Towards a functional evaluation of manipulation performance in dexterous robotic hand design

Dexterous multifingered hands are the most complex and versatile variants of robotic end effectors. Compared to simpler grippers and underactuated hands, they should be more capable of grasping and, especially, manipulating different objects. This paper explores the relationship between kinematic design and manipulation performance of robotic hands. Some evaluation criteria frequently used by hand designers to verify kinematic configurations are revisited. The results from these criteria are scrutinized and compared with the evaluation of the manipulation workspace and the ranges of motion of inhand manipulation for a set of predefined objects. Simulations and actual manipulation experiments are carried out with different kinematic configurations on a modular dexterous hand. The results show some disconnection between perceived good designs through common evaluation criteria and their actual, realizable manipulation performance. This work finally gives some insight toward a more holistic approach to design hands that better address grasp and manipulation for the intended tasks and applications.

1. Introduction

The human hand is often regarded as the best end effector in existence; as a result, it is frequently viewed as the ultimate performance goal by some roboticists. However, its multiple capabilities, including gesturing, grasping, manipulation and exploration of objects, are still difficult to replicate in a single and compact tool for use in common robotic systems. In highly structured industrial environments most of the grasping and manipulation tasks can be efficiently solved using two or three-jaw grippers, or task oriented tools such as suction cups or electromagnetic grippers [1]. Multifingered hands are better suited for less structured environments, where a broader set of capabilities is required for handling multiple objects with different mass, shape and material, which would involve an assortment of grasping and manipulation tasks. Different configurations and actuation mechanisms have been developed over several decades of research, such as the Barrett Hand [2], Robonaut Hand [3], Gifu Hand III [4], DLR/HIT Hand II [5], Shadow Dexterous Hand [6], and Awiwi Hand [7]. Replicating the same kinematics and anatomical structure of the human, as in the ACT Hand [8], is a first step towards a better understanding of the human functionality, but still requires appropriate control and sensor systems to mimic human dexterous capabilities. Fig. 1.

A five-finger modular robotic hand commanded by a teleoperator with a data glove during a telemanipulation experiment [16]. The dexterous end-effector shows both grasping and in-hand manipulation capabilities.