Three-dimensional Visual Sensing Of GTAW Pool Surface And Dynamic Modeling Of Welding Pool

With the rapid development of Marine engineering, nuclear industry andaerospace business, demand for welding become higher and higher in these limitenvironment. As the welder can’t attend the limit environment, remote welding isneeded to complete these welding tasks. So there is no doubt that to improve thelevel of intelligent welding in welding production and to reduce the dependenceon the operator automatic has the vital significance. This paper adopts the activevision sensing technology to sensing welding pool, realize the intellectualizedwelding process. The specific research based on the lattice structure light torecover3d dynamic welding pool, and thus established the dynamic model of themolten pool.First of all, the three-dimensional visual sensor experimental system hasbeen established for welding pool, which based on lattice structure light. Thesystem mainly includes the visual sensing system, the welding motion system,welding power source and control system, etc., and the control software also hasbeen developed to realize the accurate regulation of the welding speed from0to10mm/s and the welding current from20to80A.Image processing algorithms has been developed according to the collectedpictures of laser reflection point which reflected by GTAW molten pool, such asmedian filtering, regional threshold method, average size judgment of noisedeletion, center point extraction. According to the analysis of the defect of thecenter point extracted images, two kinds of typical defects “redundant point” and“missing point” has been discovered, and the methods to removal redundant pointand recover the missing point has also been studied. Finally the coordinates ofreflection points on the image screen which has been accurate extracted.The plane calibration method has been used to calibrate sensing system, andthe transformation of reflection point coordinates from image pixel coordinate toimage screen coordinate has been achieved. And the transformation of reflectionpoint coordinates from image screen coordinate to the custom world coordinatehas also been achieved according to the relations of the two kinds of coordinatesystem. The molten pool surface reflection point coordinates has been calculated through the inverse of optical reflection law, according to the reflection pointcoordinates and the corresponding incident light equations combined withboundary conditions. According to the three-dimensional curved surface fittingof the point on the surface of the welding pool at that moment,3d information ofmolten pool has been obtained. Through the comparison between the weldingpool width which achieved from the extracted3d information and the actual poolwidth at the same time, the relative error has been achieved which is3.23%.According to the welding pool surface3d restoration method, someexperiment has been made under the different welding electric currentexperiment to analyze the influence of welding current for the3-d shape ofwelding pool. Through the positive and reverse step experiment, this paperanalyses the response characteristics of the system, and thus obtain the transferequation of the system. Welding pool control model is set up to simulate andidentify, which lay a foundation for the design of the controller.