Smooth Vertical Surface Climbing With Directional Adhesion
TL;DR: 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 are described.
Abstract: 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.
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TL;DR: A critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures, and improved materials, processing methods, and sensing play an important role in future research.
Abstract: 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.
1,028 citations
06 Dec 2016
TL;DR: 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.
Abstract: 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.
831 citations
Cites background from "Smooth Vertical Surface Climbing Wi..."
...Climbing Stickybot Hierarchical structures, directional adhesion, and control of tangential contact forces (67)...
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...(D) Stickybot climbing on a glass surface by exploiting the hierarchical microstructure of its soft feet (67)....
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...2D) (67), a gecko-inspired robot that exploits some of the enabling features of its animal counterpart....
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TL;DR: 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.
Abstract: 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.
585 citations
TL;DR: The structure that allows gecko lizards and insects to climb vertical and inverted surfaces with ease has been studied extensively and attempts to replicate the structures seen in animals using synthetic materials to create adhesives with similar adhesive characteristics are made.
Abstract: The structure that allows gecko lizards and insects to climb vertical and inverted surfaces with ease has been studied extensively since the mechanism of attachment was shown to be due dominantly to intermolecular surfaces forces. Gecko toes have been shown to adhere with high interfacial shear strength to smooth surfaces (88–200 kPa) using microscale angled fiber structures on their feet. These structures exploit the weak van der Waals interaction forces at the tips of the branching keratinous fiber arrays through their conformation into intimate contact with climbing surfaces, creating a large overall adhesion through millions of sub-micrometer scale contact points. These many contacts also resist peeling by disrupting crack propagations at the interface. Since these discoveries, many attempts have been made to replicate the structures seen in animals using synthetic materials to create adhesives with similar adhesive characteristics. Applications for such adhesives include wall-climbing robots, tissue adhesives for medical applications, and grippers for manipulation. Autumn et al. molded the first synthetic mimics by creating templates using an sharp probe followed by nanomolding. This effort was followed by attempts using electron-beam lithography, carbon nanotubes, nanodrawing, and micro/nanomolding to form high aspect ratio fibrillar structures. Higher adhesion was seen in structures with wider flat mushroom tips, demonstrating that tip size is an important parameter for generating large forces. The wider flat tips increase the contact area and may eliminate the stress singularities along the edge of the interface, as described by Bogy. Adhesion strengths as high as 180 kPa have been demonstrated with vertically aligned mushroom tipped microfibers, although damage occurs to the structures during detachment. Fibrillar structures have also been fabricated to increase (or decrease) friction. In addition, fiber surfaces have been created that provide shear adhesion using vertical arrays of single and multi-walled carbon nanotubes. Unfortunately, these fibrillar structures require very high preloads in order to provide interfacial shear strength. Stiff polypropylene sub-micrometer diameter fibers have been shown to exhibit shear adhesion without requiring high preloading.
432 citations
TL;DR: The design and control of a wearable robotic device powered by pneumatic artificial muscle actuators for use in ankle-foot rehabilitation inspired by the biological musculoskeletal system of the human foot and lower leg, mimicking the morphology and the functionality of the biological muscle-tendon-ligament structure is described.
Abstract: We describe the design and control of a wearable robotic device powered by pneumatic artificial muscle actuators for use in ankle–foot rehabilitation. The design is inspired by the biological musculoskeletal system of the human foot and lower leg, mimicking the morphology and the functionality of the biological muscle–tendon–ligament structure. A key feature of the device is its soft structure that provides active assistance without restricting natural degrees of freedom at the ankle joint. Four pneumatic artificial muscles assist dorsiflexion and plantarflexion as well as inversion and eversion. The prototype is also equipped with various embedded sensors for gait pattern analysis. For the subject tested, the prototype is capable of generating an ankle range of motion of 27 ◦ (14 ◦ dorsiflexion and 13 ◦ plantarflexion). The controllability of the system is experimentally demonstrated using a linear time-invariant (LTI) controller. The controller is found using an identified LTI model of the system, resulting from the interaction of the soft orthotic device with a human leg, and model-based classical control design techniques. The suitability of the proposed control strategy is demonstrated with several angle-reference following experiments.
407 citations
Cites background from "Smooth Vertical Surface Climbing Wi..."
...The differential tendon mechanism of muscle 2, similar to the foot design of a wallclimbing robot [29], distributes the pulling force from one tendon cable to four anchors....
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References
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Book•
01 Jan 1985
TL;DR: The forces between atoms and molecules are discussed in detail in this article, including the van der Waals forces between surfaces, and the forces between particles and surfaces, as well as their interactions with other forces.
Abstract: The Forces between Atoms and Molecules. Principles and Concepts. Historical Perspective. Some Thermodynamic Aspects of Intermolecular Forces. Strong Intermolecular Forces: Covalent and Coulomb Interactions. Interactions Involving Polar Molecules. Interactions Involving the Polarization of Molecules. van der Waals Forces. Repulsive Forces, Total Intermolecular Pair Potentials, and Liquid Structure. Special Interactions. Hydrogen-Bonding, Hydrophobic, and Hydrophilic Interactions. The Forces between Particles and Surfaces. Some Unifying Concepts in Intermolecular and Interparticle Forces. Contrasts between Intermolecular, Interparticle, and Intersurface Forces. van der Waals Forces between Surfaces. Electrostatic Forces between Surfaces in Liquids. Solvation, Structural and Hydration Forces. Steric and Fluctuation Forces. Adhesion. Fluid-Like Structures and Self-Assembling Systems. Micelles, Bilayers, and Biological Membranes. Thermodynamic Principles of Self-Assembly. Aggregation of Amphiphilic Molecules into Micelles, Bilayers, Vesicles, and Biological Membranes. The Interactions between Lipid Bilayers and Biological Membranes. References. Index.
18,048 citations
TL;DR: In this paper, the influence of surface energy on the contact between elastic solids is discussed and an analytical model for its effect upon the contact size and the force of adhesion between two lightly loaded spherical solid surfaces is presented.
Abstract: This paper discusses the influence of surface energy on the contact between elastic solids. Equations are derived for its effect upon the contact size and the force of adhesion between two lightly loaded spherical solid surfaces. The theory is supported by experiments carried out on the contact of rubber and gelatine spheres.
6,981 citations
"Smooth Vertical Surface Climbing Wi..." refers methods in this paper
...Comparison of the frictional adhesion model [4] and the JKR model [18] with pull-off force data from a single toe of Stickybot’s directional adhesive patches (513 stalks)....
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TL;DR: This work provides the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects.
Abstract: Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well to strongly hydrophobic and strongly hydrophilic, polarizable surfaces. Adhesion of a single isolated gecko seta was equally effective on the hydrophobic and hydrophilic surfaces of a microelectro-mechanical systems force sensor. A van der Waals mechanism implies that the remarkable adhesive properties of gecko setae are merely a result of the size and shape of the tips, and are not strongly affected by surface chemistry. Theory predicts greater adhesive forces simply from subdividing setae to increase surface density, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects. Estimates using a standard adhesion model and our measured forces come remarkably close to predicting the tip size of Tokay gecko seta. We verified the dependence on size and not surface type by using physical models of setal tips nanofabricated from two different materials. Both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.
1,745 citations
"Smooth Vertical Surface Climbing Wi..." refers background in this paper
...The consequence of the gecko’s hierarchical system of compliances is that it can achieve levels of adhesion of over 500 kPa on a wide variety of surfaces from glass to rough rock, and can support its entire weight in shear from just one toe [7]....
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TL;DR: An extensive microscopic study has shown a strong inverse scaling effect in these attachment devices, whereas μm dimensions of the terminal elements of the setae are sufficient for flies and beetles, geckos must resort to sub-μm devices to ensure adhesion.
Abstract: Animals with widely varying body weight, such as flies, spiders, and geckos, can adhere to and move along vertical walls and even ceilings. This ability is caused by very efficient attachment mechanisms in which patterned surface structures interact with the profile of the substrate. An extensive microscopic study has shown a strong inverse scaling effect in these attachment devices. Whereas μm dimensions of the terminal elements of the setae are sufficient for flies and beetles, geckos must resort to sub-μm devices to ensure adhesion. This general trend is quantitatively explained by applying the principles of contact mechanics, according to which splitting up the contact into finer subcontacts increases adhesion. This principle is widely spread in design of natural adhesive systems and may also be transferred into practical applications.
999 citations
"Smooth Vertical Surface Climbing Wi..." refers background in this paper
...the size and shape of the contacting elements is important in sustaining adhesion [1], [14]–[16], [22], [35]....
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TL;DR: This paper discusses three fundamental problems relating to grasping and manipulating objects within an articulated, multifingered hand: determining how hard to squeeze an ob ject in order to ensure a secure grasp, determining the finger- joint motions required to produce a desired motion of the object, and determining the workspace of the hand.
Abstract: This paper discusses three fundamental problems relating to grasping and manipulating objects within an articulated, multifingered hand: determining how hard to squeeze an ob ject in order to ensure a secure grasp, determining the finger- joint motions required to produce a desired motion of the object, and determining the workspace of the hand.Squeezing the object, or the application of internal grasp forces, is reduced to a linear programming problem which considers friction and joint torque limit constraints. The relationship between the finger-joint motions and the motion of the object, for the case of pure rolling between the finger tips and the object, is formulated as a set of differential equa tions. The total workspace for a hand is determinedfor spe cial cases of planar and spatial hands.
864 citations
"Smooth Vertical Surface Climbing Wi..." refers methods in this paper
...In order to handle this tradeoff, Stickybot’s controller implements a grasp-space stiffness controller [20]....
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