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Sealed Myoelectric Hand

Background

Myoelectric prosthetic hands help many children with upper-limb deficiencies to lead better lives. Despite the many benefits these technologies bring, certain practical issues persist. One of the most important relates to environmental resistance (e.g. water and dirt). Another relates to the durability of cosmetic gloves, which not only aim to provide aesthetically pleasing prostheses, but also address the first issue by partially protecting the inner workings of the hands. Despite ongoing research and development efforts, cosmetic gloves are prone to failure, which often results in the costly failure of the entire hand.

Currently, the Electric Terminal Device (ETD) from Motion Control is the only prosthetic hand that is water resistant. This device is intended for adults, and is considerably larger and heavier than standard paediatric hands. Otto Bock Health Care manufactures a pediatric hand with an envelope that fully encloses the electronics that provides some protection from contaminants. However, it is not water resistant and the use of a glove for protective and cosmetic purposes is necessary. The hand is also considerably more expensive than other pediatric hands.

Technology

To address the shortcomings of current hand prosthesis, researchers at the Bloorview Research Institute have been working to develop new sealing technology to completely enclose the electromechanical workings of the prosthesis. They are also developing brushless motor technology for a less bulky, lighter, quieter and longer lasting prostheses.

Researchers have created a conceptual design for sealing the hand and for the implementation of the new motor. Detailed engineering analysis was performed to determine the preferred basis for the design. A prototype was fabricated and the sealing mechanism is in the process of being tested.

To improve sealing, the number and size of dynamic sealing points was minimized, which helps minimize losses due to friction and decreases the potential for leaks.

The smaller brushless motor also helps to reduce the overall size and weight of the hand, making it more appropriate for pediatric use.

Applications

It is evident that an affordable, sealed and aesthetically satisfactory hand prosthesis is needed for the effective treatment of limb deficient children. One study, focusing on pre-school children between the ages of two and five found that an average of 2-3 repairs per year were necessary. Furthermore, supplying a prosthetic limb with sufficient grip strength and an aesthetic appearance will enhance self-esteem and self-image in children with upper limb deficiencies.  

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