Study On Seam Tracking System Of NG-IG Welding

On the basis of detailed investigation and analysis of narrow gapwelding and seam tracking technology over the world, a proposal ofdesigning seam tracking system for narrow-gap TIG welding on virtualinstruments was presented, concerning its technological characteristics. Theseam tracking system was achieved through hardware integration, controlstrategy planning and software design. At last, the feasibility of the proposaland the performance of the system were verified with the results of trackingsimulation experiments.Firstly, according to the principle of seam tracking, an overall proposalof the seam tracking system on a virtual instrument was determined, inwhich a common computer and a PCI-6221E multifunction data acquisitionard was selected to be the core of the system. In addition, for integration ofthe whole hardware system, a high sensitive position sensor and a signalconditioning circuit with reliable performance were adopted, while a drive control system and an actuating mechanism were designed.Based on establishment of the hardware system and analysis of thesystem control model, the control strategy of the seam tracking system wasfurther studied. PID and fuzzy control have been widely used. However,PID control system has difficulty to deal with contradiction betweenaccuracy and stability, while fuzzy control system has poor behavior in thesituation of small deviation. Thus, after analyzing the system control model,a fuzzy-PID composite control algorithm with quick response, smallovershoot, high accuracy and good simulation performance was designedbased on the adjusting of PID control parameters, the optimization ofquantization factors and control rules of fuzzy controller, as well as thedetermination of configuration and threshold of the composite controller,which provided the reference for software design of the control system.In order to achieve the seam tracking function, an application softwareof the control system was developed on the virtual instrument platform, inwhich the LabVIEW was adopted to be the core software of thedevelopment tool Kits. The program of control system was applied with theproducer and consumer design pattern. All sub-models of control program,including signal acquisition, deviation signal conversion, fuzzy-PID controller and stepper motor drive control, etc. were designed. What is more,a friendly man-machine interface was designed for online modification ofthe control parameters and real-time display of the system running status.Finally, the control performance of the seam tracking system was testedby tracking experiments. The influence factors on accuracy and dynamicperformance of the seam tracking system were also analyzed. The resultsshowed that the fuzzy-PID composite control strategy has a good trackingperformance and that the NG-TIG welding seam tracking system on virtualinstrument meets the requirements of design for real application.