Study On Friction Modeling And Dynamic Characteristics Of Slide Guide System

Friction exists in almost all mechanical systems, and often affects the performance of a system seriously, especially when the system in the states of starting,ending and velocity reversal. That is because friction shows strong nonlinear characteristics when relative velocity is slow. Sometimes the existence of friction can lead the motion of a system into chaos. Therefore the research on dynamics of mechanical system with friction is becoming a hot issue in the current times.Friction contact is extremely complicated from the microscopic view, and in the field of mechanical system, the study on friction is often from the view point of macroscopic to explain and predict friction phenomena and behaviors. On the basis of experimental studies and analyses for friction dynamic characteristics, a new dynamical friction model structure is proposed. The procedures of friction signal processing and parameter identification are also presented. In addition, the dynamic characteristics of systems with friction are studied using numerical techniques.First, the domestic and oversea research actualities of friction dynamic characteristics have been summaried, the manifestations and formings of these friction phenomena are discussed. Based on these, various friction models are introduced, and the advantages and disadvantages of them are expounded. The methods for friction signal processing are mentioned in brief, and the work on the dynamical characters of systems with friction is introduced.The setups and schemes for experimental study are designed according to the characters of friction contact between slide guide and rail along lateral and vertical directions. Experimental results are processed and analyzed. Through comparisons and analyzing of a large amount of cases, the dynamic friction characteristics between slide guide and rail, including the variation tendency of friction with the parameters just like relative displacement,relative velocity,relative acceleration,contact area,lubrication condition and slide guide type, are discussed. This part lays the foundation for furthering study.Due to the limitations of methods and instruments for friction measurement, the measured friction signal often contains noise and other force components, such as elastic forces. And because friction model becomes more and more complicated, parameter identification result often shows high sensitivity to noise contamination, and some methods even fails. How to extract the real friction signal from measured one is important to identification work. However, the traditional Fourier methods are not suitable to deal with nonlinear signal processing. The combination of median filter and empirical decomposition (EMD) method is used to analyze and process the measured friction signal. The processing results are compared with the results from Fourier-based methods (lowpass filter, band block filter and wavelet decomposition method) in the time history,Fourier spectral space and Hilbert spectral space. The comparisons show that the EMD method has superiority in processing measured friction signal.On the basis of experimental study, and through introducing the normalized Bouc-Wen model, a new dynamical friction model structure is proposed. This model has the capability to describe nearly all the nonlinear friction dynamic characteristics in presliding,sliding and their transition state. A new nonreversible friction model is presented for sliding regime to describe friction memory effect. Parameter identification procedures for both models are given. Identified friction models are used to predict friction courses, and results are compared with measured ones in the coordinates of friction vs. time,friction vs. relative displacement and friction vs. relative velocity. The effectiveness and accuracy of the proposed models can be shown from these comparisons.A two-dimensional model for the vibration of a slide guide system subjected to lateral displacement excitation is proposed. The coupling between lateral and vertical vibration due to the existence of friction is considered sufficiently in this model. Simulation results with this two-dimensional model show full sliding motion and stick-slip motion which may appear with some proper parameters. The variation tendencies of the vibration amplitude in lateral direction with the parameters in the model are simulated. Results derived from the two-dimensional model are compared with a one-dimensional model which does not included the vibration in sliding direction. The comparisons indicate the lateral response calculated from the abbreviative one-dimensional model is larger than the result from the two-dimensional model.An elevator cabin-guide-rail coupled lateral vibration model is developed to research the dynamical characters of slide guide system in an elevator. The mass of slide guide, the nonlinear factors such as the gap and friction between slide guide and rail, in addition to the load condition (balanced or unbalanced) are all included in this model. The comparisons of simulation results from Matlab/Simulink program with the experimental results illustrate the effectiveness of this model. The exploration provided an important theoretical foundation for the optimal design of slide guide and the determination of the gap between guide and rail in assembling. In the mean time, it can be helpful in the prediction and control of elevator vibration and noise.The results of this thesis may be worthily used to understand and develop the theories about friction experimental study, dynamic friction characteristics, friction signal processing, modeling and parameter identification, and dynamical characters of systems with friction.