| A three-dimensional(3D)zigzag-line welding seam is a typical complex trajectory welding seam that is widely used in marine equipment,large lifting equipment,logistics and transportation equipment,and other manufacturing fields.A 3D zigzag-line welding seam workpiece is assembled by a zigzag-line plate and flat plate with different angles through positioning of the welding seam.Such a workpiece is usually a large component,and it is difficult to use a high-precision fixture to strictly fix its pose.Usually medium and heavy plate is used,which requires a swing gas metal arc welding(GMAW)process.At present,almost all 3D zigzag-line welding seams are manually welded.At the same time,the robot off-line programming mode or teaching mode exists to realize automatic welding.Both the robot off-line programming mode and teaching mode have several disadvantages,such as low programming efficiency,heavy teaching workload,and inability to obtain weld deviations in real time,which seriously affect the efficiency and quality of 3D zigzag-line welding seams.Realizing real-time tracking of a 3D zigzag-line welding seam is an effective way to improve welding efficiency and quality.however,real-time tracking of 3D zigzag-line welding seams is still challenging,especially at high welding speed and in swinging GMAW.In view of the above problems,in this paper,mainly the aspects that follow are studied.(1)Aimed at the problem of 3D zigzag-line welding seam real-time tracking,a welding robot system for 3D zigzag-line welding seam swing GMAW is established,for which a five-axis welding robot is designed.At the same time,the kinematic analysis of the robot is carried out,including forward,inverse,and differential kinematics analyses,which lays a theoretical kinematic foundation for the realization of real-time tracking of robot welds.The robot model is established in the MATLAB(Math Works,USA)robot toolbox,and the robot kinematics simulation includes forward kinematics simulation,robot inverse kinematics simulation,and robot workspace analysis.The feasibility of kinematics analysis and calculation of the 3D zigzag-line welding seam tracking robot is verified.(2)Aimed at the problem of pose detection in the process of locating the starting point of 3D zigzag-line welding seam,a method of detecting the pose of the starting point of a3 D zigzag-line welding seam based on laser displacement sensor is presented.The laser displacement sensor is used to obtain the 2D information of the workpiece,and the slope analysis method is used to detect the starting position of the 3D zigzag-line welding seam.The pose estimation method of a 3D zigzag-line welding seam based on RANSAC(Random Sample Consensus)3D point-cloud plane extraction is used to realize the attitude estimation of the 3D zigzag-line welding seam.Pose detection experiments on the starting point for3 D zigzag-line welding seams with different poses are carried out.Experimental results show that the position detection error is less than 0.4 mm and the attitude estimation error is less than 1.8°,which can meet the requirements of 3D zigzag-line welding seam pose detection.(3)Aimed at the problem of extracting the three-dimensional pose of the welding seam online in the real-time tracking process,a fast online extraction method of 3D zigzag-line welding seam pose information based on laser displacement sensing and density clustering point-cloud segmentation is proposed.The laser displacement sensor is used to obtain 3D zigzag-line welding seam point-cloud data and the ?-approximate DBSCAN(DensityBased Spatial Clustering of Applications with Noise)algorithm is used to segment pointcloud data online.A welding experiment of a typical corner-type 3D zigzag-line welding seam of low carbon steel is carried out using GMAW.Experimental results show that when the welding speed is up to 1,000 mm/min,the welding seam position detection error is less than 0.35 mm,attitude estimation error is less than 2°,and main algorithm running time is less than 120 ms.The online fast extraction of 3D zigzag-line welding seam pose information is realized,which meets the requirements of real-time tracking of 3D zigzagline welding seams to provide pose information.(4)Aimed at the problem of 3D zigzag-line welding seam tracking with complex structure and requiring swing GMAW technology,a real-time tracking method of 3D zigzag-line welding seam robot swing GMAW based on trajectory online detection is proposed.3D zigzag-line welding seam pose information is used to extract the pose information of a weld seam quickly.Robot shaft 5 controls the welding gun to swing around the welding seam trajectory and extract the welding seam deviation in real time.The 3D zigzag-line welding seam deviation adjustment is realized using the fuzzy-PID control method by controlling the robot axes 2 and 3,and the welding seam trajectory is corrected in real time.The swaying GMAW experiment was carried out on separate 3D zigzag-line welding seams with 130°,150°,170°,180°,190°,210°,and 230° typical angles.Results show that when the welding speed reaches 1,000 mm/min,the tracking error of the weld seam is not more than 0.4 mm,which meets the requirements of a 3D zigzag-line welding seam real-time tracking.(5)The robot trajectory planning method in the process of 3D zigzag-line welding seam swing GMAW is studied.In the welding process,3D zigzag-line welding seam pose information is obtained by the laser displacement sensor and point-cloud data processing.The welding torch trajectory is planned in Cartesian space,and the 3D zigzag-line welding seam trajectory divided into a linear welding area and a welding torch attitude adjustment area.To ensure the continuity and smoothness of the welding torch attitude change,the welding torch attitude of adjacent segments is adjusted by linear transformation.In the process of locating the welding start point,the trajectory of each robot joint is planned using the fifth-degree polynomial interpolation method.In the swing welding process,the trajectory of axis 5 of the robot is planned using an 8-degree polynomial.A welding experiment on a 3D zigzag-line welding seam with various corner angles was carried out.Experimental results show that the proposed robot trajectory planning method meets the requirements of real-time seam tracking in the 3D zigzag-line welding seam GMAW process. |
PDF Full Text Request