| Friction presented in servo systems has become an impediment to improve their performance. To overcome this impediment, not only are stick-slip and chaos oscillation induced by friction analyzed, but also three friction compensation methods which is based on intelligent cybernetics are put forwarded in this thesis.The literature relevant to friction modeling, system analyzing and friction compensation methods are outlined. The shortcomings of these studies are presented and future trends in this field are also described.Two methods for analyzing stick-slip, which is presented in servo systems with friction, are put forwarded. One of these two methods is based on nonlinear transfer fi.inction; the other is a numerical method based on Newton-Raphson algorithm. The first method is an analytic method, by which the assumption that investigation of the first harmonic provides a reasonable approximation to the behavior to the true system is not necessary. It is also applicable for analyzing the high-order systems. So the shortcomings of describing function and phase plane analysis are overcome and the effectiveness and accuracy of the analysis is improved greatly. The other method can be used to analyze the system without any difficulty, which is raised by more and more complex models, this method also overcomes the shortcomings of brute-force approach, which is time consuming and difficult to tell when the steady sate has been achieved. Based on these methods, stick-slip presented in the servo systems governed by PD controller is analyzed systematically and the relationship between stick-slip and the parameters of these systems is revealed.Chaos presented in servo systems induced by friction is studied by the first time. The impact of system parameters on the dynamics of the system and the route to chaos are analyzed. So this study provides a basis for system designing and synthesis. A method to analyze the dynamics of piecewise continuous system is presented, based on it, the chaotic oscillation of a harmonically forced spring-mass system with friction is studied. The impact of friction and other parameters on the chaotic oscillation of this system is analyzed. So the following conclusion is to be come to: First, the friction model is of great importance for the analyzing the dynamics of the servo systems with friction; Second, under some circumstances, chaos might be appeared as system parameters, circumstances and lubrication condition changing.Three friction compensation methods based on intelligent cybernetics are put forwarded. One of these methods is based on self-tuned scaling factors fuzzy controller the others are based on CMAC. The controllers designed by all these methods have the ability of on-line auto tuning or self-learning, so the under-determined friction could be compensated. Not only do these three methods overcome the shortcomings of fixed compensation and the methods existed which is based on fuzzy logic and artificial neural networks, but also have the advantages of easy implementation, small computation load and robustness compared with traditional adaptive friction compensation methods: So these methods are applicable for engineering uses. Great effectiveness of these methods is demonstrated by a series of simulation.
|
PDF Full Text Request