Design Principles and Optimization of a Planar Underactuated Hand for Caging Grasps

Abstract

In this paper we address the problem of creating planar caging grasps on objects using simple, underactuated grippers with no sensing or control. Specifically, we examine how changes in mechanical compliance, passive adaptability due to underactuation, and finger phalanx length affect the ability to create caging grasps passively, by altering the free-swing motion of the fingers. We present a simple model for simulating the underactuated hand, develop a metric for quantifying a hand design’s caging ability, and perform a design parameter space search to reveal the important design factors influencing passive caging behavior. The results show that both palm width and the interplay between joint spring stiffness and pulley radius ratios play the largest roles in determining caging behavior. The effect of varying design parameters on the caging grasp performance of the hand is discussed, the best resulting design is shown, and a list of principles to guide the design of simple underactuated hands for caging grasps is presented.