Adhesion modulation In bio-inspired micropatterned adhesives by electrical fields

With steps towards Industry 4.0, it becomes imperative to the development of next-generation industrial assembly lines, to be able to modulate adhesion dynamically for handling complex and diverse substrates. The inspiration for the design and functionality of such adhesive pads comes from gecko’s remarkable ability to traverse rough and smooth topographies with great ease and agility. The emphasis in this thesis was to equip artificial micropatterned adhesives with such functionalities of tunability and devise an on-demand release mechanism. The project evaluates the potential of electric fields in this direction. The first part of this work focusses on integrating electric fields with polymeric micropatterns and studying the synergistic effect of Van der Waals and electrostatic forces. An in-house electroadhesion set up was built to measure the pull-off forces with and without electric fields. As a function of the applied voltage, adhesion forces can be tuned. The second part of the work demonstrates a novel route that exploits the in-plane actuation of the dielectric elastomeric actuators integrated with microstructure to induce peeling in them. Voltage-dependent actuation has been harnessed to generate the requisite peel force to detach the micropatterns. Overall, the findings of this thesis combine disciplines of electroadhesion, electroactuation, and reversible dry adhesives to gain dynamic control over adhesion.Im Einklang mit dem Fortschreiten in Richtung Industrie 4.0, wird es auch für die Entwicklung von industriellen Montagelinien der nächsten Generation unerlässlich sein, die Handhabung komplexer und unterschiedlicher Objekte zu flexibilisieren. Bioinspirierte Haftpads nach dem Vorbild des Gecko könnten zukünftig hierzu wesentlich beitragen. Der Schwerpunkt dieser Arbeit bestand darin, künstliche mikrostrukturierte Haftpads mit einem elektrisch schaltbaren Adhäsions- und Ablösemechanismus zu funktionalisieren, um die Grundlage für einen schnell schaltbaren, intelligenten Greifer zu schaffen. Der erste Teil dieser Arbeit konzentriert sich auf die Kombination elektrischer Felder mit elastomeren Mikrostrukturen und die Untersuchung der synergistischen Wirkung von Van der Waals- und elektrostatischen Kräften. Zur Messung der Adhäsion wurde ein individueller Aufbau realisiert und mit diesem die Feldstärkeabhängigkeit der Haftkräfte nachgewiesen. Der zweite Teil der Arbeit demonstriert einen neuartigen Ablösemechanismus unter Ausnutzung der lateralen Bewegung dielektrischer elastomerer Aktuatoren, um so ein Abschälen der Haftpads vom Substrat zu induzieren. Durch Variation der elektrischen Spannung wurde untersucht, wie sich diese auf die Ablösegeschwindigkeit der Haftpads auswirkt. Insgesamt kombinieren die Ergebnisse dieser Arbeit die Disziplinen Elektroadhäsion, Elektroaktuation und reversible trockene Klebstoffe, um so eine dynamische Kontrolle über die Adhäsion zu erhalten

Monitoring bioinspired fibrillar grippers by contact observation and machine learning

The remarkable properties of bio-inspired microstructures make them extensively accessible for various applications, including industrial, medical, and space applications. However, their implementation especially as grippers for pick-and-place robotics can be compromised by multiple factors. The most common ones are alignment imperfections with the target object, unbalanced stress distribution, contamination, defects, and roughness at the gripping interface. In the present work, three different approaches to assess the contact phenomena between patterned structures and the target object are presented. First, in-situ observation and machine learning are combined to realize accurate real-time predictions of adhesion performance. The trained supervised learning models successfully predict the adhesion performance from the contact signature. Second, two newly developed optical systems are compared to observe the correct grasping of various target objects (rough or transparent) by looking through the microstructures. And last, model experiments are provided for a direct comparison with simulation efforts aiming at a prediction of the contact signature and an analysis of the rate and preload-dependency of the adhesion strength of a soft polymer film in contact with roughness-like surface topography. The results of this thesis open new perspectives for improving the reliability of handling systems using bioinspired microstructures.Durch die besonderen Eigenschaften bioinspirierter Mikrostrukturen können diese für verschiedene Anwendungen genutzt werden, einschließlich industrieller, medizinischer und Weltraumanwendungen. Ihre Implementierung, insbesondere als Greifer für Pick-and-Place-Robotiker, kann jedoch durch mehrere Faktoren beeinträchtigt werden. Am häufigsten sind Ausrichtungsmängel an das Zielobjekt, unausgeglichene Spannungsverteilungen, Defekte und Rauheit an der Greifschnittstelle. Die vorliegende Arbeit zeigt drei verschiedene Ansätze, um den Kontakt zwischen strukturierten Adhäsiven und Zielobjekten zu untersuchen. Zunächst werden in-situ Beobachtungen und maschinelles Lernen kombiniert, um Echtzeitvorhersagen der Adhäsionsleistung zu ermöglichen. Die trainierten Modelle werden verwendet, um die Haftungsleistung anhand der Kontaktsignatur des Pads erfolgreich zu prognostizieren. Anschließend werden zwei neu entwickelte, optische Systeme verglichen, mit denen das korrekte ” Greifen“ von verschiedenen Objekten (mit rauen oder undurchsichtigen Oberflächen) durch die Mikrostrukturen live verfolgt werden kann. Zuletzt werden Modellexperimente durchgeführt, die mit Simulationen der Signatur des Kontakts einer weichen Polymerschicht mit einer idealisierten rauen Gegenfläche direkt verglichen werden können. Die Ergebnisse dieser Arbeit eröffnen neue Perspektiven zur zuverlässigeren Verwendung von Handhabungssystemen mit bioinspirierten Mikrostrukturen.Leibniz Competition Grant MUSIGAND (No. K279/2019) awarded to Eduard Arz

Numerical and experimental study of electroadhesion to enable manufacturing automation

Robotics and autonomous systems (RAS) have great potential to propel the world to future growth. Electroadhesion is a promising and potentially revolutionising material handling technology for manufacturing automation applications. There is, however, a lack of an in-depth understanding of this electrostatic adhesion phenomenon based on a confident electroadhesive pad design, manufacture, and testing platform and procedure. This Ph.D. research endeavours to obtain a more comprehensive understanding of electroadhesion based on an extensive literature review, theoretical modelling, electrostatic simulation, and experimental validation based on a repeatable pad design, manufacture, and testing platform and procedure. [Continues.

Functional surface microstructures inspired by nature : From adhesion and wetting principles to sustainable new devices

In the course of evolution nature has arrived at startling materials solutions to ensure survival. Investigations into biological surfaces, ranging from plants, insects and geckos to aquatic animals, have inspired the design of intricate surface patterns to create useful functionalities. This paper reviews the fundamental interaction mechanisms of such micropatterns with liquids, solids, and soft matter such as skin for control of wetting, self-cleaning, anti-fouling, adhesion, skin adherence, and sensing. Compared to conventional chemical strategies, the paradigm of micropatterning enables solutions with superior resource efficiency and sustainability. Associated applications range from water management and robotics to future health monitoring devices. We finally provide an overview of the relevant patterning methods as an appendix

Functional surface microstructures inspired by nature – From adhesion and wetting principles to sustainable new devices

In the course of evolution nature has arrived at startling materials solutions to ensure survival. Investigations into biological surfaces, ranging from plants, insects and geckos to aquatic animals, have inspired the design of intricate surface patterns to create useful functionalities. This paper reviews the fundamental interaction mechanisms of such micropatterns with liquids, solids, and soft matter such as skin for control of wetting, self-cleaning, anti-fouling, adhesion, skin adherence, and sensing. Compared to conventional chemical strategies, the paradigm of micropatterning enables solutions with superior resource efficiency and sustainability. Associated applications range from water management and robotics to future health monitoring devices. We finally provide an overview of the relevant patterning methods as an appendix

Engineering Micropatterned Dry Adhesives: From Contact Theory to Handling Applications

Reversible adhesion is the key functionality to grip, place, and release objects nondestructively. Inspired by nature, micropatterned dry adhesives are promising candidates for this purpose and have attracted the attention of research groups worldwide. Their enhanced adhesion compared to nonpatterned surfaces is frequently demonstrated. An important conclusion is that the contact mechanics involved is at least as important as the surface energy and chemistry. In this paper, the roles of the contact geometry and mechanical properties are reviewed. With a focus on applications, the effects of substrate roughness and of temperature variations, and the long-term performance of micropatterned adhesives are discussed. The paper provides a link between the current, detailed understanding of micropatterned adhesives and emerging applications

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

Bio-Inspired Robotics

Modern robotic technologies have enabled robots to operate in a variety of unstructured and dynamically-changing environments, in addition to traditional structured environments. Robots have, thus, become an important element in our everyday lives. One key approach to develop such intelligent and autonomous robots is to draw inspiration from biological systems. Biological structure, mechanisms, and underlying principles have the potential to provide new ideas to support the improvement of conventional robotic designs and control. Such biological principles usually originate from animal or even plant models, for robots, which can sense, think, walk, swim, crawl, jump or even fly. Thus, it is believed that these bio-inspired methods are becoming increasingly important in the face of complex applications. Bio-inspired robotics is leading to the study of innovative structures and computing with sensory–motor coordination and learning to achieve intelligence, flexibility, stability, and adaptation for emergent robotic applications, such as manipulation, learning, and control. This Special Issue invites original papers of innovative ideas and concepts, new discoveries and improvements, and novel applications and business models relevant to the selected topics of ``Bio-Inspired Robotics''. Bio-Inspired Robotics is a broad topic and an ongoing expanding field. This Special Issue collates 30 papers that address some of the important challenges and opportunities in this broad and expanding field

Climbing and Walking Robots

Nowadays robotics is one of the most dynamic fields of scientific researches. The shift of robotics researches from manufacturing to services applications is clear. During the last decades interest in studying climbing and walking robots has been increased. This increasing interest has been in many areas that most important ones of them are: mechanics, electronics, medical engineering, cybernetics, controls, and computers. Today’s climbing and walking robots are a combination of manipulative, perceptive, communicative, and cognitive abilities and they are capable of performing many tasks in industrial and non- industrial environments. Surveillance, planetary exploration, emergence rescue operations, reconnaissance, petrochemical applications, construction, entertainment, personal services, intervention in severe environments, transportation, medical and etc are some applications from a very diverse application fields of climbing and walking robots. By great progress in this area of robotics it is anticipated that next generation climbing and walking robots will enhance lives and will change the way the human works, thinks and makes decisions. This book presents the state of the art achievments, recent developments, applications and future challenges of climbing and walking robots. These are presented in 24 chapters by authors throughtot the world The book serves as a reference especially for the researchers who are interested in mobile robots. It also is useful for industrial engineers and graduate students in advanced study

Bio-Inspired Adhesion, Friction and Lubrication

Biological systems have developed elegant adaptations during its evolution to survive and perform its functions efficiently under specific environmental constrains with enormous physical demands. In this dissertation, I make an effort to understand tribological phenomena in biology and translate them into a synthetic system for engineering applications. I emphasize on adhesion, friction and lubrication in three different biologically inspired soft condensed matter as described below.Dopa (3,4-dihydroxyphenylalanine), a post-translational modification from tyrosine (Tyr), features prominently in the mussel foot proteins (mfps), ranging from less than 5 mol % in mfp-4 to 30 mol % in mfp-5. The binding ability of the mfps to different substrates has been mostly attributed to the Dopa functionality in the protein and the role of the other peptide residues in the adhesive properties of the protein remains elusive. Here we have discovered that the adhesion between mfp-1 decapeptide films ([AKPSYPPTYK]2) and mica remained unchanged with or without the Dopa residue. This is a paradigm shift in our understanding of the molecular mechanisms underlying adhesive properties of the mfps and calls for further inquiry into the effects of peptide residues beyond Dopa chemistry. We also developed a systematic body of work linking the adhesive performance to lengths and architectures of peptides. Dopa in a peptide sequence does not necessarily lead to the formation of cross-links between peptide films through metal chelation, and the length of the peptide is a crucial parameter for enabling metal ion mediated bridging between surfaces. More recently, we have been working on designing and characterizing small molecules that mimic the properties of the adhesive mussel foot proteins. The wet adhesion and coacervation of an adhesive protein (mfp-5) was recapitulated in an order of magnitude smaller length scale which shows cohesive properties superior to the mfps. We believe that the resulting insights into the molecular structure-function relationships will enable rational design of synthetic bio-inspired adhesives that would enable de novo (suture less) sealants for injuries and surgeries and nano-scale-adhesive applications in the semiconductor industry.Geckos can attach and detach their toes reversible in matters of milliseconds from most surfaces regardless of its roughness due to the hierarchical structure of their foot-pads. Micro-flaps mimicking the function of the micron sized setae on the gecko foot pad were fabricated and investigated for its adhesion and frictional properties in a modified surface forces apparatus (SFA). A Johnson-Kendall-Roberts (JKR) model with an effective stiffness and adhesion energy parameters quantitatively described the `contact mechanics' of the tilted micro-flaps against a smooth silica surface at the macro and micro-scales. Constant attachments and detachments occurred between the surfaces during shearing and were described by an Avalanche mechanism. These results demonstrate the significance of preload, shearing velocity, shearing distances, commensurability, and shearing direction of gecko-mimetic adhesives and provide a simple model for analyzing and/or designing such systems. Biolubrication systems show ultralow friction coefficients, remarkable wear resistance properties and are far superior to any artificial system designed to date. In this work, the role of proteins (e.g., Lubricin, Lub) and polysaccharides (e.g., Hyaluronic acid, HA) found in articular joints, and mfp-1 inspired coacervates were investigated to determine the lubrication and wear protection mechanisms conferred by the naturally occurring polymers to a mica surface. We find that Lub penetrates into a chemically bound HA on mica to form a visco-elastic gel that reduces the coefficient of friction as well as boosts the strength of the surface against abrasive wear, however, physically adsorbed HA-Lub complex were poor at conferring wear protection to mica even though it showed low friction coefficients. Similarly, coacervated mfp-1/HA rescues mica from shear induced damage only when the protein is modified with Dopa, which is responsible for attaching the coacervate to the surface. Absence of Dopa resulted in severe abrasive wear to the surfaces even under low loads (< 10 mN) during shearing. These results show that strong anchoring of polymers is crucial to protect surfaces from shear induced damage. We also demonstrate that friction coefficient is not correlated to wear