The role of thumb opposition in cyclic manipulation: A study with two different robotic hands

The ability to grasp and manipulate objects can be regarded as a distinctive feature of humans in the animal world. The human hand is studied for different purposes, such as the control of anthropomorphic robotic hands. One of the fundamental features of the human hand is the thumb opposition, not always considered as active degree of freedom in the design of robotic hands. The purpose of this study is to investigate the role of thumb opposition during cyclic manipulation tasks through the interaction with different objects and a bio-inspired control architecture based on reinforcement learning. The control architecture has been implemented in simulated environment on two robotic hands with different thumb features, i.e. the iCub hand and the DLR/HIT Hand II, interacting with objects of different sizes and shapes. Furthermore, a systematic analysis of the working areas of the two hands during the manipulation of a sphere located at different positions has been carried out. The achieved results show that thumb opposition, characterizing human hands, plays a key function in fine manipulation and allows increasing the hand working area.