Robust Control of Robot Manipulators in Cartesian Space

In this paper, we consider the problem of designing a robust control scheme that will enable the end-effector of a robot manipulator to track a specified trajectory in Cartesian space. The control system is robust in the sense that the trajectory is tracked in the presence of uncertainties such as payload variations and joint friction. The robust control scheme uses linearized models of the manipulator about a prescribed, nominal Cartesian space trajectory. The models are obtained recursively, using purely numerical techniques. It is not necessary to specify the complete trajectory in advance: only a few look-ahead points are required at any given instant. The effect of payload variations is modeled as a disturbance vector. The robust control scheme is applied to the first three links of a Stanford manipulator. Simulation results show that the prescribed trajectory is tracked asymptotically in the presence of various disturbances.