Integrated force and displacement sensing in an untethered dielectric elastomer actuator with a piezoresistive element

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Dielectric elastomer actuators, owing to their fully electrical control and silent operation, are becoming increasingly popular for the development of terrestrial and underwater mobile robots with versatile locomotion capabilities. It is essential to embed the ability to sense their state and external interactions in these robots to facilitate the development of future autonomous capabilities. However, sensorizing dielectric elastomer actuators for untethered robotic applications is challenging due to their use of high voltage and the nonlinear mechanics of the elastomers utilized in them. To address this challenge, we developed a novel technique based on embedded piezoresistive sensing and high voltage feedback to simultaneously estimate the actuator displacement and external force in a fully untethered actuator driven by a miniature low-cost voltage amplifier. A data-driven regression model has been developed to accurately estimate force and displacement from the measured data. Validation tests conducted on three actuators demonstrate promising results. We achieve RMSE values as low as 29.736 mN for force estimation and 0.023 mm for displacement estimation in the zero-voltage condition, where the actuator is subjected to a triangular wave with a mechanical frequency of 0.1 Hz and an amplitude of 3 mm. Additionally, we have realized fully untethered operation by employing a power source, small-size voltage amplifier, microcontroller, and wireless connectivity module embedded in a compact form-factor. This work presents a significant advancement in soft robotics, offering a reliable and cost-effective solution for future autonomous robotic systems based on high-voltage dielectric elastomer actuators.