Estimation of unknown sinusoidal disturbances using two-step nonlinear observer

A disturbance estimation approach is presented for a class of multiple-input-multiple-output (MIMO) nonlinear robotic systems subject to sinusoidal disturbances with unknown frequencies. Different from most present works that adopt adaptive technique to identify the unknown parameters of disturbances, a new methodology is provided to estimate the unknown sinusoidal disturbances via construction of a generalized two-step disturbance observer. Simulations on a two-link robotic manipulator demonstrate the advantages of the proposed scheme.