57 research outputs found

    Designing LMPA-Based Smart Materials for Soft Robotics Applications

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    This doctoral research, Designing LMPA (Low Melting Point Alloy) Based Smart Materials for Soft Robotics Applications, includes the following topics: (1) Introduction; (2) Robust Bicontinuous Metal-Elastomer Foam Composites with Highly Tunable Mechanical Stiffness; (3) Actively Morphing Drone Wing Design Enabled by Smart Materials for Green Unmanned Aerial Vehicles; (4) Dynamically Tunable Friction via Subsurface Stiffness Modulation; (5) LMPA Wool Sponge Based Smart Materials with Tunable Electrical Conductivity and Tunable Mechanical Stiffness for Soft Robotics; and (6) Contributions and Future Work.Soft robots are developed to interact safely with environments. Smart composites with tunable properties have found use in many soft robotics applications including robotic manipulators, locomotors, and haptics. The purpose of this work is to develop new smart materials with tunable properties (most importantly, mechanical stiffness) upon external stimuli, and integrate these novel smart materials in relevant soft robots. Stiffness tunable composites developed in previous studies have many drawbacks. For example, there is not enough stiffness change, or they are not robust enough. Here, we explore soft robotic mechanisms integrating stiffness tunable materials and innovate smart materials as needed to develop better versions of such soft robotic mechanisms. First, we develop a bicontinuous metal-elastomer foam composites with highly tunable mechanical stiffness. Second, we design and fabricate an actively morphing drone wing enabled by this smart composite, which is used as smart joints in the drone wing. Third, we explore composite pad-like structures with dynamically tunable friction achieved via subsurface stiffness modulation (SSM). We demonstrate that when these composite structures are properly integrated into soft crawling robots, the differences in friction of the two ends of these robots through SSM can be used to generate translational locomotion for untethered crawling robots. Also, we further develop a new class of smart composite based on LMPA wool sponge with tunable electrical conductivity and tunable stiffness for soft robotics applications. The implications of these studies on novel smart materials design are also discussed

    Design, fabrication and stiffening of soft pneumatic robots

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    Although compliance allows the soft robot to be under-actuated and generalise its control, it also impacts the ability of the robot to exert forces on the environment. There is a trade-off between robots being compliant or precise and strong. Many mechanisms that change robots' stiffness on demand have been proposed, but none are perfect, usually compromising the device's compliance and restricting its motion capabilities. Keeping the above issues in mind, this thesis focuses on creating robust and reliable pneumatic actuators, that are designed to be easily manufactured with simple tools. They are optimised towards linear behaviour, which simplifies modelling and improve control strategies. The principle idea in relation to linearisation is a reinforcement strategy designed to amplify the desired, and limit the unwanted, deformation of the device. Such reinforcement can be achieved using fibres or 3D printed structures. I have shown that the linearity of the actuation is, among others, a function of the reinforcement density and shape, in that the response of dense fibre-reinforced actuators with a circular cross-section is significantly more linear than that of non-reinforced or non-circular actuators. I have explored moulding manufacturing techniques and a mixture of 3D printing and moulding. Many aspects of these techniques have been optimised for reliability, repeatability, and process simplification. I have proposed and implemented a novel moulding technique that uses disposable moulds and can easily be used by an inexperienced operator. I also tried to address the compliance-stiffness trade-off issue. As a result, I have proposed an intelligent structure that behaves differently depending on the conditions. Thanks to its properties, such a structure could be used in applications that require flexibility, but also the ability to resist external disturbances when necessary. Due to its nature, individual cells of the proposed system could be used to implement physical logic elements, resulting in embodied intelligent behaviours. As a proof-of-concept, I have demonstrated use of my actuators in several applications including prosthetic hands, octopus, and fish robots. Each of those devices benefits from a slightly different actuation system but each is based on the same core idea - fibre reinforced actuators. I have shown that the proposed design and manufacturing techniques have several advantages over the methods used so far. The manufacturing methods I developed are more reliable, repeatable, and require less manual work than the various other methods described in the literature. I have also shown that the proposed actuators can be successfully used in real-life applications. Finally, one of the most important outcomes of my research is a contribution to an orthotic device based on soft pneumatic actuators. The device has been successfully deployed, and, at the time of submission of this thesis, has been used for several months, with good results reported, by a patient

    4D Microprinting Based on Liquid Crystalline Elastomers

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    Two-photon laser printing (2PLP) is a disruptive three-dimensional (3D) printing technique that can afford structural fabrication at the submicrometer scale. Apart from constructing static 3D structures, research in fabricating dynamic ones, known as "4D printing”, is becoming a burgeoning field. 4D printed structures exhibit adaptability or tunability towards their environment through the control of an external stimulus. In contrast to the rapid growth in macroscale fabrication, progress in microprinted actuators has only been scarcely reported. Liquid crystal elastomer (LCE) stands out among the promising classes of smart materials for fabricating microrobotics or microactuators due to its distinct anisotropic property, which enables the printed structures to exhibit automated reversible movements upon exposure to stimuli without environmental limitations. Nevertheless, the use of 2PLP for the manufacture of 4D printed LCE microstructures with high versatility and complexity have presented some challenges, limiting their implementation in final applications. This thesis aims to overcome two main obstacles faced in this regard: first, the limitation of two-photon printable stimuli-responsive materials; and second, the lack of a facile approach for aligning liquid crystal (LC) within three dimensions. The first part of this thesis aims on expanding the library of materials used for implementing light responsiveness into LC microstructures, as light provides a higher degree of temporal and spatial control compared to other stimuli. The initial approach has involved incorporation of acrylate-functionalized photoresponsive molecules, such as azobenzene and the donor-acceptor Stenhouse adduct (DASA), into a LC ink using a conventional synthetic method. However, several challenges, such as compatibility with the LC ink, have prevented the achievement of 4D printing via 2PLP. The second approach is based on post-modifying printed LC structures and successfully fabricated microactuators with five different photoresponsive features by individually incorporating each light-absorbing molecule. Furthermore, LC microactuators that exhibit distinct actuation patterns under different colors of light were fabricated by simultaneously implementing orthogonal photoresponsive molecules. The second project presented in this thesis focuses on developing a new strategy to induce alignment domains in a more flexible manner, with the aim of spatially tailoring the LC topology of the 3D printed microstructures. This is achieved by microprinting 3D scaffolds based on polydimethylsiloxane (PDMS) to manipulate the alignment directions of LC molecules. Taking advantage of 2PLP to fabricate arbitrary scaffolds, LC alignments, including planar and radial patterns, could be introduced freely and simultaneously in three-dimensional space with varying degrees of complexity. The applicability of this alignment approach was demonstrated by fabricating responsive LC microstructures within different PDMS environments, and distinct actuation patterns were observed. Overall, these two breakthroughs have unveiled a wide array of new potentials for the utilization of responsive LC microsystems with tunable functionalities and customizable actuation responses, that can be applied across various domains and applications

    Octopus-inspired adhesive skins for intelligent and rapidly switchable underwater adhesion

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    The octopus couples controllable adhesives with intricately embedded sensing, processing, and control to manipulate underwater objects. Current synthetic adhesive–based manipulators are typically manually operated without sensing or control and can be slow to activate and release adhesion, which limits system-level manipulation. Here, we couple switchable, octopus-inspired adhesives with embedded sensing, processing, and control for robust underwater manipulation. Adhesion strength is switched over 450× from the ON to OFF state in \u3c50 ms over many cycles with an actively controlled membrane. Systematic design of adhesive geometry enables adherence to nonideal surfaces with low preload and independent control of adhesive strength and adhesive toughness for strong and reliable attachment and easy release. Our bio-inspired nervous system detects objects and autonomously triggers the switchable adhesives. This is implemented into a wearable glove where an array of adhesives and sensors creates a biomimetic adhesive skin to manipulate diverse underwater objects

    Challenges and Opportunities of Self-healing Polymers and Devices for Extreme and Hostile Environments

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    Engineering materials and devices can be damaged during their service life as a result of mechanical fatigue, punctures, electrical breakdown, and electrochemical corrosion. This damage can lead to unexpected failure during operation, which requires regular inspection, repair, and replacement of the products, resulting in additional energy consumption and cost. During operation in challenging, extreme, or harsh environments, such as those encountered in high or low temperature, nuclear, offshore, space, and deep mining environments, the robustness and stability of materials and devices are extremely important. Over recent decades, significant effort has been invested into improving the robustness and stability of materials through either structural design, the introduction of new chemistry, or improved manufacturing processes. Inspired by natural systems, the creation of self-healing materials has the potential to overcome these challenges and provide a route to achieve dynamic repair during service. Current research on self-healing polymers remains in its infancy, and self-healing behavior under harsh and extreme conditions is a particularly untapped area of research. Here, the self-healing mechanisms and performance of materials under a variety of harsh environments are discussed. An overview of polymer-based devices developed for a range of challenging environments is provided, along with areas for future research
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