Global stability of trajectory tracking of robot under PD control

It is shown that, even if there exist nonlinear unknown dynamics, a PD (proportional derivative) feedback control without higher-order nonlinear compensation can guarantee global stability for the trajectory following problem of a robot manipulator. The PD control under investigation is a position and velocity feedback control with a time-varying gain and does not contain any higher-order nonlinearity. Another novel and interesting result is that a measure of protection against saturation of actuators may be incorporated into the control design and robustness analysis