| Part damping and joint friction are the main energy dissipation sources in mechanical systems, which have an important role in the vibration and noise reduction. The accuracy of analysis will have a direct impact on the results of dynamic simulation and control of mechanical systems. For the parameter identification of part damping and joint friction in mechanical systems, a few of identification methods are studied in this thesis. The main research work is as follows:(1) Based on the time invariant parameter model method, the methods, i.e., the moving autoregressive model method, the moving exponent method and the moving Prony method, are put forward to compute the nonlinear damping. In these methods, the rectangle window theory for signal processing is adopted. According to many simulations and experiments, the empirical values of the rectangle window length are given, which assure these three methods to describe nonlinear damping better. The influences of the white noise on the identification accuracy of the methods are analyzed by means of simulation. Simulation results show that these three methods are all effective in the nonlinear damping identification of alloy.(2) According to the time varying parameter model identification theory, the time varying AR method and the time varying Prony method are presented to compute nonlinear damping based on the autoregressive model method and the Prony method. In the two methods presented, damping is considered as a time varying parameter. The effects of different kinds of basis functions on the identification of nonlinear damping are discussed. The selection standard of the basis functions is given.(3) The time frequency analysis theory is first introduced into the nonlinear damping identification. The piecewise-linearized wavelet transform method and the piecewise-linearized short time Fourier transform method are put forward to identify the nonlinear damping. From the simulation results, it is shown that the time frequency analysis theory can be used to the identification of nonlinear damping. The identification accuracy of the piecewise-linearized wavelet transform method is higher than that of the piecewise-linearized short time Fourier transform method.(4) The experimental devices for the nonlinear damping identification of damping alloy are developed. The damping characteristics of the damping alloy, Al-33Zn-6Si and Zn-27Al-lCu, are studied. The specimens with non-uniform stress field and quasi-uniform stress field are designed and manufactured respectively. The free response method and the sine sweep frequency method are used in the experiments. The relationship curves of loss factor versus strain and loss factor versus frequency are obtained by means of the nonlinear damping identification methods presented in the thesis. The damping characteristics in the quasi-uniform stress field are more reliable than that in non-uniform stress field. All of the above provide experimental supports for engineering application.(5) The moving rectangle window method is put forward by employing the moving rectangle window theory, which can identify nonlinear damping and Coulomb friction simultaneously from the free response signal. The satisfied results are obtained from the simulation of a SDOF system with nonlinear damping and Coulomb friction.(6) The Coulomb + viscous friction model is studied, the theory and arithmetic for the parameter identification of the Coulomb + viscous friction model are put forward from the time and frequency domain. Then the LuGre friction model is studied, and the static friction parameters of the model are identified by the variable scale method and the nonlinear least square method. In the identification of the dynamic parameters of the LuGre model, the relationship between the friction force and the presliding displacement is linearized to reduce the identification difficulty.(7) The SDOF rotary mechanical system and the X-Y table are designed and established for the parameter identification of the Coulomb + viscous friction model and the LuGre friction model. The friction parameters are estimated by analyzing the experimental data. The validity and feasibility of the friction parameter identification methods are verified by the good results. The experimental devices and results provide basis for related friction research.(8) The 2-DOF manipulator is studied in the thesis. The observer for the unmeasured internal state z is proposed for the friction compensation based on the LuGre friction model. The trajectory tracking of the end effector in the Cartesian coordinate is implemented by using the resolved acceleration control method. The simulation results indicate that the observer is correct. Through comparisons, the trajectory tracking results obtained by the compensation based on the LuGre friction model agree to the theoretical values better than that based on the Coulomb friction model.The research work is supported by the National Natural Science Foundation of China (50075068 and 50575180)... |
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