Physical model-based internal model control of a DE actuator

An accurate physical-based electromechanical model of a commercially available tubular dielectric elastomer actuator has been developed at University of Southern Denmark. This model has been validated for a range of different periodic input voltage signals as well as for different loading conditions. In this contribution we are interested in seeing how the physical-based electromechanical model can be used directly within a model-based control scheme. The choice of control scheme was dictated by the desire for transparency in both controller design and operation. The Internal Model Control (IMC) approach, which is based on the Internal Model Principle, which states that 'control can be achieved only if the control system encapsulates, either implicitly or explicitly, some representation of the process to be controlled' was chosen. If the IMC approach is implemented based on an exact model of the plant, perfect control is theoretically possible. IMC -based control is investigated for servo control of the dielectric elastomer actuator position as well as its ability to reject disturbances. The approach comprises (a) the use of the DE actuator model in parallel to the real actuator - the difference between the two outputs providing an estimate of any disturbance entering the system, (b) the estimated disturbance being fed back and compared with the reference input and (c) the difference between the reference and the estimated disturbance provides the input to the IMC controller which is based on an inverse model of the DE actuator. In the IMC implementation considered here the full nonlinear electromechanical model of the actuator is used to provide the disturbance estimate. The use of a linearizing gain scheduler, placed in series with the real actuator, allows a linearized inverse of the electromechanical model to be used in the formulation of the IMC controller.