Research On Kinematic Analysis And Calibration Experiments For UR5 Robot

As the representative of advanced mechatronics,six degrees of freedom(6-DOF)serial robots are widely used in industrial manufacturing.The robot accuracy,including absolute positioning accuracy and repetitive positioning accuracy,is one of the most important indexes to measure the performance of industrial robots.The repetitive positioning accuracy has already reached a higher level,generally in the order of 0.1mm,but the absolute positioning accuracy is difficult to meet the practical needs of industry.Therefore,how to improve the absolute positioning accuracy of robot plays an important role in robot calibration technology.In this paper,a UR5 serial industrial robot is taken as the research object.The robot calibration method is studied systematically from kinematics modeling,error analysis,parameter identification and compensation.The main research contents and conclusions are summarized as follows:1)According to the robots kinematics principle,an evaluation method for the accuracy is presented.Using DH modeling method to establish the kinematic model for UR5 robot,and the nominal geometry parameters are derived.The conversion formula of robot end-effector configuration is obtained,and verified by simulation.2)The errors affecting the robot accuracy are classified,and the influence degree of different parameters on the robot end-effector is studied.The transformation relation between the coordinates is deduced when the joint variables change slightly.On the basis of modifying the singularity of kinematics model,the error model of robot configuration is established.Simulation results show that on the premise of slight error,the robot error model can reflect the actual error correctly.3)Parameter redundancy of different joint in the robot error model is analyzed.In view of the robot configuration studied in this paper,the redundant parameters in the error model are removed.This proposed approach reduces the influence caused by unpredictable errors,and improves the robustness of parameter identification.The least square method is used to solve the error parameter values.In the case of considering external interference factors,the simulation results show that the identification result is basically the same as the expected errors after six iterations.4)The kinematic calibration experiment is conducted to test the methods proposed before.Using LEICA laser tracker as the external measurement system,this paper established the coordinates relation between laser tracker and robot base.By means of the optimized measurement point configuration,the parameter errors are identified and compensated to the nominal parameters.After error compensation,the position average error decreased from 1.78 mm to 0.19 mm,and the orientation average error was decreased from 0.83° to 0.13°.The experimental results indicate that the calibration method can effectively improve the robot absolute positioning accuracy.