pulse trigger connection status between the grating rotary encoder 41, the multi-channel signal distribution card 43, and the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23 is normal.

[0055] S2 coarse calibration and initial estimation of extrinsic parameters specifically include the following steps: S21. Physical environment constraints: Adjust the laser planes of the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23 to make them approximately coplanar in space, so that the three cameras can stably acquire calibration features within their respective fields of view.

[0056] S22. Acquisition Mode Configuration: For coarse calibration, the trigger mode is set to free acquisition, and the number of image acquisition rows is set to 1 row for quick acquisition of static point clouds. For fine calibration and subsequent measurements, the pulse trigger mode is used uniformly, with the frequency division number set to m, the frequency division factor set to n, and the number of image acquisition rows set to p.

[0057] S22. Kinematic Model Construction: Introducing the "pulse-displacement" scaling factor of the grating rotary encoder 41 ,in The stroke defined for the grating rotary encoder 41 Let be the number of differential pulses generated within this stroke. The real-time scan displacement corresponding to the t-th trigger line is expressed as: ,in This is the cumulative differential pulse.

[0058] Building upon this, considering that line laser 3D imaging is highly dependent on the physical stacking of temporal scan contours in space, and to address the issue that the dynamic response of the mechanical transmission system directly affects the final 3D shape, problems arise such as servo motor tracking errors, flexible deformation and backlash of the transmission mechanism, and hardware transmission delays of the camera trigger signal, all of which can cause the actual scan line spacing to deviate from the theoretical model. Therefore, the system explicitly stipulates in its control loop that the servo motor must maintain a completely consistent uniform speed scanning mode during the calibration and measurement phases, i.e., a uniform constant speed of s revolutions per minute.

[0059] This closed-loop control strategy effectively stabilizes the dynamic hysteresis effect within the system, ensuring that the kinematic boundary conditions are strictly consistent between the calibration and actual measurement stages. The servo motor must maintain a completely consistent uniform scanning mode during both calibration and measurement stages to avoid stretching or compression of the scanned point cloud along the motion axis caused by acceleration / deceleration fluctuations or mismatches between calibration and measurement conditions. This fundamentally prevents such dynamic scale distortions from being incorrectly coupled into external parameter system deviations such as camera pitch angle or spatial translation.

[0060] S23. Local Feature Fitting in Common Coordinate System B: A local common coordinate system B is established using the calibration mechanism 31 installed on the roller conveyor 11. The coordinate systems of the first line laser camera 21, the second line laser camera 22, and the third line laser camera 23 are denoted as... The calibration mechanism 31 includes geometric elements such as planes, cylindrical surfaces, and feature edges, among which the coordinates of the center of the calibration sphere 314 are only used for initializing attitude estimation.

[0061] Geometric feature point sets are extracted from the point clouds acquired by the first-line laser camera 21, the second-line laser camera 22, and the third-line laser camera 23, and geometric fitting is performed to obtain the plane normal, the cylinder axis, and the feature boundary lines. A coarse-scale objective function is constructed, including the point-to-plane distance residual, the point-to-cylinder radial residual, and the feature line consistency residual. A least quadratic or robust kernel-based optimization algorithm is used to solve for the camera coordinate system. Coarse extrinsic transformation matrix to common coordinate system B The point clouds of the first line laser camera 21, the second line laser camera 22, and the third line laser camera 23 are initially transformed into a common coordinate system using a coarse extrinsic transformation matrix. (in Let be the coordinates of the point in frame B. For the point in the camera system Using coordinates in the B-frame, the initial alignment of point clouds from multiple cameras in the B-frame is achieved.

[0062] S24. Multi-position stitching compensation for non-common-domain cameras: For cameras that cannot simultaneously observe all coarse calibration features at a single position, along the calibration mechanism 31... The direction is moved step by step, and the angular deviation of the movement is denoted as . Displacement deviation control is less than The displacement of the calibration mechanism 31 at different positions was recorded using a laser rangefinder. The distance measurement error is controlled within 0.2mm by using a grating rotary encoder 41 pulse feedback for verification.

[0063] For the Construct the displacement transformation matrix at each position. ,in The identity matrix is ​​used. The camera coarse-calibrated extrinsic parameter matrix and the translation matrix are concatenated and applied to the point cloud, i.e. This achieves preliminary stitching of point clouds from different locations. Along... The axis movement calibration mechanism 31 records the readings of the laser rangefinder. To construct The axis translation matrix is ​​used to output a coarse index matrix with rotation. Its coarse displacement matrix is ​​used as the initial solution for fine calibration.

[0064] To address the technical challenges of direct fusion of multiple visual sensors in their respective independent coordinate systems and the unknown initial extrinsic parameters, S2 constructs the initial spatial constraint relationship of the system through physical environment constraints, kinematic standardization, local feature fitting in a common coordinate system, and multi-position stitching compensation of non-common-domain cameras.

[0065] Through S2, a coarse transformation matrix was established between the coordinate systems of each camera and the common coordinate system of the calibration mechanism, which achieved the initial alignment of the point clouds of multiple cameras and provided a reliable initial solution for subsequent fine calibration, effectively avoiding the problem of non-convergence of subsequent optimization due to excessive deviation of initial external parameters.

[0066] S3 fine calibration and joint parameter optimization specifically include the following steps: S31. Establishment of the fine calibration reference coordinate system: Use calibration ring 32 to perform high-precision correction on the coarse calibration results. Establish the reference coordinate system of the calibration component. The fitting axis is based on the outer cylindrical surface / inner cylindrical surface of the calibration ring 32. Department Shaft; in the plane of the running direction of roller conveyor 11 and parallel to... The direction orthogonal to the axis is used as Department axis.

[0067] During fine calibration, switch to pulse-triggered mode. Use the initial external parameter values ​​obtained in the coarse calibration stage. As the starting point for iteration, move the camera to... Precise external parameters of the system As the main parameter to be estimated.

[0068] S32, Precise Correction of Scale Factor: Introducing a Scale Factor tiny correction amount To obtain the precise proportionality coefficient proportionality coefficient Used to compensate for axial dimensional deviations introduced by transmission backlash, frequency division error, or speed fluctuation.

[0069] S33. Construction of Joint Geometric Constraint Optimization Model: In The following constructs a joint minimum residual term for the extracted outer cylindrical surface, inner hole surface, and end face point sets: Cylindrical surface and end face constraints: Construct the radial residual from the point to the nominal cylindrical surface (the difference between the distance from the point to the axis and the nominal radius), and the distance residual from the point to the nominal end plane, and constrain the distance between the two end faces to meet the nominal height parameter.

[0070] Breaking symmetry constraints: to suppress the rotation of the body around the symmetry constraint. The equivalent solution for axis rotation, combined with the scanning timing directionality, selects non-perfectly symmetrical regions such as chamfers, edge arcs, or local notches to construct distance residuals, and only selects sampling points with the normal orientation towards the camera to participate in the fitting, thereby achieving optimized stable convergence.

[0071] Kinematic consistency constraints: based on precise displacement model Constructing adjacent contour lines in Tie Consistency residuals of the spacing.

[0072] S34. Iterative Optimization and Verification: Nonlinear least squares iterative update is adopted. and After obtaining the final external parameters, the critical dimensions of the ring component are calculated and checked to see if they meet the preset tolerance zone, in order to verify the validity of the calibration results.

[0073] To address the technical problem of insufficient measurement accuracy caused by transmission backlash, speed fluctuations, and residual errors in camera extrinsic parameters during the coarse calibration stage, S3 establishes a high-precision calibration component reference coordinate system, introduces a precise correction amount of the proportional coefficient, and constructs a joint optimization model that includes cylindrical surface constraints, end face constraints, symmetry breaking constraints, and kinematic consistency constraints to perform high-precision correction on the coarse calibration results.

[0074] Through S3, the precise external parameter matrix and precise pulse-displacement scaling factor of each camera to the measurement coordinate system were obtained, which effectively suppressed the multi-camera splicing error and axial dimension deviation, so that the back calculation results of the key dimensions of the calibration ring met the preset tolerance zone requirements, laying the foundation for the high-precision dynamic measurement of the workpiece in the future.

[0075] S4 dynamic measurement and point cloud calculation specifically includes the following steps: S41. Point cloud fusion and streaming preprocessing: Based on the extrinsic parameter matrices of each camera obtained through calibration. The original point clouds acquired by multiple cameras are uniformly transformed to the same measurement coordinate system and then stitched together to obtain a complete 3D point cloud of the workpiece. Subsequently, denoising, voxel downsampling, and outlier removal are performed to improve the stability of subsequent registration.

[0076] S42. Standard Model Registration: The CAD standard model of the workpiece is read. After initial alignment of the workpiece point cloud, robust point-to-surface registration is performed to obtain the pose transformation matrix of the workpiece relative to the standard model. A robust kernel function is introduced during the registration process to suppress misregistration caused by occlusion or reflective areas.

[0077] S43. Deviation Field Calculation and Feature Evaluation: Based on the registration results, calculate the signed point-to-surface distances from the workpiece point cloud to the standard model surface, forming a three-dimensional deviation field. Construct a tolerance band with a range of ±T / 2 along the normal to the standard model surface, where T is the given profile tolerance bandwidth. Output the maximum deviation and the proportion of out-of-tolerance points, and generate a partitioned heatmap. Perform geometric fitting on preset key features, output key dimensions and form and position errors, and automatically determine their accuracy against nominal values ​​and tolerances.

[0078] S44. Measurement result output: After the measurement is completed, stop the servo motor 13 and trigger acquisition, save the measurement results and log file, or put the measuring device into standby mode.

[0079] Figure 8 This paper presents the multi-view / multi-scan point cloud fusion results obtained by uniform sampling after precise calibration. Different colors represent point clouds from different cameras (or different scanning times / viewpoints). It can be seen that the point cloud forms a continuous spiral trajectory in the XY plane, indicating that the multi-view data maintains overall consistency under a unified coordinate system; at the same time, the thickness in the Z direction is relatively thin, indicating that the attitude error is suppressed after calibration, and the point cloud is mainly distributed in approximately the same plane / thickness band.

[0080] Figure 9 This is another set of simulation results under the same calibration conditions. The fused point cloud converges into a closed ring structure, and the three-color point clouds highly overlap in the ring region, indicating that the multi-camera extrinsic / motion parameter calibration is effective and the geometric consistency across the field of view is good. Compared to Figure 8 Its annular cross-section is more complete and its Z-axis dispersion is smaller, indicating that error compensation and extrinsic parameter optimization make the reconstruction result closer to the ideal geometry. This embodiment, through the above steps, achieves high-precision, flow-through 3D scanning measurement of workpieces during dynamic transmission on a roller conveyor line. It can adapt to the online inspection needs of various types of workpieces, improving inspection efficiency and measurement accuracy.

[0081] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A measuring device based on large field-of-view scanning of a roller conveyor line, characterized in that, It includes a roller conveyor assembly (1), a vision acquisition assembly (2), and a calibration reference assembly (3); The roller conveyor assembly (1) is used to convey workpieces; The vision acquisition component (2) is disposed above and to the side of the roller conveyor component (1), and the vision acquisition component (2) is used to acquire the contour information of the workpiece surface; The calibration reference component (3) is used to provide a calibration benchmark.

2. The measuring device according to claim 1, characterized in that, The visual acquisition component (2) includes a first-line laser camera (21), a second-line laser camera (22), and a third-line laser camera (23).

3. The measuring device according to claim 2, characterized in that, The first line laser camera (21) and the third line laser camera (23) are installed upright, while the second line laser camera (22) is installed upside down.

4. The measuring device according to claim 2, characterized in that, The visual acquisition component (2) also includes an adjustable camera mount (24), which includes a tilt angle adjuster (242) and a pitch angle adjuster (243).

5. The measuring device according to claim 4, characterized in that, The adjustable camera mount (24) also includes a translation stage (244) and a rotary stage (245).

6. The measuring device according to claim 1, characterized in that, The calibration reference component (3) includes a calibration mechanism (31) and a calibration ring (32).

7. The measuring device according to claim 1, characterized in that, The testing device also includes a drive calculation component (4), which is connected to the roller conveyor component (1) and the vision acquisition component (2). The drive calculation component (4) is used to control the conveying, trigger acquisition and data processing.

8. The measuring device according to claim 7, characterized in that, The driving operation component (4) includes a grating rotary encoder (41) and a multi-channel signal distribution card (43), which is connected to the grating rotary encoder (41) and the vision acquisition component (2) respectively.

9. The measuring device according to claim 1, characterized in that, The roller conveyor assembly (1) also includes a drive belt (16), which connects the servo motor (13) of the roller conveyor assembly (1) to the roller conveyor (11).

10. A measurement method based on large field-of-view scanning of a roller conveyor line, characterized in that, The measuring device according to any one of claims 1-9 comprises the following steps: S1 system initialization and parameter configuration; S2 coarse calibration and initial estimation of external parameters; S3 fine calibration and joint parameter optimization; S4 Dynamic Measurement and Point Cloud Solving.

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