Based on the influence of nonlinear factors on the low-speed performance of opto-electronic tracking servo systems,the system design was divided into two parts.All disturbance was equivalent to an equivalent input disturbance(EID) existed on the control input channel.A sliding mode disturbance observer(SDOB) was put up to observe the system state for the nominal mode.By using the state observe error to estimate EID and derived the stable convergence conditions of this observer by Lyapunov function.By design...