A mechanics-based approach to realize high–force capacity electroadhesives for robots

Abstract

Materials with electroprogrammable stiffness and adhesion can enhance the performance of robotic systems, but 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 and high activation voltages 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. Here, we use a fracture mechanics framework to understand the relationship between clutch design and force capacity. We demonstrate and verify a mechanics-based model that predicts clutch performance across multiple geometries and applied voltages. On the basis of this approach, we build a clutch with 63 times the force capacity per unit electrostatic force of state-of-the-art electroadhesive clutches. Last, we demonstrate the ability of our electroadhesives to increase the load capacity of a soft, pneumatic finger by a factor of 27 times compared with a finger without an electroadhesive.

A Low‐Voltage, High‐Force Capacity Electroadhesive Clutch Based on Ionoelastomer Heterojunctions

“…In addition to the presented demonstrations, these clutches could be implemented for improved performance in reconfigurable robotic systems or electronics manufacturing processes. [ 6 ]…”

“…These results confirm that the electroadhesive force capacity can vary significantly under a constant area, which reinforces the importance of considering the clutch compliance in an ionoelastomer clutch design with a soft interface, as was established in our previous work with thin, flexible electroadhesives with rigid dielectric layers. [ 6 ]…”

“…The prior clutches are from references. [4,6,[9][10][11]15] This surface enhancement reflected a preferential segregation of the 15-Fa comonomer to the surface due to its lower surface energy, thereby driving the observed increase in water contact angle.…”

“…[4][5] Electroadhesive clutches, to date, have been made from overlapping electrodes separated by an insulating dielectric layer. [4,[6][7][8][9][10][11] When a voltage is applied, opposing charges on either electrode are attracted to one another [12,13] and the electrostatic forces produced at the contact interface prevent sliding and increase the in-plane stiffness. [5] This simple design has been used to provide haptic responses to virtual objects in gloves [4,10,11,14] , and enable robotic exoskeletons, [8,9] fingered gripping systems, [2] modular robotic teams, [15] shape-locking of pneumatic actuators, [7,16] and electrostatic zipping actuators.…”

Predicting the Electrical, Mechanical, and Geometric Contributions to Soft Electroadhesives through Fracture Mechanics

“…These compliance effects were previously rationalized using a confinement parameter a/h, where a is the interfacial length and h is the material thickness. 13 The importance of geometry was recently demonstrated for electrostatic clutches, 14 where the performance of the clutch was enhanced over 60-fold when the geometry was optimized, compared to other state-of-theart devices. These influences of confinement, along with parameters like the Young's modulus, are critical to place in context with adhesion from electrostatic interactions, particularly in soft materials where the intrinsic adhesion is not negligible.…”