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Smart Prosthetics About 600 million years ago an adventurous ape climbed down from a tree and stood upright upon the African Savannah. It was a significant moment in human history. Standing up meant that our hands became free and our vision became panoramic. It opened up an intimate space where eye, hand and brain could interact. A small step for an ape, a giant leap for human intelligence. So it is fitting that the same intelligence is now being used to provide new high tech limbs and hands for amputees, allowing them to experience and interact with the physical world in a way far more like their able-bodied peers. The latest prosthetic limbs are a significant improvement on previous designs. They are called Intelligent Prostheses because they are able to adapt to each individual.
The knee joint is adjustable, so the user can set the swing resistance and the level of resistance the joint offers when weight is put on the leg. The result: a greater freedom of movement, that has hitherto been impossible with traditional prosthetic limbs. Ernest continues: "Previously the systems were quite heavy, bulky and power-hungry. The new systems are lighter, more effective, more functional, and they use less power."
But if prosthetic limbs provide a glimpse of things to come, then the new 'SensorHand', also developed by Otto Bock, is a long hard stare into the future. Using a microchip and two sensor pads, the SensorHand allows the user to clasp any object securely. Ernest explains: "With a SensorHand, if a patient picks up a glass for instance, he'll have complete control. If the glass starts slipping out of his hand, the prosthesis will tighten the grip, but won't crush the glass."
Training is essential in order to use these new prostheses successfully. Just as newborn humans must learn to walk, so must prosthetic users learn to control their new limbs. In the case of the sensor hand, this means learning to produce an electrical signal three seconds long.
Sally asks Ernest: "How developed is South Africa in terms of this technology?" Ernest responds: "All modern prosthetic equipment is available in SA. The only problem is that it costs a lot of money to import it because of the weak South African Rand (ZAR). Presently a below-elbow prosthesis will cost approximately ZAR60'000 to ZAR120'000, and an above-elbow prosthetics about ZAR120'000 to ZAR350'000." (For cost in US $, divide by 6.5 for approx price as at Dec 1998, or visit the Otto Bock websites (see below). It may take a little while yet, but certainly, the days of pirate hooks and wooden legs are numbered. And it is not difficult to imagine a time when technology produces artificial limbs and hands that rival the human hand in dexterity and range of application. Although Ernest concludes: "In the future I think that prostheses will continue to develop, they will become faster and lighter and they'll use less power. However, I don't think they'll ever compare to the actual human hand." Subtle interaction between mind and the environment is what created intelligence. Now the circle is closing: intelligence is again redefining the way our bodies interact with the physical world. Sally concludes: "From body to mind, and back to body, the link between mind and matter, between thought and technology will continue to make history." CONTACTS:
Ernest Porter
Otto Bock Prosthetics
Otto Bock knee joint:
Otto Bock SensorHand: |
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Ernest Porter, an orthotist and prosthetist, explains: "Intelligent Prosthetics refers to microprocessor-controlled components of prosthetics. When a patient walks on a 'smart' prosthetic knee, the microprocessor can sense when it starts buckling under the weight, and it will actually lock the knee. With new 'intelligent' prosthetic hands, the patient can grip an object, and if it starts slipping out of the hand, the prosthesis will tighten the grip, using this system."
Companies like Otto Bock in Germany specialise in intelligent prosthetics that make life easier for the user. A prosthetic leg developed by Otto Bock called the 3R80 contains a simple but significant innovation: a rotary hydraulic chamber inside the knee. Every time the user takes a step, a metal piston rotates in the chamber, displacing hydraulic oil, which dampens the swinging motion of the leg.
The development of this technology depends upon computer modelling and the latest methods of laser alignment. It is an excellent example of how progress in one field rubs off on another.
The SensorHand works by converting the electrical energy in our muscles into kinetic energy, which causes the hand to close. Two electrodes placed at key points upon the user's skin pick up electrical impulses in the muscle stands of the lower arm stump. One electrode causes the prosthetic hand to close; the other causes it to open.
There is no need to keep a constant watch over objects in hand. When the object is about to slip, the sensor pads detect changes in the object's weight or centre of gravity. The data is then sent to the microprocessor, which adjusts the force of the grip.
They also have to learn to differentiate between a muscle impulse that will cause the hand to close, and one that will cause it to open.