Robust reduced-order observer-based controller design for robotic systems with persistent bounded disturbances

In the study, a robust nonlinear L_∞-gain output feedback tracking control design for robotic systems is proposed under persistent bounded disturbances. The design objective is to find a reduced-order observer-based controller such that the peak of the tracking error in time domain must be as small as possible under persistent bounded disturbances. Since the nonlinear L_∞-gain optimal tracking control for robotic systems can not be solved directly, the nonlinear L_∞-gain optimal tracking problem is transformed into a nonlinear L_∞-gain tracking problem by giving a desired (prescribed) disturbance attenuation level for the L_∞-gain tracking performance. The proposed robust L_∞-gain controller is based on a reduced-order observer, which is constructed to estimate the velocity signal only and whose dimension is half of the dimension of robotic systems, and is suitable for practical control design of robotic systems.