Control of redundant robots in presence of external forces

In this paper we study the influence of generalized external forces, which can act anywhere on the body of the manipulator, on the behavior of the manipulator. These forces are considered as disturbances which are not measurable. First we analyze how these forces act in the task space and in the null space, and define the equivalent generalized forces in both subspaces. Next we propose tracking controller and analyze the influence of external forces on tracking accuracy. We consider also the effects of different pseudoinverses on the behavior of the system. In the end some examples of control of a four DOF planar manipulator with revolute joints are given illustrating the influence of the external forces.