Weld seam fitting and welding torch trajectory planning based on NURBS in intersecting curve welding

In the industrial applications of intersecting curve welding, in order to improve the accuracy and quality of welding, the automation program of weld seam positioning, data processing, and the actual welding is widely used. In this paper, a lot of research has been carried out, and a method based on non-uniform rational B-spline (NURBS) curve fitting is presented, while the trajectory of the welding torch is planned. The method can use the position data of the discrete weld seam points obtained by manual teaching or weld seam location. By the improved least squares method and the White rule, the outliers are eliminated and the weld seam points for intersecting curve fitting are obtained. These points are fitted based on NURBS, and then the parameter expressions of the fitted intersecting curve are given. For the purpose of obtaining the orientation of the welding torch, the coordinate system which can describe the feature of the fitted intersecting curve is established. The coordinate system is combined with the theoretical intersecting curve model and the fitted intersecting curve model and gives a novel approach to compute the orientation of the welding torch according to the position of the fitted intersecting curve. In the process of planning the welding trajectory, a fitted intersecting curve discrete algorithm based on the equal arc length principle is proposed to reduce the fluctuation of the feed rate according to the restriction of chord error. Finally, this method gives the position and orientation of the welding torch in the form of a homogeneous matrix and verifies the correctness and flexibility of the algorithm by MATLAB simulation and intersecting curve welding experiment.