Page 180 - Handbook of Biomechatronics

178 Georgios A. Bertos and Evangelos G. Papadopoulos

of instruments” (Childress, 1980). The complexity of the human hand is evi-
dent of its complex anatomy and its dexterity. There are 33 muscles acting on
the hand.Ofthese33muscles,18are intrinsicand 15 areextrinsicmuscles.The
humanhandalsohas27major bones,andover 20 jointarticulationswitha total
of 27 or more-degrees of freedom (DoF). The arm contributes another 7 DoF.
Approximately1/6ofallthebonesandmusclesinthehumanbodyresideinthe
twohands.TherearecomplexroboticarmsliketheMIT/Utahdexteroushand
( Jacobsen et al., 1986) which mimic the human hand. The controller of this
arm, for example, takes the same space as the space taken by two filing cabinets
and is powered by electrical mains. These facts make it impossible to use these
robotic arms in replacing the human hand, where power, space, and size are of
criticalimportancefortheportableapplicationofprosthetics.Evenifthehandis
replacedwithasimplesingle-degree-of-freedom(single-DoF)prosthetichand,
as is usually the case nowadays, this still remains a challenging control problem
(Weir and Childress, 1996). Technology miniaturization, surgical creativity,
and computer science evolution have already enabled the way to multi-degree
of freedom (multi-DoF) prosthetic arms.

1.2 How is Success Defined for Upper-Limp Prosthetics?

Childress (1992) presented the following attributes as desirable for prosthesis
control:
1. Low mental loading or subconscious control. This means that the person
should not put mental effort on how to operate the prosthesis. This
should be done subconsciously. In that way a close to the natural way
of controlling the human limb is achieved.
2. User friendly or simple to learn to use. In that way the amputee is
attracted of learning to use the prosthesis with a minimal effort.
3. Independence in multifunctional control. This means that in
multifunctional prostheses, control of one function should not affect
the control of any other function.
4. Simultaneous coordinated control of multiple functions (parallel con-
trol). This is the ability to coordinate multiple functions of the prosthesis,
simultaneously.
5. Direct access and instantaneous response (speed of response). Prosthetic
systems should be directly accessible to the user and they should respond
immediately.
6. No sacrifice of human functional ability. That is, the prosthesis should be
used to supplement, not subtract from, available function.