Sensorless force control for dielectric elastomer transducers

Multilayer stack-transducers made of dielectric elastomers generate considerable tensile forces and deformations when they are electrically stimulated. Thus, due to their capacitive behavior, they are for example energy efficient substitutes for conventional electromagnetic drives and enable various further completely new applications. Within this contribution, we present a sensorless force control for dielectric elastomer stack-transducers driven by a bidirectional flyback-converter. This force control for example can be used as interface for superimposed application-oriented controls. First of all, the properties of dielectric elastomer stack-transducers and the flyback-converter as well as its control structure are summarized. Due to the characteristic behavior of the power converter, the design of a sliding mode force controller is carried out based on an analytical model of the coupled electromechanical system containing the transducer and driving electronics. Using this model, the transducer force can be determined with the measured driving voltage and deformation so that an explicit force measurement is not required. In a first step, a two-point controller is developed for the variable structure control that is afterward extended in order to improve the control quality, for example, by adapting the inner power converter control. Finally, the experimental validations with a prototype stack-transducer and bidirectional flyback-converter demonstrate the feasibility as well as the precision and dynamics of the developed force control.