Experimental Demonstration of the Grasp Admittance Center Concept

This paper demonstrates a new approach to achieving decoupled dynamic behavior in multifingered robotic hands. The approach is based on a new concept termed the Grasp Admittance Center. This concept is a generalized version of the Compliance Center concept, well known within the robotics literature for over a decade. The proposed admittance center concept provides a framework for simultaneously achieving four useful features in robotic grasps²: (i) decoupled³ force-motion relationship ¿ a relationship between a motion imposed on the object and the reaction force that the object exerts to resist the motion; (ii) decoupled time-response ¿ the motion response of the system to a force disturbance; and (iii) stability ¿ the ability of the grasp to be in equilibrium despite disturbances. (iv) the task of assigning grasp dynamic behavior becomes transparent. These four features play important roles in the functioning of robotic hands, particularly when engaged in constrained manipulation tasks. Achieving these features in robotic grasps requires that the grasp impedance parameters⁴ satisfy certain analytical conditions. These conditions are collectively referred to in this work as the admittance center concept. Of the four advantages, conceptualizing the decoupled time response is difficult while the remaining 3 advantages are easily comprehendable. In view of this, the present work describes experiments wherein a carefully built passive compliant device emulates the dynamic behavior of multifingered grasps.