| Industrial robots have the advantages of high degree of automation,high safety performance,ability to adapt to harsh operating conditions,small batch customized production,and low prices,which become one of the key development areas of China smart manufacturing industry.However,due to the multi-link series structure of the industrial robot,its rigidity is weak,and it is easy to cause chatter during milling,which seriously affects the processing efficiency and stability.In this paper,based on the research of domestic and foreign scholars,The robot milling process are simulated dynamically by MATLAB/Simulink combined with milling force and industrial robot dynamics model,the vibration characteristics of the industrial robot under different configurations are analyzed,the milling stability prediction drawn with the change of of configurations,and on this basis,an industrial robot configurations optimization strategy is proposed to improve machining stability.Firstly,this paper uses the modified D-H method to establish the kinematics model of the KUKA KR60-3 industrial robot,derives the analytical formula of the Jacobian matrix,introduces the forward and inverse kinematics solution method;the instantaneous milling force model is established,and the prediction model of the milling force coefficient was verified by orthogonal experiments.The traditional static stiffness model of the industrial robot was deduced.The relationship between the external load and deformation of the end of the industrial robot was obtained through loading experiments and the joint stiffness value was identified by the least square method.Then,the Lagrange method was used to derive the differential equation of industrial robot motion,and the milling dynamics model of the industrial robot was established considering the effects of instantaneous milling force and joint damping.A closed-loop dynamic solution program for the milling process was written based on the MATLAB/Simulink platform.In the same cutting path,simulation experiments were carried out under constant milling processing parameters for four different processing configurations of industrial robots.The tool tip vibration trajectory,robot joint trajectory and milling force were obtained when the end mill was fed in the positive direction of the X axis.Experiments results show that the milling posture of industrial robots has a significant effect on milling vibration.Finally,according to the vibration equation of the multi-degree-of-freedom system,the natural frequencies of the four different robot machining configurations are calculated.The vibration characteristics of robot milling are analyzed combined with the experimental data in the literature.Considering the influence of the end posture of the industrial robot on the machining chatter,the prediction formula of the limit cutting depth is derived using the zero-order approximation(ZOA)method.The relationship between the milling posture and the limit cutting depth were drawn,and the stable area of the milling process is predicted.Subsequently,under the same milling processing parameters,7075 aluminum alloy specimens were subjected to milling processing experiments with two different processing configurations of A and B to verify the correctness of the extreme cut depth prediction map.Based on this,the paper finally puts forward the optimization strategy of industrial robot milling posture: taking the processing stability as the optimization goal,the genetic algorithm is used to optimize the terminal gamma angle on the segmented processing path,and a cubic polynomial is used to smoothly interpolate the obtained joint trajectory.Experimental results show that the optimization strategy in this paper can improve the stability of industrial robot milling to a certain extent. |
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