Anthropomorphic Robot hand

This paper presents an anthropomorphic robot hand called the Gifu hand II, which has a thumb and four fingers, all the
joints of which are driven by servomotors built into the fingers and the palm. The thumb has four joints with four-degrees-of-freedom (DOF); the other fingers have four joints with 3-DOF; and two axes of the joints near the palm cross orthogonally at one point, as is the case in the human hand. The Gifu hand II can be equipped with
six-axes force sensor at each fingertip and a developed distributed tactile sensor with 624 detecting points on its surface. The design concepts and the specifications of the Gifu hand II, the basic characteristics of the tactile sensor, and the pressure distributions at the time of object grasping are described and discussed herein. Our results demonstrate that the Gifu hand II has a high potential to perform dexterous object manipulations like the human hand.

INTRODUCTION

IT IS HIGHLY expected that forthcoming humanoid robots will execute various complicated tasks via communication with a human user. The humanoid robots will be equipped with anthropomorphic multifingered hands very much like the human hand. We call this a humanoid hand robot. Humanoid hand robots will eventually supplant human labor in the execution of intricate and dangerous tasks in areas such as manufacturing, space, the seabed, and so on. Further, the anthropomorphic hand will be provided as a prosthetic application for handicapped individuals.

Many multifingered robot hands (e.g., the Stanford-JPL hand by Salisbury et al. [1], the Utah/MIT hand by Jacobsen et al. [2], the JPL four-fingered hand by Jau [3], and the Anthrobot hand by Kyriakopoulos et al. [4]) have been developed. These robot hands are driven by actuators that are located in a place remote from the robot hand frame and connected by tendon cables. The elasticity of the tendon cable causes inaccurate joint angle control, and the long wiring of tendon cables may obstruct the robot motion when the hand is attached to the tip of the robot arm. Moreover, these hands have been problematic commercial products, particularly in terms of maintenance, due to their mechanical complexity.

To solve these problems, robot hands in which the actuators are built into the hand (e.g., the Belgrade/USC hand by Venkataraman et al. [5], the Omni hand by Rosheim [6], the NTU hand by Lin et al. [7], and the DLR's hand by Liu et al. [8]) have been developed. However, these hands present a problem in that their movement is unlike that of the human hand because the number of fingers and the number of joints in the fingers are insufficient. Recently, many reports on the use of the tactile sensor [9]-[13] have been presented, all of which attempted to realize adequate object manipulation involving contact with the finger and palm. The development of the hand, which combines a 6-axial force sensor attached at the fingertip and a distributed tactile sensor mounted on the hand surface, has been slight.

Our group developed the Gifu hand I [14], [15], a five-fingered hand driven by built-in servomotors. We investigated the hand's potential, basing the platform of the study on dexterous grasping and manipulation of objects. Because it had a nonnegligible backlash in the gear transmission, we redesigned the anthropomorphic robot hand based on the finite element analysis to reduce the backlash and enhance the output torque. We call this version the Gifu hand II