<p>Twisted and coiled polymer actuators (TCPAs), made from polymer precursor fibers via twisting and coiling process, show great advantages of large stroke, higher actuation force, low cost, etc. TCAPs are thermally driven actuators. When the temperature rises, TCPAs shrink and the driving force is increased. There is little hysteresis between the temperature and driving force. Thus, temperature is always measured to predict the status of TCPAs. However, introducing independent temperature measuring system makes the quite complex, causing an increase in cost and weight. When the temperature range is not large, the resistance of copper wires increases linearly with temperature, making it a sensor of temperature. In this paper, self-sensing TCPAs, i.e., TCPAs wrapped with copper wires were manufactured, their resistances were firstly measured in various temperatures. In the experiment, the two ends of the TCPAs were constrained and the load cell directly measured the driving force of the TCPAs. The experimental results shown that TCPAs have constant thermal driving capacity in a wide temperature region from low temperature (below zero) to high temperature (above zero). The driving force of TCPA changes linearly with temperature. Based on the experimental data, a mathematical model of the temperature with respect to resistance was derived, and then verified with experimental results measured via a thermal camera from 20℃ to 100 ℃. This model was subsequently used to investigate the driving force of TCPAs. When the temperature measurement is not convenient, such as the low temperature experimental environment, the temperature change of TCPAs is obtained through the resistance. Despite the linear relationship between temperature and driving force, hysteresis between the TCPA temperature and the wire temperature was observed. During the entire drive cycle of TCPAs, the rise and fall of the wire resistance is faster than that of TCPAs, which can be seen from the temperature difference between TCPAs and copper wires. There is also a hysteresis between the resistance of the wire and temperature of TCPA. In their relationship, when the TCPAs temperature is the same, the resistance of the wire in the heating stage is higher than the resistance of the wire in the cooling stage. A model of TCPA temperature with respect to resistance was derived, its parameters were obtained by parameter identification. These parameters are related to the diameter of TCPAs and the experimental environment. The proposed model is feasible for resistance and temperature measurement, which facilitates the control of TCPAs temperature and driving force. Both the experiment and the model characterizes the mechanical properties of TCPA over the effective temperature range.</p>

Wire Resistance Model for Temperature and Force Analysis of Twisted and Coiled Polymer Actuators

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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