Controllable load sharing for soft adhesive interfaces on three-dimensional surfaces

Abstract

For adhering to three-dimensional (3D) surfaces or objects, current adhesion systems are limited by a fundamental trade-off between 3D surface conformability and high adhesion strength. This limitation arises from the need for a soft, mechanically compliant interface, which enables conformability to nonflat and irregularly shaped surfaces but significantly reduces the interfacial fracture strength. In this work, we overcome this trade-off with an adhesion-based soft-gripping system that exhibits enhanced fracture strength without sacrificing conformability to nonplanar 3D surfaces. Composed of a gecko-inspired elastomeric microfibrillar adhesive membrane supported by a pressure-controlled deformable gripper body, the proposed soft-gripping system controls the bonding strength by changing its internal pressure and exploiting the mechanics of interfacial equal load sharing. The soft adhesion system can use up to ∼26% of the maximum adhesion of the fibrillar membrane, which is 14× higher than the adhering membrane without load sharing. Our proposed load-sharing method suggests a paradigm for soft adhesion-based gripping and transfer-printing systems that achieves area scaling similar to that of a natural gecko footpad.soft gripper | equal load sharing | fracture mechanics | fibrillar adhesives | gecko B y exploiting principles of equal load sharing (1) and interfacial crack pinning (2), geckos' fibrillar foot-hairs can firmly adhere to a wide range of surfaces using intermolecular interactions, such as van der Waals forces (3). Using the same attachment method, gecko-inspired synthetic elastomeric fibrillar adhesives achieve bond strengths of over 100 kPa on smooth flat surfaces (4), surpassing the performance of the gecko on such surfaces (5), and exhibit quick release through peeling (6) or buckling (7) of the microfibers. For the past decade, gecko-inspired adhesives have been applied to a variety of systems including numerous robotic applications for wall climbing (8, 9), perching devices for flyers (10), and grippers (11)(12)(13)(14). However, difficulties arise in dealing with 3D surfaces because the current gecko-inspired synthetic adhesive systems are often supported by a rigid backing, which limits their ability to conform to nonplanar surfaces. In our previous work, we created elastomeric fibrillar adhesives integrated with a soft membrane, which we named as fibrillar adhesives on a membrane (FAM), and fixed the membrane onto a 3D-printed rigid plastic body so that the system could handle various 3D objects (15). Despite demonstrating a significant improvement over an unstructured elastomeric membrane with 10× higher adhesion, the tested FAM could achieve only 2 kPa of adhesion stress, a small fraction of the 55 kPa measured with rigid-backed microfiber arrays (16). This implies that the improved conformability to 3D surfaces enabled by the more compliant membrane backing is at the expense of a 96% reduction in adhesion strength. Considering that the adhesion of a membrane scales with the circumferential ...

Soft Robotic Grippers

“…Thanks to the large membrane area, the gripper has demonstrated simultaneous transfer of steel balls of different size. A similar research has been performed by Song et al, where an elastomer membrane with mushroom‐shaped microfibers has exhibited holding of various objects as shown in Figure c: a rounded glass flask, a coffee cup, a pair of cherry tomatoes, and a plastic bag. In this system, adhesion is controlled by the internal pressure of the elastomer membrane, and the loading force normal to the interface.…”

Bio‐inspired Design and Additive Manufacturing of Soft Materials, Machines, Robots, and Haptic Interfaces

“…It also generates high shear forces with small compression forces,and therefore is advantageous when handling fragile objects (Figure 5b). [194][195][196] Nature offers the best examples of manipulation using soft bodies.M uscular hydrostats,i ncluding the tongues of mammals and lizards,t he arms and tentacles of cephalopods,a nd the trunks of elephants,d emonstrate the best manipulation capabilities,namely,effective grasping of various objects and agile movement when holding the object. [197] This remarkable feat is carried out by ah ighly integrated system, where complex movements are conducted through the coordination of intricate musculature (coupled actuations from transverse and longitudinal muscles), and impressive grasping is facilitated by designated components (patterned suckers and the distal end of the octopus arm).…”

“…Reproducedf rom Ref. [196].c)Dexterouss oft robotic gripper inspired by an octopus arm. Reproducedfrom Ref.…”

“…[200] Octopus sucker-mimicking suction cap patterns have also been engineered to enhance gripping capacities. [196] Instead of mimicking the muscular hydrostat with amodular approach, Schanffner et al patterned the actuation mode in astiffer "fiber" architecture,inspired by the fibrous structure in elephant trunks and many plants (Figure 5d). [201] Enabled by multi-material 3D printing,composites with asoft silicone base and rigid silicone patterns can be programmed to demonstrate aw ide range of motions,i ncluding the four modes observed with elephant trunks:t wisting,b ending, contracting,a nd grabbing.C omplex motions that couple various actuation modes remain ac hallenge.F or soft manipulators,t he integration of more efficient gripping mechanisms,s uch as adhesion control, with agile movement mechanisms requires more developments at as ystem level.…”

Integrating Soft Robotics with the Robot Operating System: A Hybrid Pick and Place Arm

“…There are numerous designs and actuation methods for soft grippers, such as those that use the jamming properties of granular materials under a vacuum (Amend et al, 2012), electro-adhesion (Shintake et al, 2016), shape memory alloys (Wang et al, 2016), gecko-inspired adhesion (Song et al, 2017), and capillary action (Arutinov et al, 2015). We used the four fingered pneumatic soft gripper as detailed in Finio et al (2013).…”