A Study On Underwater Welding Seam Forming And Tracking Based On Rotating Arc Sensor

The scale of ocean project becomes larger with the exploiting of marine resources. As a key technology of ocean project construction and maintenance,underwater welding is one of the main points in advanced technology of manufacturing . Due to the restrict of underwater welder in deep water, underwater robot, instead of underwater welder, is in urgent need to excute automatic underwater welding.The underwater robot seam tracking system based on rotating arc sensor track seam with welding current signal. When rotating arc sensor is rotating above the V groove, the offset between the center of the welding torch and the middle of seam can be identified for arc length and welding current change in accordance. Seam tracking system based on rotating arc sensor is one of the most effective methods to seam tracking for simple structure, excellent accessibility and lower cost.Compring to the visual sensor, underwater rotating arc sensor is more suitable for underwater welding for its advantages. It is difficult to acquire and process the signal for the arc in underwater welding is more unstable than in land, it is need to study underwater seam track system based on rotating arc sensor.The minitype rotating arc sensor is designed for improving accessibility and reducing vibration,and the structure of mini drain cap. Hence, underwater seam tracking system based on the rotating arc sensor is built for experiment. The system contains rotating arc sensor, speed control system, current sensor, data acquired card, computer and robot control system. The underwater seam tracking software system is developed by Visual C++ 2005, includes signal capture, speed control module, signal processing, offset identification, and serial port communication.The underwater welding based on rotating arc sensor is affected by many factors, it is necessary to do a great deal of experiments to get the optimized technological parameters. The orthogonal experiment with four major factors is designed to obtain the optimized technological parameters on welding forming and characteristic of welding signal, which provide experiment basis for the seam tracking. Then the regression equation which is built form the geometry of underwater welding is used to periform sensitivity analysis.RVM (Relevance vector machine) is used to build a model to predict the geometry of underwater rotating welding.Due to the disturbance of the arc light, splash, soot and so forth, the acquired signal often is disturbed by the break circuit and noise. Wavelet filter and median filter is used to process the welding signal by comparing some denoise algorithm. The result shows that the filter method can filter the disturb, keep the characteristic of welding signal, and obtain more direct signal.The underwater seam offset identification method that combine PCA(Principal component analysis) and RVM is presented.The principal component analysis is usded to process the data set which acquired in the underwater welding experiment, which can reduce the dimension of data set. Then the processed data is trained in the RVM.The result shows that, the precision of PCA_RVM is as good as RVM, and better than interval integral method, neural network and support vector machine; The runtime of PCA_RVM is more than interval integral method and less than neural network,support vector machine and RVM,PCA_RVM is more suitable for seam tracking system.Finally a set of land、wet and local dry with mini drain cap welding experiments are performed on the steel plate with v-groove. The seam tracking system is used to track oblique line and s-curve in land、wet and local dry with mini drain cap. The results of the tracking experiments show that seam tracking system is successful.local dry with mini drain cap underwater welding have better welding quality and tracking result than wet underwater welding ,and more suitable for engineering applications.