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Mind-Controlled Prosthesis

During my morning scan of the headlines, I noticed an article about prosthetic devices that are powered by a person’s own brain. In fact, these types of prostheses are the culmination of research and practical prototype building stretching back for decades. It’s very rewarding to know that Nordex was involved in fabricating prototype components for some of the scientists who developed brain-wave driven prosthetics.

Sometime around 1990, we received a phone call from an engineer at one of the top-tier institutes of technology asking us if we would be willing to help them build a special gear box. My answer is always “yes,” depending on the size of it (cannot be bigger than a breadbox). This gear box involved high torque, but had to be very lightweight.

We started getting drawings – no computer models then – and it turned out that what we were trying to build was a below-the-shoulder, above-the-elbow prosthesis. We wanted to bend the elbow and turn the wrist. The whole idea was that it would be thought-activated and mediated by computer. Computer technology wasn’t sophisticated enough at that time to be practical for use in prostheses; the computer was literally the size of a refrigerator! The amputee would practice with it with an umbilical cord from the computer going to this prosthetic arm that we were contracted to build.

There were two functions in the prosthesis: one was to bend the elbow, and the other was to rotate the wrist. The coupling from the elbow out to the wrist that would rotate the prosthetic wrist was a long, slender tube made of aluminum, and the gears inside that would bend the elbow were made of high-strength, lightweight alloys. We made a herringbone gear – a pair of 45 degree helical gears, left-hand and right-hand, very thin and segmented, so it only would rotate 90 degrees or 120 degrees – how far do you bend your elbow anyway? This unit was attached to a molded boot, provided by the customer, that fits over the amputee’s shoulder and arm. The customer’s engineer came to Nordex where we did all the final assembly, and he showed us how it worked. We saw the electrical contacts that were in the boot that would make contact with your skin so you would think about flexing a muscle that may or may not be there anymore, and there would be an electrical impulse at the nerves where the electrical contact was, and that would be a signal that would start a motor inside the arm that would bend the elbow, or another one would maybe simultaneously start the wrist to rotate.

I have no idea why they called us to do this, except that much of our advertising is word of mouth. Also, customers will often look at what our standard offering is and then say, “It’s kind of like what I’m looking for, but really what I need is this.” And that’s where our engineering group comes into play.

Dan Agius