Research On Tool Path Planning And Attitude Control Of NURBS Surface Milling By 6DOF Robot

Industrial robots have made great progress since they were introduced in the 1950 s.Now they have been widely applied in manufacturing processes,such as assembly,transportation,spraying,packaging,product inspection,etc.Due to their advantages of simple operation,easy installation and low cost,industrial robots can completely replace CNC machine tools in some environments where the machining accuracy is not high and the material is soft,which requires a reasonable position planning of robot machining ends to improve the quality of processing.The multi degree of freedom of industrial robots determines that it can fabricate complex curves and surfaces.In the curve and surface design,NURBS(Non-Uniform Rational B-Spline)is an excellent design method.Currently,part of NC system can implement NURBS interpolation,but NURBS interpolation for industrial robots is still under study.Based on an MOTOMAN-UP6 industrial robot with a repeat accuracy of 0.08 mm,this paper analyzed the planning of cutter path and the problems of posture during NURBS surface processing,and proposes the tool radius compensation for industrial robots,realizing NURBS curve and surface interpolation on industrial robot platforms.First of all,the inverse kinematics of UP6 robot is solved,while the main problem is the non-uniqueness of the solution.The numerical solution method and algebraic method are generally used to solve the inverse problem of robots.In experiments,we found that in most cases,there were only a few solutions to the problem once the robot end pose was determined.However,the subject of this study is about the milling problem of industrial robot.In order to ensure the efficiency of robot operation,we need to input the smallest pulse to make the robot reach the designated position.Therefore,we use an optimization principle of energy accuracy to determine the inverse solution of each joint.Secondly,the algorithm of NURBS curve and surface is studied,and the interpolation point on the surface is calculated from the surface parameters.And we can keep the motorized spindle of industrial robot on the normal vector of curved surface,combined with the characteristics of flexible movement and great freedom of the industrial robots.This method does not need to establish tool radius compensation for the model.The surface points generated by the NURBS algorithm can be directly used as the interpolation points of the robot.However,in the study,it was found that this method has a high requirement for the processing environment.In addition,if the surface undulations are large,the tool will interfere the work-piece.In order to solve this problem,a new fixed posture milling method is put forward.Set the posture of the cutter shaft before the processing begins.In this case,the tool radius compensation should to be added so that the knife edge is tangent to the point on the NURBS surface to avoid over cutting.Finally,the generated program is imported into the robot control cabinet for actual machining.Due to the lack of rigidity of the robot,nylon PA66 and pine were used as the blank materials.Comparing and analyzing the surfaces processed via different methods,the error can be kept within 0.2mm,which verifies the accuracy and feasibility of the algorithm in this experiment.To some extent,it promotes the development of milling technology of industrial robot.