Real-Time Control Of Back Weld Width In Aluminum Alloys Pulse GTAW Based On Sensor Servoing

In aluminum alloy automatic welding process, heat dissipation conditions and butt gap are often different, it is difficult to guarantee the uniform of back weld width using constant parameters, this will reduce the performance of the weld, so it is necessary to study real-time control of back weld width. Besides, in process of large-size parts welding, welding torch need to move, in this case, CCD and welding torch must move synchronously. In order to solved these two problems, the change of back weld pool's position was used to control sensor's motion, on this basis, back weld width was controlled.Firstly, experimental system was built, this system can be used to capture and process the back weld's image, on this basis, CCD's motion and back weld width could be controlled.Secondly, back weld pool's image processing algorithm was studied. According to the characteristics of the image, the molten pool and weld edge detection algorithm was developed, including maximum between-class variance method, binary opening operation method, binary closing operation method, contour extraction method. On the basis of above algorithm, back weld's information about position and width was accurately extracted, laid a good foundation for servo control and control of back weld width.Thirdly, backside sensor's servo control method and back weld width control method was studied. A PID controller was designed for backside sensor's servo control, trial and error method was used in PID parameters tuning, a good control effect had been achieved. As welding process has strongly nonlinear characteristics, fuzzy controller was designed with Matlab fuzzy logic toolbox to control back weld width. Fuzzy controller's input is back weld width's error and error change, its output was welding speed. The second-order transfer function between back weld width and welding speed was identified by area method. On the basis of this transfer function, Simulink was used to verify fuzzy controller's control effect, quantized factor and proportional factor's impact effects to control performance were studied, through these works a basic guidance was provided for parameters' adjustment during actual welding process.Finally, sensor servo control experiment and back weld width control experiment were done at the same time. Experiment results show that: PID controller works well, servo control's steady-state error is less than 3.2mm.Fuzzy controller has a strong adaptability, when back weld width's given value, parts' shape, or gap size is different, good formation of weld can always be obtained, when parameters are suitable, back weld width control's steady-state error is less than 0.4mm.