Grasp-based visual servoing for gripper-to-object positioning

The positioning of a gripper with respect to an object is one of the basic steps involved in the manipulation of that object. In particular, in a grasping task the fingers of the gripper should be placed at a set of selected grasp points belonging to the object. In this paper, a two-finger gripper and a stereo pair of cameras mounted in an eye-in-hand configuration are considered for this task. A visual servoing control system is proposed for the guidance of the positioning movement in which the grasp points are tracked in image space and used as input features for the control law. This tracking is based on the use of an invariant description of the grasp with respect to the object. The control law is restricted to control the degrees of freedom that produce movements that respect the invariance required by the grasp tracking.