Peeling in electroadhesion soft grippers

Electroadhesion endows robots with super-human abilities: mechanical geckoes that climb vertical walls and soft grippers that grasp the most delicate objects. Based on electrostatics, the adhesion forces are turned on and off by an electrical signal, promising extremely fast operation, from silent fully solid-state devices. Practical applications of electroadhesion have however been limited to date by two main challenges: (1) the adhesion forces can vary over 1000x by simply changing the angle between the electroadhesive tape and the object, (2) release is often slow due to residual adhesion when voltage is removed. This paper describes a solution to both these issues by understanding and leveraging peeling in electroadhesion. We present simple models for peeling of electroadhesive tapes, predicting a change in peeling force from < 1 mN to over 1 N by changing the angle between the tape and the object from 90° to 0°. The models are in excellent agreement with our peeling experiments with 30 mm long, 20 mm wide, 300μm thick electroadhesion tapes made of silicone rubber with carbon electrodes. We demonstrate an electroadhesion soft gripper that uses motorized fingers to control the peeling angle, as a practical application of our peeling models. By moving the fingers to ensure a low peeling angle (0°) when grasping, the same gripper can successfully pick up from a 10 g cherry tomato (2.5 cm wide) to a 600 g Mango (9 cm wide). By then setting a high peeling angle (> 30°), the gripper reliably and rapidly (< 300 ms) releases those objects, despite residual adhesion. Electroadhesion soft grippers have many advantages, including grasping without squeezing, silent operation, low power consumption (< 1 W) and low weight (1 g per soft finger). Understanding and modelling contact mechanics in electroadhesion devices was an essential missing step for practical applications of electroadhesion in robots and grippers. This paper sheds light on how peeling influences electroadhesion and provides practical tools to design and operate electroadhesion systems.