The Development of an Antagonistic SMA Actuation Technology for the Active Cancellation of Human Tremor.

Abstract

Human Tremor is an unintentional bodily motion that affects muscle control among both healthy individuals and those with movement disorders, occasionally to severe detriment. While assistive devices avoid the risk of side effects from pharmacological or surgical treatments, most devices are impractical for daily use due to limitations inherent in conventional actuators. The goal of this research is to address these limitations by developing an antagonistic Shape Memory Alloy (SMA) actuation technology, enabling a new class of active tremor cancellation devices. This is accomplished through the construction of a model and body of empirical support that provides the necessary design insight and predictive power for an antagonistic actuator that ensures stable amplitude and high frequency motion with low power draw. Actuation frequency and power draw were improved while balancing their competing effects through the development of: 1) a method that accurately measures the convective coefficient of SMA to enhance actuator design, 2) a growth process for carbon nanotube cooling fins to enhance cooling in a fixed medium, and 3) an understanding of the antagonistic architecture to produce increased frequency in a controllable manner. To enable applications requiring predictability for positioning and complex control, a thermodynamic model for antagonistic SMA was derived to account for inertial, slack, boiling, friction, and convective effects. Using the model, a series of simulation studies provided design insight on the effect of operating environment, driving signal, and environmental conditions so that the generic actuation system can be utilized in a wide variety of applications beyond tremor cancellation. If high forces are required in such applications, stability issues can arise, which were addressed in experimental shakedown research that broadens the high-stress SMA design space. The technology enabled by this dissertation was demonstrated in a working Active Cancellation of Tremor (ACT) prototype that produced 71% RMS cancellation of human tremor. The cancellation results show significant improvement over the current state of the art by providing intuitive, lightweight, compact hand-held tremor cancellation that is a promising solution to numerous assistive applications in medical, military, and manufacturing sectors.