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Abstract: We provide the design method of multi-step magnetic self-assembly using ferromagnetic-hinged structures. The process uses the magnetostatic torque generated by an external magnetic field perpendicular to the substrate to lift hinged structures. Hinged structure is composed of a rigid plate connected by elastic hinges to one side of a substrate. If hinged structures are raised in sequential order, it is possible to assemble like Japanese “origami” complex three-dimensional structures. In our previous study, we found that a dimensionless factor that depends on its shape determines the sensitivity of the hinged microstructures to a magnetic field. This factor can be used as a criterion in designing a process for sequential batch self-assembly, because the factor indicates the differences in the sensitivity. In this study, we designed multi-step sequential assembly by using the dimensionless factor. Four-step sequential batch assembly was demonstrated using this method. This method will be useful for optical systems, which consist of many complex three-dimensional structures. [Copyright &y& Elsevier]

In this paper, we have developed a process for multistep sequential batch assembly of complex three-dimensional (3-D) ferromagnetic microstructures. The process uses the magnetic torque generated by an external magnetic field perpendicular to the substrate to lift hinged structures. We found that a dimensionless factor that depends on the volume of the magnetic material and the stiffness of the hinges determines the sensitivity of the hinged microstructures to a magnetic field. This factor was used as a criterion in designing a process for sequential batch assembly, i.e., for setting appropriate differences in sensitivity. Using a dimensionless factor in the design of the sequential assembly simplified the assembly process, which requires only placing the structures on a permanent magnet, and which can be used to carry out multistep sequential batch assembly. We fabricated hinged microstructures, which consist of 4.5-µm-thick electroplated Permalloy plates and 200-nm-thick nickel elastic hinges of various sizes. In an experiment, four plates (600 µm × 800 µm) were lifted sequentially and out-of-plane microstructures were assembled in a four-step process. Assembly of more complex out-of-plane microstructures (e.g., regular tetrahedrons, 800 pm long on one side) was also shown to be feasible using this method of sequential batch assembly. [ABSTRACT FROM AUTHOR]

Recently, a new technology has come to the fore, namely four-dimensional (4D) printing. Conventional research has, however, mostly been in a glass state after a shape change such as self-folding of 4D printing, because the heat shrinkage or shape memory effect of polymers is used. Therefore, the 4D printed hinges are rigid and cannot be folded or unfolded after 4D printing below the glass transition temperature of the shape memory polymer (SMP). Hence, in this study, we proposed a hybrid hinge structure that is elastic and can be largely deformed as an origami structure even after 4D printing. On the hybrid hinge, a soft elastomer hinge was arranged beside the rigid 4D printing hinges to achieving the elastic folding deformation after self-folding. We confirmed that the samples recovered to almost their original shape without failure after 500 cycles of folding. They exhibited high durability and elasticity. Finally, the usefulness of the hybrid hinge was demonstrated by fabricating a miura-ori and an origami compliant mechanism gripper, which could be deformed as origami structure below the glass transition temperature of the SMP. We believe that our 4D printing method can be applied for developing self-folding actuators and robots, which require origami deformation. [Display omitted] • A hybrid hinge composed of 4D printed hinges and an elastomer hinge was proposed to realize hinge elasticity. • The effect of the hybrid hinge structure on the self-folding angle was evaluated experimentally and analytically. • The hybrid hinges have large deformability and were unbroken and resilient even after 500 cycles of repeated folding. • A miura-ori structure that can be folded and unfolded after self-folding is demonstrated. • An origami gripper using a compliant mechanism that can be gripped and released was realized. [ABSTRACT FROM AUTHOR]