Welding-torch Deviation And Inclination Detection And Fillet Seam Tracking Based On A Mobile Robot With Rotational Arc Sensor

With the development of modern industry, there is a growing application of large welding structures, so there are many curved fillets and broken-lined fillets need to be welded. For improvement of production efficiency and guarantee of product quality, it is essential to realize arc welding automation in the manufacturing of these workpieces. Because of the large scale, these structures must been welded in out of workshop, so the arm welding robot can not be used and the welding paths are not easily pre-programmed. Moreover it is necessary to control welding torch moving along with the seams and adjust the torch's inclination simultaneously for obtain highly welding quality when tracking these seams.In this dissertation, a wheeled mobile robotic arc welding seam tracking system is developed, and the system uses a rational arc sensor to detect the deviation and inclination of welding torch. The main research contents are: the filtering of welding currents; the identification of welding torch deviation and inclination; the control methods designing for automatic tracking curved fillets, lattice box fillets and broken-lined fillets.In consideration of the fact that welding current signals are often disturbed by outside noises, soft threshold wavelet filtering method is applied to process the welding current signals, that make the welding current shape is obviously smoothed and the signal-to-noise ratio is much improved.It is researched in theory and experiments that the character harmonic method can be used to detect deviation and inclination of welding torch simultaneously. The results show that the traditional method of using the amplitude of one-order harmonic to detect deviation would result in big error when the inclination is not zero. For improve the detection precition, the character plane method is developed in this dissertation, which fits the arc currents to a plane in three dimensions using a least-square fitting method. The deviation of welding torch is obtained through calculating the intersection line slope of the fitting plane with the YZ plane, and the inclination is calculated through the intersection line slope of the fitting plane with the XZ plane. Because of the deviation and inclination is projected to two orthogonal planes, so they can be decoupled.A multi-segment controller is designed to track lined fillet and small curvature fillet, which is composed of a proportion controller and a self-turning fuzzy controller to control horizontal slider. When the deviation is large the proportion controller will be used to quickly reduce the deviation, otherwirse the self-turning fuzzy controller will be used to avoid overshoot and achieve smooth tracking, and the immunity feedback method is applied to modify proportion gene of fuzzy controller. For the curved seam tracking problem a predictive fuzzy controller is designed to coordinate control cross-slider and wheels. This method uses the information of weld torch deviation to estimate the robot's orientation errors, and uses predictive control theories to offset the control outputs. The experiment results show that the presented method is valid to track curved fillets.In the welding of lattice box fillets, there are many right-angle corners that make tracking seam become very difficult. The method of using welding torch inclination to detect the corner and using ultrasonic sensor to detect the position of frontage seam is detail discussed in this dissertation. The mathematical model of mobile robot is built and the controller is designed to tracking these seams.For the broken-lined welding seams tracking problem, a welding torch with rotation axis is designed which is placed in the flat of mobile robot. A controller is proposed that use of the welding torch deviation and inclination information as input values, meantime use of the mathematical model of mobile robot to control rotation axis, horizontal silder and wheels to track welding seam and adjust torch inclination.In the last though experiment results show that the feasibility and validity of thisresearch work. In addition, the designed arc welding seam tracking system was triedout in Jiujiang Tongfang Jiangxin Shipyard Co., Ltd, and anticipant result is acquired.