  In this paper, we consider the tracking control problem for robot
manipulators which are affected by constant bounded disturbances. Three control
schemes are applied for the problem, which composed of integral action and
tracking controllers. The goal is improving the accuracy of tracking procedure
for a robot manipulator to track a specified reference signal in the presence
of constant bounded disturbances. Inverse dynamics controller, improved
Lyapunov-based controller with integral action and discontinuous Lyapunov-based
controller are three schemes that are evaluated in this paper. Third one is a
novel controller that achieves trajectory following without requiring exact
knowledge of the nonlinear dynamics. Based on the disturbance rejection scheme,
tracking controllers are constructed which are asymptotically stabilizing in
the sense of Lyapunov. Furthermore the closed loop system has strong
disturbance rejection property. It is shown that how under proper assumptions,
the proposed schemes succeed in achieving disturbance rejection at the input of
a nonlinear system. Computer simulation results given for a two degree of
freedom manipulator with a large payload and fast maneuver, demonstrate that
accurate trajectory tracking can be achieved by using the proposed controllers.
