MEAM Ph.D. Thesis Defense: “High Performance Electroadhesives for Materials and Robots with Electroprogrammable Stiffness”

Materials with electroprogrammable stiffness and adhesion can enhance the performance of robotic systems, including prosthetics, medical devices, wearables, exoskeletons, and grippers. However, achieving large changes in stiffness and adhesive forces in real time is an ongoing challenge. Electroadhesive clutches can rapidly adhere high stiffness elements, although their low force capacities, high activation voltages, and inability to separate and turn off stiffness changes reliably have limited their applications.

A major challenge in realizing stronger electroadhesive clutches is that current parallel-plate models poorly predict clutch force capacity and cannot be used to design better devices. Thus, current electroadhesive clutches suffer from force capacities below that of other materials with an electrically-programmable stiffness. Furthermore, soft material interfaces have not been utilized for stronger electroadhesive clutches due to latent adhesion at the contact interface that prevents programmable release.

This work demonstrates strategies to improve electroadhesive clutch designs for high-performance applications in material systems and robots with an electrically-programmable stiffness. Using a fracture mechanics framework, we build an improved understanding of the relationship between clutch design, force capacity and contact area. This mechanics-based framework predicts clutch performance across multiple geometries and applied voltages. Based on this approach, a Coulombic electrostatic clutch with 63 times the force capacity per unit electrostatic force of state-of-the-art electroadhesive clutches is realized. By doing so with traditional dielectrics and electrode materials, we demonstrate the power of our mechanics-based design methodology to increase clutch performance without relying on expensive materials or intensive manufacturing processes, making our approach optimal for widespread adoption by robotics researchers.

Finally, this mechanics-based design methodology is applied to the design of clutches with soft material interfaces. We demonstrate that this approach in conjunction with an engineered electroadhesive surface enables the use of elastomeric materials and low-voltage ionoelastomers in electroadhesive clutches with increased force capacities, which are capable of programmable release at reduced device sizes. We utilize these high-performance clutch designs in novel applications with an electrically-programmable stiffness, including soft robotic hands with enhanced load carrying capacity, wearable haptic interfaces, and morphing fabrics.