Robotic Pinching by Means of a Pair of Soft Fingers with Sensory Feedback

This paper proposes a pair of single or multi D.O.F. robot fingers with soft and deformable tips that can pinch an object stably in a dynamic sense with the aid of realtime sensory feedback. To realize dynamic stable pinching, a practical method of using optical devices is proposed for measuring both the maximum displacement of finger-tip deformation and the relative angle between the object surface and each of finger links. It is shown theoretically and by computer simulation that the overall closed-loop system of a pair of two single-D.O.F. fingers with soft tips with real-time sensory feedback of the difference between centers of two area-contacts at both sides of the object becomes asymptotically stable. This means that the pair achieves dynamic stable grasping (pinching). In the case of a pair of 1 D.O.F. and 2 D.O.F. fingers with soft tips, it is shown that the proposed method of closed-loop feedback of the difference between centers of two area-contacts and the rotational angle of the object can establish not only dynamic stable grasping but also regulation of the posture of the object.