Sensors Mag

Can You Give Me a Hand?

June 26, 2006 By: Stephanie vL Henkel, Sensors


E-mail Stephanie vL Henkel

The current conflict in Iraq is proving to be a war of amputations. Most of these are traumatic—hands, feet, entire limbs torn off by explosive devices. Many combatants and support personnel would, not so long ago, have died of such injuries. Now they're being saved and home they come, in their teens, 20s, and 30s, to resume their lives as best they can. If it's any consolation, an extremely well engineered prosthetic, the Boston Digital Arm (BDA), promises to reproduce much of a lost limb's functionality.

The BDA's operating principle has been well demonstrated-the user's remaining muscles and nerves activate the device and control its movements. This arm goes beyond conventional prosthetics, though, by having five axes of motion as well as a variable gripping force in the hand that gives the user the ability to "sense" a held object.

The Why

Developed by Dr. Todd Kuiken and the Rehabilitation Institute of Chicago, and made by Liberating Technologies, the BDA incorporates five motors controlled by digital signal controllers from Texas Instruments (TI). According to Bill Hansen, president of Liberating Technologies, "When we developed our system we considered both microcontrollers and digital signal controllers. We selected TI's C2000 controllers because they provide vastly superior abilities to generate pulse-width-modulated (PWM) signals for the most efficient method of driving the DC motors that are used in prostheses. One TI digital signal controller gives us the ability to drive five motors, expandable to nine with an add-on module. In contrast, some competing solutions require two microcontrollers to drive only three motors."

And the How

The BDA System, which was developed using TI's Code Composer Studio Integrated Development Environment, is controlled by signals generated from one or more of the user's intact upper limb muscles. TI's operational and instrumentation amplifiers detect, condition, and amplify the signals. The C2000 controller then compares the strength of the signals to those from other sensors, and determines how much voltage to send to motors in the elbow, wrist, and hand. The five PWM outputs also provide shoulder movement for amputees without working shoulder muscles.

The device can use the controller's I/O options, such as a serial port interface D/A converter, to control up to four additional motors on an independent prosthetic controller. This enhancement allows the prosthetic arm to swing while the wearer walks, providing a more natural, comfortable motion. The controllers' additional processing power also makes it possible for users to move their joints simultaneously, making it much easier to reach for and grab an object.

A Bonus

Perhaps even more remarkable is that the BDA physically resembles a human arm and hand. Various studies of upper-limb amputees have yielded a surprising conclusion: Given the choice between aesthetics and functionality, the majority of those fitted for prosthetic arms go for the former. So one more cheer for the BDA.

We're Not Lizards, But Still . . .

Certain animals, none of them mammals, can regenerate lost limbs or tails. It's not yet absolutely clear just how they do that, but the ability is being studied with particular interest these days. Which brings us to genetic engineering. I believe that when brought to fruition this discipline is going to make a great many medical procedures obsolete. How far-fetched is it, really, to imagine a time when stem cells could cause a new limb to grow?

Stem cell research has been raising holy hell in the political, scientific, and medical communities, not to mention those that sit around the dinner table. There might very well be other routes of investigation, but so far they've stayed in hiding. And I find it really hard to believe that anyone whose arm (or other limb) has been destroyed either by violence or medical necessity wouldn't like to have it back.

Put It To a Vote?

We as a country owe our armed forces the chance to become again as they were before they left home. The government should heavily fund the research that could make this possible. If this requires some sort of voting, my vote is to limit the voting to those with the most vested interest in the outcome. Guess who they are. I also propose that each voter get to cast one ballot for each missing limb.

So I nominate Max Cleland, former Democratic senator from Georgia, to head any organizational effort this might require. Perhaps Senator Daniel Inouye of Hawaii might be willing to serve as second in command.


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