Page 118 - Human Inspired Dexterity in Robotic Manipulation

116 Human Inspired Dexterity in Robotic Manipulation

Nail

Skin
Finger pulp
Bone parts
Fig. 7.1 Fingertip anatomy. (Modified image from Sydney Hand Surgery Clinic, Anatomy.
Available at: http://www.sydneyhandsurgeryclinic.com.au/anatomy.asp.)

to grasp various objects. On the other hand, softness limits the weight of
objects that the hand can grasp and cause contact uncertainties with regard
to estimating the contact position, normal direction, friction, and so on.
These uncertainties make motion and grasp planning of robotic hands dif-
ficult. However, reducing the burden of controlling hand functions would
result to lowering required grasping accuracy. Therefore, a hybrid structure
that is both soft and hard is preferable in the development of a versatile
robotic hand.
Consider the structure of the human fingertip. Although the human fin-
gertip consists of many components, its structure can be simply described by
focusing on the softness of those components. These simplified parts are the
skin, pulp, bone, and nail, as shown in Fig. 7.1. The skin and pulp are soft,
whereas the bone and nail are hard. Thus, the human fingertip can be
regarded as a hybrid structure made of soft and hard components. Viewed
from the state of matter, the pulp is fluid while the other parts are solid.
Therefore, it can also be regarded as a hybrid structure of fluid and solid. This
latter point of view on the structure of the human fingertip gives an idea on
how a versatile robotic hand can be developed. This chapter presents a novel
fluid fingertip inspired by the structure of the human fingertip, and a robotic
hand in which the fluid fingertip is embedded.

7.2 FLUID FINGERTIP

In this section, the developed fluid fingertips [1–3], originally designed for
delicate food grasping are introduced.

7.2.1 Basic Structure of Fluid Fingertip
Fig. 7.2 shows the basic structure of the fluid fingertip fabricated from a
deformable rubber bag filled with incompressible fluid. In this first version