| With the development of Chinese 2025 manufacturing plan,high grade CNC machine tools ushered in a golden development opportunity,but also facing great challenges.Friction is one of the main factors that affect the machining precision in high precision NC servo system,especially at low speed,the increase of contour error due to its nonlinearity is an urgent problem to be solved at present,but also the current research focus in Engineering.In this paper,the influence of various parameters on friction is studied by numerical calculation,building the friction force model of servo feed system,and analysing the relationship between load variation and friction and verified when preload is existing.Finally,based on the analysis of the influence of friction on the motion performance of the servo feed system,the feedforward control compensation based on the friction model is studied,and have achieved effective results.The friction coefficient of rough surface under lubrication condition was calculated by numerical simulation,and the influence of the main parameters on the friction curve was analyzed,such as pressure and surface roughness.When two rough surfaces are moving at a certain speed,the contact friction was calculated from the shear force generated by the rough peak contact deformation,the non-Newtonian rheological model was used to calculate the fluid friction force formed by the shear force in the oil film.Using the central oil film thickness formed in the movement process to judge the lubrication stage,two kinds of friction force in the total friction account for different proportions in different lubrication stage.In this way,the relationship between friction coefficient and velocity is obtained by numerical calculation.Based on the numerical calculation,the changing trend of the friction curves under different conditions of pressure and surface roughness are analyzed.CNC machine tools usually need to process different quality of the workpiece,but in order to ensure the system stiffness,ball linear guide and ball screw will be applied to preload,this causing friction is not a linear relationship with quality.In this paper,the ball carried out a specific force analysis from a theoretical point of view,to calculate the relationship between force and friction.After the servo feed system friction signal filtering processing,carry out static and dynamic parameter identification of LuGre friction model then through the experiment to verify the theoretical relationship.Then the mathematical model of servo feed system is established,and the effect of friction on the performance of the feed system is simulated and analyzed in Simulink,designing speed feedforward controller to reduce the position error caused by the system lag.On the basis of this,the friction compensation feedforward controller is designed and the order of the controller is reduced.The friction compensation method is based on the friction model of feedforward controller,the control precision of the servo system is improved effectively. |
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