Development of a Fabrication Technique for Soft Planar Inflatable Composites

Soft robotics is a rapidly growing field in robotics that combines aspects of biologically inspired characteristics to unorthodox methods capable of conforming and/or adapting to unknown tasks or environments that would otherwise be improbable or complex with conventional robotic technologies. The field of soft robotics has grown rapidly over the past decade with increasing popularity and relevance to real-world applications. However, the means of fabricating these soft, compliant and intricate robots still poses a fundamental challenge, due to the liberal use of soft materials that are difficult to manipulate in their original state such as elastomers and fabric. These material properties rely on informal design approaches and bespoke fabrication methods to build soft systems. As such, there are a limited variety of fabrication techniques used to develop soft robots which hinders the scalability of robots and the time to manufacture, thus limiting their development. This research focuses towards developing a novel fabrication method for constructing soft planar inflatable composites. The fundamental method is based on a sub-set of additive manufacturing known as composite layering. The approach is designed from a planar manner and takes layers of elastomeric materials, embedded strain-limiting and mask layers. These components are then built up through a layer-by-layer fabrication method with the use of a bespoke film applicator set-up. This enables the fabrication of millimetre-scale soft inflatable composites with complex integrated masks and/or strain-limiting layers. These inflatable composites can then be cut into a desired shape via laser cutting or ablation. A design approach was also developed to expand the functionality of these inflatable composites through modelling and simulation via finite element analysis. Proof of concept prototypes were designed and fabricated to enable pneumatic driven actuation in the form of bending soft actuators, adjustable stiffness sensor, and planar shape change. This technique highlights the feasibility of the fabrication method and the value of its use in creating multi-material composite soft actuators which are thin, compact, flexible, and stretchable and can be applicable towards real-world application

Soft manipulators and grippers: A review

Soft robotics is a growing area of research which utilizes the compliance and adaptability of soft structures to develop highly adaptive robotics for soft interactions. One area in which soft robotics has the ability to make significant impact is in the development of soft grippers and manipulators. With an increased requirement for automation, robotics systems are required to perform task in unstructured and not well defined environments; conditions which conventional rigid robotics are not best suited. This requires a paradigm shift in the methods and materials used to develop robots such that they can adapt to and work safely in human environments. One solution to this is soft robotics, which enables soft interactions with the surroundings while maintaining the ability to apply significant force. This review paper assesses the current materials and methods, actuation methods and sensors which are used in the development of soft manipulators. The achievements and shortcomings of recent technology in these key areas are evaluated, and this paper concludes with a discussion on the potential impacts of soft manipulators on industry and society

Fabric-based eversion type soft actuators for robotic grasping applications

Humans have managed to simplify their lives by using robots to automate dull and repetitive tasks. Traditional robots have been very helpful in this respect, but in certain applications, the complexity of manufacturing and the requisite control strategies have rendered these systems inadequate. The concept of robots made of soft materials has increasingly been explored and a new avenue of research has opened up within the robotics community. In terms of construction, robots made of soft and flexible materials have several advantages over their rigid-bodied counterparts, among them simple design, simple control mechanisms, inexpensive constituent materials and the fact that they can be easily integrated into existing systems. Soft grippers in particular have been the subject of extensive research and we have witnessed significant development in terms of attributes like grasping, payload and sensing methodologies. Progress has been enhanced by the development of new materials used in the construction of actuators or end effectors of the grippers. The use of lightweight, non-stretch fabrics is a relatively new concept but initial studies have demonstrated their effectiveness in grasping applications. This thesis sets out a comparative study of popular gripping systems, focusing on the advantages of using fabrics in the construction of soft grippers. Multiple designs for fabric based finger like actuators, each addressing the drawbacks of the preceding design, are discussed along with the experimental evaluation of each design. A novel gripping mechanism in which the fingers of the gripper grow lengthwise from the tip (evert) to access and grasp the object is also presented. Large-scale fabric based eversion robots have been constructed to access environments with restricted access and for monitoring purposes. An experimental evaluation of the eversion capable finger is also presented, outlining important attributes such as payload, bending and force capability of the designed finger. An optical fibre based sensing methodology is also presented, capable of measuring the bending behaviour in soft actuators. The proposed sensor can be configured to sense bending angles, as well as the contact forces along different points along the length of the actuators

Additively Manufactured Dielectric Elastomer Actuators: Development and Performance Enhancement

The recently emerging and actively growing areas of soft robotics and morphing structures promise endless opportunities in a wide range of engineering fields, including biomedical, industrial, and aerospace. Soft actuators and sensors are essential components of any soft robot or morphing structure. Among the utilized materials, dielectric elastomers (DEs) are intrinsically compliant, high energy density polymers with fast and reversible electromechanical response. Additionally, the electrically driven work principle allows DEs to be distributed in a desired fashion and function locally with minimum interference. Thus, a great effort is being made towards utilizing additive manufacturing (AM) technologies to fully realize the potential of DE soft actuators and sensors. While soft sensors have received more attention and development due to their simpler implementation, DE actuators (DEAs) set stricter AM and electrode material requirements. DEAs’ layered structure, compliant nature, and susceptibility to various defects make their manufacturability challenging, especially for non-trivial biomimetic soft robotics geometries. This dissertation comprehensively analyzes DE materials’ transition into a soft actuator using AM to facilitate effective DEA soft actuator fabrication. Closely interrelated fabrication techniques, material properties, and DEA geometries are analyzed to establish a fundamental understanding of how to implement high-quality DEA soft actuators. Furthermore, great attention is paid to enhancing the performance of printed DEAs through developing printable elastomer and electrode materials with improved properties. Lastly, performance enhancement is approached from the design point of view by developing a novel 3D printable DEA configuration that actuates out-of-plane without stiffening elements

Electromechanical Performance of HASEL Actuators: Fundamentals and Applications

Soft robotic systems are well-suited to unstructured, dynamic tasks and environments, but are currently limited by the soft actuators that power them. Most current soft actuators are based on pneumatics or shape-memory alloys, which have issues with efficiency, response speed, and portability. More recently, dielectric elastomer actuators (DEAs) have shown promise, but they have limited material selection, fabrication methods, and modes of actuation. As such, there remains a need for new types of high performance and well-rounded soft actuators. This dissertation focuses on the development and exploration of a new class of soft electrohydraulic actuators called hydraulically amplified self-healing electrostatic (HASEL) actuators. The first part of this dissertation (Chapter 2) presents of a subclass of HASEL actuators called Peano-HASELs that simultaneously introduce a breakthrough materials system based on thermoplastic films as well as a novel contractile mode of actuation. This approach enables industrially-amenable fabrication techniques, vastly expands the usable materials for actuator construction, and results in high performance actuators with fast linear contraction on activation. The second part of this dissertation (Chapter 3) elucidates the fundamentals of the electromechanical coupling that drives HASEL actuators. An analytical model is developed that accurately describes the quasi-static actuation behavior of Peano-HASEL actuators without relying on fitting parameters. Using this model, we identify a theory-driven approach to actuator design, including a roadmap for actuators with drastically improved specific energies. The final section of this dissertation (Chapter 4 and 5) looks towards more integrated and applied designs of HASEL actuators. First, a new type of articulating actuator is presented that integrates both compliant and rigid components. These spider-inspired electrohydraulic soft-actuated (SES) joints demonstrate high torque and high-speed actuation in an independently-addressable multi-joint limb, a bidirectional actuator, and a versatile gripper. Second, a biodegradable materials system is presented for high performance Peano-HASEL actuators that reduce environmental impact. Finally, a new method of capacitive self-sensing is presented that enables inexpensive and compact circuits that use only off-the-shelf and low voltage components. The results presented in this dissertation provide a framework for the development of high-performance actuators that may one day power the next generation of capable soft robots.</p

Design and characterization of thermally-induced shape memory polymers

Les polymères à mémoire de forme (SMP) sont des matériaux intelligents qui peuvent récupérer leur forme permanente à partir d'une forme temporaire lorsqu'ils sont exposés à un stimulus externe. Ils ont attiré beaucoup d’attention en raison de leurs propriétés uniques. Par rapport aux SMPs doubles, les SMPs complexes ayant des mémoires triples, multiples ou bidirectionnelles sont plus attirants en raison de leurs propriétés distinctes. Les SMPs multiples peuvent mémoriser trois formes ou plus, tandis que les SMPs bidirectionnels peuvent basculer entre deux formes distinctes. L'objectif principal de cette thèse est de concevoir des SMPs complexes par des méthodes simples pour des applications particulièrement en biomédecine. Deux systèmes SMP complexes biodégradables à base de bio-composés ou de monomères synthétiques ont été synthétisés. Pour les SMPs de mémorises multiples, nous avons synthétisé une série de copolymères statistiques avec des groupes pendants d'acide cholique en utilisant une méthode de polymérisation radicalaire simple. Ces copolymères ont une température de transition vitreuse (Tg) réglable, selon le ratio de comonomères, qui montrent à la fois des effets mémoires à double et triple états (PME). Les rapports entre la fixité et la récupération de la mémoire de forme double ou triple peuvent être améliorés par l'incorporation d'un groupe cinnamate dans les copolymères afin de permettre la photo-réticulation du polymère. Les polymères réticulés présentent des rapports de récupération améliorés pour la mémoire de forme double et triple et présentent même des PME quadruples. Le degré de réticulation affecte également les propriétés de mémoire de forme. Les meilleurs comportements de mémoire de forme dans ce genre de polymères ont été obtenus avec une réticulation de 2,2% molaire des monomères. Les SMP doubles, triples et multiples sont généralement SMP unidirectionnels et leurs transformations de formes sont irréversibles. Les SMP réversibles bidirectionnels (2W-SMP) peuvent basculer automatiquement entre deux formes distinctes lorsqu'elles sont exposées à deux stimuli externes différents. Cependant, la température d'actionnement (TA) de 2W-SMP est une valeur fixe telle que déterminée par la température de fusion (Tm) du segment actuateur du réseau polymère. Dans cette étude, une série de copolymères statistiques contenant ε-caprolactone (CL) et ω-pentadécalactone (PDL) ont été synthétisés par polymérisation par ouverture de cycle avec un catalyseur de lipase B de Candida antarctica (CALB). Les segments polymères de ces deux monomères sont co-cristallisables et la Tm des copolymères peut être adapte en ajustant le rapport molaire des comonomères. Après irradiation pour la réticulation de thiol-ène, le réseau de polymères a montré des 2W-PME dans des conditions avec ou sans tension, avec un changement de forme absolu de 13,2%. Des mouvements réversibles comme flexion-extension et enroulement-déroulement ont été observés pour le réseau de polymère. La TA de 2W-SMP sous conditions sans stress peut être facilement contrôlée en sélectionnant un ou deux prépolymères comme segments du réseau polymère. Le changement de l’élongation absolue des 2W-SMP est augmenté sous les conditions avec ou sans stress, mais le changement d’élongation relative est réduit avec l'augmentation de tension sous condition de stress. L'évolution de la microstructure de 2W-SMPs sous condition sans stress a également été conçu. Les 2W-SMPs sont souvent actionnés thermiquement, mais le chauffage indirect est souhaitable pour certaines applications. Une série de 2W-SMPs composites actionnés par la lumière a ainsi été préparée par l’incorporation de nanosphères de PDA dans les réseaux polymères contenant le CL et le PDL. Les nanosphères de PDA ont un effet photothermique très prononcé qui peut convertir l'énergie lumineuse en chaleur. La température de l'échantillon augmente selon l’intensité lumineuse et du contenu en nanosphères de PDA. Ces composites polymères présentent d'excellentes 2W-PME sensibles à la lumière sous condition sans stress avec un changement d'angle réversible de 45° lorsque la lumière est allumée puis éteinte. L'échantillon avec un contenu plus élevé en nanosphères de PDA ou sous une intensité lumineuse plus forte cause une ouverture d’angle plus rapide. Un micro-robot qui peut marcher sur une piste en dents de scie lorsque la lumière est allumée et éteinte a également été conçu arec un composite 2W-SMPs.Shape memory polymers (SMPs) are smart materials that can recover the permanent shape from a temporary shape when exposed to an external stimulus. They have drawn much attention due to their unique properties. In comparison to dual SMPs, complex SMPs with triple, multiple and two-way shape memories are more attractive due to their versatile properties. Triple and multiple SMPs could memorize three and more shapes, while two-way SMPs may automatically switch forth and back between two distinct shapes. The main purpose of this thesis is to design simple complex SMPs for their applications especially in biomedicine. Two biodegradable complex SMP systems based on bio-compounds or synthetic monomers have been synthesized. For multiple SMPs, we synthesized a series of random copolymers with pendent cholic acid groups by the use of a simple free radical polymerization method. Such copolymers have a glass transition temperature (Tg) range tunable by varying the monomers ratios, allowing the dual and triple shape memory effects (SMEs). The fixity and recovery ratios of dual and triple shape memory may be further improved by the incorporation of cinnamate groups into copolymers to enable a photo-cross-linking of the terpolymer. The cross-linked polymers show much improved recovery ratios for both dual and triple shape memory and even exhibit quadruple SMEs. The degree of cross-linking also affects the shape memory properties. The best shape memory behaviors were obtained with a 2.2 mol% cross-linking of the total monomers in the terpolymer. Dual, triple and multiple SMPs are usually one-way SMPs, and their shape transformations are irreversible. Two-way reversible SMPs (2W-SMPs) may switch between two different shapes automatically when they are exposed to two reverse external stimuli. However, the actuation temperature (TA) of 2W-SMP is at a fixed value as it is determined by the melting temperature (Tm) of the actuator segment of the polymer network. In this study, a series of random copolymers containing ε-caprolactone (CL) and ω-pentadecalactone (PDL) were synthesized through ring opening polymerization catalyzed by Candida antarctica lipase B (CALB). The polymers segments made of these co-monomers are co-crystallizable and the Tms of the copolymers may be changed by adjusting the molar ratio of the co-monomers. Upon light irradiation which induces thiol-ene cross-linking, the polymer network showed 2W-SMEs under both stress-free and stress conditions with the absolute shape change up to 13.2%. Bending-unbending and coiling-uncoiling reversible shape motions were observed for the polymer network. The TA of the 2W-SMP under stress-free conditions may be tuned by simply selecting one or two different prepolymers as segments in the polymer network. The absolute strain change of 2W-SMPs increased under both stress-free and stress conditions, but the relative strain change reduced with increasing tensile stress under stress conditions. The evolution of the microstructure of 2W-SMPs under stress-free conditions was also elaborated. The 2W-SMPs are often actuated thermally, but indirect heating is desirable for certain applications because of its convenience. Thus, a series of light-actuated 2W-SMP composites were prepared via the incorporation of tiny amounts of polydopamine (PDA) nanospheres into polymer networks made of CL and PDL. PDA nanospheres have a strong photothermal effect which may convert energy of light into heat. The temperature change of the sample is larger with higher light intensity and higher content of PDA nanospheres. Such polymer composites exhibited excellent light-responsive 2W-SMEs under stress-free conditions with a reversible angle change of 45° when the light was turned on and off. The sample with a higher content of PDA nanospheres or under a stronger light led to a faster angle opening. A micro-robot is also designed and made of the 2W-SMP composite, which may walk on a home-made track with right triangle sawteeth when the light is turned on and off

Soft Actuators and Robotic Devices for Rehabilitation and Assistance

Soft actuators and robotic devices have been increasingly applied to the field of rehabilitation and assistance, where safe human and machine interaction is of particular importance. Compared with their widely used rigid counterparts, soft actuators and robotic devices can provide a range of significant advantages; these include safe interaction, a range of complex motions, ease of fabrication and resilience to a variety of environments. In recent decades, significant effort has been invested in the development of soft rehabilitation and assistive devices for improving a range of medical treatments and quality of life. This review provides an overview of the current state-of-the-art in soft actuators and robotic devices for rehabilitation and assistance, in particular systems that achieve actuation by pneumatic and hydraulic fluid-power, electrical motors, chemical reactions and soft active materials such as dielectric elastomers, shape memory alloys, magnetoactive elastomers, liquid crystal elastomers and piezoelectric materials. Current research on soft rehabilitation and assistive devices is in its infancy, and new device designs and control strategies for improved performance and safe human-machine interaction are identified as particularly untapped areas of research. Finally, insights into future research directions are outlined