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Design, modelling and development of origami-inspired tubular compliant mechanisms towards radially closable applications
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Date
2025
Authors
Ye, Siyuan
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Publisher
University College Cork
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Abstract
This dissertation investigates the design, modelling, and development of origami-inspired tubular compliant mechanisms tailored for radially closable applications. Origami technology has been extensively explored in engineering applications, and tubular origami structures offer broader functional applications due to their unique 3D geometries. Their bistable characteristics, negative Poisson's ratio, and tunable stiffness have found wide application in fields such as aerospace, medical devices, and robotics. However, their potential for radial closability remains unexplored. This study identifies the similarity between the radial closability of the Kresling structure and the iris mechanism. Additionally, an optimized crease pattern, RC-ori (radial closable origami) is created to avoid twisting motion without adding extra length to the tube. The RC-ori structure enhances the functionality of the iris mechanism and opens up potential applications in areas such as valves, grippers, and drug carriers.
However, most tubular origami structures are over-constrained, meaning they are not rigidly foldable. Therefore, their engineering implementation requires addressing not only panel-thickness interference but also the additional degrees of freedom (DOFs) being necessary for folding. This dissertation conducts comprehensive kinematic analysis of the RC-ori crease pattern to understand its characteristics, focusing on the origins of over-constraint. Two main hinge forms, smooth folds and compliant joints, were investigated. Three solutions for achieving non-rigid foldability in RC-ori were proposed: (1) utilizing the stretching of flexible membrane materials to provide additional DOFs, (2) disconnecting over-constrained creases to make it rigidly foldable, and (3) leveraging the parasitic motion of compliant joints for deformation-induced DOFs.
In the study of smooth folds, a silicone-based solution was initially explored. However, due to manufacturing complexities and experimental constraints, fabric materials (nylon-spandex) were investigated as a better alternative. These commercially available materials demonstrated high elasticity and resilience, allowing the required range of stretching. Uniaxial tensile tests of the fabric material provided its mechanical properties, which were incorporated into theoretical analyses and hyperelastic modelling. However, the load-bearing capacity of the model required additional rigid materials for structural support, making the bonding methods between the two materials a critical area of study.
Compliant joints, by contrast, facilitate bending along crease lines using the same material as the panels, thereby eliminating the need for auxiliary flexible materials to achieve folding. This simplifies the design by reducing the number of components and assembly requirements. After evaluating various compliant joint designs, the outside LET joint was deemed the most suitable for this application. To address the non-rigid foldability of RC-ori, two approaches were explored: (1) removing over-constrained connections, which proved simple yet effective, supported by theoretical modelling, simulations, and experimental validation; and (2) leveraging the LET joint's parasitic motion, which is often considered undesirable but was found to provide the necessary DOFs in over-constrained creases. The latter approach preserved the monolithic structure while enabling non-rigid foldable origami designs. The compliance matrices for individual LET joints and the kinematic analysis of over-constrained creases were developed, leading to force-displacement relationships for the overall model, which were verified through finite element analysis (FEA).
To balance the strengths of the above approaches, a hybrid method combining fabric and LET joints was proposed. In this design, fabric's high elasticity replaces over-constrained creases, while LET joints substitute other creases. This minimizes the risk of damage to LET joints caused by large deformations and mitigates the adverse effects of excessive parasitic motion from highly flexible fabrics, which could otherwise compromise folding accuracy. The hybrid model was further analysed through parameter optimization of LET joints.
Throughout the research, various manufacturing methods for the models were explored. Although some models showed suboptimal performance, their fabrication processes offer valuable insights for constructing origami or over-constrained structures. The manufacturing processes of these models are documented with brief performance evaluations, while experimental analyses are conducted on some relatively successful designs.
Description
Mechanical Engineering
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Controlled Access
Keywords
Origami , Compliant joint , Iris mechanism , Radial closability , 3D printing , Fabric-based design
Citation
Ye, S. 2025. Design, modelling and development of origami-inspired tubular compliant mechanisms towards radially closable applications. PhD Thesis, University College Cork.