App SnapsJuly 1, 2006 By: Stephanie vL Henkel, Sensors Sensors
A (Nearly) Bionic Arm
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.
Safe Boating, Everyone!
The cry of "man overboard!" is second only to "fire on shipboard!" as a general alarm for all hands. But what if no one sees that fellow boater or shipmate (or pet) fall into the drink? The Raymarine (www.raymarine.com) LifeTag system, using Ember's ZigBee (www.zigbee.org) networking technology, does away with that unhappy scenario.
Detect and locate an overboard boater
LifeTag consists of a base station and wearable tags, which can be fitted around an arm or attached to a belt. The tags transmit wirelessly to the base station. If a person or a pet falls overboard, immersion in saltwater rapidly degrades the signal and triggers an alarm that alerts the rest of the crew. An alarm is activated as well when the wearer of a tag moves beyond 30 ft. of the boat, and can also be manually deployed by pressing and holding a red button for 3 s.
The base station handles communication with each of up to 16 LifeTags and provides outputs for external alarm sirens and relay contacts. It also speaks SeaTalk, Raymarine's interdevice communications network that enables it to activate the man-overboard mode on Ray-marine's multifunction displays to help quickly locate the missing person. The devices can operate a year or more on a single lithium battery (more than 200 operational hours).
The LifeTag System is the first commercially available product to use Ember's EM250 ZigBee system-on-a-chip and EmberZNet ZigBee-compliant networking software. And the LifeTag device took less than 50 days to create. According to Kieran Breheny, director of engineering development at Raymarine, "The nature of ZigBee makes it an ideal wireless standard for our LifeTag man overboard system. Ember's complete ZigBee platform and integrated tools enabled us to meet an aggressive product development cycle time."
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