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12 Human Inspired Dexterity in Robotic Manipulation

the human hand and the object (hand-held product) for promoting ergo-
nomic product design, taking the individual differences in hand
properties into account.
For this purpose, we realize a synthesis of various hand models, including
individual [1] and representative hands [2], based on a template hand model,
a hand dimension database, and spatial deformation of the template model.
Also, the individual model was used for motion analysis of the human hand
in collaboration with a motion-capturing system [3], while the representa-
tive model was used for the mechanical analysis of grasp and manipulation by
using a hand model in a grasping posture [4].
Interestingly, the digital hand is applicable to not only ergonomic prod-
uct design as previously described, but to interface the robotic and human
informatics. For example, the digital-hand model with a simplified anatom-
ical link structure enabled us to reproduce the motion of the human hand.
Once the motion is quantified, it is possible to summarize representative
hand postures in the lower dimensional space by using a statistical method
such as principal component analysis [5]. This is quite useful in designing
robot hands and in synthesizing the posture of robot hands [6]. Also, the uni-
fied theory of grasp and manipulation established in robot-hand research
provides a deep insight about the stability of grasp and its impact on the ease
of grasp while human subjects are using hand-held products. This is indis-
pensable for understanding the strategies behind the motion synthesis of
human hands and how the subjective response arises during product use.
In this chapter, we review the basics of digital-hand technology, (1) hand
anatomy, link structure, and surface mesh, (2) individual and representative
hand models, and (3) example cases where the digital-hand model was used
in motion and mechanical analysis of the human hand, hoping that digital-
hand technology will be an interface between robots and humans; enabling
dexterous manipulations in robotics and introducing mechanical and quan-
titative understanding of grasp in human informatics.

2.2 STRUCTURE OF THE HUMAN HAND AND DIGITAL HAND
2.2.1 Anatomy of the Human Hand

The skeleton of the human hand is composed of eight carpal bones, five
metacarpal bones, and fourteen phalangeal bones as shown in Fig. 2.1.
The thumb has two phalangeal bones, and the four fingers have three
phalangeal bones [7].