Sigmoid-based Force Modeling and Shape Recovery Characteristics of SMA Spring Actuator

The widely used component in most Engineering applications is a spring actuator; proper choice, design and its configuration in a mechanism is very important. The active spring actuator i.e., shape memory alloy (SMA) spring offers better functionality and improved technology. The use of SMA spring allows larger work space, force and controllable stiffness than SMA wires. This paper presents a simple thermo-mechanical model of an SMA helical spring actuator with natural cooling. The thermal behavior is depicted by the classical first order differential equation of heat transfer while the mechanical aspect is represented by a sigmoid function. The model is capable of extracting the attributes of the SMA spring actuator without involving any complexity. An experimental facility is realized; experiments are performed to identify the relevant parameters, determine the fundamental characteristics and validate the model.