Analysis Of Dynamic And Static Errors In Robot Milling System Of Aluminum Alloy Body Weld

The high-speed train body is welded by large aluminum alloy,and a large number of long straight welds are formed on the surface of the train body.When the robot is used to mill welds on the car body,the weak rigidity of the robot and the action of milling load lead to the end of the milling cutter deviating from the predetermined trajectory,resulting in the reduction of milling accuracy and the damage of the surface quality of the car body.Therefore,in order to solve the problem of low precision of automatic milling by weld robot,this paper starts with the analysis of the source of milling system error,and the milling error is divided into static error and dynamic error.The static stiffness model and rigid-flexible coupling dynamic simulation model of the milling system are established,and the influence degree of different milling factors on the end error of the milling cutter is analyzed based on the model.The main research contents of this paper are as follows:(1)Based on the requirements of welding seam milling for aluminum alloy car body,a welding seam milling system model with KR210 robot as the main body was established.In order to describe the relationship between the end position of the milling cutter and the joint motion of the robot,the kinematics model of the milling system was established by D-H method,and the forward kinematics and inverse kinematics of the model were deduced and calculated.Robotics Toolbox was used for simulation tests.The calculated values of the forward and inverse kinematics theories were consistent with the simulation results,which verified the correctness of the kinematics model and the correct derivation of the inverse kinematics.(2)Based on the kinematic model of the milling system,the static stiffness model is established according to the principle of static Jacobi and virtual work,which takes into account the flexible deformation of the robot joint and the gravity of the connecting rod.According to the model,the influence of milling equipment gravity on milling error is analyzed.On this basis,different degrees of milling force are added to the end of the milling cutter according to milling conditions to obtain the end positioning error of the milling cutter.Milling depth has the greatest influence on the error deformation,and spindle speed has the least influence on the error.When the spindle speed is 4000 r/min,the feed rate per tooth is0.06 z /mm,and the milling depth is 2.5mm.The error is small when the milling width is 7.0mm.Then,the milling deformation under four milling positions of the same weld is compared and analyzed.The error of link 2 is the smallest when the arm span is small,and the milling error can be reduced by the position and posture optimization in actual machining.(3)In order to further obtain the characteristics of dynamic error variation in the milling process,the dynamic simulation analysis of the weld milling system was carried out.Based on the stiffness simulation model,a simulation model of joint flexity-link rigidity milling system was established,and the weld milling trajectory was planned.The stiffness coefficient was applied to the model joint,and the maximum joint Angle deformation under no-load condition was-0.0039°,-0.0332°,-0.0205°,and the maximum error deformation in each direction of the end of the milling cutter was 0.1996 mm,0.1261 mm,-1.3626 mm.The results show that the maximum error caused by gravity is more than 1mm in no-load state,and gravity compensation should be carried out before weld machining.On this basis,four groups of milling forces are applied to the end of the milling cutter,and the joint torque curve is obtained.The milling force has little effect on the dynamic characteristics of joint 1,while joint 2 and 3 the torque increases greatly with the increase of milling force.According to milling conditions,four groups of different feed speeds were used to simulate the same weld.When the feed speed was 1.98 m /min,the milling cutter end wobble was obvious and the milling error was large.When the feed speed was 0.96 m /min,the displacement error was more than doubled and the error amplitude tended to be stable.