Nonlinear Extended State Observer Based on Output Feedback Control for a Manipulator With Time-Varying Output Constraints and External Disturbance

This paper presents an adaptive output feedback control for a manipulator under the presence of the time-varying output constraint and uncertainties. The proposed control is formulated based on a nonlinear extended state observer and a barrier Lyapunov function. The nonlinear extended state observer is developed to estimate the unmeasured states and the lumped uncertainties. Because the observer term in the nonlinear observer includes a linear term and a fractional-order term, its performance is enhanced significantly. Additionally, the barrier Lyapunov function is applied to guarantee the time-varying output constraint, which changes with respect to the desired trajectory in time. The asymptotic stability and output constraint satisfaction are theoretically demonstrated by using the Lyapunov theory. Finally, some simulations are conducted on a 3-DOF manipulator to verify the effectiveness of the proposed control.