Electromechanically coupled beam models for stacked dielectric elastomer actuators

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The overall objective of this work is to provide computationally cost efficient but also accurate dynamic beam simulation models for dielectric elastomer actuators to be used in optimal control problems. Stacked dielectric elastomer actuators bear analogy to the behaviour of human muscles in terms of contracting in length direction when stimulated. They are suitable for point-by-point application of a force. Therefore, dielectric elastomers allow for a sophisticated, efficient and noiseless actuation of systems. However, the use of elastic actuators is also accompanied by new control challenges. Advanced control strategies need to avoid undesirable oscillations, bring the system as quickly as possible into its steady state and follow prescribed trajectories as closely as possible. Optimal control theory is used to avoid oscillations that are inherent with the elastic nature of dielectric actuators and to obtain optimised control trajectories. As the computational cost for solving optimal control problems is significantly affected by the number of model degrees of freedom, reduced and problem specific actuator models are superior to general but cost-intensive finite element models. In the first two years of the project, a cost-efficient beam actuator model that covers applications with stacked dielectric actuators is developed and tested. The cost-efficient dielectric actuator model is compared to an existing finite element based simulation framework as well as to an existing lumped model regarding simulation time and accuracy. Moreover, the beam actuator model is exemplarily coupled to a multibody system to investigate the behaviour of dielectric elastomer actuated systems. In the continuation of the project after the first two years, the coupling between the actuator model and an actuated structure is formulated in a structured and modular way that allows for arbitrarily complex scenarios and the cost-efficient beam model is used to solve optimal control problems of dielectric elastomer actuated systems. Numerical examples show the application of the simulation framework to simple biomechanical systems, such as an elbow joint, in order to investigate the requirements on dielectric elastomers to replace skeletal muscles. Small experiments addressing the identification of parameters and the validation of small simulation examples are planned.