Development of microstructures for application on a controllable bioinspired adhesive mechanism for gripping system in pick-n-place task

Dissertação de mestrado integrado em Engenharia MecânicaA natureza oferece uma variedade de ideias para uma adesão transitória e reversível a diferentes substratos. Até agora, os soft dry adhesives (SDAs) bioinspirados mais estudados são superfícies com matrizes de micropilares. A inspiração veio de espécies terrestres, como as osgas, cujas almofadas dos pés são cobertas por intrincadas fibrilhas que permitem uma forte adesão (que se deve a forças intermoleculares) bem como uma fácil libertação. Um dos objetivos atuais dos esforços da investigação é transferir a solução da natureza para estruturas artificiais que possam um dia encontrar aplicações tecnológicas. Este trabalho visa replicar os comportamentos de agarra e libertação das osgas, utilizando como base as suas estruturas fibrilares pegajosas. Para este objetivo, serão utilizadas várias técnicas de fabrico e ensaios experimentais para determinar o melhor protocolo para a criação de microestruturas. Foram estudados micropilares cilíndricos lisos e micropilares com forma de cogumelo, tendo sido escolhidos estes últimos dado que aderem melhor aos substratos lisos em comparação com pilares cilíndricos. O presente trabalho começou por delinear o estado de arte, no qual se investiga o desenvolvimento de SDAs bioinspirados e as suas qualidades adesivas. Além disso, também foram abordados os fundamentos de adesão fibrilar. Prosseguiu-se para o desenvolvimento de amostras em polidimetilsiloxano (PDMS) com o objetivo de caracterizar este material num equipamento de ensaio universal (UTM). Neste trabalho foram examinadas várias técnicas de microfabricação. Tendo em consideração a dimensão das micropartículas utilizadas, foram produzidas microestruturas utilizando uma metodologia de baixo custo. Foram utilizados e testados vários tipos de métodos para fabricar os moldes, ou seja, para produzir pilares cilíndricos lisos foi utilizada fresagem e para produzir micropilares em forma de cogumelo foi utilizada impressão 3D. Devido à sua forma, os micropilares em forma de cogumelo requerem uma dupla moldagem, com um molde intermediário constituído por um material altamente flexível. Finalmente, com o auxílio do UTM para realizar testes de aderência, foi avaliada a eficiência das microestruturas.Nature offers a variety of ideas for transient and reversible adhesion to different substrates. Geckos and insects use hairy structures whose adhesion is due to intermolecular forces. So far, the most widely studied SDAs are surfaces with arrays of micropillars. The inspiration came from terrestrial species including lizards and geckos whose toe pads are covered by intricate fibrils that enable strong attachment as well as easy release. The current goal of research and development efforts is to transfer nature's solution into artificial structures that might someday be applied in different technologies. Hence, this work aims to replicate the grasping and releasing behaviors of geckos using their fibrillar sticky structures as a basis. In order to achieve this goal, different kinds of designs, fabrications, and testing will be used to determine the best protocol for creating microstructures. Smooth cylindrical and mushroom-shaped micropillars were studied. The latter were chosen because they adhere to smooth substrates better than cylindrical micropillars. This work began by outlining the state of the art on the development of soft dry adhesives (SDAs) with natural inspiration and an examination of their dry adhesive properties. Additionally, the fundamentals of fibrillar adhesion were also covered. The work then proceeded to the development of polydimethylsiloxane (PDMS) specimens with the goal of characterizing this material in a universal testing machine (UTM). A number of microfabrication techniques were examined. Based on the size of the employed microparticles, microstructures were produced applying a low-cost method. Different methods were employed depending on the shape of the molds, i. e., to produce cylindrical flat pillars, it was used a CNC milling machine whereas to produce mushroom shaped micropillars, it was used 3D printing. Due to their design, the micropillars with the mushroom shape required double molding with an intermediary mold made of a highly flexible material. Finally, using the UTM to perform adhesion tests, the efficiency of the microstructure was evaluated

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

SYNTHETIC GECKO INSPIRED DRY ADHESIVE THROUGH TWO- PHOTON POLYMERIZATION FOR SPACE APPLICATIONS

This work aims to develop an advanced and cost-effective fabrication process to produce a simplified gecko-inspired microstructure with two-photon polymerization and polymer molding, aimed to improve the adhesive properties of microstructures. Such adhesive microstructures can be implemented for multi-purpose adhesive grasping devices, which have recently gained significant interest in the space exploration sector. Previous gecko-inspired microstructures were reviewed, and the new gecko-inspired microstructures have been developed with the adaptation of additive manufacturing methods for facile fabrication. The examined microstructures in this thesis were the tilted mushroom-shaped and wedge-shaped designs, which could both maximize adhesion by shearing the micropillars toward the tilted direction when preload force is applied. The improved microstructure fabrication process could produce micropillars in the height of 270 μm with soft polymer without defects. However, the miniaturized micropillars in the height of 40 μm, frabricated with the same process, had broken tips and missing structures. The effects of the scale, height, and shape of the micropillars in controllable dry adhesion were investigated through the experiments. The adhesion of the microstructures with artificial gecko setae in the height of 270 μm was 2 times higher than the microstructures with 40 μm of height. Meanwhile, the microstructures that consisted of long and short artificial gecko setae had inferior adhesive performance to the microstructures having uniform long setae on all tested surfaces. Meanwhile, the result showed no direct correlation between the surface roughness of the attached surface and the adhesive performance of the microstructures. The wedge-shaped design was determined to have higher adhesion than the tilted mushroom-shaped design due to lower structural resistance on bending and higher effective contact area

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&gt

Actuation Technologies for Soft Robot Grippers and Manipulators: A Review

Purpose of Review The new paradigm of soft robotics has been widely developed in the international robotics community. These robots being soft can be used in applications where delicate yet effective interaction is necessary. Soft grippers and manipulators are important, and their actuation is a fundamental area of study. The main purpose of this work is to provide readers with fast references to actuation technologies for soft robotic grippers in relation to their intended application. Recent Findings The authors have surveyed recent findings on actuation technologies for soft grippers. They presented six major kinds of technologies which are either used independently for actuation or in combination, e.g., pneumatic actuation combined with electro-adhesion, for certain applications. Summary A review on the latest actuation technologies for soft grippers and manipulators is presented. Readers will get a guide on the various methods of technology utilization based on the application

Switchable and Memorable Adhesion of Gold-Coated Microspheres with Electrochemical Modulation

Switchable adhesives using stimuli-responsive systems have many applications, including transfer printing, climbing robots, and gripping in pick and place processes. Among these adhesives, electroadhesive surface can spontaneously adjust their adhesion in response to an external electric field. However, electroadhesives usually need high voltage (e.g. kV) and the adhesion disappears upon turning off the signal. These limitations make them complicated and costly. In this research, we demonstrated a gold-coated silica microsphere (GCSM) with highly switchable and memorable adhesion triggered by a relatively small voltage (<30 V). In the experiment, a silica microsphere with a diameter of 15 μm was glued to a tipless atomic force microscope (AFM) cantilever. The nanoscale thick gold coating was sprayed on the surface of the microsphere by a sputter coater. AFM was used to explore the tunable adhesion with an external voltage at different relative humidity (RH). The results revealed that when applying a positive electrical bias at high RH, the adhesive force increased dramatically while it decreased to almost zero after applying a negative potential. Even if the bias was turned off, the adhesive force state could still be kept and erased on demand by simply applying a negative voltage. The adhesive force can be altered repeatedly by an alternative electrical bias. This adhesion modulated by the external electrical signals is attributed to the electrochemical effect of the nanoscale-thick gold coating, where an oxide layer can be formed and thus becomes positively charged when applying a positive voltage, and counter electric field cancel out the applied negative voltage to decrease the adhesion force

Developing a 3-DOF Compliant Perching Arm for a Free-Flying Robot on the International Space Station

This paper presents the design and control of the 3-DOF compliant perching arm for the free-flying Astrobee robots that will operate inside the International Space Station (ISS). The robots are intended to serve as a flexible platform for future guest scientists to use for zero-gravity robotics research - thus, the arm is designed to support manipulation research. It provides a 1-DOF underactuated tendon-driven gripper capable of enveloping a range of objects of different shapes and sizes. Co-located RGB camera and LIDAR sensors provide perception. The Astrobee robots will be capable of grasping each other in flight, to simulate orbital capture scenarios. The arm's end-effector module is swappable on-orbit, allowing guest scientists to add upgraded grippers, or even additional arm degrees of freedom. The design of the arm balances research capabilities with Astrobee's operational need to perch on ISS handrails to reduce power consumption. Basic arm functioning and grip strength were evaluated using an integrated Astrobee prototype riding on a low-friction air bearing