Research On Parameter Calibration Of Serial Manipulator Based On Tool Coordinate System

With the development of modern information technology and the transformation of manufacturing industry,the application of serial manipulators relies more on off-line programming technology for motion planning,which puts forward higher requirements for the absolute positioning accuracy of the robotic arm.Owing to the geometric parameter errors caused by factors such as machining,assembly,wear and creep,the absolute positioning accuracy of the robotic arm is low,which limits its application in the field of high-precision manufacturing.Kinematic parameter calibration is the most economical and effective approach to improve the absolute positioning accuracy of the robotic arm,and it also has an important impact on improving the accuracy of offline programming,which results in important theoretical significance and practical value for expanding the application field of the robotic arm.The subject relied on “Research on Accuracy Compensation Method for Reconfigurable Robots Based on Errors Measuring and Decoupling Between Assembled Modules”(Project ID: 51605004)in the support of the National Natural Science Fund Project of China,which aims on accuracy compensation of serial manipulators based on tool coordinate system.The main works are as follows:Firstly,the kinematic modeling and reference coordinate system selection of serial manipulator are studied.Aiming at the spiral axis represented in different coordinate systems,the kinematics model of the n degree of freedom serial manipulator is established by using the product of exponential(POE).The selection of reference coordinate system for serial manipulator error model is analyzed,and the influence of the error models established with different coordinate systems(the base coordinate system and the tool coordinate system)as the reference coordinate system on the calibration and identification accuracy of the serial manipulator is compared.Secondly,the related research on kinematic parameter calibration of serial manipulator based on the tool coordinate system is studied.To solve the problem that the error model contains the product of the orientation error and the position vector,which affects the accuracy of parameter calibration and recognition,when the pose error of robot end-effector is represented in the basic coordinate system.The tool coordinate system is selected as the reference coordinate system,an improved pose calibration model of the series manipulator with joint constraints is given based on POE.In addition,according to the different application requirements,the position calibration model is given.Compared with the existing error model based on POE,the improved model avoids the influence of the product term of attitude error and position vector on the accuracy of parameter calibration and identification.The correctness and effectiveness of the above error calibration model are verified by the calibration test of the serial manipulator.After that,the related research on minimum kinematic parameter calibration of serial manipulator is studied based on tool coordinate system.Aiming at the problem of redundant parameters in the traditional error model based on POE,the joint auxiliary coordinate system is introduced to simplify and unify the expression of joint twists.According to the geometric relationship between the "actual value" and "nominal value" of the joint twists in the joint auxiliary coordinate system,the independent kinematic parameters in the joint screw coordinates are extracted,and the initial pose error of the end effector is expressed in the actual tool coordinate system,so as to give the actual kinematics model of series manipulator with minimum parameters and better consistency in mathematical form.Taking the tool coordinate system as the reference coordinate system,the pose error calibration model of the serial manipulator is deduced.In addition,according to the different application requirements,the position calibration model is given.The correctness and effectiveness of the above calibration model are verified by the parameter calibration test of the serial manipulator.Finally,the research on kinematic parameter calibration of series manipulator considering joint variable error based on tool coordinate system is carried out.At present,the joint variable error caused by the manufacture,assembly and joint wear of the serial manipulator is large,and the absolute positioning accuracy of the serial manipulator is reduced due to the step-by-step amplification of the arm length.The tool coordinate system is selected as the reference coordinate system,and a pose error calibration model of the serial manipulator is established based on POE,which comprehensively considers the joint variable error and joint twist error.The correctness and effectiveness of the calibration model are verified by the calibration simulation test of a typical industrial manipulator.