Design and Fabrication of Origami Elements for use in a Folding Robot Structure

The aim of the research is to investigate the methodology of the design and fabrication of folding robots that depend on the origami structures. The use of origami structures as a foundation to build reconfigurable and morphing robots that could assist in search and rescue (SAR) tasks are investigated. The design of the origami folding structures divided into three stages: consideration of the geometry of the origami structure, the hinge design, and the actuation system. The result of investigating three origami structures shows the ability to use the unit cell of the origami ball structure as a self-folding element. Furthermore, the novel type of origami structure for manipulation was created according to this result. This novel structure was designed to be a soft manipulation robot arm. Two approaches are used to design and fabricate flexure hinge. The first is by using a 3D printed multi-material technique. By this technique, the hinge printed using soft and solid material at the same time, which is Tango plus flx930 for soft material and Vero for solid material. The soft material act as a flexure hinge. Therefore, three tests were operated for it to calculate the tensile force, fatigue limit, and the required bend force. The second approach is by using acrylic and Kapton materials. Two types of actuation systems were studied: the external actuation system and embedded actuation system. The external actuation system was used for the Origami structure for manipulation, while the embedded actuation system was used for the self-folding structure. The shape memory alloy wires in torsion (TSW) and bending (BSW) was used in an embedded actuation system. A unit cell of origami ball was fabricated as a self-folding element by using three approaches: manually, acrylic, and Kapton and 3D printing. It is actuated by using shape memory alloy wire. Furthermore, an origami structure for manipulation was fabricated and actuated using an external actuation system. This novel type of origami structure provided an excellent bend motion ability

Mechanically Active Electrospun Materials

Electrospinning, a technique used to fabricate small diameter polymer fibers, has been employed to develop unique, active materials falling under two categories: (1) shape memory elastomeric composites (SMECs) and (2) water responsive fiber mats. (1) Previous work has characterized in detail the properties and behavior of traditional SMECs with isotropic fibers embedded in an elastomer matrix. The current work has two goals: (i) characterize laminated anisotropic SMECs and (ii) develop a fabrication process that is scalable for commercial SMEC manufacturing. The former ((i)) requires electrospinning aligned polymer fibers. The aligned fibers are similarly embedded in an elastomer matrix and stacked at various fiber orientations. The resulting laminated composite has a unique response to tensile deformation: after stretching and releasing, the composite curls. This curling response was characterized based on fiber orientation. The latter goal ((ii)) required use of a dual-electrospinning process to simultaneously electrospin two polymers. This fabrication approach incorporated only industrially relevant processing techniques, enabling the possibility of commercial application of a shape memory rubber. Furthermore, the approach had the added benefit of increased control over composition and material properties. (2) The strong elongational forces experienced by polymer chains during the electrospinning process induce molecular alignment along the length of electrospun fibers. Such orientation is maintained in the fibers as the polymer vitrifies. Consequently, residual stress is stored in electrospun fiber mats and can be recovered by heating through the polymer\u27s glass transition temperature. Alternatively, the glass transition temperature can be depressed by introducing a plasticizing agent. Poly(vinyl acetate) (PVAc) is plasticized by water, and its glass transition temperature is lowered below room temperature. Therefore, the residual stress can be relaxed at room temperature simply by hydrating the PVAc fibers. This work investigated the response of PVAc to the application of water on one surface. More specifically, the folding of films of PVAc fibrous webs in response to water lines drawn locally on the mat surface was quantified and characterized based on fiber mat characteristics

An end-to-end approach to self-folding origami structures

This paper presents an end-to-end approach to automate the design and fabrication process for self-folding origami structures. Self-folding origami structures are robotic sheets composed of rigid tiles and joint actuators. When they are exposed to heat, each joint folds into a preprogrammed angle. Those folding motions transform themselves into a structure, which can be used as body of 3-D origami robots, including walkers, analog circuits, rotational actuators, and microcell grippers. Given a 3-D model, the design algorithm automatically generates a layout printing design of the sheet form of the structure. The geometric information, such as the fold angles and the folding sequences, is embedded in the sheet design. When the sheet is printed and baked in an oven, the sheet self-folds into the given 3-D model. We discuss, first, the design algorithm generating multiple-step self-folding sheet designs, second, verification of the algorithm running in O(n 2 ) time, where n is the number of the vertices, third, implementation of the algorithm, and finally, experimental results, several self-folded 3-D structures with up to 55 faces and two sequential folding steps

Building a novel nanofabrication system using MEMS

Micro-electromechanical systems (MEMS) are electrically controlled micro-machines which have been widely used in both industrial applications and scientific research. This technology allows us to use macro-machines to build micro-machines (MEMS) and then use micro-machines to fabricate even smaller structures, namely nano-structures. In this thesis, the concept of Fab on a Chip will be discussed where we construct a palette of MEMS-based micron scale tools including lithography tools, novel atomic deposition sources, atomic mass sensors, thermometers, heaters, shutters and interconnect technologies that allow us to precisely fabricate nanoscale structures and conduct in-situ measurements using these micron scale devices. Such MEMS devices form a novel microscopic nanofabrication system that can be integrated into a single silicon chip. Due to the small dimension of MEMS, fabrication specifications including heat generation, patterning resolution and film deposition precision outperform traditional fabrication in many ways. It will be shown that one gains many advantages by doing nano-lithography and physical vapor deposition at the micron scale. As an application, I will showcase the power of the technique by discussing how we use Fab on a Chip to conduct quench condensation of superconducting Pb thin films where we are able to gently place atoms upon a surface, creating a uniform, disordered amorphous film and precisely tune the superconducting properties. This shows how the new set of techniques for nanofabrication will open up an unexplored regime for the study of the physics of devices and structures with small numbers of atoms

Pouch Motors: Printable Soft Actuators Integrated with Computational Design

We propose pouch motors, a new family of printable soft actuators integrated with computational design. The pouch motor consists of one or more inflatable gas-tight bladders made of sheet materials. This printable actuator is designed and fabricated in a planar fashion. It allows both easy prototyping and mass fabrication of affordable robotic systems. We provide theoretical models of the actuators compared with the experimental data. The measured maximum stroke and tension of the linear pouch motor are up to 28% and 100 N, respectively. The measured maximum range of motion and torque of the angular pouch motor are up to 80° and 0.2 N, respectively. We also develop an algorithm that automatically generates the patterns of the pouches and their fluidic channels. A custom-built fabrication machine streamlines the automated process from design to fabrication. We demonstrate a computer-generated life-sized hand that can hold a foam ball and perform gestures with 12 pouch motors, which can be fabricated in 15 min.National Science Foundation (U.S.) (1240383)National Science Foundation (U.S.) (1138967)United States. Department of Defens

An Untethered Miniature Origami Robot that Self-folds, Walks, Swims, and Degrades

A miniature robotic device that can fold-up on the spot, accomplish tasks, and disappear by degradation into the environment promises a range of medical applications but has so far been a challenge in engineering. This work presents a sheet that can self-fold into a functional 3D robot, actuate immediately for untethered walking and swimming, and subsequently dissolve in liquid. The developed sheet weighs 0.31g, spans 1.7cm square in size, features a cubic neodymium magnet, and can be thermally activated to self-fold. Since the robot has asymmetric body balance along the sagittal axis, the robot can walk at a speed of 3.8 body-length/s being remotely controlled by an alternating external magnetic field. We further show that the robot is capable of conducting basic tasks and behaviors, including swimming, delivering/carrying blocks, climbing a slope, and digging. The developed models include an acetone-degradable version, which allows the entire robot’s body to vanish in a liquid. We thus experimentally demonstrate the complete life cycle of our robot: self-folding, actuation, and degrading.National Science Foundation (U.S.) (Grant 1240383)National Science Foundation (U.S.) (Grant 1138967)American Society for Engineering Education. National Defense Science and Engineering Graduate Fellowshi

Single-Crystalline Graphene by Low-Pressure CVD Method: Nucleation Limited Growth, Transfer, and Characterization

Graphene has attracted enormous attention due to its unique characteristics. However, the LPCVD graphene grown on copper turns out to be polycrystalline because of the high nucleation density (ND) on the copper foil surface. In order to realize better quality LPCVD graphene, this ND needs to be significantly reduced. Based on the observations from our initial graphene growths on as-received copper, we figured that the uneven Cu surfaces with defects produce large NDs. At a large ND, the graphene flakes nucleated at different sites coalesced to produce polycrystalline graphene. Due to such issues, we have implemented an electropolishing technique to smoothen the native surface of the copper foil. We will discuss the successful implementation of the surface smoothening process to reduce nucleation site formation while limiting the surface defects (which leads to wrinkle formation). The annealing process was also helpful to flatten the surface during the growth process further. We have also observed that graphene grows across Cu grain boundaries and, in the process, produces an additional surface area for graphene growth. That later causes to form wrinkles, which affect graphene properties negatively. In the next project, the effect of multi-step copper surface oxidization, base pressure vacuum in the middle of the process, and integration of Cu enclosures on suppressing the ND will be discussed. The technique is based on the self-cleaning characteristics of copper oxides and the metal evaporation in a high vacuum at high temperatures. The ND has reduced to ~5 nucleation/cm2 on average (an improvement compared to the previously reported minimum value, ten nucleation/cm2 which was obtained using copper enclosures), and the graphene/copper surface has become smoother. The self-aligned graphene island geometry and shape of the flakes have reflected the symmetry and the single crystallinity of graphene. The final project will discuss the growth of cm-scale graphene flakes on Cu and 3D-multilayered graphene on 3D-Ni foams and used Ni\u27s gettering carbon diffusion effect to make the Cu foil carbon-free. The Ni-foam/Cu enclosure was oxidized in situ to assist with the self-cleaning process of metal oxides. The ND has been reduced to ~0.57 nucleation/cm2 and obtained cm-scale graphene flakes

Study of soft polymer actuators driven by an order-disorder phase transition

Les actionneurs souples à base de polymère pouvant être actionnés de manière réversible suscitent un grand intérêt car ils peuvent être construits à partir d’une vaste source de polymères et être déclenchés par divers types de stimuli pour la production répétée de travaux physiques. Parmi ceux-ci, les actionneurs thermo-sensibles et photo-sensibles à base de polymères semi-cristallins (SCPs) et / ou de polymères à cristaux liquides (LCPs) se développent rapidement en raison de leurs applications potentielles en tant que dispositifs intelligents dans de nombreux domaines. Les chercheurs ont consacré des efforts considérables ces dernières années à la mise au point de nouveaux matériaux et de nouvelles fonctions basés sur les SCPs et les LCPs, mais la demande de construction d'actionneurs en polymère robustes dotés de fonctions avancées utilisant des matériaux facilement disponibles et des stratégies faciles n'a pas été satisfaite. Le but principal de cette thèse est de développer et d’étudier de tels actionneurs polymères fonctionnels avancés et contrôlables thermiquement ou par la lumière afin de produire de l’énergie mécanique par un actionnement réversible, en utilisant du poly (éthylène-acétate de vinyle) (EVA) semi-cristallin disponible dans le commerce et un type de LCP photoréticulable avec addition de petites quantités d'additifs générant de la chaleur. Nos approches étaient simples, pratiques et robustes, car nous n’avions utilisé qu’un laser ou un substrat isothermique pour réguler plusieurs comportements d’actionnement réversibles de pointe. L’utilisation d’EVA a donné lieu à deux projets présentés dans les chapitres 1 et 2, respectivement, en tant que première partie de cette thèse. Dans cette partie, deux comportements d'actionnement réversibles ont été décrits. Le premier est contrôlé par une commutation marche / arrêt du laser, tandis que le second est auto-entretenu sur un substrat isotherme. Les deux comportements sont associés à un gradient de température établi dans la direction de l'épaisseur de l'actionneur et entraîné par une transition de phase cristallisation – fusion. La deuxième partie est présentée au chapitre 3 et démontre qu'une bande de LCP monolithique réticulée de manière non uniforme peut fonctionner comme un photoactionneur multifonctionnel commandé par une transition de phase LC – isotrope. Dans le premier chapitre, nous avons préparé un type d'actionneur optique contenant des nanoparticules d'or basé sur une bande d'EVA étirée recevant des cristallites orientés. Lors de l'irradiation avec un laser (longueur d'onde de 532 nm), la résonance plasmonique de surface (SPR) de nanoparticules d'or (AuNP) est activée pour libérer de la chaleur qui fond partiellement les cristallites à Tlight. Les cristallites dont la température de fusion (Tm) est inférieure à Tlight sont fondus en tant que domaine d'actionnement afin de contracter la bande de manière asymétrique en raison du gradient de température, tandis que les cristaux de Tm supérieurs à Tlight soutiennent en tant que cadre. Lorsque le laser est retiré, la recristallisation orientée du domaine d’actionnement induit une expansion dans la direction d’étirage pour détendre la bande. Les résultats montrent que la luminosité, la force mécanique optique, l'amplitude d'actionnement et la vitesse d'activation peuvent être réglés en ajustant l'intensité du laser, le contenu en AuNPs, l'allongement et l'épaisseur de l'actionneur. Une application potentielle de l'actionneur optique en tant que commutateur sans fil et contrôlable à distance a été démontrée. Dans le deuxième chapitre, nous avons démontré le mouvement autonome sans précédent d’une bande d’EVA déposée sur un substrat en acier isotherme. La bande est fabriquée à partir d'EVA pur réticulé contenant des cristallites alignés de manière uniaxiale. Une fois en contact avec le substrat chaud, un gradient de température est immédiatement établi sur toute l'épaisseur et élève la section médiane de la bande en arc, provoqué par la contraction induite par la fusion asymétrique. Dans l'air, une recristallisation dirigée se produit et dilate la bande pour retomber à la forme plate initiale. Dans cet état, le substrat chaud chauffe la bande pour qu'elle se plie à nouveau afin de répéter le cycle de mouvement précédent. Une boucle de rétroaction thermo-mécanique-thermique est ainsi facilement établie et validée pour commander le mouvement continu, qui peut durer une heure ou environ 1 000 cycles. Nous avons étudié les facteurs qui affectent l'amplitude et la période du mouvement autonome et avons constaté que la température du substrat et l'allongement de la bande sont des paramètres importants, tandis que la durabilité est principalement altérée par le contact de plus en plus étroit entre la bande et le substrat. Le potentiel de conversion de l’énergie thermique en énergie mécanique a été démontré par une fonction d’auto-marche et la capacité de promouvoir la rotation d’une roue. Dans le troisième chapitre, un photoactionneur à base de LCP contenant un colorant proche infrarouge (NIR) a été préparé par photoréticulation d’une bande de LCP alignée de manière uniaxiale d’un côté en monodomaine et de l’autre en polydomaine LC relaxée. L'actionneur est multifonctionnel et remplit trois fonctions: le transport guidé par la lumière, la rotation flexible en locomotion et le mouvement autonome. Avec deux extrémités confinées sur un substrat et maintenues à plat, la bande peut générer une bosse sur le site de l'irradiation laser, résultant du réarrangement des chaînes polymères lors de la contraction iso-contrainte à l'état isotrope et du passage ultérieur à l'état LC. Une cargaison en forme de tige placée à côté de la bosse peut être transportée de bout en bout lorsque la bosse se propage sous balayage laser. Avec une extrémité fixée sur le substrat et l’autre libérée dans l’air, la bande soumise à une irradiation laser constante peut exécuter un mouvement auto-entretenu selon plusieurs modes, qui sont dictés par l’angle incident du laser. Le mouvement autonome est basé sur le mécanisme d’observation automatique et piloté par le retour photo-thermo-mécano-thermique. Numériser la bosse découpée de la bande de manière uniforme avec le laser peut faire en sorte que la bosse rampe directement sur les surfaces horizontales et inclinées, tandis qu'un balayage asymétrique peut guider le sens de rotation avec souplesse.Abstract: Polymer-based soft actuators capable of reversible actuation are attracting wide interest and attention as they can be constructed from a broad range of polymers and triggered by various types of stimuli to output physical work repeatedly. Among them, thermoresponsive and photoresponsive actuators based on semicrystalline polymers (SCPs) and liquid crystalline polymers (LCPs) are increasingly developed due to their potential applications as smart devices in numerous fields. In recent years, massive efforts have been devoted by researchers to developing new materials and functions based on SCPs and LCPs, but the demand for constructing robust polymer actuators with advanced functions using readily available materials and facile strategies has not been fulfilled. The main purpose of this thesis is to develop and study such advanced and functional polymer actuators controllable by thermal or light to output mechanical energy through reversible actuation, using commercially available semicrystalline poly(ethylene-co-vinyl acetate) (EVA) and a type of photocrosslinkable LCP with addition of small amounts of heat-generating additives. Our approaches are simple, convenient and robust as we only use a laser or an isothermal substrate to regulate several leading-edge reversible actuation behaviors. The use of EVA elicited two projects which are presented in Chapter 1 and Chapter 2, respectively, as the first part of this thesis. In this part, two reversible actuation behaviors were described. The first one is controlled by on/off switching of the laser, while the second one is self-sustained on an isothermal substrate surface. Both behaviors are associated with a temperature gradient established in the thickness direction of the actuator and driven by melting–crystallization phase transition. The second part of this thesis, presented in Chapter 3, deals with an LCP actuator. We show that a monolithic LCP strip crosslinked non-uniformly can perform as a multifunctional photoactuator driven by LC–isotropic phase transition. In the first chapter, we prepared a type of gold nanoparticle-containing optical actuator based on a stretched EVA strip accommodating oriented crystallites. Upon irradiation with a laser (532 nm in wavelength), surface plasmon resonance (SPR) of gold nanoparticles (AuNPs) is activated to release heat that partially melts the crystallites at Tlight. The crystallites with their melting temperature (Tm) below Tlight are melted as the actuation domain that bends the strip towards the laser direction as a result of uneven contraction forces along the thickness due to the temperature gradient, while the crystallites with Tm higher than Tlight sustain as the framework. When the laser is removed, oriented recrystallization in the actuation domain induces expansion along the stretching direction to unbend the strip. Results show that Tlight, the photomechanical force, the actuation magnitude and the actuation speed are tunable by adjusting the laser intensity, the content of AuNPs, the elongation and thickness of the actuator. A potential application of the optical actuator as a wireless and remotely controllable switch was demonstrated. In the second chapter, we demonstrate an unprecedented autonomous motion of an EVA strip deposited on an isothermal steel substrate. The strip is made from crosslinked pure EVA containing uniaxially aligned crystallites. Once in contact with the hot substrate, a temperature gradient is immediately established across the thickness and elevates the middle section of the strip to form an arch, caused by the melting-induced-contraction of the bottom side of the strip. Once in the air, the melted EVA chains are cooled and recrystallize, which generates opposite extensional force on the bottom side and brings the strip to fall back to the initial flat shape. In this state, the hot substrate heats the strip to bend it again, and the arching up and flattening down motion cycle is repeated. A thermo-mechanical-thermal feedback loop is thus easily established to drive the self-sustained motion, which can last hour-long or around 1000 cycles. We investigated the factors that affect the amplitude and period of the autonomous motion and found that both the substrate temperature and elongation of the strip are important parameters, while the durability is mainly decayed by the looser and looser contact between the strip and the substrate. Potential of converting thermal energy to mechanical energy was demonstrated by a self-walking function and the ability to promote the rotation of a wheel. In the third chapter, a multifunctional LCP-based photoactuator containing a near-infrared (NIR) dye is described. It was prepared by photocrosslinking a uniaxially aligned LCP strip on one side in monodomain and the other side in relaxed LC polydomain. The actuator has three functions, which are the light-guided transportation, flexible turning in locomotion and autonomous motion. First, with its two ends fixed on a substrate and kept flat, the strip can generate a bump at the site of laser irradiation, arising from polymer chains rearrangement during isostrain contraction in isotropic state and subsequent transition to LC state. A rod-shape cargo put beside the bump can be conveyed from end to end as the bump propagates under laser scanning. Secondly, with one end fixed on the substrate and the other released in air, the strip under constant laser irradiation can execute self-sustained motion in multiple modes, which are dictated by the incident angle of the laser. The autonomous motion is based on a self-shadowing mechanism and driven by the photothermo-mechano-thermal feedback. Thirdly, scanning the bump cut from the strip uniformly, with the two ends free, laser scanning can make the actuator crawl straightly on both horizontal and inclined surfaces, while unsymmetrical laser scanning can guide the turning direction in its movement