| With the development of industrial manufacturing to intelligent manufacturing direction,industrial robot with its large workspace,high flexibility and low cost advantages are gradually applied in the field of milling processing,and is often used in the processing of complex parts,so the programming efficiency and machining traj ectory accuracy have higher requirements.However,at present,the robot programming methods mostly adopt the field teaching programming,which not only has low programming efficiency and traj ectory accuracy,but also can not be qualified for complex milling tasks.On the other hand,industrial robots are generally used in series structure,whose stiffness is far lower than the traditional CNC machine tools,low milling accuracy and poor machining stability,easy to lead to the occurrence of chatter.Therefore,this paper developed a robot milling offline programming simulation software to improve the programming efficiency and machining trajectory accuracy.At the same time,the redundancy existed in the 5-axis milling task of the six-axis industrial robot was optimized to improve the stability and accuracy of robot milling.The main research contents and related work of this paper are as follows:(1)Overall design of offline programming simulation software for robot milling.By analyzing the requirements of the software,three main functional modules were determined,including Python,Qt and OpenGL as the development platform,robot milling simulation module,machine joint motion planning module and off-line programming post-processing module,and the overall architecture of the software was designed.(2)Development of robot milling simulation module.OpenGL is used to build a threedimensional visual simulation environment to realize the loading of the robot connecting rod and other three-dimensional models.By modeling the forward kinematics of the robot,the forward kinematics simulation of the robot is realized in the simulation environment.The inverse kinematics of the robot was solved by the analytical method.On the basis of the kinematics algorithm,the simulation of the motion instructions commonly used in robot milling was realized by using the trajectory planning in joint space,the linear trajectory planning in Cartesian space,the circular are trajectory planning in Cartesian space and the pose interpolation algorithm.(3)Development of off-line programming post-processing module and experimental verification.In order to solve the problems of programming efficiency and machining trajectory precision of complex milling tasks,a method of converting 3-axis and 5-axis double swing head numerical control program into robot program was adopted.By defining the rules of conversion between the numerical control program and the robot program,the key instructions and pose data in the numerical control program are extracted and calculated by the program conversion algorithm,and then converted into the robot program.The feasibility and correctness of the conversion program are verified by robot milling simulation and actual machining experiments.(4)Redundancy optimization based on stiffness performance index.In order to improve the stability and precision of the six-axis industrial robot,the redundancy of a six-axis industrial robot in five-axis milling was optimized.Firstly,a dynamic model of robot milling system was established,and the relationship between redundancy and ultimate stable cutting depth was obtained by zero-order approximation method and frequency response experiment.The influence of redundancy on machining stability was verified by experiments.Then,based on the robot stiffness model,a global stiffness performance index with redundancy as a variable is proposed.Finally,with the objective of maximizing the global stiffness index,the optimization model was established under the condition of ensuring the machining stability,and the discrete optimization method was used to optimize the redundancy,and the effectiveness of the method was verified by experiments. |
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