Modelling and control of double-cone dielectric elastomer actuator

Among various dielectric elastomer devices, cone actuators are of large interest for their multidegree- of-freedom design. These objects combine the common advantages of dielectric elastomers (i.e. solid-state actuation, self-sensing capability, high conversion efficiency, light weight and low cost) with the possibility to actuate more than one degree of freedom in a single device. The potential applications of this feature in robotics are huge, making cone actuators very attractive. This work focuses on rotational degrees of freedom to complete existing literature and improve the understanding of such aspect. Simple tools are presented for the performance prediction of the device: finite element method simulations and interpolating relations have been used to assess the actuator steady-state behaviour in terms of torque and rotation as a function of geometric parameters. Results are interpolated by fit relations accounting for all the relevant parameters. The obtained data are validated through comparison with experimental results: steady-state torque and rotation are determined at a given high voltage actuation. In addition, the transient response to step input has been measured and, as a result, the voltage-to-torque and the voltage-to-rotation transfer functions are obtained. Experimental data are collected and used to validate the prediction capability of the transfer function in terms of time response to step input and frequency response. The developed static and dynamic models have been employed to implement a feedback compensator that controls the device motion; the simulated behaviour is compared to experimental data, resulting in a maximum prediction error of 7.5%.