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Definition
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. In fact, the artificial hands for prosthetics
applications pose challenging specifications and problems, as is usually the case
for devices to be used for functional replacement in clinical practice. These
problems have forced the development of simple, robust, and reliable commercial
prosthetic hands, as the Otto Brock Sensor Hand prostheses which is widely implanted
and appreciated by users. The Otto Bock hand has only one degree of freedom(DOF),
it can move the fingers at proportional speed from 15-130 mm/s and can generate
grip force up to 100 N. According to analysis
of the state of art, the main problems to be solved in order to improve the performance
of prosthetic hands are 1) lack of sensory
information gives to the amputee;
2) lack of "natural" command interface;
3)
limited grasping capabilities;
4) Unnatural movements of fingers during grasping. In
order to solve these problems, we are developing a biomechatronic hand, designed
according to mechatronic concepts and intended to replicate as much as possible
the architecture and the functional principles of the natural hand. The
first and second problems can be addressed by developing a "natural"
interface between the peripheral nervous system (PNS) and the artificial device
(i.e., a "natural" neural interface (NI) to record and stimulate the
PNS in a selective way. The neural interface is the enabling technology for achieving
ENG-based control of the prostheses, i.e., for providing the sensory connection
between the artificial hand and the amputee. Sensory feedback can be restored
by stimulating in an appropriate way user's afferent nerves after characterization
of afferent PNS signals in response to mechanical and proprioceptive stimuli.
The "biomechatronic" design process described above is illustrated in
the scheme.
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