Design and development of a self-sensing control for spin crossover based soft electrothermal actuators

Abstract Soft electrothermal actuators have been studied and proven to be useful in wide range of applications. Use of spin crossover materials in soft matrix for bilayer actuation is well documented with proven capability to deliver high flexibility and reliability. However, the use of these actuators is limited by their dependency on external sensors for position control. Such soft thermal actuators often exhibit hysteresis and non-linearity, making them challenging to operate in absence of sensor feedback. This work proposes a novel control scheme capable to effectively address the hysteresis thereby making it possible to actuate without dependency over external sensing. The proposed scheme allows the position control with the self-sensing without the need of any dedicated external sensor or any integrated sensing tool on the device. The device makes use of the resistance changes of the conductive layer which is primarily used to enable Joule heating of the electrothermal actuator. The presence of hysteresis has been effectively taken into account by a dedicated recursive temperature function based analytical model. Experimental studies validate the robustness of the model with a final error value less than 6.5 % . Different studies to track sinusoidal position over multiple cycles validate the repeatability of the performance. With an electric current of 850 mA , approximately 3.8 mm of displacement is controlled where the corresponding resistive change of 0.25 Ω is observed. The proposed strategy can also be helpful in performing other dedicated sensor-less actuations, which therefore strengthens the autonomy as well as applicability of such devices.