Mini Review: Comparison of Bio-Inspired Adhesive Feet of Climbing Robots on Smooth Vertical Surfaces

Developing climbing robots for smooth vertical surfaces (e.g., glass) is one of the most challenging problems in robotics. Here, the adequate functioning of an adhesive foot is an essential factor for successful locomotion performance. Among the various technologies (such as dry adhesion, wet adhesion, magnetic adhesion, and pneumatic adhesion), bio-inspired dry adhesion has been actively studied and successfully applied to climbing robots. Thus, this review focuses on the characteristics of two different types of foot microstructures, namely spatula-shaped and mushroom-shaped, capable of generating such adhesion. These are the most used types of foot microstructures in climbing robots for smooth vertical surfaces. Moreover, this review shows that the spatula-shaped feet are particularly suitable for massive and one-directional climbing robots, whereas mushroom-shaped feet are primarily suitable for light and all-directional climbing robots. Consequently, this study can guide roboticists in selecting the right adhesive foot to achieve the best climbing ability for future robot developments

A concept selection method for designing climbing robots

This paper presents a concept selection methodology, inspired by the Verein Deutscher Ingenieure (VDI) model and Pugh's weighted matrix method, for designing climbing robots conceptually based on an up-to-date literature review. The proposed method is illustrated with a case study of ongoing research, the investigation of an adaptable and energetically autonomous climbing robot, in Loughborough University

Multi-Technique Investigation of a Biomimetic Insect Tarsal Adhesive Fluid

There is substantial motivation to develop novel adhesives which take advantage of the superior adhesive strength and adaptability of many natural animal adhesives; however, the tools typically used to study these mechanisms are incapable of determining the precise interactions of molecules at an adhesive interface. In this study, a surface specific, order sensitive vibrational spectroscopy called sum frequency generation (SFG) is, for the first time, combined with multiple bulk characterization techniques to examine a novel, simple biomimetic adhesive fluid inspired by tarsal fluid of insects. Insects perform complex adhesive demands, including sticking, climbing vertically and running upside-down with little difficulty. Thus, we hypothesize that both bulk and surface specific properties of the fluid contribute to the success of this wet adhesive mechanism. SFG spectra of biomimetic emulsion exhibited similar hydrocarbon organization on hydrophobic and hydrophilic substrates to natural beetle fluid previously studied with the same method. Bulk characterization techniques indicated that the emulsion had a shear-thinning profile with the ability to enhance traction forces during climbing and low surface tension ideal for surface wetting on the majority of natural surfaces. Multi-technique comparisons between emulsion and pure squalane revealed that a hydrocarbon only based fluid could not replicate the traction promoting properties of the emulsion. We conclude that the insect tarsal fluid adhesive mechanism relies upon contributions from both surface-specific properties optimizing traction force and bulk properties promoting rapid surface wetting and maintaining pull-off force for fast detachment

A Perching Mechanism for Flying Robots Using a Fibre-Based Adhesive

Robots capable of hover flight in constrained indoor environments have many applications, however their range is constrained by the high energetic cost of airborne locomotion. Perching allows flying robots to scan their environment without the need to remain aloft. This paper presents the design of a mechanism that allows indoor flying robots to attach to vertical surfaces. To date, solutions that enable flying robot with perching capabilities either require high precision control of the dynamics of the robot or a mechanism robust to high energy impacts. We propose in this article a perching mechanism comprising a compliant deployable pad and a passive self-alignment system, that does not require any active control during the attachment procedure. More specifically, a perching mechanism using fibre-based dry adhesives was implemented on a 300~g flying platform. An adhesive pad was first modeled and optimized in shape for maximum attachment force at the low pre-load forces inherent to hovering platforms. It was then mounted on a deployable mechanism that stays within the structure of the robot during flight and can be deployed when a perching maneuver is initiated. Finally, the perching mechanism is integrated onto a real flying robot and successful perching maneuvers are demonstrated as a proof of concept

Multi-Technique Characterizations of Natural and Biomimetic Adhesives

There have been many attempts to characterize and mimic natural fluid-based adhesive systems. However, very few of these studies have examined surface or interfacial interactions between adhesive and substrate. Furthermore, until now no study has used a combination of surface analytical and kinematic techniques to determine the precise chemical mechanisms that govern the success or failure of a natural adhesive in different environments. The work presented here demonstrates how the composition, order and relative orientation of adhesive molecules at functional interfaces can be determined using complementary surface analytical techniques. Initially, the chemical makeup and pressure-sensitive nature of frog mucus was examined with Near Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy and Sum Frequency Generation (SFG) Vibrational Spectroscopy to determine if mucus glycoprotein molecules located at the mucus-prey interface formed fibrils during prey capture. NEXAFS sampled photons associated with bond orbitals of molecular bonds within the top few nanometers of the interface while SFG measured order-sensitive intensity of vibrational modes at this same surface with sub-monolayer resolution. NEXAFS images at the N1s and C1s K-edges at two incident x-ray angles were collected by rastering the x-ray beam at across the surface of the mucus, showed that surface chemical bonds associated with glycoproteins were uniformly distributed. Angle-resolved NEXAFS experiments and SFG spectra indicated a glycoprotein tertiary structure consistent with fibril formation and methyl and methylene groups on amino acid side chains oriented normal to fibrils on the surface. Next, insect tarsal fluid adhesive was investigated, utilizing SFG spectroscopy to probe the presence of ordered molecular bonds at the functional interface between adhesive fluid and substrate. Fluid footprints of a model species, the seven-spotted ladybird beetle, were collected on three substrates with varying surface energies and hydrophobicities. Film thickness and roughness were determined with profilometry and atomic force microscopy respectively to ensure only smooth surfaces were tested. Resulting SFG spectra revealed that the chemical environment at the interface was not affected by substrate hydrophobicity. However, the ordering of observed hydrocarbon groups within the fluid increased with a corresponding increase in substrate hydrophobicity. The interfacial layer of beetle adhesive fluid was determined to promote lubrication of foot contact, rather than adhesion. Building upon these results, a biomimetic adhesive fluid inspired by ladybird beetle foot adhesive was designed. A water-in-oil emulsion was formulated using 3 components - squalane, deuterated stearic acid and water. SFG spectra of the mimetic fluid on both hydrophilic and hydrophobic surfaces revealed that molecular vibrations in each case closely resembled those of the natural fluid, with squalane the only surface-active component. Preexisting molecular dynamics simulation of squalane at solid surfaces showed that it prefers to orient parallel to the surface with its methyl branches pointing in the surface normal direction. Spectra of pure squalane and a squalane/deuterated stearic acid mixture on the same substrates revealed the that the surface-inactive components (d-stearic acid and D2O) have an observable effect on the ordering of these squalane layers at the interface. Pull-off force, traction force and viscometry measurements of each fluid showed an increase in viscosity and pull-off force and a decrease in traction force with increasing fluid complexity. Based upon this, it is concluded that the surface-inactive components of ladybird beetle adhesive created a more cohesive fluid which allowed it to accurately mimic the functional properties of natural ladybird beetle adhesive

InspiRat: biologisch inspirierter Kletterroboter für die externe Inspektion linearer Strukturen

TETRA GmbH Ilmenau und drei universitäre Lehrstühle zeigen im Projekt InspiRat, dass bei wissenschaftlicher Unterstützung auch die deutsche Industrie in der Lage ist, in der Robotik internationale Standards zu setzen. InspiRat und RatNics als Akronyme sollen Assoziationen wecken: Analyse des Kletterns insbesondere von Ratten trieb den Bau einer neuen Klasse von Robotern. Waren zu Beginn des Projektes integrierte Kletterroboter mit Massen > 35 kg verfügbar, so gibt es nun Maschinen mit 1 kg bis 2 kg Masse, experimentell modulare Systeme mit 250 g Masse. Nebenergebnis ist die weltweite Definition des Standes der Technik der Röntgenvideographie zusammen mit der Siemens® AG: biplanar 2.000 Röntgenbilder/Sekunde in HD. Ergebnisse universitärer Studien werden in Journalen publiziert, doch belegt die Nachfrage nach dem Abschlussbericht des Projektes für das BMBF das Interesse an einer übergreifenden, transdisziplinären Darstellung des bionischen Entwicklungsprozesses. Wir publizieren deswegen diesen Abschlussbericht nur geringfügig redaktionell überarbeitet. Er beschreibt somit den wissenschaftlichen Stand 2011 in einer auf den Fördermittelgeber zugeschnittenen Darstellungsweise. Die Wissenschaft ist nicht stehen geblieben, wir erleichtern die Nachverfolgung durch Angabe einiger Publikationen aus der Zeit nach Projektende. Doch ist unser Anspruch nicht prospektiv wie bei Zeitschriftenartikeln, wir wollen retrospektiv die Analyse eines erfolgreich abgeschlossenen Prozesses ermöglichen