Prescribed performance motion control of nonlinear servo mechanisms with extended state observer

In this paper, a prescribed performance motion control method is proposed for a class of nonlinear servo mechanisms to guarantee the prescribed error bound. A prescribed performance function (PPF) is used to characterize the convergence rate and steady-state error, such that the motion tracking control error of the studied system can be retained within a priori prescribed bound. To address the effects of unknown dynamics and bounded disturbances, an extended state observer (ESO) is adopted to estimate the unknown system state vector and the lumped uncertainties in an integrated manner. The ESO can be easily designed based on the bandwidth of the control system. The stability of the proposed control system is analyzed via the Lyapunov theory. The effectiveness of ESO and the ESO-based prescribed performance controller are demonstrated through simulations.