Abstract: According to the complex nonlinear properties of hydraulic excavator arm’s servo system, a Hammerstein model which contains static nonlinearity and dynamic linearity was adopted to describe the system instead of linear model. The dynamic linear module was described by a discrete AutoRegressive eXogeneous (ARX) model, and the static nonlinearity module was described by a twosegment polynomial. The forgetting factor recursive least square method was applied to realize decomposition identification of the parameters for both linear and nonlinear module through multifrequency sinusoidal input and angle output signal. The comparison experiments between the identified Hammerstein model and ARX model indicated that the error of Hammerstein model was reduced by 77%, the results demonstrated that Hammerstein model meets the need for describing the servo system of excavator arm.

Key words: mechatronics engineering, electrohydraulic servo system, Hammerstein model, recursive
least square method, nonlinear identification