Research On Weld Seam Measurement And Tracking Control In Tailored Blank Laser Welding Based On Three-line Structured Light Vision

Laser welding,as a welding method with small deformation,high-speed,and non-contact thermal processing,is suitable for massive and continuous production processes.Tailored blank laser welding as one of the laser welding technologies has a wide range of applications in aerospace,automotive and other industries.For tailored blank laser welding,the same kind or different kinds of plates are automatically assembled and welded to form a monolithic board.For the robotic tailored blank laser welding,the positional deviation between the welding torch and the butt joint will occur during the actual welding process due to the robot position error and the weld deformation of butt joint,which is difficult to meet the process requirements of tailored blank laser welding.Therefore,it is urgent to study the seam measurement method and tracking compensation method of the position deviation for the butt joint of tailored blank laser welding.A seam tracking system is also needed to ensure the high precision of the robotic laser welding which can improve greatly the quality and efficiency of the welding.In this thesis,in order to solve the problems of weld seam tracking in tailored blank laser welding,the seam measurement and the tracking system in the tailored blank laser welding based on three-line structured light vision was analyzed.The specific research works are as follows.A weld seam tracking system for tailored blank laser welding based on three-line structured light was designed including the design of three-line structured light vision sensor,motion actuator and controller.For the butt joints with the same and different thicknesses,different measurement methods were proposed which could measure the parameters such as gap,mismatch,position of center point,etc.At the same time,the radius of curvature of any point on the curve joint could also be measured.In order to solve the error compensation problem in the tracking control of straight line,curve and polyline joint,the compensation models were established to realize the real-time compensation of the position deviation for the joints,and the corresponding formula of the actual compensation value for the welding point was derived.According to the compensation formula,tracking trajectory was planned and then the tracking speed was adjusted.For the tracking control,the fuzzy PID-based weld seam tracking control method is studied based on the existing control methods.The anti-interference performance of the fuzzy PID controller is studied during the weld seam tracking process.The actual compensation value of the welding points could be compensated and controlled by this control method.The experiment platform of weld seam measurement and tracking for tailored blank laser welding was developed.The parameters measurement experiments were carried out for the straight line joint of the same thickness blanks and straight line and curve joint of different thickness blanks.The verification method was designed to verify the accuracy and reliability of the measurement method.And the simulation experiment of tracking control was carried out to verify the effectiveness of the compensation model and the tracking control method.Finally,the thesis were summarized and the future research work was introduced.