| The development of industrial manufacturing is gradually changing from the large batch and singular characteristics to the small batch and customization.The arrival of intelligent manufacturing era also puts forward higher requirements for machinery manufacturing equipment.Industrial robot has a broad application prospect in industrial production,but the machining quality and precision in metal material processing,especially in milling processing still need to be improved.This study aims at improving the quality of robot milling,and optimizes the milling posture of robot from two aspects of robot kinematics and dynamics.The main research contents are as follows:(1)In order to accurately describe the robot's motion state,a homogeneous transformation matrix of its joint coordinate system is derived for the KUKA KR60 robot.Based on the accurate measurement of the joint position and size of the robot,the kinematic model of the robot was established by the D-H method.On this basis,the Jacobian matrix of robot kinematics is introduced to lay a foundation for the derivation of stiffness matrix.The kinematic simulation model of the robot is built with the help of MATLAB to simulate the exact motion position of the joints and ends of the robot,providing a reference for the error analysis of dynamic simulation.(2)In order to realize the joint stiffness identification of the robot,the joint transmission system of the robot is analyzed.,and the equivalent simplified model of joint stiffness is established,derived the Lagrangian dynamics equation of the robot considering joint flexibility,and using ADAMS to build dynamic model of the robot.A method of joint stiffness identification of robot based on modal measurement is proposed.By means of force hammer modal test,the natural frequency and modal mode of the robot are measured,and the joint stiffness identification of robot is completed by combining with ADAMS modal analysis and the influence of joint stiffness on the dynamic characteristics of the robot is analyzed.(3)In order to optimize the stiffness performance in robot processing,based on the stiffness ellipsoid theory,the advantages and disadvantages of the traditional direction radius and ellipsoid volume as stiffness indicators are analyzed;and aiming at the mapping relationship between the stress of the tool tip and the ellipsoid in the milling process,a two-stage optimization method of optimal posture based on the equilibrium stiffness was proposed.A comparative analysis between the proposed method and the traditional method in the established ADAMS model verifies the effectiveness of the method.(4)The simulation experiment of boss milling is designed.Then,the end displacement,velocity and acceleration of the tool operation are analyzed.The results show that this method can effectively improve the precision of the end operation,reduce the vibration of the robot,improve the dynamic performance of the robot,and reduce the geometric error of the workpiece.Finally,based on the requirements in robot motion control,UG-KUKA offline programming platform was established.The UG is used to realize the processing path planning,and C++ programming is used to read the path and determine the optimal posture of the robot,then the redundant sixth axis of the robot is removed and the motion control files of KRL(KUKA Robot Language)robot in format of “.dat” and “.src” are generated. |
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