Design Of Stereo Vision System For Gantry Welding Robot

In traditional industrial processing,manual welding of large workpieces has the problems of low precision,poor reliability and long time consuming.The gantry welding robot has a large working range and high positioning accuracy,which is suitable for welding large workpieces.Stereo vision technology can help the robot to realize the autonomous positioning of the weld trajectory and effectively improve the accuracy and efficiency of robot welding.The traditional line laser and other visual measuring devices are difficult to meet measurement requirements of the welding system for large workpieces.Moreover,since the end effector of the gantry robot has only three translational degrees of freedom,the hand-eye calibration of robots and vision measuring devices cannot be achieved by traditional methods.In view of the above problems,this paper designs a gantry type welding robot stereo vision system.Through the surface 3D measurement system can efficiently measure the 3D data of the workpiece and locate the weld trajectory from the 3D data.Combined with the result of hand-eye calibration,the weld trajectory is converted to the reference frame of robot motion control as the feedback data of robot control.The main research contents of this paper are as follows:1)The composition and function of the stereo vision system of gantry welding robot are analyzed.The system is composed of 3D measurement,weld positioning and hand-eye calibration.The development status,the advantages and application scenarios of the three technical links are introduced respectively.And the technical route of this paper is proposed.2)A surface 3D measurement system based on fringe projection is designed.According to the basic principle of surface three-dimensional measurement,a gray code combined with phase shift method is designed to obtain the phase of the object surface.Realizing the elimination of the non-linear error of the wrapped phase and the order jump of the unfolding phase.Deduced the mathematical model of the 3D measurement system and established the pixel-by-pixel phase difference-height mapping model.Combined with the two-dimensional camera model,the height-three-dimensional coordinate mapping model is established.For the model of the 3D measurement system,a calibration method based on a plane calibration board and a precise mobile platform is designed.Finally,the accuracy of the 3D measurement system is evaluated by experiments and the flatness error is less than 0.03 mm and the absolute error is less than 0.05 mm.3)The welding spot location method in 3D data is designed and analyzed the characteristics of the data obtained by the three-dimensional measurement system.Taking the structural stiffeners as an example and for the welding object with obvious geometric structures,the welding seam positioning method is designed to analyze the three-dimensional geometric structure from the three-dimensional point cloud data.Taking the steel plate seam as an example,for welding objects with unobvious geometric structures,a method is designed to analyze the position of the weld from the two-dimensional image,and combine the two-dimensional-three-dimensional mapping relationship of the three-dimensional measurement system to realize the weld positioning in the three-dimensional space.Taking the joint of steel plate as an example and for the welding object with unobvious geometric structures,the method is designed to analyze the position of the weld seam from the two-dimensional image.By combining the dimensional mapping relationship of the two-dimensional and three-dimensional to realize the welding seam positioning in the three-dimensional space.4)The hand-eye calibration method of gantry robot is designed and analyzed the reason about the traditional hand-eye calibration method is not suitable for gantry robot.Based on the mathematical model of the hand-eye system of the gantry robot,a hand-eye calibration method suitable for the gantry robot is designed.The method is simple to operate and suitable for on-site calibration.The method to accurately locate the mark points of the plane calibration board from the data obtained from the three-dimensional measurement system is designed and the precision of the stereo vision system is verified by the experiments of±0.3mm.