Research On Micro-Hydrodynamic Lubrication And Dynamic Characteristics Of Contact Pairs In Rolling Linear Guide

Rolling linear guide is a key functional component of CNC machine tools,industrial robots and other equipments,and the contact characteristics will directly affect the performance of the machine.The modern high-end intelligent equipments usually require rolling linear guide working in high-speed,heavy load and other conditions with the high motion accuracy and reliability,so the lubrication of the contact pairs obviously plays an important role.The traditional mechanics design method based on the Hertz contact theory can not satisfy the actual functional demands of the rolling linear guide.Currently,there are few systematic studies on the lubrication of the contact pairs in the rolling linear guide.In fact,the rolling linear guide usually involves three kinds of contact problems of the point,line and surface contact pairs.Affected by the different working parameters and contact forms,the lubrication conditions are different,and the film lubrication characteristics are also correspondingly different.Therefore,considering the actual working conditions of the rolling linear guide in the dissertation,the film lubrication and dynamic characteristics of three kinds of contact pairs are studied from the lubrication mechanism,to provide the theoretical reference for the dynamic optimization design of the rolling linear guide.In detai,this study work chiefly includes:The model of the line contact elastohydrodynamic lubrication(EHL)of the roller linear guide is built,and the line contact micro-EHL problems are analyzed based on a fractal method.The full numerical simulations are performed by using the multi-grid method,and the effects of the working parameters and surface topography parameters on the film lubrication characteristics are predicted in the roller-raceway line contact pair.The results reveal that the working conditions of the low speed,heavy load or low viscosity of the lubricant oil can reduce lubrication characteristics of the roller linear guide.The rough surface topographies can yield the random fluctuations in the pressure and film thickness,and the fluctuations become more dramatic with the increasing surface roughness.The film lubrication characteristics of the point contact pair in the ball linear guide are studied based on the point contact EHL theory.In order to predict effects of the surface roughness,a fractal-based method is introduced to characterize the 3D surface topography of the isotropic material.The pressure and film thickness distributions under the isothermal condition are numerically solved by using the multi-grid method and multilevel multi-integration method.The effects of the load,velocity,ambient viscosity of the lubricant oil and fractal roughness on the film characteristics of the steel ball-raceway contact pair are investigated.Based on the fractal method,the squeeze film damping model of the surface contact pair between the damper and rail is established with consideration of the surface topography effects.The test of the damping performance on the rolling linear guide system is carried out.The mathematical model of the film damping produced by the squeeze movement between the damper and rail is derived based on the two-variable Weierstrass-Mandelbrot function and the stochastical Reynolds equation,and the effect analyses of the relevant parameters are performed.The results show that the rough surfaces have an adverse effect on the film damping,and the relationships of the film damping coefficient,the surface roughness and the film thickness are deeply discussed.The film damping coefficient can increase significantly with the decreasing film thickness or the increasing damper length.Furthermore,the structural modal tests show that the squeeze film damping effect of the surface contact pair can improve significantly the anti-vibration performance of the rolling linear guide system.The dynamic characteristics of the point and line contact pairs are studied for the rolling linear guide under the EHL condition.The free vibration models of the steel ball-raceway contact pair and the roller-raceway contact pair are established,respectively.The effects of the vibrations on the pressure and film thickness distributions of the lubrication contact region are analyzed.Based on the EHL theory,the film stiffness and damping models of the point and line contact pairs in the rolling linear guide are built,respectively.The effects of the different working conditions on the dynamic characteristics of the contact pairs are predicted,and the results show that the conditions of the low speed and heavy load can increase the film stiffness of the contact pairs,but reduce the film damping.The stiffness model of the roller linear guide is built and the stiffness test is also performed.The test results show the validity of the theoretical model.