Decoupled direct visual servoing

This article addresses the problem of direct vision-based robot control where the equilibrium state is defined via a reference image. Direct methods refer to intensity-based nonmetric techniques to perform that stabilization. Intensity-based strategies provide for higher accuracy, whereas not requiring any metric information improves their versatility. However, existing direct techniques either have a coupled error dynamics, or are designed for planar objects only. This paper proposes a new direct technique that decouples the translational motion from the rotational one for the general case of both planar and nonplanar targets under general translational and rotational displacements. Furthermore, for the important case of a fronto-parallel planar object, the proposed technique leads to a fully diagonal interaction matrix. The equilibrium state is made locally exponentially stable for all those cases. These improvements are theoretically proven and experimentally demonstrated using a 6-DoF robotic arm.