Scientists Develop 'Clever' Artificial Hand

Every year 200 people in the UK lose their hands. Common causesinclude motorbike accidents and industrial incidents. Currentlyavailable prosthetic hands are either simple mimics that look like ahand but don't move or moving hands which have a simple single-motorgrip.

The human hand has 27 bones and can make a huge number ofcomplex movements and actions. Dr Paul Chappell, a medical physicistfrom the University of Southampton has designed a prototype hand thatuses 6 sets of motors and gears so that each of the five fingers canmove independently. This enables it to make movements and grip objectsin the same way a real human hand does.

The new hand, called the 'Southampton Remedi-Hand', can beconnected to muscles in the arm via a small processing unit and iscontrolled by small contractions of the muscles which move the wrist.

Dr Chappell said: "With this hand you can clutch objects suchas a ball, you can move the thumb out to one side and grip objects withthe index finger in the way you do when opening a lock with a key, andyou can wrap your fingers around an object in what we call the powergrip -- like the one you use when you hold a hammer or a microphone."

Dr Chappell and colleagues in the School of Electronics andComputer Science at the University of Southampton set out to try andbuild a hand which could mimic the movement and flexibility of thehuman hand and which was also very light. Heavy prosthetics can beextremely uncomfortable and cause injury to the area where it joinswith the arm. The new hand they've developed is only 400g (even lighterthat a real hand which weighs on average 500g).

They built the Remedi-Hand in three parts -- the three middlefingers are very similar in size and movement so they made thoseidentical. The pinky is a smaller version of the same. Each of thesefour fingers are made up of a motor attached to a gearbox attached to acarbon fibre finger. All of this is fitted to a carbon fibre palm. Butthe thumb was much more complicated and is the first artificially-madeopposable thumb.

The human thumb can move in special ways the fingers can't. Itcan rotate as well as flex and also move in a variety of differentdirections. It can also oppose (touch) each of the fingers in the handto form a 'pinch'. To mimic this, the Remedi-Hand uses two motors --one to allow it to rotate and one to allow it to flex. "The real thumbcan move in five types of way, we've managed to create a thumb that canmimic at least two of these which is a really exciting achievement.It's a thumb that has really good flexibility and functionality" saysDr Chappell.

One of the key differences between mechanical, artificial,limbs is that they arn't able to sense pressure or touch in the sameway human limbs can. The next stage of Dr Chappell's research is tointegrate the latest sensors technology with the Remedi-Hand to createa 'clever' hand which has better functionality and move like a realhand, but which can also sense how strongly it's gripping an object orwhether an object is slipping.

Dr Chappell and colleagues have already designed this 'clever'hand and are about to start building a fully functioning prototype. Itwill have piezo-electric sensors in each of the five fingertips whichwill detect how much force is being exerted on the tip and translatethis information into an electrical signal which will be fed to a smallprocessor.

Dr Chappell said: "The aim is to create a hand with the sort offunctionality a human hand has but also a sense of touch. This will letthe hand know how tightly to grip an object like a coffee cup withoutdropping it, but not so tightly that it's crushed. It'll also have anintegrated slip-sensor which will tell the hand if something isbeginning to slip out of its grip so it can grip slightly harder. It'llbe quite a clever system."

The development of the prototype hand was funded by Remedi and this research is funded by EPSRC.