Multi Axis Machining Composite Constraint Modeling And Posture Trajectory Planning Based On Potential Field Algorithm

Multi-axis machining is an important process method in the field of complex parts manufacturing.It plays an important role in the manufacturing of aviation,aerospace,navigation and other equipment.Among them,the machining accuracy is comprehensively affected by geometry,kinematics,statics,dynamics and other factors of the machining system.Through the posture trajectory planning,on one hand,the cutting performance such as milling force and milling stability can be optimized in the tool posture space,on the other hand,the machining system performance such as motion smoothness,dynamic and static stiffness can be optimized in the joint axis space.Therefore,machining posture trajectory planning under composite constraints is an important way to improve the multi-axis machining accuracy.In the existing research,the posture trajectory planning algorithms with kinematics constraint are studied deeply,and the statics and dynamics constraints are studying.Therefore,combined with the specific working conditions,establishing an accurate composite constraint model and planning the machining posture trajectory under composite constraints is of great practical significance to improve the machining accuracy.The main contents are as follows:A potential field algorithm framework for machining system trajectory planning under composite constraints is proposed.The virtual potential field function is constructed to realize the transformation from the composite constraints of kinematics,geometry,dynamic and static mechanics of the machining system to the virtual repulsion torque.By giving the virtual modal parameters of the tool posture,the virtual dynamic model of machining posture is established,and the functional expression of virtual potential field torque and tool posture motion is realized.The algorithm for solving the virtual dynamic model is proposed,and the machining posture trajectory planning on the whole tool path under the action of virtual repulsion torque is realized.Through the potential field algorithm simulation of machining posture trajectory planning under geometric composite constraints,the feasibility of the algorithm framework under composite constraints is verified,and the calculation efficiency is 3～30 times higher than that of discrete algorithm.Considering the high-order continuity of posturetrajectory,a virtual potential field function and parameter optimization method under kinematic constraints is proposed.By analyzing the motion function relationship between the joint axis and the end effector of different machining systems,a virtual potential field function satisfying the motion C~3 continuity of the joint axis of the machining system is proposed.According to the constraints of velocity,acceleration and swing of end effector,the calculation formula of virtual parameter optimization is given.The above virtual potential field function optimization method is integrated into the virtual potential field method,and the corresponding posture trajectory is generated by simulation.Experiments show that the machining posture trajectory generated by the potential field algorithm has better motion jerk continuity than the discrete space algorithm.Considering the regenerative chatter,the composite constraint model under the milling condition of low feed per tooth in the machining of propeller scale parts is established,and the machining posture trajectory planning and application verification are carried out combined with the potential field method.It is found that the stability prediction accuracy of the low feed per tooth milling method used to reduce the tool deformation is greatly affected by the nonlinearity of the cutting force coefficient.The decoupling process of nonlinear dynamic cutting force is deduced,and a composite constraint model considering the stability of five axis milling of bull-nose cutter with nonlinear dynamic cutting force is established.The composite constraint model is combined with the potential field algorithm to simulate the machining posture trajectory of the machine tool.The simulation results show that the composite constraint model considering stability can realize the balance among constraints,and the comprehensive performance index is better.Through the actual machining of propeller scale parts,it is verified that the composite constraint model has higher milling accuracy than the single constraint model,and the milling error decreases by 50%.Considering forced vibration of the robot end,the composite constraint model of propeller robot milling is established,and the machining posture trajectory planning and application verification are carried out combined with the potential field method.It is found that in order to reduce the influence of forced vibration on surface accuracy,it is necessary to characterize the dynamic characteristics of the end.The calibration of joint relative frequency response function is realized by using self excitation operational mode analysis method.Combined with the forward and inverse kinematics and milling force model of the robot,a composite constraint model considering the robot end relative dynamic compliance index is established.Combining the composite constraint model with the potential field algorithm,the robot machining posture trajectory is simulated.The simulation results show that the composite constraint model considering the robot end relative dynamic compliance index can realize the balance among composite constraints,and the comprehensive performance index is better.Through the actual robot machining of propeller,it is verified that the composite constraint model has higher milling accuracy than the single constraint model,and there are none of vibration pattern on the surface.