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CHAPTER1
INTRODUCTIO
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Prosthetic hand is an artificial hand that replaces a missing part of the human hand. The
missing part of human hand is caused either by congenital absence or amputation. Initial
writing and work on the prostheses were driven by as a result of war injuries. But today,
large amount of research is being done inorder to help people who have lost their limbs due
to amputation or whose limbs are paralysed. The main goal of prosthetic hand is to imitate
the human hand movement in all aspects. Thus, it needs a complex mechanism in order to
achieve realistic human hand movement. The technical challenge of replicating the human-like (anthropomorphic) movements of a prosthetic hand is to integrate both the software
and hardware of the prostheses systematically. The weight carried by the prosthetic hand is
another major challenge with most users feeling that the hand is too heavy to use at present.
The bionic arm technology is possible primarily because of two facts about amputation:
1.The motor cortex in the brain still sends out control signals even if certain voluntary
muscles are no longer available for control; and 2.When doctors amputate a limb, they dont
remove the nerves that once carried signals to that limb.
Commercially available myoelectric hands have an advantage on human like appear-
ance, light weight and low price. However, these simple grippers have only one or two
degree of freedom(DOF) just for pinching objects and, thus, they cannot grasp small cylin-
ders and spheres. The underactuated mechanism enables us to achieve multiple degrees of
freedom using only limited actuators and differential mechanism. This enables the
prosthetic hand to obtain self-adaptive grasping capabilities. Many humanoid hands were
developed for space operation and complicated with heavy weight. On the other hand,
simple structured and lightweight anthropomorphic hands have been developed. These
hands are mainly used as prosthetic hands. However, surveys revealed that 30% to 50%
handicap persons only used their prosthetic hands once in a while. The main factors for the
rejections include the heavy weight of prosthetic hands. the low functionality of pros- thetic
hands resulting in single and unstable grasp caused by few fingers DOFs, unnatural
movements caused by the limited DOFs. and appearance of prosthetic hands is far from
human hand. Through this report, we look into the working of the prosthetic hand and the
various constraints involved in the design.