Output feedback control of uncertain Euler–Lagrange systems by internal model

In this paper, we investigate the trajectory tracking control problem of a class of uncertain Euler–Lagrange systems subject to disturbances. In sharp contrast to existing approaches where the position, the velocity, and the acceleration of the reference trajectory are assumed to be measurable, we propose a class of dynamic output feedback control laws which depends on the tracking error of the position and that of the velocity. Specifically, by characterizing the reference trajectory and the disturbances with an exosystem, we design an internal model to learn the desired feedforward input such that the reference trajectory can be tracked in spite of unknown system parameters and disturbances. The effectiveness of the proposed approach is illustrated by its application to trajectory tracking control of a three-link cylindrical robot arm.