Model validation and feedback controller design for a dielectric elastomer actuator

Abstract

Tubular dielectric elastomer actuators have been utilized for a number applications where bi-directional positioning is required, for example, positioning of loads and haptic interfaces. Previous model validation and control design research carried out by the authors on extendable metal electrode–based actuators (which need no internal stressing) has concentrated on the design of open-loop type model-based controllers to reject both measurable and unmeasurable vibration disturbances on a prototype tubular actuator developed by Danfoss A/S. A developed electromechanical model and its linearized form were important components in the control design work carried out previously. This work examines the design and implementation of a closed-loop controller on a second-generation extendable metal electrode dielectric elastomer tubular actuator. This actuator has the same strain characteristics as the original prototype but contains more rolled material leading to greater push–pull force capability. Electromechanical model validation of the larger actuator is initially carried out for a range of different operating conditions both with and without loading. Additionally, the increased capacitance of this actuator, due to a greater amount of dielectric elastomer material, could have implications for the accuracy of the gain scheduling term (which is used to linearize the model), when there is dynamic input voltage stimuli. The overall popularity of the proportional, integral and derivative controller, due to its transparency and simple structure, made it the obvious choice for the feedback controller to be considered here. Model-based design of the proportional, integral and derivative controller, via the internal model control design procedure, is then achieved using a reduced-order linear representation of the linearized electromechanical model. The real-time performance of the designed controller is examined to changes in desired position of the payload (servo performance) and its ability to reject periodic vibratory base disturbances to try and maintain the payload in a fixed position.