Closed-Loop Control of Electro-Ribbon Actuators

Abstract

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.

Solvent‐Free Synthesis and Processing of Conductive Elastomer Composites for Green Dielectric Elastomer Transducers

“…Additionally, the excellent adhesion of the electrode to PET was demonstrated with a ribbon actuator tested at different frequencies from 0.1 to 10 Hz (Movie S3, Supporting Information). [54] To sum up, the optimized GNP6 material showed a high starting conductivity of 8.2 S cm −1 , relatively low change in resistivity for up to 80% uniaxial strains, a low elastic modulus of 167 kPa, and a large strain at break of 305%. Although the conductivity of GNP6 is significantly lower compared to stretchable elastomers consisting of Ag fillers embedded in an elastic matrix, it is sufficiently high for DET applications and shows no hysteresis under repetitive stretching.…”

The-state-of-the-art of soft robotics to assist mobility: a review of physiotherapist and patient identified limitations of current lower-limb exoskeletons and the potential soft-robotic solutions

“…Dielectric fluid electrostatic actuators have been developed as a new soft robotics actuation technology. Examples include dielectrophoretic liquid zipping actuator [ 104 – 106 ], hydraulically amplified self-healing electrostatic (HASEL) actuators [ 107 – 109 ], soft fluidic pumps, such as a stretc.hable pump [ 110 ] and an electro-pneumatic pump [ 111 , 112 ]. The recent stretc.hable pump and electro-pneumatic pump demonstrated important capability to integrate with soft fluidic actuators, e.g.…”

Electro-pneumatic pumps for soft robotics

“…Last, different materials with higher permittivity and electrical breakdown will be explored to improve electrostatic force and actuation performance. In addition, the control schemes and self-sensing of similar dielectric zipping actuators (42,43) can be implemented in the EPP to improve actuation precision and performance.…”