Evaluation of finger configuration for partial caging

In caging, an object is geometrically confined by position-controlled robots and never escapes from the constraint. Caging has some advantages over conventional grasping, and its applications have been performed not only in 2D but also in 3D scenes with various actual robots. However, the conditions of complete caging are not always satisfied due to limited robot configuration. This paper studies partial caging, in which an object is incompletely confined by robots or obstacles and is able to escape from the constraint. As an example of partial caging, a circular object moving in the planar hand is considered. We investigate an effect of arrangement of its fingertips, which prevents the object from escaping outside through the gap between the fingertips. Some simulation results show differences of difficulty of escaping for the object according to width of the gap and angle of the fingers. In addition, ease of entering the hand through the gap of the fingers is also evaluated. From these two scores on partial caging, we define an ability index for the hand, which represents the hand can easily capture an object and confine it without any finger motion.