Research Of Resistance Seam Welding Control Method Based On Fuzzy Control Theory

Strip is an important steel product, and its production level indicates the development level of a national metallurgical industry, machinery industry and control technology. The two rolls of strip must be welded together by welder, in order to keep the production line continuous and improve the strip productivity. Resistance seam welding is a kind of highly efficient welding method, which is wiedly used in steel industry. The main control object of welding process is the welding current, which directly affect the quakity of the seam. The strip will break due to the seam’s poor quality, as the result, the strip material is severe damage and the production line has to stop.This thesis takes the strip production line of a cold rolling stainless steel plant as the research background, focuses on its resistance seam welder, and makes a deep research on the control system of welding current. The control of welding current is a complex process iteself, so it is hard to establish a accurate mathematical mode. The thesis establishes a similar model of the welding current control system based on the approximate and empirical data, and analyses the conventional single closed-loop PID method which used to control the welding current in most strip plant. While there are many uncertain factors which affects the welding current when the welder is working, such as AC voltage fluctuation, the variation of welding resistance, traditional PID control has poor ability to thses anti-interference, and has long dynamic regulation time and high overshoot, all this will lead to bad seam quality. To resolve these existed probloms, this thesis designes a cascade PID control system whose minor loop use voltage feedback and major loop is welding cuttent feedback. At last, fuzzy control is drown into use, and this thesis attempts to band fuzzy control and PID control together, obtain a fuzzy PID controller. It intelligently corrected the three parameters of PID through the online learning of the running system. The PID controller could control the on-off time of the inverter’s switches by the six independent PWM waveforms. The duty ratio of the PWM waveforms were changed real time with feedback, and eventually realized the constant current output control of the system.Finally, the thesis uses the matlab to simulate and verify the control effect of the designed fuzzy PID controller of the welding current control system. The simulation results indicate that the designed variable universe fuzzy PID controller not only has smaller overshoot, but also has better anti-interference ability and adaptive capacity to the parameters variation, satisfies the constant welding current output requirement of welding process.