41 research outputs found
Toward Micro Wall-Climbing Robots Using Biomimetic Fibrillar Adhesives
Climbing is a challenging task for autonomous mobile robots primarily due to requirements for agile locomotion, and high maneuverability as well as robust and efficient attachment and detachment. A novel miniature wall-climbing robot is proposed. The robot is adapted for the wall-climbing task by taking advantage of down scaling and its low design. Challenges encountered during robot miniaturization and performances of the robot are reported. The miniature robot prototype proved to be able to climb on inclined surfaces with a slope of up to 90° at a speed of 3.3mm/s. It is equipped with sensors that enable it to avoid obstacles, follow walls and detect free-falls. It can be controlled by remote control or act autonomously. Animals, such as Geckos, have developed amazing climbing ability through micro- and nano-fibers on their feet. These structures have inspired the study of dry adhesion and the design of synthetic fibrillar pads presented in the paper
Bio-Inspired Adhesive Footpad for Legged Robot Climbing under Reduced Gravity: Multiple Toes Facilitate Stable Attachment
This paper presents the design of a legged robot with gecko-mimicking mechanism and mushroom-shaped adhesive microstructure (MSAMS) that can climb surfaces under reduced gravity. The design principle, adhesion performance and roles of different toes of footpad are explored and discussed in this paper. The effect of the preload velocity, peeling velocity and thickness of backing layering on the reliability of the robot are investigated. Results show that pull-force is independent of preload velocity, while the peeling force is relying on peeling velocity, and the peel strength increased with the increasing thickness of the backing layer. The climbing experiments show that the robot can climb under mimic zero gravity by using multiple toes facilitating adhesion. The robot with new type of footpads also provides a good platform for testing different adhesive materials for the future space applications
The Problem of Adhesion Methods and Locomotion Mechanism Development for Wall-Climbing Robots
This review considers a problem in the development of mobile robot adhesion
methods with vertical surfaces and the appropriate locomotion mechanism design.
The evolution of adhesion methods for wall-climbing robots (based on friction,
magnetic forces, air pressure, electrostatic adhesion, molecular forces,
rheological properties of fluids and their combinations) and their locomotion
principles (wheeled, tracked, walking, sliding framed and hybrid) is studied.
Wall-climbing robots are classified according to the applications, adhesion
methods and locomotion mechanisms. The advantages and disadvantages of various
adhesion methods and locomotion mechanisms are analyzed in terms of mobility,
noiselessness, autonomy and energy efficiency. Focus is placed on the physical
and technical aspects of the adhesion methods and the possibility of combining
adhesion and locomotion methods
Tunable Reversible Dry Adhesion of Elastomeric Post Enabled by Stiffness Tuning of Microfluidic LMPA Thin Film
The goal of this study is to investigate the effects and underlying mechanisms of stiffness tuning on tunable reversible dry adhesion of an elastomeric post. This research introduces a novel device constructed out of a soft elastomer, polydemethylsiloxane (PDMS), with micro channels injected with low melting point alloy (LMPA) that can soften by applying a voltage. In contrast to traditional handling devices, such as metallic robot handlers, this soft gripper enables compliant manipulation of delicate fragile objects such as a thin glass slide. In this thesis, the design and fabrication of the elastomeric posts and the effects of three adhesion testing conditions will be presented. The first testing condition provided the baseline adhesion values that would be later referenced to certify adhesion reversibility. The second condition demonstrates the device’s ability to change adhesion forces on the spot, or dynamically. The third condition displays the ability of the device to maintain this adhesion change when activated and deactivated repeatedly. Theoretical Finite Element modeling provides insights indicating a maximum adhesion when varying one critical geometrical parameter, which was later confirmed with experiments. Experimental results prove the device’s capability of dynamically tunable reversible dry adhesion. This novel approach to tunable dry adhesion exhibits the feasibility of soft grippers that would not require complicated systems for activation but instead only need low power and simple circuitry, and thus have potential to function as effective soft gripping devices
Shape memory polymers as direct contact dry adhesives for transfer printing and general use
For most diminutive life on Earth, control over external adhesive forces is crucial for survival. As humans, we pay little notice because at our scale inertial forces typically overwhelm adhesive forces by a wide margin. Nonetheless, the study and development of dry adhesives, which rely on ubiquitous intermolecular attractions to repeatedly form and break attachment to their adherends, have garnered substantial interest in recent decades. High performance artificial dry adhesives may unlock the door for many exciting new technologies from nanoscale manufacturing to wall climbing robots, but thus far the challenges have proven substantial and few successful commercial applications have come to fruition.
This dissertation represents an initial investigation into the benefits and potential limitations of developing shape memory polymer (SMP)-based dry adhesives. Prior to the presentation of experimental results, a review of the current state of dry adhesive knowledge including both theory, observations of the natural world, and lessons learned by other researchers in their attempts to develop a wide variety of synthetic dry adhesives is provided. It is concluded that dry adhesives fundamentally function through careful control of elastic energy, an idea that is very well suited to explore using SMPs which offer a large change in compliance across their thermal transition temperature. Thermoset epoxy SMPs are identified as an ideal choice for the investigation due to their mechanical strength, chemical resistance, manufacturability and convenient glass transitions among other features. The dry adhesive performance of a selected SMP is first evaluated for the purpose of microscale transfer printing, wherein micro-objects are assembled through precise control of adhesive surface forces. Significant benefits over existing solutions in terms of maximum adhesive strength during loading (~7 MPa), minimum strength for release (~0 MPa), and process versatility are confirmed, culminating in demonstrations of several challenging assemblies. The increase in adhesive strength is explained by invoking arguments from linear fracture mechanics and considering the dramatic compliance change experienced by the SMP between bond and load events. Advanced methods of heating and meaningful steps towards commercial-scale parallel printing processes are demonstrated.
The suitability of SMP for larger-scale applications is considered next. Strength rivaling or exceeding known alternatives is demonstrated, showing adhesion exceeding 2 MPa for 6 mm diameter adhesives while retaining excellent releasability through the use of microstructuring. A method of internally heating the SMP by adding conductive carbon nanoparticles is explored, including quantitative analyses of conductivity and the SMP composite's storage and loss moduli. The resulting flexible and conductive bi-layer SMP adhesive supports load while attached to surfaces of varied curvature. Variations on the SMP formula have their adhesive and mechanical properties tested, and are used to produce a self-contained SMP prototype wall-hanging adhesive
Applications of Bioinspired Reversible Dry and Wet Adhesives: A Review
<jats:p>Bioinspired adhesives that emulate the unique dry and wet adhesion mechanisms of living systems have been actively explored over the past two decades. Synthetic bioinspired adhesives that have recently been developed exhibit versatile smart adhesion capabilities, including controllable adhesion strength, active adhesion control, no residue remaining on the surface, and robust and reversible adhesion to diverse dry and wet surfaces. Owing to these advantages, bioinspired adhesives have been applied to various engineering domains. This review summarizes recent efforts that have been undertaken in the application of synthetic dry and wet adhesives, mainly focusing on grippers, robots, and wearable sensors. Moreover, future directions and challenges toward the next generation of bioinspired adhesives for advanced industrial applications are described.</jats:p>
Limpet II: A Modular, Untethered Soft Robot
The ability to navigate complex unstructured environments and carry out inspection tasks requires robots to be capable of climbing inclined surfaces and to be equipped with a sensor payload. These features are desirable for robots that are used to inspect and monitor offshore energy platforms. Existing climbing robots mostly use rigid actuators, and robots that use soft actuators are not fully untethered yet. Another major problem with current climbing robots is that they are not built in a modular fashion, which makes it harder to adapt the system to new tasks, to repair the system, and to replace and reconfigure modules. This work presents a 450 g and a 250 × 250 × 140 mm modular, untethered hybrid hard/soft robot—Limpet II. The Limpet II uses a hybrid electromagnetic module as its core module to allow adhesion and locomotion capabilities. The adhesion capability is based on negative pressure adhesion utilizing suction cups. The locomotion capability is based on slip-stick locomotion. The Limpet II also has a sensor payload with nine different sensing modalities, which can be used to inspect and monitor offshore structures and the conditions surrounding them. Since the Limpet II is designed as a modular system, the modules can be reconfigured to achieve multiple tasks. To demonstrate its potential for inspection of offshore platforms, we show that the Limpet II is capable of responding to different sensory inputs, repositioning itself within its environment, adhering to structures made of different materials, and climbing inclined surfaces
Improved Adhesion and Compliancy of Hierarchical Fibrillar Adhesives
The gecko relies on van der Waals forces to cling onto surfaces with a variety of topography and composition. The hierarchical fibrillar structures on their climbing feet, ranging from mesoscale to nanoscale, are hypothesized to be key elements for the animal to conquer both smooth and rough surfaces. An epoxy-based artificial hierarchical fibrillar adhesive was prepared to study the influence of the hierarchical structures on the properties of a dry adhesive. The presented experiments highlight the advantages of a hierarchical structure despite a reduction of overall density and aspect ratio of nanofibrils. In contrast to an adhesive containing only nanometer-size fibrils, the hierarchical fibrillar adhesives exhibited a higher adhesion force and better compliancy when tested on an identical substrate
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Biomechanics of the fibrillar adhesive system in insects
Many animals are able to scale smooth surfaces using adhesive structures on their feet. These organs are either soft pads with a relatively smooth surface or dense arrays of microscopic adhesive hairs with both designs having independently evolved in diverse taxa of arthropods and vertebrates. Biological adhesive pads out-perform conventional adhesives in many respects, making them important models for biomimetics. Hairy pads have attracted particular attention, because it has become feasible to fabricate similar synthetic microstructures. Nevertheless, the detailed performance and functional properties have not been characterised for any natural fibrillar adhesive system, and many fundamental aspects are still not understood. The aim of this thesis was therefore to investigate the fibrillar adhesive system of leaf beetles as a model.
To investigate the functional implications of hairy pad design, the attachment performance between hairy pads of the leaf beetle Gastrophysa viridula and smooth pads of stick insects (Carausius morosus) was compared. Adhesive and frictional stresses were found to be similar in smooth and hairy pads, inconsistent with contact splitting theory, which predicts higher adhesive stresses for fibrillar adhesives. Hairy pads showed a greater direction-dependence of friction forces than smooth pads, confirming the importance of the asymmetric design of individual setae for effortless detachment. Experiments with contaminating particles also showed that hairy pads removed contamination more rapidly and efficiently than smooth pads. Self-cleaning ability had not been previously documented for adhesive organs of insects. To investigate to what extent the hairy system is able to compensate for surface roughness, whole-body attachment forces were measured for varying roughness levels. Attachment was reduced for all length scales of surface roughness, but in particular for asperity sizes smaller than the diameter of individual seta tips.
Leaf beetles possess adhesive pads on three tarsal segments, which vary in setal morphology. However, the functional implications of this variation are unknown. The mechanical and adhesive properties of individual pads were therefore tested and their use during climbing observed. Proximal pads were shown to be stiffer than distal pads, conferring stability during pushing. In contrast, the softer distal pads allowed better attachment to rough surfaces. Hence the morphological variation is explained by an effective division of labour between the pads. To investigate an extreme example of pushing in a hairy system, pad use was studied during jumping in flea beetles. The pushing forces needed during take-off were exclusively produced by the proximal pads, again confirming the division of labour. To characterise the effects of different hair morphologies and to understand how individual setae contribute to array and whole-animal performance, single hair forces were measured using a glass capillary cantilever. Male-specific discoidal hairs were shown to be both stiffer and more adhesive than pointed and spatula-tipped setae, likely affecting overall pad stability and attachment.
This thesis has shown that hairy pads are similar to smooth pads in the magnitude of adhesive stress supported yet outperform them in detachability and self-cleaning. It was also demonstrated that there are considerable differences in design and performance even within setal arrays of the same insect, indicating the limitations of general models of fibrillar adhesion and underlining the importance of specialised adaptations.Funded by research grants from the UK Biotechnology and Biological Sciences Research Council and the Cambridge Isaac Newton Trust