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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.