Dynamic model for the tensile actuation of thermally and electro-thermally actuated twisted and coiled artificial muscles (TCAMs)

Twisted and coiled artificial muscles (TCAMs) represent an emerging class of actuators. These lightweight muscles provide high power/weight ratio, close to that of skeletal muscles, and can substitute heavy electromagnetic and pneumatic motors in applications requiring low weight, fine motion, and high contractile work. In a recent work we proposed a theoretical model to describe the static behavior of electro-thermally actuated TCAMs. In this study we use the previous static formulation to develop a physics-based dynamic model able to estimate the time varying tensile actuation of TCAMs, according to a specific thermal and electro-thermal input. The proposed model is experimentally validated on a new type of low-cost TCAMs that we recently developed from Carbon Fibers and Silicone Rubber (CF/SR). Satisfactory agreement is shown between the theoretical predictions and the experimental results (maximum errors of 3.4% and 13% are measured on the TCAMs displacement during heating and cooling, respectively). The proposed dynamic model allows to describe the time-varying actuation of TCAMs, fundamental to analyze their response to time-varying phenomena such as high frequency inputs, disturbances, or noises injected into the system. This model represents a useful tool for the design and control of TCAMs-based devices, for applications ranging from the robotic to the biomedical field.