A metric to design spring stiffness of underactuated fingers for stable grasp

The underactuated hand has the advantage of adaptation for grasping irregularly shaped objects by combining the active actuators with passive springs to achieving a stable grasp. The design of the spring parameter will affect the region of the stable grasp. This paper presents a metric to design the spring stiffness to keep the tradeoff between the adaption of objects and ability of stable grasp. Firstly, the relationship between the spring stiffness and stable region is qualified and visualized according to grasp state plane together with the spring stiffness's delimiter between regimes. Then, a quantitative way by analytical equations and graphs is proposed to evaluate the grasp stabilization with respect to spring stiffness. Finally, applications of designing the optimal spring stiffness by giving the particular conditions are presented to validate the efficiency of the proposed method. (C) 2018 Elsevier B.V. All rights reserved.