On the use of velocity feedback in hybrid force/velocity control of industrial manipulators

This paper deals with the implementation of a hybrid force/velocity control for contour tracking tasks of unknown objects performed by industrial robot manipulators. In particular, we address the problem of the configuration dependent dynamics of the manipulator in constrained motion and we propose a method, based on inertial and stiffness ellipses, that allows to predict the presence of the consequent force oscillations. We also show that these oscillations can be highly reduced by employing an additional normal velocity feedback loop. A large number of experimental results obtained with a two degrees-of-freedom SCARA robot are shown.