Optimization of parallel spring antagonists for Nitinol shape memory alloy actuators

While there has been a steady progression of research in robotic and mechatronic systems that utilize nickel titanium alloy (Nitinol) as an actuator, the design of the antagonistic element for the inherently “one-way” technology has not been thoroughly investigated and described. In this paper, we discuss the properties of Nitinol-based shape memory alloy actuators as they relate to the design of passive spring antagonists. We describe the major classes of design goals as they relate to the choice of properties of the antagonistic element, and present techniques for optimizing parallel antagonists through passive linear springs in order to maximize the generally most desirable property of the actuator - the maximal repeatable strain of the antagonist pair.