Modern externally powered upper-body prostheses are conventionally actuated by electric
servomotors. Although these motors achieve reasonable kinematic performance, they
are voluminous and heavy. Deterring factors such as these lead to a substantial
proportion of upper extremity amputees avoiding the use of their prostheses.
Therefore, it is apparent that there exists a need for functional prosthetic devices
that are compact and lightweight. The realization of such a device requires an
alternative actuation technology, and biological inspiration suggests that tendon based
systems are advantageous. Shape memory alloys are a type of smart material
that exhibit an actuation mechanism resembling the biological equivalent. As
such, shape memory alloy enabled devices promise to be of major importance
in the future of dexterous robotics, and of prosthetics in particular. This paper
investigates the design, instrumentation, and control issues surrounding the practical
application of shape memory alloys as artificial muscles in a three-fingered robot
hand.
Air springs are highly nonlinear devices. Linear and quasi-linear models of air springs have been developed over the years to analyze and predict their behavior. Such models are shown here to be inadequate to describe the behavior of this highly nonlinear element. A nonlinear mathematical model of air springs has been developed and reported in this paper. The model has been verified experimentally, and has been shown to be effective in predicting the behavior of air springs. The sensitivity of the model to uncertainties in two key parameters is examined.
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