Development Of Auxiliary Control System Of Variable Polarity PMIG Welding Equipment

The variable polarity pulsed MIG is a new welding technology. It has the predominance of DCEP MIG and DCEN MIG. The DCEP MIG has the characteristic of deeper penetration which can reduce defective fusion and good arc stabilization. The DCEN MIG has the characteristic of shallow penetration of welding seam, and the welding wire has a high melting speed. So the variable polarity pulsed MIG is a new technology for the welding of aluminium alloy sheet.It has important significance to study the welding technology of variable polarity pulsed MIG for high efficiency weding and good quality of welding products. We should control the welding current, output voltage and the process of melting drop more effectively. The paper is s sub-topic of the research of variable polarity pulsed MIG welding device and its welding stabilization. The main content is design of digital man-machine interface system, a speed regulating system of good stabilization and dynamic performance; software for appraising the performance of wire feeder.The first, a digital man-machine interface system using AT89S8252 singlechip is designed. The system uses SD7218A keyboard/display chip with serial bus interface. The welding parameters can be seleted and regulated easily with the cooperation of digital encoder and keystoke. At the same time the system has the function of storage and call of optimum parameters. The man-machine interface system communicates with the master system using RS-485 bus. Aimming at the man-machine interface system, we have done high frequency anti-interference experiment, it proves that the system has good performance of anti-interference.The second, we adopt the mean-squared deviation of speed as the index of dynamic stability and design an appraisal software of the performance of wire feeder. The software can not only appraise the performance of wire feeder but direct the design of speed regulating system.The third, the paper analyses and expatiates three mode of speed regulating which are speed negative feedback, voltage negative feedback and voltage negative feedback plus cuttent positive feedback and designs a speed regulating control system adopting the mode of voltage negative feedback plus cuttent positive feedback. At the same time we optimize the speed regulating system using the appraisal software of the performance of wire feeder. Finally designs the interface cirvuit with the master control system. The analog singal is isolated by linear optical isolator and the digital signal is isolated by common optical isolator.Finally, a comparison experiment is performed between the speed regulating system this paper designed and the speed regulating system of NBC-350 welding power source. The result indicates that the system this paper designed has good dynamic stability and control accuracy.