Limiting Mechanisms and Scaling of Electrostatically Controlled Adhesion of Soft Nanocomposite Surfaces for Robotic Gripping

Abstract

Surfaces with switchable adhesive properties are employed by robots to quickly grip and release objects and thereby to perform dexterous manipulation and locomotion tasks. Robotic grippers with switchable adhesion have been developed using structured polymers and electrostatic mechanisms. However, manipulating delicate items can be challenging as this requires strong, switchable gripping forces that do not damage the target object. Soft nanocomposite electroadhesives (SNEs) were recently introduced as an option for handling such objects. The technology integrates an electrostatic adhesion mechanism into a mechanically compliant surface formed from dielectric-coated carbon nanotubes (CNTs) to ensure soft contact with target objects. In this study we explore the scaling of the electrostatic adhesion of SNEs, toward their potential application in macroscale grasping and manipulation. We measure electroadhesive pressures on millimeter-scale areas of up to ∼20 kPa with an on/off adhesion ratio of ∼700. Based on the measured forces and simple modeling, we conclude that the maximum achievable SNE adhesion forces are determined by dielectric breakdown in the insulating coating and surrounding air. Consequently, the SNE surface behaves as a parallel capacitor plate placed at an effective distance of 2.9 μm from the target object, despite being in contact with the target and therefore having the contacting CNTs separated from the surface by ∼2 nm dielectric coating. This mechanistic understanding of soft nanocomposite electroadhesives outlines the capabilities of the technology and informs their design for advanced manufacturing applications.

Low-Profile, Large-Range Compressive Strain Sensing Using Micromanufactured CNT Micropillar Arrays

“…To characterize the tactile sensing performance, PVACNT were fixed to a sample stage and quasi-statically compressed by a flat-end indenter (whose inscribed area is larger than the lateral dimension of the entire PVACNT array) under our custom-built setup, 39 with stepper motors controlling the XYZ movement and load cells sensing the applied force (Figure 1d). The total impedance change was measured at 1 and 10 kHz using an LCR meter (Hioki IM3536) during compression with a constant loading/unloading rate of 1 μm/s.…”

Advancement of Electroadhesion Technology for Intelligent and Self‐Reliant Robotic Applications

“…Sanha et al introduced a soft nanocomposite of Al 2 O 3 ‐coated carbon nanotube structures to manipulate the microscale objects. [ 89 ] A meager 0.2 nm thickness of Al 2 O 3 has attained the high electrostatic attraction forces with a small voltage of 10 V. Lim et al fabricated the gripper with 1–10 wt% of Al 2 O 3 nanoparticle embedded PDMS matrix and found that 10 wt% composition attained a high force of 612 mN cm −2 which was twofold higher than the pristine PDMS gripper due to the high dielectric constant and field strength of the composite. [ 90 ] Vasudev et al utilized the barium strontium titanate interfacial layers due to its high dielectric constant which is easy to polarize by applying high potential.…”

“…[ 178 ] Recently, Michael et al fabricated the carbon nanotube covered with ultrathin aluminum oxide which makes an interesting biomimetic natural structure without complicated lithography steps. [ 89 ] The device achieved the on/off ratio of 700 with an effective distance of ≈3 μm and a maximum adhesive force of 20 kPa. Different materials adhered and the maximum adhesion was the function of dielectric break down in air which is governed by Paschen's law and the dielectric thickness as discussed in Section 2.…”

Switchable Adhesion: On‐Demand Bonding and Debonding

“…For example, in robotics, on‐demand bonding and debonding allow the robot arm to grip and release things. [ 8 , 9 , 10 , 11 ] Robots based on switchable adhesive can climb and stay on the wall, which attract more and more attention. [ 9 , 12 ] In smart printing systems, switchable adhesive can transfer printing small‐scale micro‐nano materials onto arbitrary substrates to fabricate integrated semiconductor devices.…”