| Intersection curve welding is a typical welding task in the fields of petrochemical industry,pipeline engineering,pressure vessel manufacturing,etc.Due to the complexity of intersection welding seam and the functional limitation of existing automatic welding equipment,the degree of automation of intersection curve welding has been at a low level.Especially for the intersecting pipes of common main pipe,manual welding is a common way of operation.It is of great significance to study and solve the key technical problems of the automatic welding of intersection curve,which can improve the level of welding automation in our country.Intersecting pipes of common main pipe being the welding object,two key problems of automatic welding of intersection curve are studied,which are trajectory planning and trajectory control.The trajectory planning is to plan the trajectory of the welding torch relative to the workpiece and obtain the mathematical expression of the trajectory according to the specific conditions of the pipes and the welding technological requirements.Based on the results of the trajectory planning,the trajectory control is responsible for controlling the actuator to make sure that the welding torch moves in accordance with the desired trajectory in order to realize the automatic welding.The trajectory planning and trajectory control are two closely related aspects of the study and implementation of the automatic welding of intersection curve.According to the different conditions of the pipes and the different precision requirements of the welding path,the study of trajectory planning is divided into two parts to deal with the welding requirements of intersection curve of ideal model and non-ideal model.Firstly,the trajectory planning of the intersection welding seam with different types of welding groove-non-groove,main pipe groove,and slave pipe groove-is studied based on the model of ideal non-orthogonal intersecting pipes.The theories and algorithms of welding passes layout,welding orientation control,weaving welding planning,welding speed planning,and welding passes partition are presented As a result the analytic expression of the welding torch's trajectory across welding passes is formulated which is for ideal intersection curve.Secondly,according to the information of welding seam location and the characteristics of intersection curve,the sources leading to the deviation from the welding seam are analyzed.The algorithm of quantization and compensation of the deviations are presented,which include the coordinate error of the slave pipe and straightness deviation of the main pipe.The trajectory planning method for non-ideal intersection curve is created by combining the actual intersection curve with the trajectory planning method based on ideal model.The study on trajectory control is based on the results of trajectory planning.The main pipe rotating welding scheme is designed for the com-main intersecting pipes welding.Then the whole frame of the trajectory control system of automatic welding of intersection curve is established.Afterwards the direct interpolation algorithm of the welding torch's trajectory with swing motion and across welding passes is presented,as well as the selection algorithm of the intersection nodes for piecewise interpolation which can limit the maximum path deviation exactly.The welding seam location system is created based on laser scanning displacement measuring,and the corresponding welding seam recognition algorithm is presented.At last the implementation scheme of welding seam tracking is investigated based on arc sensor.A 6-axis automatic welding machine of intersection curve is designed for the automatic welding of com-main intersecting pipes,and the numerical control system is developed based on some results of the study on trajectory planning and trajectory control.The feasibility of the numerical control system is verified by the welding experiments,and the correctness of the corresponding algorithms are proved. |
PDF Full Text Request