Research On The Calibration Method Of Absolute Positioning Error Parameters Of 6-DOF Industrial Robots

The 6-DOF industrial robots are widely used in assembly,welding,spraying and other fields.The errors in the production,manufacturing and assembly of industrial robots lead to the low absolute positioning accuracy,which is one of the main obstacles to the large-scale application of robots.Therefore,it is necessary to compensate the errors of industrial robots.Starting from the factors affecting the absolute positioning accuracy of robots,this paper proposes to carry out research on the error compensation of industrial robots and study the calibration scheme and implementation of error parameters of 6-DOF industrial robots.The main research contents include:(1)Calibration methods of joint deceleration ratio and coupling ratio were studied.The causes of error of joint deceleration ratio and coupling ratio are analyzed,and the error measurement and calibration method based on laser tracker is proposed.And design the calibration experiment scheme of the speed saving ratio and coupling ratio.The comparison results of motion accuracy of the joint before and after calibration were obtained through experiments,and the influence of joint deceleration ratio and coupling ratio on the absolute positioning accuracy of the robot was analyzed.(2)Research on the identification method of MD-H parameter error.Firstly,according to the D-H parameter modeling method,the forward and inverse kinematics model of industrial robot is established.Secondly,in order to solve the singularity problem of D-H model generated in parallel axis,MD-H modeling method is adopted to model in parallel axis.Then,the mapping relationship between the terminal pose error and MD-H parameter error is established.Finally,the least square method is used to solve the overdetermined equations,and 25 MD-H parameter error values are identified.(3)Error compensation method for MD-H parameters.Aiming at the problem that only 10 error parameters can be directly compensated in robot kinematics and the compensation efficiency is low,a two-step error compensation scheme combining rough compensation and fine compensation is proposed.Coarse compensation of parameter error: 4important MD-H parameters of the robot were measured by axometric method and compensated into the robot kinematics model.Based on rough compensation of parameter error,three precise compensation methods for parameter error are proposed: 1.10 parameters that can be directly compensated are selected from the 25 identified error parameters(direct 10-parameter error compensation method).2.The 25 parameter errors identified are equivalent converted into 10 parameter errors that can be directly compensated,and then compensated(converted into a10-parameter error compensation method).3.Newton-Raphson algorithm was used to convert error parameters other than 10 parameter errors into joint Angle error parameters for compensation(Newton-Raphson parameter error compensation method).Eft ER6B-C60 industrial robot was used as the object to calibrate the error parameters of the above methods,and the compensation effects of different compensation methods were compared.The experimental results showed that the absolute positioning accuracy of the robot was increased by about 90%after coarse compensation of parameter error + fine compensation,and the average absolute positioning error of the robot’s end was guaranteed to be around 0.5mm.(4)The robot joint stiffness calibration: according to the robot joint stiffness matrix is deduced and the cartesian robot calculation formula of stiffness matrix,establishing the joint stiffness and descartes stiffness matrix transformation relations,so as to build a robot end force and displacement at the end of the mapping relationship,respectively,using the dynamometer and pulling end of the laser tracker measurement and displacement at the end;Then the least square method is used to identify the joint stiffness of the robot.Kawasaki RS007 L industrial robot was used for joint stiffness identification experiment to analyze the influence of joint stiffness on the robot end accuracy.