Analysis and compensation of nonlinear friction effect on frequency identification

This paper considers the issue of nonlinear friction effect on frequency identification. Without loss of generality, a mass-spring-damping system with nonlinear Coulomb friction is adopted to examine the mechanism of this nonlinear distortion. Based on the describing function (DF) analysis method, the gain reduction and phase lead-lag phenomena seen in actual frequency identification are examined in detail, which leads to a new understanding of the nonlinear friction effect. Built-upon the analysis results, a new identification method with nonlinear friction compensation is also proposed. Theoretical analysis shows that this novel identification method has two freedoms to guarantee a good identification result in practice, which makes it possible to obtain an accurate frequency response of the linear dynamics. In addition, this method is less sensitive to the limitations of amplifier and the stroke and the type of excitation signals. Both the simulation and experiment results verify the effectiveness of the proposed DF based analysis and the new identification method.