Soft Robot Locomotion via Mechanical Metamaterials: Application in Pipe Inspection

Pipe inspections are performed using large robots that utilize wheels or tracks for locomotion. Due to their large size, weight and hard exterior, these robots can occasionally cause damage to the pipe interiors during inspection. In addition, these pipe inspection robots struggle with the ability to move in a congested environment and adapt to obstacles or geometry changes within the pipe. This project investigates the capabilities of auxetic and conventional metamaterials to achieve locomotion in an enclosed channel through the different metamaterials reactions to an axial force. The resulting robot is capable of both horizontal and vertical locomotion. Computer simulation is used to confirm the metamaterials effective Poissons ratio through testing deformation under applied loads at small displacements. Physical testing of the soft-bodied robot is employed to demonstrate the force needed for movement and validate the auxetic and conventional metamaterial behavior. The extensive work serves as a proof of concept of auxetic metamaterials as a viable solution for less invasive movement through enclosed channels. Further work and alterations to the soft-bodied robot body may allow for future applications in realms such as medical device development

Shape-matching soft mechanical metamaterials

Architectured materials with rationally designed geometries could be used to create mechanical metamaterials with unprecedented or rare properties and functionalities. Here, we introduce "shape-matching" metamaterials where the geometry of cellular structures comprising auxetic and conventional unit cells is designed so as to achieve a pre-defined shape upon deformation. We used computational models to forward-map the space of planar shapes to the space of geometrical designs. The validity of the underlying computational models was first demonstrated by comparing their predictions with experimental observations on specimens fabricated with indirect additive manufacturing. The forward-maps were then used to devise the geometry of cellular structures that approximate the arbitrary shapes described by random Fourier's series. Finally, we show that the presented metamaterials could match the contours of three real objects including a scapula model, a pumpkin, and a Delft Blue pottery piece. Shape-matching materials have potential applications in soft robotics and wearable (medical) devices

Tiled Auxetic Cylinders for Soft Robots

Compliant structures allow robots to overcome environmental challenges by deforming and conforming their bodies. In this paper, we investigate auxetic structures as a means of achieving this compliance for soft robots. Taking a tiling based approach, we fabricate 3D printed cylindrical auxetic structures to create tiled auxetic cylinders (TACs). We characterise the relative stiffness of the structures and show that variation in behaviour can be achieved by modifying the geometry within the same tiling family. In addition, we analysed the equivalent Poisson's ratio and found the range between the investigated designs to span from -0.33 to -2. Furthermore, we demonstrate a conceptual application in the design of a soft robot using the auxetic cylinders. We show that these structures can reactively change in shape, thereby reducing the complexity of control, with potential applications in confined spaces such as the human body, or for exploration through unpredictable terrain.</p

Additive Manufacturing of Resettable-Deformation Bi-Stable Lattices Based on a Compliant Mechanism

Metamaterials allow for the possibility to design and fabricate new materials with enhanced me- chanical properties, through the use of additive manufacturing. There are some certain materials’ struc- tures that exhibit excellent properties to withstand externally applied forces. One example of this type of structure is a bi-stable switching mechanism which can regain its original position, after being sub- mitted to a compressive force. This kind of structure should be flexible and strong since it needs to undergo a certain deflection. Another important aspect that was addressed in this work is the structure’s geometry, because of the effect that it has on flexibility. Therefore, this thesis will focus on the proper study, design, 3D printing, and mechanical characterization of a novel unitary compliant bi-stable struc- ture, and its use to build two larger cellular compliant bi-stable structures, a four-cell and a multicell structure, using the unitary one as a building block. All structures were designed in the CAD software Fusion 360 and fabricated with Polylactic Acid filament using the Fused Filament Fabrication process. The fabricated structures were submitted to compressive tests, from where Force vs. Displacement plots were obtained. These results proved that the multicell structure was the stiffest, since it required higher compressive force to perform its function, when compared to the other two structures. The conducted tests were important to check the behavior of each structure while being compressed, where both struc- tures that had more than one cell showed a layered switching behavior. Also, the tests were important to check if the position recovery of the structures was possible to achieve, which was observed in all of them. After the compressive tests, all structures were also submitted to repetitive solicitation tests, to study their repeatability behavior. These results envisage the successful application of these mechanisms towards their implementation in microelectromechanical systems.Os metamateriais permitem fabricar novos materiais com propriedades mecânicas aprimoradas, através do uso de manufatura aditiva. Existem algumas estruturas de determinados materiais que apresentam excelentes propriedades para resistir às forças externas aplicadas sobre eles. Um exemplo deste tipo de estrutura é um mecanismo complacente biestável que pode recuperar a sua posição original, após ser submetido a uma força de compressão. Este tipo de estrutura precisa de ser flexível e forte, porque é projetado para sofrer uma certa deflexão. Outro aspeto importante que foi abordado neste trabalho é a geometria da estrutura, devido ao efeito que esta tem na flexibilidade. Portanto, esta dissertação concentrar-se-á no estudo adequado, desenho, impressão 3D e caracterização mecânica de uma nova estrutura complacente biestável unitária, e o seu uso para construir duas estruturas celulares complacentes biestáveis, uma de quatro células e outra multicelular, usando a estrutura unitária como bloco de construção. Todas as estruturas foram desenhadas no software de CAD Fusion 360 e fabricadas com filamento de Ácido Poliláctico usando o processo de Fabricação com Filamento Fundido. As estruturas fabricadas foram submetidas a ensaios de compressão, de onde foram obtidos gráficos de Força vs. Deslocamento. Estes resultados comprovaram que a estrutura multicelular era a mais rígida, porque necessitou de uma maior força compressiva para desempenhar a sua função. Os testes realizados foram importantes para analisar o comportamento de cada estrutura durante a compressão, onde ambas as estruturas multicelulares apresentaram um comportamento de transição camada a camada. Além disso, os testes foram também importantes para verificar se a recuperação da posição das estruturas era possível, o que foi observado para todas. Após os ensaios de compressão, todas as estruturas foram submetidas a ensaios de solicitação repetitiva, para estudar o seu comportamento de repetibilidade. Estes resultados vislumbram o sucesso da implementação destes mecanismos em sistemas microelectromecânicos

Continuum Mechanical Models for Design and Characterization of Soft Robots

The emergence of ``soft'' robots, whose bodies are made from stretchable materials, has fundamentally changed the way we design and construct robotic systems. Demonstrations and research show that soft robotic systems can be useful in rehabilitation, medical devices, agriculture, manufacturing and home assistance. Increasing need for collaborative, safe robotic devices have combined with technological advances to create a compelling development landscape for soft robots. However, soft robots are not yet present in medical and rehabilitative devices, agriculture, our homes, and many other human-collaborative and human-interactive applications. This gap between promise and practical implementation exists because foundational theories and techniques that exist in rigid robotics have not yet been developed for soft robots. Theories in traditional robotics rely on rigid body displacements via discrete joints and discrete actuators, while in soft robots, kinematic and actuation functions are blended, leading to nonlinear, continuous deformations rather than rigid body motion. This dissertation addresses the need for foundational techniques using continuum mechanics. Three core questions regarding the use of continuum mechanical models in soft robotics are explored: (1) whether or not continuum mechanical models can describe existing soft actuators, (2) which physical phenomena need to be incorporated into continuum mechanical models for their use in a soft robotics context, and (3) how understanding on continuum mechanical phenomena may form bases for novel soft robot architectures. Theoretical modeling, experimentation, and design prototyping tools are used to explore Fiber-Reinforced Elastomeric Enclosures (FREEs), an often-used soft actuator, and to develop novel soft robot architectures based on auxetic behavior. This dissertation develops a continuum mechanical model for end loading on FREEs. This model connects a FREE’s actuation pressure and kinematic configuration to its end loads by considering stiffness of its elastomer and fiber reinforcement. The model is validated against a large experimental data set and compared to other FREE models used by roboticists. It is shown that the model can describe the FREE’s loading in a generalizable manner, but that it is bounded in its peak performance. Such a model can provide the novel function of evaluating the performance of FREE designs under high loading without the costs of building and testing prototypes. This dissertation further explores the influence viscoelasticity, an inherent property of soft polymers, on end loading of FREEs. The viscoelastic model developed can inform soft roboticists wishing to exploit or avoid hysteresis and force reversal. The final section of the dissertations explores two contrasting styles of auxetic metamaterials for their uses in soft robotic actuation. The first metamaterial architecture is composed of beams with distributed compliance, which are placed antagonistic configurations on a variety of surfaces, giving ride to shape morphing behavior. The second metamaterial architecture studied is a ``kirigami’’ sheet with an orthogonal cut pattern, utilizing lumped compliance and strain hardening to permanently deploy from a compact shape to a functional one. This dissertation lays the foundation for design of soft robots by robust physical models, reducing the need for physical prototypes and trial-and-error approaches. The work presented provides tools for systematic exploration of FREEs under loading in a wide range of configurations. The work further develops new concepts for soft actuators based on continuum mechanical modeling of auxetic metamaterials. The work presented expands the available tools for design and development of soft robotic systems, and the available architectures for soft robot actuation.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163236/1/asedal_1.pd

Towards an ontology for soft robots: What is soft?

The advent of soft robotics represents a profound change in the forms robots will take in the future. However, this revolutionary change has already yielded such a diverse collection of robots that attempts at defining this group do not reflect many existing ‘soft’ robots. This paper aims to address this issue by scrutinising a number of descriptions of soft robots arising from a literature review with the intention of determining a coherent meaning for soft. We also present a classification of existing soft robots to initiate the development of a soft robotic ontology. Finally, discrepancies in prescribed ranges of Young’s modulus, a frequently used criterion for the selection of soft materials, are explained and discussed. A detailed visual comparison of these ranges and supporting data is also presented