Directional Redundancy for Robot Control

The paper presents a new approach to design a control law that realizes a main task with a robotic system and simultaneously takes supplementary constraints into account. Classically, this is done by using the redundancy formalism. If the main task does not constrain all the motions of the robot, a secondary task can be achieved by using only the remaining degrees of freedom (DOF). We propose a new general method that frees up some of the DOF constrained by the main task in addition of the remaining DOF. The general idea is to enable the motions produced by the secondary control law that help the main task to be completed faster. The main advantage is to enhance the performance of the secondary task by enlarging the number of available DOF. In a formal framework, a projection operator is built which ensures that the secondary control law does not delay the completion of the main task. A control law can then be easily computed from the two tasks considered. Experiments that implement and validate this approach are presented. The visual servoing framework is used to position a six-DOF robot while simultaneously avoiding occlusions and joint limits.