A laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor and a control method thereof

Abstract

This invention relates to a laser galvanometer scanning welding system and its control method based on voice coil motor dynamic focusing. The system includes a welding robot and a human-machine interface terminal. The welding robot consists of an industrial robot, a laser end effector, and a control module. The laser end effector integrates a voice coil motor dynamic focusing module and a two-axis galvanometer module to form a three-axis laser scanning system, achieving nine-axis linkage in conjunction with the industrial robot. The voice coil motor dynamic focusing module drives movable lenses to move along the optical axis via a voice coil motor, changing the lens spacing and achieving continuous adjustment of the system's equivalent focal length. The control method establishes an optical model based on the thick lens ray transmission matrix, combines high-order aberration compensation to achieve high-precision focal length prediction, and achieves electronic flat-field control through field curvature compensation. This invention has advantages such as fast response speed, high positioning accuracy, and large effective scanning area, meeting the requirements of high-precision laser flying welding with large format and complex three-dimensional trajectories.

Description

Technical Field

[0001] This invention belongs to the field of laser welding technology, specifically relating to a laser galvanometer scanning welding system and its control method based on dynamic focusing by a voice coil motor. Background Technology

[0002] With the widespread application of laser welding technology in automobile manufacturing, aerospace, power batteries, electronic devices and other fields, laser-in-flight welding (also known as remote welding or flying laser welding) has become an important process for improving production efficiency and welding quality. This technology typically combines a six-axis industrial robot with a two-axis galvanometer scanning system to form an eight-axis linkage scheme: the industrial robot is responsible for large-scale spatial positioning and attitude adjustment, while the two-axis galvanometer is responsible for high-speed two-dimensional scanning within a small area, realizing a highly efficient "welding while moving" mode.

[0003] However, existing laser flying welding systems still face the following major technical bottlenecks in practical applications:

[0004] First, traditional galvanometer systems mostly use a fixed focal length optical design. When the laser beam passes through the galvanometer for deflection and scanning, the optical path lengthens as the deflection angle increases, resulting in obvious field curvature and defocusing phenomena in the edge area of ​​the working plane. This severely limits the effective scanning area and causes quality defects such as insufficient weld penetration, uneven weld width, and increased porosity in the edge welds.

[0005] Secondly, actual workpiece surfaces often exhibit Z-axis height variations due to machining errors, assembly gaps, thermal deformation, or uneven coating thickness. Fixed-focus systems cannot track and compensate for these dynamic deviations in real time, causing the focal point to deviate from the optimal focal plane, resulting in poor consistency and stability during the welding process. For example, patents CN102451955A and CN101695790A disclose methods for adding spacers or reserving gaps at the lap joint of galvanized steel. By reserving zinc vapor exhaust channels, these methods alleviate the porosity problem in galvanized sheet welding to some extent. However, these methods require additional processes, increase costs, and cannot fundamentally solve the general dynamic focusing requirements.

[0006] Third, while a few systems are equipped with focus adjustment mechanisms, they mostly employ mechanical transmission methods (such as lead screws or manual adjustment), resulting in slow response speeds, backlash, and limited positioning accuracy, making it difficult to meet the high-speed, real-time requirements of laser flying welding. For example, patent CN101439441A discloses a fiber laser dynamic focusing galvanometer scanning spot welding system, which achieves a certain degree of Z-axis adjustment through a dynamic focusing unit. However, its adjustment range and response speed are still limited by the mechanical structure, making it insufficient for continuous welding of complex three-dimensional curved surfaces or workpieces with undulating surfaces.

[0007] Fourth, in terms of multi-axis collaboration, changes in robot posture can cause distortion in the mapping of the galvanometer coordinate system relative to the workpiece coordinate system. Without a real-time compensation mechanism, this can easily lead to scanning trajectory deviations and positional errors. For example, patent CN120362705A discloses a method for three-dimensional dynamic display and processing triggering of robot laser flying welding, which mainly solves the problems of offline programming and simulation display. However, it involves relatively little attention to core control algorithms such as multi-axis kinematic coupling, real-time coordinate system transformation, and posture error compensation in the actual processing.

[0008] Fifth, regarding system integration and reliability, if the dynamic focusing module is installed separately from the galvanometer system, it will increase the size and weight of the end effector, affecting the robot's dynamic performance. Insufficient rigidity in the mechanical connections between multiple modules can easily lead to optical path drift under high-speed motion and vibration environments, reducing overall accuracy and stability. For example, patent CN110560938A discloses a laser flying welding device, which mainly optimizes the dustproof structure design, but does not fundamentally solve the problems of efficient integrated design and multi-axis collaborative control of the dynamic focusing module and galvanometer.

[0009] The aforementioned limitations restrict the further application of laser flying welding technology in large-format, high-precision, and complex working conditions. Therefore, there is an urgent need for a dynamic focusing scheme that is fast-responding, highly accurate, and well-integrated, and can efficiently coordinate with galvanometer scanning and robot motion to achieve real-time and precise control of the focal point position, thereby improving welding quality and production efficiency. Summary of the Invention

[0010] In view of this, the purpose of this invention is to provide a laser galvanometer scanning welding system and its control method based on voice coil motor dynamic focusing. By integrating the voice coil motor dynamic focusing module with the two-axis galvanometer module to form a three-axis laser scanning system, and combining it with a six-axis industrial robot to achieve nine-axis linkage control, this effectively solves the problems of field curvature defocusing, inability to compensate for Z-axis height changes in real time, and slow mechanical focusing response and low accuracy in existing fixed-focal-length optical systems. The high-response characteristics of the voice coil motor enable rapid and precise focal length adjustment. A high-precision focal length prediction across the entire dynamic range is achieved through an optical theoretical model based on a thick lens transmission matrix and high-order aberration compensation. Combined with electronic flat-field control, the field curvature effect during galvanometer scanning is effectively compensated, significantly improving the coverage area, welding quality consistency, and production efficiency of laser flying welding.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: a laser galvanometer scanning welding system based on voice coil motor dynamic focusing, comprising a welding robot and a human-machine interaction terminal. The welding robot consists of an industrial robot, a laser end effector, and a control module. The laser end effector consists of a two-axis galvanometer module and a voice coil motor dynamic focusing module, which together constitute a three-axis laser scanning system. The two-axis galvanometer module provides two scanning degrees of freedom, X and Y, and the voice coil motor dynamic focusing module provides a Z-axis focusing degree of freedom.

[0012] The voice coil motor dynamic focusing module includes a voice coil motor, a movable lens, a fixed lens group, and a reflector. The voice coil motor is a linear voice coil motor, whose mover reciprocates along the laser optical axis. The movable lens is a negative lens, fixedly connected to the mover of the voice coil motor via a lens bracket. The fixed lens group includes a positive lens and a focusing objective lens arranged sequentially along the optical axis. The movable lens and the fixed lens group are arranged sequentially along the optical axis to form a zoom optical system. The laser passes through the movable lens, the positive lens, and the focusing objective lens in sequence. The voice coil motor drives the movable lens to move along the optical axis, changing the distance between the movable lens and the positive lens, thereby achieving continuous adjustment of the system's equivalent focal length. The reflector is located on the light-emitting side of the focusing objective lens, and its reflecting surface forms a set angle with the optical axis, used to deflect the laser beam and guide it to the biaxial galvanometer module.

[0013] The laser end effector is mounted on the industrial robot; the control module is used to realize the communication connection and coordinated control of the industrial robot, the two-axis galvanometer module and the voice coil motor.

[0014] Furthermore, the distance between the movable lens and the positive lens is an adjustable distance d1, and the adjustable distance d1 is adjustable from 20.0 mm to 24.0 mm; the distance between the positive lens and the focusing objective lens is a fixed distance d2, and the fixed distance d2 is 20.0 mm; the voice coil motor drives the movable lens to move along the optical axis to change the adjustable distance d1, so that the back focal length of the system is continuously adjustable within the range of 491.4 mm to 708 mm.

[0015] Furthermore, the movable lens is a plano-concave negative lens, with a first surface being a concave spherical surface with a radius of curvature of -25.840 mm, a second surface being a plane, and a center thickness of 3.500 mm; the positive lens is a plano-convex lens, with a first surface being a plane, a second surface being a convex spherical surface with a radius of curvature of -51.680 mm, and a center thickness of 9.690 mm; the focusing objective is a convex-plano lens, with a first surface being a convex spherical surface with a radius of curvature of 126.680 mm, a second surface being a plane, and a center thickness of 7.290 mm; the movable lens, the positive lens, and the focusing objective are all made of BK7 optical glass, with a working wavelength of 1064 nm and a corresponding refractive index of 1.50669.

[0016] Furthermore, the voice coil motor is driven and controlled by a servo driver, which communicates with the control module using the Modbus RTU protocol. The voice coil motor is equipped with a position feedback device to provide real-time feedback on the displacement of the movable lens along the optical axis. The servo driver supports position mode, speed mode, and torque mode. In dynamic focusing control, the position mode is used to achieve precise positioning of the movable lens.

[0017] Furthermore, the biaxial galvanometer module includes an X-axis galvanometer and a Y-axis galvanometer, used to control the deflection and scanning of the laser in the X and Y directions; both the X-axis and Y-axis galvanometers are galvanometer-type galvanometers, each driven by an independent galvanometer motor; the biaxial galvanometer module communicates with the control module using the XY2-100 protocol and receives deflection angle commands sent by the control module.

[0018] Furthermore, the voice coil motor dynamic focusing module and the two-axis galvanometer module are integrated into one unit through a rigid connection structure and are fixedly connected to the end shaft of the industrial robot through a flange; the rigid connection structure is made of aluminum alloy and has a laser optical path channel inside.

[0019] This invention also provides a laser flight welding control method based on dynamic focusing of a voice coil motor, implemented using the aforementioned laser galvanometer scanning welding system, comprising the following steps:

[0020] (1) Optical modeling: Based on the paraxial thick lens transfer matrix, establish the mapping relationship between the distance d1 between the movable lens and the positive lens and the back focal length BFL of the system;

[0021] (2) Coordinate transformation: Establish the transformation relationship between the position of the voice coil motor and the lens spacing d1, as well as the bidirectional solution relationship between the lens spacing d1 and the back focal length BFL;

[0022] (3) Dynamic focusing: Calculate the back focal length of the target based on the target focal position, solve the target position of the voice coil motor through coordinate transformation, control the voice coil motor to drive the movable lens to move, and realize the dynamic adjustment of the focal position in the Z-axis direction.

[0023] Furthermore, the optical modeling in step (1) includes:

[0024] (1-1) The zoom optical system is modeled using a thick lens ray transfer matrix, and the basic transfer matrix operator is defined, including:

[0025] A refraction matrix used to describe the refraction of light at the surface of a lens. :

[0026]

[0027] Medium propagation matrix used to describe the propagation of light in a lens :

[0028]

[0029] Where R' is the radius of curvature. The refractive index of the incident medium is... Let d be the refractive index of the exit medium, d be the propagation distance, and n be the refractive index of the medium; when the surface is a plane, The refraction matrix is ​​simplified to a diagonal matrix;

[0030] (1-2) For a single lens with a center thickness d, its transmission matrix is... The model is as follows:

[0031]

[0032] Among them, R back T is the refraction matrix of the rear surface of the lens. glass Let R be the medium propagation matrix of the lens. front This is the refraction matrix of the front surface of the lens;

[0033] Based on the transmission matrix Establish movable lens matrices respectively Positive lens matrix and focusing objective matrix ;

[0034] (1-3) Based on the optical path sequence, multiply each lens matrix by the propagation matrix of the air gap between the lenses to establish the overall system transmission matrix. :

[0035]

[0036] in, and They are the spacings and The corresponding free propagation matrix in the air, A(d1), B(d1), C(d1), and D(d1) are the four elements in the total transmission matrix of the system;

[0037] (1-4) For a parallel incident beam, calculate the paraxial back focal length based on the system's overall transmission matrix. :

[0038]

[0039] (1-5) Introducing the system aberration transfer function The actual back focal length Represented as:

[0040]

[0041] in, It represents the ratio of the actual focal point to the theoretical focal point under a given lens spacing;

[0042] (1-6) The aberration transfer function Modeling as Higher-order polynomials:

[0043]

[0044] Where m is the order of the polynomial. These are the polynomial coefficients;

[0045] (1-7) Obtain several sets of calibration results using optical simulation software. Data pairs, among which To obtain the measured focal length, the coefficient vector was fitted using the least squares method. .

[0046] Furthermore, the polynomial order m is automatically determined through a leave-out verification method, the specific process of which is as follows:

[0047] 1) Divide the calibration data into a fitting set and a validation set according to the sequence number, with odd-numbered data points used as the fitting set and even-numbered data points used as the validation set;

[0048] 2) Perform polynomial fitting on each order in the candidate order set and calculate the maximum relative error on the validation set for each order. :

[0049]

[0050] in, This is the measured back focal length;

[0051] 3) Select the order that minimizes the maximum relative error of the validation set as the final polynomial order, control the model prediction error within 0.5% in the full dynamic range, and suppress overfitting and boundary oscillations of higher-order polynomials.

[0052] Further, in step (2), the coordinate transformation includes:

[0053] (2-1) Establish the conversion relationship between the voice coil motor position and the lens spacing:

[0054]

[0055] in, This is the reference value for the lens spacing corresponding to the zero position of the voice coil motor. This is the current position of the voice coil motor. For encoder resolution;

[0056] (2-2) Forward calculation: Calculate the lens spacing based on the current position of the voice coil motor. ,Will Substitute into the optical model to calculate the back focal length of the current system. This enables real-time monitoring of the focal point.

[0057] (2-3) Reverse solution: Given the target focal length The corresponding lens spacing is solved in reverse using a numerical iterative method. Then calculate the target position of the voice coil motor. :

[0058]

[0059] In step (3), the dynamic focusing includes:

[0060] (3-1) Based on the real-time deflection angle of the biaxial galvanometer module Calculate the horizontal offset distance of the laser beam from the optical axis :

[0061]

[0062] (3-2) Calculate the Z-axis defocus compensation amount caused by the change in optical path. :

[0063]

[0064] The defocus compensation is superimposed on the target position of the voice coil motor to achieve electronic flat field control, so that the laser focus always falls on the workpiece surface.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] 1. The voice coil motor dynamic focusing module provided by this invention uses a linear voice coil motor to drive the movable lens to reciprocate along the optical axis. Compared with traditional mechanical transmission methods such as lead screws and racks and pinions, it has the advantages of fast response speed, no mechanical backlash, high positioning accuracy, and smooth movement. It can meet the high-speed and high-precision requirements of real-time dynamic adjustment of focus during laser flying welding. The voice coil motor is equipped with a position feedback device to form a closed-loop control. The position mode of the servo driver realizes the micron-level precise positioning of the movable lens, which effectively overcomes the technical bottlenecks of slow response and limited accuracy of existing mechanical focusing mechanisms.

[0067] 2. The zoom optical system provided by this invention adopts a structural design that combines a movable lens (negative lens) with a fixed lens group (positive lens, focusing objective lens). The equivalent focal length of the system can be continuously adjusted by changing the distance between the movable lens and the positive lens. A high-precision optical theoretical model is established based on the ray transmission matrix of the thick lens. The higher-order aberration compensation function is combined to correct higher-order aberrations such as spherical aberration. The leave-out verification method is used to automatically optimize the polynomial order. The focal length prediction error is controlled within 0.5% in the entire dynamic range, which is significantly better than the traditional thin lens approximation model, and provides a reliable theoretical basis for dynamic focusing control.

[0068] 3. The field curvature compensation method provided by this invention calculates the horizontal offset distance of the laser beam from the optical axis and the Z-axis defocus compensation amount caused by the change in optical path based on the real-time deflection angle of the biaxial galvanometer. Electronic flat field control is achieved by controlling the voice coil motor to adjust the position of the movable lens in real time, which effectively compensates for the field curvature effect during galvanometer scanning and ensures that the laser focus always falls on the workpiece surface. This method breaks through the bottleneck of the limited effective scanning area of ​​the traditional fixed focal length galvanometer system, significantly expands the effective working area of ​​the galvanometer, and eliminates quality defects such as insufficient weld penetration, uneven weld width, and increased porosity in edge welds.

[0069] 4. This invention integrates the voice coil motor dynamic focusing module and the two-axis galvanometer module through a rigid connection structure to form a compact three-axis laser scanning system. Compared with the scheme of separate installation of the dynamic focusing module and the galvanometer system, it significantly reduces the size and weight of the end effector and improves the system rigidity and optical path stability. The integrated structure is made of aluminum alloy and has a laser optical path channel, which can effectively suppress optical path drift in high-speed motion and vibration environments, ensuring overall processing accuracy and long-term reliability. Attached Figure Description

[0070] Figure 1 A schematic diagram of the structure of a laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor, provided in an embodiment of the present invention;

[0071] Figure 2 This is a schematic diagram of the dynamic focusing module of the voice coil motor in an embodiment of the present invention;

[0072] Figure 3 A schematic diagram of the working state of a laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor, provided in an embodiment of the present invention;

[0073] Figure 4 A flowchart of a laser flight welding control method based on dynamic focusing of a voice coil motor, provided for an embodiment of the present invention;

[0074] Figure 5 This is a flowchart of dynamic focusing in an embodiment of the present invention.

[0075] In the diagram: 1. Human-machine interface terminal; 2. Industrial robot; 3. Laser end effector; 4. Control module; 5. Battery pack module; 31-Voice coil motor; 32-Modible lens; 33-Positive lens; 34-Focusing objective lens; 35-Reflecting mirror; 36-Two-axis galvanometer module; 37-Rigid connection structure; 38-Flange. Detailed Implementation

[0076] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0077] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0078] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0079] like Figure 1-3 As shown, this embodiment provides a laser galvanometer scanning welding system based on voice coil motor dynamic focusing, including a welding robot and a human-machine interface terminal 1. The welding robot consists of an industrial robot 2, a laser end effector 3, and a control module 4. The laser end effector 3 consists of a voice coil motor dynamic focusing module and a two-axis galvanometer module 36, which together constitute a three-axis laser scanning system. The two-axis galvanometer module provides X and Y scanning degrees of freedom, and the voice coil motor dynamic focusing module provides Z-axis focusing degree of freedom. The three-axis laser scanning system, combined with a six-axis industrial robot, achieves nine-axis linkage control, suitable for high-speed laser flying welding operations with large-scale, three-dimensional complex trajectories.

[0080] like Figure 2As shown, the voice coil motor dynamic focusing module includes a voice coil motor 31, a movable lens 32, a fixed lens group, and a reflector 35. The voice coil motor is a linear voice coil motor, whose mover reciprocates along the laser optical axis. The movable lens 32 is a negative lens, fixedly connected to the mover of the voice coil motor 31 via a lens bracket. The fixed lens group includes a positive lens 33 and a focusing objective lens 34 arranged sequentially along the optical axis. The movable lens 32 and the fixed lens group are arranged sequentially along the optical axis to form a zoom optical system, through which the laser passes in sequence. The movable lens 32, the positive lens 33, and the focusing objective lens 34 are driven by the voice coil motor 31 to move the movable lens 32 along the optical axis, changing the distance between the movable lens 32 and the positive lens 33, thereby achieving continuous adjustment of the system's equivalent focal length. The reflecting mirror 35 is disposed on the light-emitting side of the focusing objective lens 34, and its reflecting surface forms a 45° angle with the optical axis. It is used to deflect the laser beam and guide it to the biaxial galvanometer module 36. The biaxial galvanometer module 36 includes an X-axis galvanometer and a Y-axis galvanometer, which are used to control the deflection and scanning of the laser in the X and Y directions.

[0081] In this embodiment, the movable lens 32 is a plano-concave negative lens, with a first surface being a concave spherical surface with a radius of curvature of -25.840 mm, a second surface being a plane, and a center thickness of 3.500 mm. The positive lens 33 is a plano-convex lens, with a first surface being a plane, a second surface being a convex spherical surface with a radius of curvature of -51.680 mm, and a center thickness of 9.690 mm. The focusing objective lens 34 is a convex-plano lens, with a first surface being a convex spherical surface with a radius of curvature of 126.680 mm, a second surface being a plane, and a center thickness of 7.290 mm. The movable lens 32, the positive lens 33, and the focusing objective lens 34 are all made of BK7 optical glass, with a working wavelength of 1064 nm and a corresponding refractive index of 1.50669.

[0082] The distance between the movable lens 32 and the positive lens 33 is an adjustable distance d1, and the adjustable distance d1 can be adjusted from 20.0 mm to 24.0 mm. The distance between the positive lens 33 and the focusing objective lens 34 is a fixed distance d2, and the fixed distance d2 is 20.0 mm. The voice coil motor 31 drives the movable lens 32 to move along the optical axis to change the adjustable distance d1, so that the back focal length of the system is continuously adjustable within the range of 491.4 mm to 708 mm.

[0083] The voice coil motor 31 is driven and controlled by a servo driver. The servo driver communicates with the control module 5 using the Modbus RTU protocol, with an RS485 communication interface and a baud rate of 115200. The voice coil motor 31 is equipped with a position feedback device to provide real-time feedback on the displacement of the movable lens 32 along the optical axis. The servo driver supports three control modes: position mode, speed mode, and torque mode. In dynamic focusing control, the position mode is used to achieve precise positioning of the movable lens 32.

[0084] The biaxial galvanometer module 36 includes an X-axis galvanometer and a Y-axis galvanometer, used to control the deflection and scanning of the laser beam in the X and Y directions. Both the X-axis and Y-axis galvanometers are galvanometer-type galvanometers, each driven by an independent galvanometer motor, enabling high-speed deflection and scanning of the laser beam in a two-dimensional plane. The biaxial galvanometer module communicates with the control module 5 using the XY2-100 protocol, receiving deflection angle commands from the control module 5.

[0085] The industrial robot 2 includes a robotic arm, and the laser end effector 3 is fixedly mounted on the end shaft of the robotic arm via a flange 39. The voice coil motor dynamic focusing module and the biaxial galvanometer module are integrated into one unit via a rigid connection structure 37 and fixedly connected to the end shaft of the industrial robot 2 via a flange 38. The rigid connection structure 37 is made of aluminum alloy and has a laser optical path channel, which can effectively suppress optical path drift under high-speed motion and vibration environments, ensuring overall processing accuracy and long-term reliability.

[0086] The control module is used to realize the communication connection and coordinated control of the industrial robot, the two-axis galvanometer module and the voice coil motor.

[0087] like Figure 4 As shown, this embodiment also provides a laser flying welding control method based on dynamic focusing of a voice coil motor, which is implemented based on the above-mentioned laser galvanometer scanning welding system. The specific implementation steps are as follows.

[0088] (1) Optical modeling: Based on the paraxial thick lens transfer matrix, the mapping relationship between the distance d1 between the movable lens 32 and the positive lens 33 and the system back focal length BFL is established. The implementation process is as follows.

[0089] (1-1) The zoom optical system is modeled using a thick lens ray transfer matrix, and the basic transfer matrix operator is defined, including:

[0090] A refraction matrix used to describe the refraction of light at the surface of a lens. :

[0091]

[0092] Medium propagation matrix used to describe the propagation of light in a lens :

[0093]

[0094] Where R' is the radius of curvature. The refractive index of the incident medium is... Let d be the refractive index of the exit medium, d be the propagation distance, and n be the refractive index of the medium; when the surface is a plane, The refraction matrix is ​​simplified to a diagonal matrix.

[0095] (1-2) For a single lens with a center thickness d, its transmission matrix is... The model is as follows:

[0096]

[0097] Among them, R back T is the refraction matrix of the rear surface of the lens. glass Let R be the medium propagation matrix of the lens. front Let be the refraction matrix of the front surface of the lens.

[0098] Based on the transmission matrix Establish movable lens matrices respectively Positive lens matrix and focusing objective matrix .

[0099] (1-3) Based on the optical path sequence, multiply each lens matrix by the propagation matrix of the air gap between the lenses to establish the overall system transmission matrix. :

[0100]

[0101] in, and They are the spacings and The corresponding free propagation matrix in the air, A(d1), B(d1), C(d1), and D(d1) are the four elements in the total transmission matrix of the system.

[0102] (1-4) For a parallel incident beam, calculate the paraxial back focal length based on the system's overall transmission matrix. :

[0103] .

[0104] The optical modeling further includes the following higher-order aberration compensation steps.

[0105] (1-5) Introducing the system aberration transfer function The actual back focal length Represented as:

[0106]

[0107] in, It represents the ratio of the actual focal point to the theoretical focal point under a given lens spacing.

[0108] (1-6) The aberration transfer function Modeling as Higher-order polynomials:

[0109]

[0110] Where m is the order of the polynomial. These are the polynomial coefficients.

[0111] (1-7) Obtain several sets of calibration results using optical simulation software. Data pairs, among which To obtain the measured focal length, the coefficient vector was fitted using the least squares method. .

[0112] The order m of the polynomial is automatically selected and determined by the leave-out verification method, and the specific process is as follows.

[0113] 1) Divide the calibration data into a fitting set and a validation set according to the sequence number, with odd-numbered data points used as the fitting set and even-numbered data points used as the validation set.

[0114] 2) Perform polynomial fitting on each order in the candidate order set and calculate the maximum relative error on the validation set for each order. :

[0115]

[0116] in, This is the measured focal length.

[0117] 3) Select the order that minimizes the maximum relative error of the validation set as the final polynomial order, control the model prediction error within 0.5% in the full dynamic range, and suppress overfitting and boundary oscillations of higher-order polynomials.

[0118] (2) Coordinate transformation: Establish the transformation relationship between the position of the voice coil motor 31 and the lens spacing d1, as well as the bidirectional solution relationship between the lens spacing d1 and the back focal length BFL. The implementation process is as follows.

[0119] (2-1) Establish the conversion relationship between the voice coil motor position and the lens spacing:

[0120]

[0121] in, This is the reference value for the lens spacing corresponding to the zero position of the voice coil motor. This is the current position of the voice coil motor. This refers to the encoder resolution.

[0122] (2-2) Forward calculation: Calculate the lens spacing based on the current position of the voice coil motor. ,Will Substitute into the optical model to calculate the back focal length of the current system. This enables real-time monitoring of the focal point.

[0123] (2-3) Reverse solution: Given the target focal length The corresponding lens spacing is solved in reverse using a numerical iterative method. Then calculate the target position of the voice coil motor. :

[0124] .

[0125] (3) Dynamic focusing: Calculate the target back focal length based on the target focal position, solve for the target position of the voice coil motor through coordinate transformation, control the voice coil motor 31 to drive the movable lens 32 to move, and realize dynamic adjustment of the focal position in the Z-axis direction, thereby achieving field curvature compensation. For example... Figure 5 As shown, the process of dynamic focusing is as follows.

[0126] (3-1) Based on the real-time deflection angle of the biaxial galvanometer module Calculate the horizontal offset distance of the laser beam from the optical axis :

[0127]

[0128] (3-2) Calculate the Z-axis defocus compensation amount caused by the change in optical path. :

[0129]

[0130] The defocus compensation is superimposed on the target position of the voice coil motor to achieve electronic flat field control, so that the laser focus always falls on the workpiece surface.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor, comprising a welding robot and a human-machine interface terminal, wherein the welding robot consists of an industrial robot, a laser end effector, and a control module, characterized in that, The laser end effector consists of a two-axis galvanometer module and a voice coil motor dynamic focusing module, which together constitute a three-axis laser scanning system. The two-axis galvanometer module provides two scanning degrees of freedom, X and Y, and the voice coil motor dynamic focusing module provides a Z-axis focusing degree of freedom. The voice coil motor dynamic focusing module includes a voice coil motor, a movable lens, a fixed lens group, and a reflector. The voice coil motor is a linear voice coil motor, whose mover reciprocates along the laser optical axis. The movable lens is a negative lens, fixedly connected to the mover of the voice coil motor via a lens bracket. The fixed lens group includes a positive lens and a focusing objective lens arranged sequentially along the optical axis. The movable lens and the fixed lens group are arranged sequentially along the optical axis to form a zoom optical system. The laser passes through the movable lens, the positive lens, and the focusing objective lens in sequence. The voice coil motor drives the movable lens to move along the optical axis, changing the distance between the movable lens and the positive lens, thereby achieving continuous adjustment of the system's equivalent focal length. The reflector is located on the light-emitting side of the focusing objective lens, and its reflecting surface forms a set angle with the optical axis, used to deflect the laser beam and guide it to the biaxial galvanometer module. The laser end effector is mounted on the industrial robot; the control module is used to realize the communication connection and coordinated control of the industrial robot, the two-axis galvanometer module and the voice coil motor.

2. The laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor according to claim 1, characterized in that, The distance between the movable lens and the positive lens is an adjustable distance d1, and the adjustable distance d1 can be adjusted from 20.0 mm to 24.0 mm; the distance between the positive lens and the focusing objective lens is a fixed distance d2, and the fixed distance d2 is 20.0 mm; the voice coil motor drives the movable lens to move along the optical axis to change the adjustable distance d1, so that the back focal length of the system is continuously adjustable within the range of 491.4 mm to 708 mm.

3. The laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor according to claim 1, characterized in that, The movable lens is a plano-concave negative lens, with a first surface being a concave spherical surface and a radius of curvature of -25.840 mm, a second surface being a plane, and a center thickness of 3.500 mm; the positive lens is a plano-convex lens, with a first surface being a plane, a second surface being a convex spherical surface, a radius of curvature of -51.680 mm, and a center thickness of 9.690 mm; the focusing objective is a convex-plano lens, with a first surface being a convex spherical surface and a radius of curvature of 126.680 mm, a second surface being a plane, and a center thickness of 7.290 mm; the movable lens, the positive lens, and the focusing objective are all made of BK7 optical glass, with a working wavelength of 1064 nm and a corresponding refractive index of 1.50669.

4. The laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor according to claim 1, characterized in that, The voice coil motor is driven and controlled by a servo driver, which communicates with the control module using the Modbus RTU protocol. The voice coil motor is equipped with a position feedback device to provide real-time feedback on the displacement of the movable lens along the optical axis. The servo driver supports position mode, speed mode, and torque mode. In dynamic focusing control, the position mode is used to achieve precise positioning of the movable lens.

5. The laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor according to claim 1, characterized in that, The biaxial galvanometer module includes an X-axis galvanometer and a Y-axis galvanometer, used to control the deflection and scanning of the laser in the X and Y directions; both the X-axis and Y-axis galvanometers are galvanometer-type galvanometers, each driven by an independent galvanometer motor; the biaxial galvanometer module communicates with the control module using the XY2-100 protocol and receives deflection angle commands sent by the control module.

6. The laser galvanometer scanning welding system based on dynamic focusing of a voice coil motor according to claim 1, characterized in that, The voice coil motor dynamic focusing module and the two-axis galvanometer module are integrated into one unit through a rigid connection structure and are fixedly connected to the end shaft of the industrial robot through a flange; the rigid connection structure is made of aluminum alloy and has a laser optical path channel inside.

7. A laser-flying welding control method based on dynamic focusing by a voice coil motor, implemented using the laser galvanometer scanning welding system as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Optical modeling: Based on the paraxial thick lens transfer matrix, establish the mapping relationship between the distance d1 between the movable lens and the positive lens and the back focal length BFL of the system; (2) Coordinate transformation: Establish the transformation relationship between the position of the voice coil motor and the lens spacing d1, as well as the bidirectional solution relationship between the lens spacing d1 and the back focal length BFL; (3) Dynamic focusing: Calculate the back focal length of the target based on the target focal position, solve the target position of the voice coil motor through coordinate transformation, control the voice coil motor to drive the movable lens to move, and realize the dynamic adjustment of the focal position in the Z-axis direction.

8. The laser flight welding control method based on dynamic focusing of a voice coil motor according to claim 7, characterized in that, In step (1), the optical modeling includes: (1-1) The zoom optical system is modeled using a thick lens ray transfer matrix, and the basic transfer matrix operator is defined, including: A refraction matrix used to describe the refraction of light at the surface of a lens. : Medium propagation matrix used to describe the propagation of light in a lens : Where R' is the radius of curvature. The refractive index of the incident medium is... Let d be the refractive index of the exit medium, d be the propagation distance, and n be the refractive index of the medium; when the surface is a plane, The refraction matrix is ​​simplified to a diagonal matrix; (1-2) For a single lens with a center thickness d, its transmission matrix is... The model is as follows: Among them, R back T is the refraction matrix of the rear surface of the lens. glass Let R be the medium propagation matrix of the lens. front This is the refraction matrix of the front surface of the lens; Based on the transmission matrix Establish movable lens matrices respectively Positive lens matrix and focusing objective matrix ; (1-3) Based on the optical path sequence, multiply each lens matrix by the propagation matrix of the air gap between the lenses to establish the overall system transmission matrix. : in, and They are the spacings and The corresponding free propagation matrix in the air, A(d1), B(d1), C(d1), and D(d1) are the four elements in the total transmission matrix of the system; (1-4) For a parallel incident beam, calculate the paraxial back focal length based on the system's overall transmission matrix. : (1-5) Introducing the system aberration transfer function The actual back focal length Represented as: in, It represents the ratio of the actual focal point to the theoretical focal point under a given lens spacing; (1-6) The aberration transfer function Modeling as Higher-order polynomials: Where m is the order of the polynomial. These are the polynomial coefficients; (1-7) Obtain several sets of calibration results using optical simulation software. Data pairs, among which To obtain the measured focal length, the coefficient vector was fitted using the least squares method. .

9. The laser flight welding control method based on dynamic focusing of a voice coil motor according to claim 8, characterized in that, The polynomial order m is automatically selected and determined using the leave-out verification method. The specific process is as follows: 1) Divide the calibration data into a fitting set and a validation set according to the sequence number, with odd-numbered data points used as the fitting set and even-numbered data points used as the validation set; 2) Perform polynomial fitting on each order in the candidate order set and calculate the maximum relative error on the validation set for each order. : in, This is the measured back focal length; 3) Select the order that minimizes the maximum relative error of the validation set as the final polynomial order, control the model prediction error within 0.5% in the full dynamic range, and suppress overfitting and boundary oscillations of higher-order polynomials.

10. The laser flight welding control method based on dynamic focusing of a voice coil motor according to claim 7, characterized in that, In step (2), the coordinate transformation includes: (2-1) Establish the conversion relationship between the voice coil motor position and the lens spacing: in, This is the reference value for the lens spacing corresponding to the zero position of the voice coil motor. This is the current position of the voice coil motor. For encoder resolution; (2-2) Forward calculation: Calculate the lens spacing based on the current position of the voice coil motor. ,Will Substitute into the optical model to calculate the back focal length of the current system. This enables real-time monitoring of the focal point. (2-3) Reverse solution: Given the target focal length The corresponding lens spacing is solved in reverse using a numerical iterative method. Then calculate the target position of the voice coil motor. : In step (3), the dynamic focusing includes: (3-1) Based on the real-time deflection angle of the biaxial galvanometer module Calculate the horizontal offset distance of the laser beam from the optical axis : (3-2) Calculate the Z-axis defocus compensation amount caused by the change in optical path. : The defocus compensation is superimposed on the target position of the voice coil motor to achieve electronic flat field control, so that the laser focus always falls on the workpiece surface.

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