A (Nearly) Bionic ArmJuly 1, 2006 By: Stephanie vL Henkel, Sensors Sensors
The current conflict in Iraq is proving to be a war of amputations. 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.
Give a prosthetic arm additional functionality
Developed by Dr. Todd Kuiken and the Rehabilitation Institute of Chicago, and made by Liberating Technologies (www.liberatingtechnologies.com), 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."
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 accomplish tasks like reaching for and grabbing an object.
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