A low cost artificial hand was developed
at lIT Bombay under a project funded by the Ministry
.of Social Justice and Empowermeni (MSJ&E) 1999-2001
(budget Rs.6.65 lakhs) (Investigators: Suresh Devasahayam,
R Lal. and P C Pandey). The initial design was done
at lIT Eombay, (Version-I), and after preliminary testing
at the Rehabilitation Institute in Mumbai, clinical
trials with long term follow-up was done at CMC-Vellore.
The design was revised substantially at CMCVellore in
2003, (Version-II), and production of the revised version
started in 2004.
Version 1: Only hand - single
motor for grasp/prehension. Two-motor hand grasp and
forearm rotation. Discrete electronics with low-cost
lead-acid battery. Overload detection and protection.
lIT-Bombay design: 1999-2002.
Version 2: Hand and forearm - additional motor
for forearm supination/ pronation. Microcontroller based
electronics. Improved control using 3 switches. Two
mobile phone batteries. Redesigned at CMCVellore: 2002-2004.
Version 3: Hand, forearm and elbow third motor
for elbow f1exion/ extention. Single mobile phone battery,
12 volt motors, 2 switch control for multiple functions.
Elbow movement. CMC-Vellore
design: 2005-
Features
The artificial hand comprises two
main modules: (a) the terminal device consisting of
the motor controlled hand, and (b) a patient interface
to enable the patient to smoothlyoperate the hand in
as natural a manner as possible.
The terminal device in Version I was
a motorized hand with two degrees of freedom - finger
grasp and forearm rotation. In Version II, another degree
of freedom is added with elbow articulation. The design
consists of a set of internally geared motors with eiectronic
controls. Each degree of freedom uses one motor. An
important criterion for the design was low cost. Version
I operates on a 12V supply; a rechargeable sealed lead
acid battery was used to keep the cost low. A 1.2V battery
works well for about 2 days between charges (about 1500
finger opening and closing cycles).
Version II uses rechargeable Li-Ion
batteries which reduces weight and bulk substantially.
Version II also uses a microcontroller based circuit
to decode the controls from the patient switches to
motor selection and direction of movement. Pressure
sensing to turn off the motors when excessive force
is exerted is also done by the circuitry, by monitoring
the motor current.
The Bombay-Vellore hand is modular
in design, and various subsets of it can be used depending
on the needs of ind ividual users. Many users need only
hand function (finger grasp/prehension) and use a single
motor artificial hand. Only a few users require a full
three motor hand with elbow articulation.
Several patient interfaces were tested
in the laboratory in order to decide upon a very robust
as well as convenient controller. For patient testing,
considering factors like lowcost, robustness, failure-proof
and speed of response, mechanical SWitches seemed the
most viable.
The following two pictures show two
views of the three motor hand for above elbow amputees:
Source:
Christian Medical College
Bagayam, Vellore 632002
