Self-sensing of dielectric elastomer tubular actuator with feedback control validation

Abstract

The need to measure accurately the movement and behavior of the soft material without external sensors in tight spaces has led scientists to design soft actuators that have compact self-sensing mechanisms. Dielectric elastomer (DE) materials, a category of electroactive polymers, are able to provide such properties since dielectric elastomers (DEs) have built-in sensing and actuation mechanisms. In this paper, a self-sensing mechanism without the need of using external devices to measure displacement is developed for a dielectric elastomer actuator (DEA). By superimposing actuation and probing voltages and applying them to the DE tube, the actuation voltage activates the movement of the DE tube while the probing voltage excites the sensing current. Using Fast Fourier Transform (FFT) to filter a given probing frequency, the capacitance can be extracted from the sensing current and probing voltage during each time window. With the relationship between displacement and the capacitance of the DE tube, one can estimate the movement online and achieve self-sensing without an external sensor. To validate this self-sensing approach, a tubular DE actuator is designed and fabricated. A physics-based self-sensing model is developed and validated by experiments. In feedback control validation, the displacement of the actuator was controlled using a proportional-integral controller with the capacitance change measured with a high probing frequency as the self-sensing mechanism component of the actuator. The self-sensing signal was used as a feedback signal in the closed-loop control system which guilds the DE tubular actuator to track a reference signal without external displacement sensor. The experimental results have successfully validated the self-sensing of the DE actuator in feedback control.