The Bombay-Vellore Artificial Hand

Introduction

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