Compliance and Adaptive Underactuation for Prosthetic Terminal Devices
Posted December 22, 2011
Aaron Dollar, Ph.D., Yale University, New Haven, Connecticut
Over 300,000 people in the United States are currently living with some form of upper limb loss. In addition, approximately 20 percent of the nearly 40,000 injured service members from the Iraqi and Afghan conflicts have suffered trauma to their upper extremities. These numbers highlight the challenge faced by the medical establishment to provide new and innovative functional interventions that enhance the quality of life of these patients. To date, anyone who has need of an upper limb prosthetic device must balance their preference for esthetics, functionality, durability, and cost. In general, passive devices tend to be more life-like but provide little to no functionality. On the other hand, the mechanical cable prosthesis with a two-pronged hook, which was invented in the early 20th century, though not esthetically pleasing, remains the most functionally preferred device. In the last several years, there have been great strides in the development of novel prosthetic hands and terminal devices that take advantage of the latest materials and technological advances. A variety of prosthetic terminal devices have appeared on the market designed to perform all kinds of activities from golf, wall climbing and racquetball, to guitar playing and cooking. However, the ultimate goal of a highly functional, durable, and anthropomorphic prosthetic hand, as widely popularized in movies like Star Wars and I, Robot, remains confined to the realm of science fiction.
In fiscal year 2009, Dr. Aaron Dollar was granted a Hypothesis Development Award by the Department of Defense Peer Reviewed Orthopaedic Research Program to develop an anthropomorphic body-powered prosthetic hand prototype that is mechanically compliant and passively adaptive. Although body-powered anthropomorphic hands have been developed in the past, the new design achieves mechanical compliance through the distribution of force from a single body-powered cable input to the five fingers. In addition, polymer-based flexion joints actively bend, thus allowing for passive deflection of the fingers during contact with an object, as well as keeping contact forces low during object acquisition. Another aspect of this novel prototype is that the thumb can be rotated to a number of different positions, permitting the hand to accomplish a larger range of grasps, thereby greatly improving the practical use of this terminal device. Laboratory testing of the hand has already proven the functionality of this device in achieving a range of grasping positions, as well as various areas for improvement. Dr. Dollar's future work will focus on developing an actuated wrist to accompany the hand and conducting clinical trials in upper limb amputees to evaluate the devices' real-world performance, and in doing so, bringing the world of fantasy and science fiction within grasp.
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Public and Technical Abstracts: Compliance and Adaptive Underactuation for Prosthetic Terminal Devices
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