| Friction nonlinearity is a complex and uncertain tribological phenomenon prevalent in engineering practice,and it has become a serious obstacle to improve the servo system performance and the quality of parts manufactured under extreme conditions.Powder particles with well lubrication performance and carrying capacity,as well as the good adaptability to extreme conditions,are widely used in many research areas.The powder particles are introduced into the fr ictional interface in this paper.With the use of UMT-2 friction and wear tester,and combined with a variety of observation and analysis techniques,the research on the friction nonlinearity of the powder lubrication interface is carried out deeply,and the friction compensation under powder lubrication is explored preliminarily.Firstly,a series of friction nonlinear comparison tests were carried out in this paper.The effects of different conditions on the friction nonlinearity were studied by changing lubrication methods(dry friction,oil lubrication and powder lubrication),the particle hardness and particle size under oil lubrication.The results show that oil lubrication and powder lubrication obviously weaken the friction nonlinear problem compared with dry friction.The friction nonlinearity will become more serious when there is larger particle size or harder particles in the friction interface under oil lubrication.Secondly,a series of friction nonlinearity tests under powder lubrication were carried out emphatically.By changing the parameters,such as the contact load,the speed,the powder layer thickness and the roughness of the original surface,and combined with the analysis of friction coefficient nonlinear fluctuation,typical microscopic morphology and the 3D morphological parameters of the boundary layer after test,the mechanism of friction nonlinearity in the powder lubrication interface was studied deeply.The conclusion are that the larger contact load,relative velocity and powder layer thickness are favorable to form a dense boundary layer,improve the lubrication performance and reduce the friction nonlinearity under certain conditions.However,the excessive load and speed will speed up the destruction of the powder layer,and the more thick powder layer is,the more brittle boundary layer is.The surface roughness is larger under the above conditions.So they result in poor lubrication and more serious friction nonlinearity.Moreover,a reasonable choice and use of powder lubricants can reduce the friction nonlinearity problem according to the actual application.Finally,the model of friction error compensation under powder lubrication was studied preliminarily.Based on the more common classical friction compensation model-Stribeck(exponential)model,and combined with the principle of least squares method,the parameters of the above model under powder lubrication are fitted.The Stribeck curve mechanism of powder lubrication is analyzed briefly.The parameters obtained by the fitting are introduced into the Lu Gre model at the same time.It can be seen from the Simulink simulation results that the larger velocity,stiffness coefficient and viscous damping coefficient have a significant effect on the nonlinearity of friction. |
