Advances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201707035

Soft Robotic Grippers.

The proliferation of soft robotics research worldwide has brought substantial achievements in terms of principles, models, technologies, techniques, and prototypes of soft robots. Such achievements are reviewed here in terms of the abilities that they provide robots that were not possible before. An analysis of the evolution of this field shows how, after a few pioneering works in the years 2009 to 2012, breakthrough results were obtained by taking seminal technological and scientific challenges related to soft robotics from actuation and sensing to modeling and control. Further progress in soft robotics research has produced achievements that are important in terms of robot abilities-that is, from the viewpoint of what robots can do today thanks to the soft robotics approach. Abilities such as squeezing, stretching, climbing, growing, and morphing would not be possible with an approach based only on rigid links. The challenge ahead for soft robotics is to further develop the abilities for robots to grow, evolve, self-heal, develop, and biodegrade, which are the ways that robots can adapt their morphology to the environment.

Soft robotics: Technologies and systems pushing the boundaries of robot abilities.

A highly versatile soft gripper that can handle an unprecedented range of object types is developed based on a new design of dielectric elastomer actuators employing an interdigitated electrode geometry, simultaneously maximizing both electroadhesion and electrostatic actuation while incorporating self-sensing. The multifunctionality of the actuator leads to a highly integrated, lightweight, fast, soft gripper with simplified structure and control.

/pdf/versatile-soft-grippers-with-intrinsic-electroadhesion-based-10fu4b42iq.pdf

Versatile Soft Grippers with Intrinsic Electroadhesion Based on Multifunctional Polymer Actuators

Stickybot is a bioinspired robot that climbs smooth vertical surfaces such as glass, plastic, and ceramic tile at 4 cm/s. The robot employs several design principles adapted from the gecko including a hierarchy of compliant structures, directional adhesion, and control of tangential contact forces to achieve control of adhesion. We describe the design and fabrication methods used to create underactuated, multimaterial structures that conform to surfaces over a range of length scales from centimeters to micrometers. At the finest scale, the undersides of Stickybot's toes are covered with arrays of small, angled polymer stalks. Like the directional adhesive structures used by geckos, they readily adhere when pulled tangentially from the tips of the toes toward the ankles; when pulled in the opposite direction, they release. Working in combination with the compliant structures and directional adhesion is a force control strategy that balances forces among the feet and promotes smooth attachment and detachment of the toes.

/pdf/smooth-vertical-surface-climbing-with-directional-adhesion-zb2xusy7bv.pdf

Smooth Vertical Surface Climbing With Directional Adhesion

There is a significant medical need for tough biodegradable polymer adhesives that can adapt to or recover from various mechanical deformations while remaining strongly attached to the underlying tissue We approached this problem by using a polymer poly(glycerol-co-sebacate acrylate) and modifying the surface to mimic the nanotopography of gecko feet, which allows attachment to vertical surfaces Translation of existing gecko-inspired adhesives for medical applications is complex, as multiple parameters must be optimized, including: biocompatibility, biodegradation, strong adhesive tissue bonding, as well as compliance and conformability to tissue surfaces Ideally these adhesives would also have the ability to deliver drugs or growth factors to promote healing As a first demonstration, we have created a gecko-inspired tissue adhesive from a biocompatible and biodegradable elastomer combined with a thin tissue-reactive biocompatible surface coating Tissue adhesion was optimized by varying dimensions of the nanoscale pillars, including the ratio of tip diameter to pitch and the ratio of tip diameter to base diameter Coating these nanomolded pillars of biodegradable elastomers with a thin layer of oxidized dextran significantly increased the interfacial adhesion strength on porcine intestine tissue in vitro and in the rat abdominal subfascial in vivo environment This gecko-inspired medical adhesive may have potential applications for sealing wounds and for replacement or augmentation of sutures or staples

/pdf/a-biodegradable-and-biocompatible-gecko-inspired-tissue-50nd1zg80y.pdf

A biodegradable and biocompatible gecko-inspired tissue adhesive

Directional arrays of branched microscopic setae constitute a dry adhesive on the toes of pad-bearing geckos, nature's supreme climbers. Geckos are easily and rapidly able to detach their toes as they climb. There are two known mechanisms of detachment: (1) on the microscale, the seta detaches when the shaft reaches a critical angle with the substrate, and (2) on the macroscale, geckos hyperextend their toes, apparently peeling like tape. This raises the question of how geckos prevent detachment while inverted on the ceiling, where body weight should cause toes to peel and setal angles to increase. Geckos use opposing feet and toes while inverted, possibly to maintain shear forces that prevent detachment of setae or peeling of toes. If detachment occurs by macroscale peeling of toes, the peel angle should monotonically decrease with applied force. In contrast, if adhesive force is limited by microscale detachment of setae at a critical angle, the toe detachment angle should be independent of applied force. We tested the hypothesis that adhesion is increased by shear force in isolated setal arrays and live gecko toes. We also tested the corollary hypotheses that (1) adhesion in toes and arrays is limited as on the microscale by a critical angle, or (2) on the macroscale by adhesive strength as predicted for adhesive tapes. We found that adhesion depended directly on shear force, and was independent of detachment angle. Therefore we reject the hypothesis that gecko toes peel like tape. The linear relation between adhesion and shear force is consistent with a critical angle of release in live gecko toes and isolated setal arrays, and also with our prior observations of single setae. We introduced a new model, frictional adhesion, for gecko pad attachment and compared it to existing models of adhesive contacts. In an analysis of clinging stability of a gecko on an inclined plane each adhesive model predicted a different force control strategy. The frictional adhesion model provides an explanation for the very low detachment forces observed in climbing geckos that does not depend on toe peeling.

/pdf/frictional-adhesion-a-new-angle-on-gecko-attachment-4kaek4feu2.pdf

Frictional adhesion: A new angle on gecko attachment.

A traffic informational system provides information to traffic moving along a road and may include a plurality of traffic information devices mountable to the road, each having an integral power producing source, at least a first set of illumination sources, and a wireless communications subsystem. The traffic informational system may further include at least a first external control device comprising at least one antenna and a transmitter communication wirelessly with the traffic information devices and/or with one another. The traffic information device may communicate with one another, and may include sensor for sensing ambient conditions. The system employs various approaches to reducing power consumption and improving communications, and is suitable for a wide range of applications, including use in remote environments.

Methods, systems and devices related to road mounted indicators for providing visual indications to approaching traffic

Using the gecko as inspiration, important principles are revealed for reliable maneuvering on vertical surfaces. Foremost among these is the directional behavior of the gecko adhesive system, which permits control of adhesion via control of the tangential forces at the feet. Multiple hierarchical levels of compliance are also important for conforming intimately to surfaces with varying degrees of roughness and different length scales. In light of these requirements, most previously developed synthetic adhesives are not well suited for application on a climbing robot. We describe a synthetic fibrillar adhesive, termed Directional Polymer Stalks, made from relatively soft polyurethane (modulus of elasticity ≈ 300 kPa). The fibrils are angled 20° with respect to vertical and are approximately 1 mm long and 380 μm in diameter. Rather than having a flat top, they have angled faces at 45°. The directional nature of these angled stalks is shown, achieving a maximum adhesion of approximately 1 N for a 3.9 cm2 pat...

http://web.mit.edu/sangbae/Public/JAST.pdf

Directional adhesion for climbing: theoretical and practical considerations

Systems and methods for altering the shape of a reconfigurable surface area are presented. The present systems and methods facilitate efficient and effective interaction with a device or system. In one embodiment, a surface reconfiguration system includes a flexible surface; an elevation unit that creates alterations in the contours of the surface; and an elevation control component that controls adjustments to the elevation unit. Thus, the surface of the device is reconfigurable based on system, application, mode, and/or user needs. Accordingly, the surface can be used to provide input and output functionality. The surface can include touch detection functionality for added input functionality.

D. Santos

Papers

Frictional adhesion: A new angle on gecko attachment.

Smooth Vertical Surface Climbing With Directional Adhesion

Methods, systems and devices related to road mounted indicators for providing visual indications to approaching traffic

Directional adhesion for climbing: theoretical and practical considerations

Physically reconfigurable input and output systems and methods