Dynamic Modeling, Parameters Identification And Errors Compensation Of Ball Screw Feed Drive Systems

High speed and high precision have become a main development direction of numerically-controlled machine tools,which puts forward higher requirement on linear feed drive systems.With the continuous improvement of velocity,dynamic errors have become the primary bottleneck for the improvement of the accuracy of ball screw feed drive systems.In order to improve the dynamic accuracy of ball screw feed drive systems,researches of dynamic modeling,parameters identification and errors compensation are conducted from the following aspects:(1)Based on analysis of the force transmission at the joint part of the nut,the transmission characteristic of tangential torque is uncovered and a mathematic model for studying the relationship between the thrust and the torque is established.A kinematic compatibility equation is proposed based on analysis of the kinematic transmission of components.Axial deformation of preloaded double-nut is analyzed according to the Hertz contact theory.Then a lumped dynamic model of ball screw drive feed systems is built with the consideration of the tangential torque based on the above analysis.(2)In order to conduct experimental research on parameters identification,dynamic characteristic analysis,and errors compensation,a tested bench is built.Based on the requirement of stiffness identification of preloaded double-nuts,a preload-adjustable double-nut mechanism is designed,which can adjust and measure the preload in real time.According to the requirement of stiffness identification and friction identification,an axial loading system is constructed,which can apply an axial load on the feed drive system dynamically and continuously,and measure axial load in real time.(3)In order to improve the identification accuracy of axial stiffness of preloaded double-nuts,a model of axial stiffness is established with consideration of geometry errors of balls,ball screw grooves,and nut grooves.Experiment and simulation results show that accuracy of the proposed stiffness model is improved because of the introduction of geometry errors.In order to identify multi-stiffness of ball screw feed drive systems,an integral identification method and an experimental testing method are proposed.The stiffness identification accuracy and efficiency are improved by the methods.(4)The friction of critical components is modeled based on the Stribeck friction model.In order to identify parameters of friction models,an identification method is proposed based on the dynamic model.By conducting experimental analysis with different load and speed,and simulation analysis of the proposed dynamic model,friction parameters which are relative are identified entirely.Accuracy and efficiency of friction identification are improved.According to frequency characteristic analysis,the accuracy of the dynamic model and parameters identification method is verified.(5)The influence of structural parameters and motion parameters on dynamic errors is analyzed based on the proposed dynamic model and parameters identification method.The fluctuation principle of dynamic errors is analyzed according to the Fourier transform and short time Fourier transform.A method to predict dynamic errors and compensate them in real time is proposed.Compensation experiments of typical trajectories are conducted.The experimental results show that dynamic accuracy is improved greatly.Therefore,the effectiveness of the proposed dynamic model,parameters identification,and dynamic errors compensation method on the improvement of dynamic accuracy of the ball screw feed drive system is verified.The research work of this paper provides a theoretical basis and technical support for dynamic modeling,parameters identification and errors compensation of numericallycontrolled machine tools,and therefore promotes the popularization and industrialization of dynamic error compensation.