The identification of parameters for servo system model

Aiming at the linear and nonlinear friction characteristics that servo control system present, this paper brings up a novel identification approach, which decouples the servo system into a combination of a linear component and a nonlinear component in identification process. The system is converted to a structure which is a linear model plus a nonlinear feedback model. In order to avoid the effects of nonlinear friction and obtain the accurate model of linear component, two-set non-zero-crossing velocity square waves are used to excite the system response characteristics. The respective differences of the input and output signals of these two-set square waves are utilized as the identification signals to estimate the parameters of the linear model. Based on the obtained linear model of the system, the steady-state velocity outputs are used to determine the magnitudes of Coulomb friction. The results of simulation have proved the reliability of the model and the identification method.