Research On Automatic Welding System And Control Technology Of Stainless Steel Corrugated Sheet

With the increase of global energy consumption,the manufacturing industry of LNG carrier has been developing rapidly.As the core technology of LNG carrier,membrane cabin technology has always been the focus of research in the world shipbuilding field.One of the difficulties in the construction of membrane chamber of LNG ship is that the stainless steel corrugated plate on the primary barrier of membrane chamber has irregular size,small thickness and large thermal expansion coefficient,and the welding condition is very special.Manual TIG welding is mostly used for welding manufacturing at home,which is not only complicated,low efficiency,high risk factor,but also difficult to ensure quality.Therefore,it is of great significance and application value to study the equipment and control method for automatic welding of corrugated stainless steel sheet in membrane chamber.Firstly,the mechanical structure,hardware and software of the control system are introduced.Based on membrane tank stainless steel corrugated sheet welding conditions and process requirements,a series-parallel-series compound configuration light weight welding robot is designed.Through the design of walking and fast assembly and disassembly mechanism,the robot not only has the characteristics of stability and obstacle surmounting,but also can quickly switch between different welding stations to achieve efficient welding of cabin roof and bulkhead and other special positions;Through the compound configuration design,the robot has good working space and kinematic characteristics,and realizes the decoupling of rotational and mobile DOF motion.The strength and stiffness of the structure are verified by statics analysis,and the driving system is calculated and checked.On this basis,the hardware architecture of the control system is designed with an open structure based on upper and lower computers,and the selection of important hardware is completed.Based on the analysis of system requirements,the software design of the control system is carried out by adopting the design concept of multi-thread concurrency and modularization.Secondly,the kinematics model of the robot is established and the trajectory planning of the system is studied.Based on the screw theory,the degree of freedom of the robot is quantified and the motion law of the parallel mechanism is analyzed to realize the equivalent treatment of the parallel mechanism.Based on the D-H model,the forward and inverse kinematics solutions of the equivalent robot are studied.On the basis of the forward solution,the good adaptability of the robot to corrugated plate welding is proved through the study of the workspace.A virtual prototype is established in ADAMS to verify the kinematics model.Aiming at the trajectory problem of robot welding operation,the cubic spline fitting algorithm of joint space is derived,the interpolation method of cartesian space line and arc trajectory is studied,and the transition method of space multi-segment line trajectory is proposed and interpolation is realized based on S-curve,which provids theoretical basis for the research of automatic welding operation method.Then,the automatic welding method of corrugated welds is studied.Based on the analysis of the difficulties of corrugated welding,an automatic welding operation scheme is proposed.The contour lines of corrugated trajectory ware extracted by image processing,and the trajectory planning method is used to realize the trajectory planning of corrugated welding seam.Aiming at the characteristics of nonlinear and time-varying of the weld tracking control system,a dynamic compensation scheme for weld errors is designed.The fuzzy control is used to adjust the traditional PID parameters in real time which forms the fuzzy PID controller.The simulation model is established in MATLAB and the performance is compared with the traditional PID controller,the results show that the fuzzy PID controller has faster response and higher precision,which verifies the superiority of the designed fuzzy PID controller and provides guarantee for automatic welding.Finally,the finite element model of corrugated sheet welding process is established to explore the transient temperature field under different parameters and experiments are carried out.Aiming at the welding defects of corrugated stainless steel sheet,a finite element simulation model of corrugated plate lap self-fusing TIG welding is established based on Ansys.The transient temperature field distribution of corrugated stainless steel sheet in the welding process is studied,and the influence of different velocity and current on the characteristics of molten pool is explored.Based on the designed automatic welding system and control scheme,kinematic experiments are carried out to verify the feasibility of trajectory planning and tracking compensation scheme.Based on the simulation results and welding experiments under different technological parameters,the best welding technological parameters are obtained,and the performance of the designed automatic welding system for corrugated stainless steel sheet is verified by welding experiments.The results show that the system can meet the requirements of automatic welding for corrugated stainless steel sheet in membrane chamber.