03-12-2012, 12:40 PM
BIONIC HAND
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INTRODUCTION
The objective of the work describe in this paper is to develop an artificial hand aimed at replicating the appearance and performance of the natural hand the ultimate goal of this research is to obtain a complete functional substitution of the natural hand. This means that the artificial hand should be felt by the user as the part of his/her own body (extended physiological proprioception(EPP) ) and it should provide the user with the same functions of natural hand: tactile exploration, grasping , and manipulation (“cybernetic” prosthesis). Commercially available prosthetic devices, as well as multifunctional hand designs have good (sometimes excellent) reliability and robustness, but their grasping capabilities can be improved. It has been demonstrated the methodologies and knowledge developed for robotic hands can be apologies and knowledge developed for robotic hands can be applied to the domain of prosthetics to augment final performance. The first significant example of an artificial hand designed according to a robotic approach is the Belgrade/USC Hand. Afterwards, several robotic grippers and articulated hands have been developed, for example the Stanford/JPL hand and the Utah/MIT hand which have achieved excellent results. An accurate description and a comparative analysis of state of the art of artificial hands can be found in. These hands have achieved good performance in mimicking human capabilities, but they are complex devices requiring large controllers and their mass and size are not compatible with the strict requirements of prosthetic hands.
DESIGN OF THE BIONIC HAND
Bio mechatronic Design
The main requirements to be considered since the very beginning of prosthetic hand design are the following: cosmetics, controllability, noiselessness, lightness, and low energy consumption. These requirements can be fulfilled by an integrated design approach aimed at embedding different functions within a housing closely replicating the shape, size and appearance of human hand. This approach can synthesize with the term: “bionic” design.
Architecture of the Bionic Hand
The design goal of the bionic hand is to improve to some extent one of the most important limitations of current prosthetic hands (no dexterity and no adaptability), while preserving the main advantages of such hands, that is lightness and simplicity. This objective has been pursued by using small actuators(two of each finger) instead of one single large actuator( as in most current prosthetic hands) And by designing a kinematic architecture able to provide better adaptation to object shape during grasping. It turns out that the use of “micro motors” allows augmenting functionality in grasping objects by means of “human-like” compliant movements of fingers. This result addresses the very basic requirements of “cosmetic” appearance of the hand in static and dynamic conditions.
DESIGN OF HAND PROTOTYPE.
In order to demonstrate the feasibility of the described bionic approach, we have developed a three fingered hand prototype with two identical fingers (index and middle) and thumb. Actuators, position sensors and a 2-D force sensor are integrated in the hand structure.
The index/middle finger has been designed by reproducing, as closely as possible, the size and kinematics of a human finger. Each finger consists of three phalanges and a palm needed to house the proximal actuator (see fig 5).
HAND FABRICATIONS
The hand protected (see fig 7) comprises the three fingers (index middle and thumb), each with two-DOF’s actuated by micro motors and sensor by hall-effect position sensors and by strain gage-based force sensors. The characteristics of the position sensors and of the force sensors are illustrated in following sections.
The three fingers have been fabricated using the fused suppositions modeling (FDN) process. This process allows obtaining 3-E complex shapes from CAD models easily, quickly and cheaply. The main limitation of the FDM process resides in poor mechanical characteristics of the material that must be used, which is acrylonitrile/butadiene/styrene (ABS).how ever; this is acceptable for a prototype.