Modeling And Analysis Of Phase Characteristics Of Linear Feed System For NC Machine Tools

High speed,acceleration and precision are the main development direction of high-grade CNC machine tools.The feed system is the core component of the machine tool’s spatial movement.Compensating the dynamic error of the feed system in highspeed machining is the key to improve the machining accuracy of the machine tool.The vital problem for dynamic error compensation is that there is a time-varying and random response lag between the displacement signal from the feed system and the input signal from the control system,which is the phase difference between the output signal and the control signal.The existence of phase difference makes it impossible to compensate the error with high accuracy.This paper focuses on the phase characteristics of linear feed system.By establishing the phase characteristic simulation platform,the influence of the change of dynamic model parameters on the phase difference of linear feed system under different working conditions is analyzed.It provides a theoretical basis for realizing high-precision coupling between axes of CNC machine tools and reducing dynamic errors.In view of the hysteresis between the displacement signal and the controller signal of the feed system,a phase difference calculation model is established.In order to explore the change law of phase characteristics,the dynamic models of the two axis drive system and the single axis drive system of the machine tool are established respectively.However,the traditional dynamic model uses fixed dynamic parameters,which cannot reflect the time-varying dynamic characteristics,so the dynamic parameters of the feed system are identified.The change rules of the rigidity of the guide slide pair,the friction force of the feed system,the axial rigidity of the lead screw and the center of gravity of the worktable under different working conditions are emphatically explored.On the basis of the above theoretical analysis,the finite model of the worktable linear feed system is established.Dynamic characteristic analysis of worktable feeding system through finite element model.Then the finite element analysis results are compared with the dynamic characteristics analysis results of the dynamic model to verify the correctness of the dynamic modelBased on the results of dynamic model and model parameter identification,a threeaxis electromechanical coupling simulation platform for machining center is established.Then,the phase characteristics of single axis feed system under different working conditions can be analyzed.It is found that the axial stiffness of the lead screw,the friction force of the workbench and the shift of the gravity center of the workbench in the X direction have significant effects on the phase characteristics.Based on the above three factors,the response surface analysis shows that increasing the axial stiffness of the lead screw and reducing the friction force of the workbench can significantly improve the phase characteristics.At the same time,the phase difference of the three-axis feeding system is solved through simulation,and the phase difference of each axis is compensated by the control system to reduce the contour error of the two axes.Finally,the effectiveness of improving linkage accuracy through phase adjustment of feed system is verified.