Research On The Influence Of Industrial Robot Joint Stiffness And Posture On Milling Process

Series industrial robots have the advantages of high flexibility,high degree of automation,low cost and so on.They have significant advantages in the manufacturing of large size and complex shape components,and are widely used in aerospace,shipbuilding industry and auto parts manufacturing.However,the low stiffness of this kind of industrial robot often affects its accuracy and dynamic performance,which leads to the problem of machining instability.In robot milling,due to the comprehensive function of insufficient robot stiffness and dynamic stiffness,milling force will cause robot end milling cutter is deviating from the desired trajectory,lead to the instantaneous cutting thickness changes in milling process,the industrial robot flutter problems,which not only seriously affected the surface machining quality of the material processed,but also decrease the service life of tool wear with robots.Based on the above problems,the main work of this paper is to identify the joint stiffness of the serial industrial robot,analyze the changes of the overall stiffness of the robot with different postures,and analyze and compare the influence of the robot’s milling postures on the milling force and surface machining quality.(1)First of all,this paper analyses the structure characteristics of industrial robots,and establish industrial robot kinematics model based on the modified D-H method.Then this paper uses the vector product method to derive the velocity jacobian matrix and the force jacobian matrix.Finally,this paper derives the mapping relationship between robot stiffness model and joint stiffness,and based on this robot static stiffness model is established.(2)Based on joint stiffness identification methods of the load and the deformation,this paper innovatively proposes a method of robot terminal deformation measurement based on 3D point cloud,and uses repeated collection error experiment,translation error experiment,and torsion error experiment to verify the reliability of the proposed method.compared with getting deformation of robot end by using laser tracker,this method possess high maneuverability and versatility and guarantee the accuracy at the same time.Six deformation values of the robot end can be obtained by one acquisition before and after loading,and there is no need for complex decoupling process.(3)The joint stiffness identification experiment was designed.Firstly,several groups of robot postures were selected,and stable loads were added to the robot ends.Then,force sensors and 3D scanners were used to obtain the load and deformation of the robot ends.Finally,the joint stiffness was identified.(4)Analyze the influence of milling posture on milling force and machining quality.Under the same milling parameters,6061 aluminum alloy was milling with four groups of different milling postures.The stiffness ellipsoid volume was taken as the overall stiffness evaluation,and the Angle between the maximum stiffness vector of force-linear stiffness ellipsoid and force-angular stiffness ellipsoid and the machining direction was calculated.The law of the maximum stiffness vector and the milling force and the surface machining quality were studied.