| The welding stress can be reduced and the smooth and consistent surface of the connected parts can be obtained by robot grinding to remove the weld after welding of the structural parts.At present,robot polishing trajectory programming mainly adopts "teaching reappearance" and off-line programming,but with the increasing complexity of welding seam trajectory,"teaching reappearance" has been difficult to meet the requirements of practical industrial production on the efficiency and quality of welding seam polishing.Although offline programming can carry out relatively complex trajectory programming,it needs to establish the model of workpiece and robot,and there are still differences between the ideal workpiece and the actual workpiece,so it is difficult to apply in the actual industrial production.At present,most welding grinding robots are aimed at long straight welds,but there are few researches on curved welds of structural parts.In order to solve the above problems,this paper uses a weld-polishing robot guided by line structural light vision to polish the curved welds at the joints of structural parts.Firstly,the measurement principle of line structured light vision is studied,and the resolution and application of direct and oblique light vision are compared and analyzed.The method of obtaining and processing weld point cloud data and extracting weld feature is introduced,and the measurement accuracy of visual measurement system is verified by using standard measuring block.The weld morphology was scanned by visual sensor,and the center point of weld track was extracted.The transformation relationship between robot coordinates,laser sensor coordinates and workpiece coordinates was analyzed,and the forward and inverse kinematics of the robot was solved.The kinematics modeling of the robot was carried out by MATLAB,and the accuracy of kinematics modeling and forward and inverse kinematics calculation was verified by simulation.Secondly,the algorithm of quintic polynomial interpolation and NURBS curve interpolation based on the visual guidance of line structured light is studied,and the calculation process of coefficients of two-node and multi-node quintic polynomial interpolation method is deduced,and the construction of NURBS curve and interpolation parameters are deduced.When using the methods of equal chord length and equal chord difference to discretized grinding and polishing trajectory with large curvature changes,there would be large trajectory deviation and poor surface uniformity of machined workpieces.Therefore,a NURBS curve trajectory planning method with variable curvature based on structured light vision guidance was proposed.The weld curvature calculation and the selection process of the feature points of the weld are studied,and the trajectory interpolation method of variable curvature is used to fit and discret the polishing trajectory,and the planned trajectory is transmitted to the robot to improve the polishing accuracy of the robot weld and guide the robot to grind the weld.Finally,the curve of the polishing robot based on visual guiding weld the polishing experiment platform are introduced,using five times polynomial interpolation and NURBS interpolation and variable curvature NURBS curve interpolation method of trajectory planning on the weld of different curvature polishing experiments,the experimental results verify the change of curvature of the superiority of NURBS curve interpolation method of trajectory planning. |
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