COMSOL multiphysics based modeling of coiled nylon actuator (Conference Presentation)

Abstract

Coiled nylon actuator is an important field of actuators in soft robotics due to its negative thermal expansion, large actuation stroke and high force output. Coiled nylon actuators are easily manufactured and an inexpensive material. They are produced by attaching one end to a rotating motor and at the bottom to a suspended mass. The bottom end is constrained to prevent rotation in the axial direction. After coiling, it is annealed to reduce any internal strain. Its means of actuation is due to the torqueing behavior when heated which is induced by nylons thermal expansion, but by constraining the rotation, its response is to displace in the negative axial direction. The goal in this study is to capture the displacement and force output of the nylon actuator using COMSOL Multiphysics with the thermomechanical properties, heat and suspended mass (force) being the inputs of the model. The model will heavily rely on the classical lamination theory where the on-axis thermomechanical properties are obtained first and then the off-axis reduced stiffness matrix and effective coefficient of thermal expansion is obtained. The COMSOL Multiphysics displacement and force output results will be compared to experimentally obtained results. The experimental results will be obtained using a TA Instrument Dynamic Mechanical Analysis (DMA) which will be used to perform a strain controlled dynamic temperature scan at a frequency of 1 Hz on the nylon actuator. Temperature will be scanned from room temperature 24°C to 150°C at 1 °C/min.