Adaptive Sliding-Mode Position Control for Dielectric Elastomer Actuators

Multilayer stack transducers made from dielectric elastomers (DEs) generate considerable tensile forces and deformations when they are electrically stimulated. Hence, due to their capacitive behavior, they are energy-efficient substitutes, for example, for conventional electromagnetic drives, and enable various completely new applications. Within this contribution, we present the design of a position control for DE stack actuators electrically fed by a bidirectional flyback converter. Due to the unique property of the flyback converter providing an almost constant feeding power for charging and discharging, the sliding-mode control approach is used for the proposed position control. In a first step, a two-point controller is developed and extended afterwards to a three-point controller with hysteresis to significantly reduce the switching frequency. In order to further improve the control behavior and energy efficiency, an adaptation approach for the inner power converter control is carried out that is used to adapt the hysteresis threshold of the three-point controller. Finally, the experimental validations with a prototypic silicone DE stack actuator and bidirectional flyback converter demonstrate that the proposed adaptive three-point controller combines both high dynamics and accuracy with high efficiency due to a significantly reduced switching frequency.