Study On The Calibration Technology And Stiffness Optimization For Robot Milling

In recent years,industrial robots are widely used in the field of machining because of the advantages of large workspace?high flexibility and low cost.But the overall low stiffness caused by the robot structure of serial links will easily contribute to deformations of the robot end-effector in the process of milling and it will affect the quality of machining.Based on the knowledge of the relation between the robot stiffness and the robot posture,the thesis optimizes the milling path according to the robot stiffness performance index.It enhances the robot overall stiffness along the milling trajectory so as to improve the milling quality.Firstly,the forward and inverse kinematics of the robot ABB IRB 6660-205/1.9 are derived respectively by the modified D-H method and the Pieper rule.Then the inverse kinematics model is testified by the ABB simulation software RobotStudio.The Jacobian matrix is derived by the vector product method and testified according to the Matlab GUI interface programming and Robotics Toolbox.A hand-eye calibration model of the robot base frame is established.This thesis improves the classical Differential Evolution algorithm to select optimal robot poses after analyzing the applicability of the algorithm.Comparing calibration results of random robot poses and optimal robot poses,the latter can increase the accuracy of the calibration obviously.And the base frame tracking is realized based on the point set matching through the unit quaternion method.After investigating the flexibility area of the robot and the distinction between two static stiffness models,a robot joints stiffness identification model and a joint deformation compensation model are derived.Robot joints stiffness values are testified through experiments.The joint deformation compensation experiment based on the joint stiffness shows that position deformations of the robot end-effector can be reduced by 50% after the compensation manipulation.Finally,this thesis analyzes CLSF cutter location files generated by NX10.0 and the transformation between CLSF files and the ABB program language RAPID.Then,considering the min value of eigenvalues of stiffness ellipsoid located at the robot end-effector as the stiffness performance index,a posture optimization algorithm is proposed based on this index.The effectiveness of the algorithm is proved through a five axis cutter path simulation and the milling experiment of a U-shape slot on a workpiece.