A Circular Trajectory Planning Method for the Welding Robot under the Arch Rib Segment

Abstract

The invention discloses a circular trajectory planning method for a welding robot under an arch rib segment, which relates to the technical field of welding robots. The invention includes establishing a numerical model by obtaining the structural parameters of the arch rib segment. The numerical model includes an arch rib environment model, a welding path pose model, and a kinematic model of the welding robot. The arch rib environment model is used to provide an obstacle avoidance environment for obstacle avoidance calculation. The invention establishes a corresponding numerical model according to the arch rib construction parameters, generates an initial welding path, combines an obstacle avoidance algorithm to generate an execution path, and then adjusts according to the feedback of the vision mechanism, so as to complete the circular welding trajectory planning of the arch rib segment of a long-span arch bridge, effectively avoiding the collision between the welding torch and the workpiece, and improving the welding accuracy and efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of welding robots, and particularly to a method for planning a circular trajectory of a welding robot under an arch rib segment. Background Art

[0002] In the construction of long-span arch bridges, the welding workload of arch rib segments accounts for a large proportion of the total workload. The labor-intensive production method mainly based on manual operation has low welding efficiency, high labor intensity, and unstable quality. Therefore, it has become an inevitable trend to use welding robots for arch rib segments of long-span arch bridges. However, due to the complex shape of arch rib segments and the variable welding paths, how to accurately and efficiently plan the motion trajectory of the welding robot is an urgent problem to be solved.

[0003] In the existing published literature, in the planning of the circular trajectory of welding robots, most are the trajectory planning of welding robots carried by large fixed platforms for small pure circular trajectories, while the welding robots fixed on small platforms lack a systematic control method. On the one hand, the construction site of arch rib segments of long-span arch bridges is often at high altitude, and the labor cost of building a large fixed platform for welding is too high. Therefore, it is necessary to use a light fixed structure for welding and propose a corresponding trajectory planning method; on the other hand, some arch rib segments of long-span arch bridges have splicing structures on the outside, which will form obstructions around the circular path;

[0004] Therefore, a new method needs to be proposed to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to further realize the trajectory control of the welding robot through the trajectory.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A method for planning a circular trajectory of a welding robot under an arch rib segment, at least including:

[0007] S1: Establish a numerical model by obtaining the structural parameters of the arch rib segment and the structural parameters of the welding robot. The numerical model includes an arch rib environment model, a welding path pose model, and a kinematic model of the welding robot. The arch rib environment model is used to provide an obstacle avoidance environment for obstacle avoidance calculation. The welding path pose model defines the trajectory and posture of the robot during welding through the end coordinate system of the robotic arm. Combining the relative distances of the robot joints, using the D-H parameter method, a kinematic model of the welding robot is constructed to determine the mathematical relationship between the joint angles and the pose of the end coordinate system of the robot and the joint angles;

[0008] S2: Solve the inverse kinematics of the target welding point by using the numerical model to generate a discrete initial path and its corresponding joint angles;

[0009] S3: Combine with the CHOMP obstacle avoidance algorithm to generate a safe and effective execution path away from environmental obstacles;

[0010] S4: Adopt a visual feedback mechanism to monitor the actual welding process, calculate the deviation between the weld seam and the actual position of the welding torch. When there is a deviation, perform continuous transformation through the D-H parameter matrix, change the corresponding joint rotation angles, and thus achieve real-time deviation correction welding of the arch rib segments of a long-span arch bridge.

[0011] Preferably, the structural parameters of the arch rib segment at least include the equivalent radius of the vertical curve of the long-span arch bridge, the radius of the arch rib, the welding position, the position of the robot operating base, and the structural parameters of the welding robot.

[0012] Preferably, the arch rib environment model is mainly composed of externally connected arch rib segments, flanges, and connecting plates. The arch rib environment model is used to provide a reference for the subsequent welding path model and the welding robot kinematics model and to provide an environmental obstacle model for the subsequent obstacle avoidance algorithm.

[0013] Preferably, the welding path pose model is obtained from the solder deposition path on the welding end face of the arch rib segment, which is basically the same as the weld seam path and presents as one or more circles on a plane perpendicular to the vertical curve of the long-span arch bridge in terms of mathematical characteristics;

[0014] By discretizing the welding trajectory, the positions of multiple welding points are obtained. Then, taking the vector from each discrete point to the center of the welding arc as the x-axis, the vector from the discrete point to the tangent vector of the arc as the y-axis, and determining the z-axis by the vector product of the x and y axes, finally, the establishment of the welding path pose model is completed.

[0015] Preferably, the welding robot kinematics model is established by the D-H parameter method. Taking the center of the welding path as the reference point of the robot, the welding robot is simplified into six relative coordinate systems. The relative positions between different coordinate systems are defined by joint rotation angles, link offsets, link lengths, and link twist angles, and thus the establishment of the welding robot kinematics model is completed, which is convenient for the trajectory planning and control of the welding robot.

[0016] Preferably, the initial path includes the welding path position and the corresponding six joint rotation angles obtained by performing inverse kinematics solution through the welding path pose matrix.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] The present invention establishes a corresponding numerical model based on the construction parameters of the arch rib, generates an initial welding path, combines with the obstacle avoidance algorithm to generate an execution path, and then adjusts according to the feedback of the vision mechanism, thus completing the circular welding trajectory planning of the arch rib segments of a long-span arch bridge, which can effectively avoid the collision between the welding torch and the workpiece and improve the welding accuracy and efficiency. Description of the Drawings

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0020] Figure 1 It is a schematic flow diagram of the present invention;

[0021] Figure 2 It is a schematic structural diagram of the arch rib segment of the present invention;

[0022] Figure 3 It is a model diagram of the welding path of the present invention;

[0023] Figure 4 It is a schematic diagram of the robot kinematic model of the present invention. Specific embodiments

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments.

[0025] Refer to Figure 1 , a circular trajectory planning method for a welding robot under an arch rib segment, at least including:

[0026] S1: Establish a numerical model by obtaining the structural parameters of the arch rib segment and the structural parameters of the welding robot. The numerical model includes an arch rib environment model, a welding path pose model, and a welding robot kinematic model. The arch rib environment model is used to provide an obstacle avoidance environment for obstacle avoidance calculation. The welding path pose model defines the trajectory and pose of the robot during welding through the end coordinate system of the robotic arm. Combining the relative distances of the robot joints, the D-H parameter method is used to construct the welding robot kinematic model to determine the mathematical relationship between the joint angles and the pose of the end coordinate system of the robot and the joint angles;

[0027] S2: Solve the inverse kinematics of the target welding point using the numerical model to generate a discrete initial path and its corresponding joint angles;

[0028] S3: Combine the CHOMP obstacle avoidance algorithm to generate a safe and effective execution path away from environmental obstacles;

[0029] S4: Adopt a visual feedback mechanism to monitor the actual welding process, calculate the deviation between the weld seam and the actual position of the welding torch. When there is a deviation, continuous transformation is performed through the D-H parameter matrix to change the corresponding joint angles, thereby realizing real-time deviation correction welding of the arch rib segment of a long-span arch bridge.

[0030] The structural parameters of the arch rib segments at least include the equivalent radius of the vertical curve of the long-span arch bridge, the radius of the arch rib, the welding position, the position of the robot operating base, and the structural parameters of the welding robot.

[0031] The arch rib environment model is mainly composed of the externally connected arch rib segments, flanges, and connecting plates. The arch rib environment model is used to provide references for the subsequent welding path model and the welding robot kinematics model and to provide an environmental obstacle model for the subsequent obstacle avoidance algorithm.

[0032] The welding path pose model is obtained from the solder accumulation path on the welding end face of the arch rib segment, which is basically the same as the weld path and presents as one or more arcs on a plane perpendicular to the vertical curve of the long-span arch bridge in terms of mathematical characteristics. As shown in Figure 3 (a), it is the appearance model.

[0033] By discretizing the welding trajectory, the positions of multiple welding points are obtained. Then, taking the vector from each discrete point position to the center of the welding arc as the x-axis (welding torch axis), the vector from the discrete point position to the tangent vector of the arc as the y-axis, and determining the z-axis by the vector product of the x and y axes, the establishment of the welding path pose model is finally completed. As shown in Figure 3 (b), it is the discrete pose model.

[0034] The welding robot kinematics model is established by the D-H parameter method. Taking the center of the welding path as the reference point of the robot, the welding robot is simplified into six relative coordinate systems. The relative positions between different coordinate systems are defined by joint rotation angles, link offsets, link lengths, and link twist angles, and then the establishment of the welding robot kinematics model is completed, which is convenient for the trajectory planning and control of the welding robot. As shown in Figure 4 shown.

[0035] The initial path includes the welding path position and the corresponding six joint rotation angles obtained by inverse kinematics solution through the welding path pose matrix.

[0036] The obstacle avoidance algorithm refers to CHOMP (Convex Hulls for Motion Planning), which is an algorithm for path planning and obstacle avoidance, especially suitable for the motion planning of robots and other mobile devices in complex environments, and can meet the requirements of the obstacle avoidance welding trajectory planning of the arch rib segments of long-span arch bridges. This algorithm generates a smooth and safe trajectory by optimizing a non-linear objective function. This method allows the algorithm to dynamically adjust the motion trajectory of the robot while considering obstacles, the dynamic limitations of the robot, and the desired trajectory characteristics (such as smoothness). In addition, since this algorithm uses a discrete modeling method of multiple spheres when modeling the environment, this algorithm does not require a large amount of calculation of the possible trajectory space, so it can find a feasible solution faster.

[0037] Visual feedback is an automated device with a visual sensor that can provide feedback control signals. By combining various optical characteristics during welding with corresponding optical and image processing technologies, and through the laser characteristics on the weld seam, real-time monitoring and precise control of the welding process can be achieved. Specifically, this mechanism first emits a laser beam during the welding process, and this laser beam irradiates on the weld seam. Since factors such as the shape and position of the weld seam affect the reflection and scattering characteristics of the laser, by analyzing these characteristics, accurate information about the weld seam can be obtained. Then, this information is transmitted to the image processing system, and various algorithms are used to analyze and process this information to obtain parameters such as the actual position and shape of the weld seam. Finally, the vector difference between the weld seam position and the actual welding position is calculated, and continuous transformation is performed through the D-H parameter matrix to change the corresponding joint rotation angles, thereby realizing real-time deviation correction welding of the arch rib segments of long-span arch bridges. This real-time deviation correction function enables the welding visual feedback mechanism to maintain a stable welding effect in various complex environments, greatly improving the efficiency and quality of welding.

[0038] Through the above method, the trajectory planning of the automatic circular welding of the arch rib segments of long-span arch bridge welding robots can be completed.

[0039] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A circular trajectory planning method for an under-welding robot of an arch rib segment, characterized in that: At least including: S1: Establish a numerical model by obtaining the structural parameters of the arch rib segment and the structural parameters of the welding robot. The numerical model includes an arch rib environment model, a welding path pose model, and a kinematic model of the welding robot. The arch rib environment model is used to provide an obstacle avoidance environment for obstacle avoidance calculation. The welding path pose model defines the trajectory and pose of the robot during welding through the end coordinate system of the robotic arm. Combining the relative distances of the robot joints, the kinematic model of the welding robot is constructed using the D-H parameter method to determine the mathematical relationship between the joint angles and the pose of the end coordinate system of the robot and each joint angle; S2: Solve the inverse kinematics of the target welding point using the numerical model to generate a discrete initial path and its corresponding joint angles; S3: Combine the CHOMP obstacle avoidance algorithm to generate a safe and effective execution path away from environmental obstacles; S4: Adopt a visual feedback mechanism to monitor the actual welding process, calculate the deviation between the weld seam and the actual position of the welding torch. When there is a deviation, perform continuous transformation through the D-H parameter matrix, change the corresponding joint angles, and then realize the real-time deviation correction welding of the arch rib segment of the long-span arch bridge; The structural parameters of the arch rib segment at least include the equivalent radius of the vertical curve of the long-span arch bridge, the arch rib radius, the welding position, and the position of the robot operation base; The arch rib environment model is mainly composed of externally connected arch rib segments, flanges, and connecting plates. The arch rib environment model is used to provide a reference for the subsequent welding path model and the kinematics model of the welding machine and to provide an environmental obstacle model for the subsequent obstacle avoidance algorithm; The welding path pose model is obtained from the solder deposition path on the welding end face of the arch rib segment, which is basically the same as the weld seam path and presents as one or more arcs on a plane perpendicular to the vertical curve of the long-span arch bridge in terms of mathematical characteristics; By discretizing the welding trajectory, the positions of multiple welding points are obtained. Then, taking the vector from each discrete point to the center of the welding arc as the x-axis, the vector from the discrete point to the tangent vector of the arc as the y-axis, and determining the z-axis by the vector product of the x and y axes, finally, the establishment of the welding path pose model is completed; The kinematic model of the welding robot is established by the D-H parameter method. Taking the center of the welding path as the reference point of the robot, the welding robot is simplified into six relative coordinate systems. The relative positions between different coordinate systems are defined by joint angles, link offsets, link lengths, and link twist angles, and then the establishment of the kinematic model of the welding robot is completed, which is convenient for the trajectory planning and control of the welding robot; The initial path includes the welding path pose and the corresponding six joint angles obtained by solving the inverse kinematics through the welding path pose matrix.

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