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Electro-ribbon actuators are lightweight, flexible, high-performance actuators for next generation soft robotics. When electrically charged, electrostatic forces cause the electrode ribbons to progressively zip together through a process called dielectrophoretic liquid zipping (DLZ), delivering contractions of more than 99% of their length. Electro-ribbon actuators exhibit pull-in instability, and this phenomenon makes them challenging to control: below the pull-in voltage threshold, actuator contraction is small, while above this threshold, increasing electrostatic forces cause the actuator to completely contract, providing a narrow contraction range for feedforward control. We show that application of a time-varying voltage profile that starts above pull-in threshold, but subsequently reduces, allows access to intermediate steady-states not accessible using traditional feed-forward control. A modified proportional-integral closed-loop controller is proposed (Boost-PI), which incorporates a variable boost voltage to temporarily elevate actuation close to, but not exceeding, the pull-in voltage threshold. This primes the actuator for zipping and drastically reduces rise time compared with a traditional PI controller. A multi-objective parameter-space approach was implemented to choose appropriate controller gains by assessing the metrics of rise time, overshoot, steady-state error, and settle time. This proposed control method addresses a key limitation of the electro-ribbon actuators, allowing the actuator to perform staircase and oscillatory control tasks. This significantly increases the range of applications which can exploit this new DLZ actuation technology.
Bibliographical noteFunding Information:
This research was supported by Royal Society Grant (TA\R1\170060) and EPSRC Impact Acceleration Funding. RD was supported by EPSRC Centre for Doctoral Training in Future Autonomous and Robotic Systems (FARSCOPE, grant EP/L015293/1) and EPSRC grant EP/S021795/1. AF was supported by Royal Society Grant (TA\R1\170060), EPSRC Impact Acceleration Funding, and The James Dyson Foundation. TH was funded by the Royal Academy of Engineering and the Office of the Chief Science Adviser for National Security under the UK Intelligence Community Postdoctoral Fellowship Programme. MT was supported by EP/R02961X/1. JR was supported by EPSRC grants EP/L015293/1, EP/M020460/1, EP/S026096/1, P/S021795/1, and EP/R02961X/1 and by the Royal Academy of Engineering as Chair in Emerging Technologies.
© Copyright © 2020 Diteesawat, Fishman, Helps, Taghavi and Rossiter.
Copyright 2020 Elsevier B.V., All rights reserved.
- dielectrophoretic liquid zipping
- pull-in instability
- soft robotics