Design Innovation Paper

Reconfigurable Modular Chain: A Reversible Material for Folding Three-Dimensional Lattice Structures

[+] Author and Article Information
Zhe Xu

Department of Mechanical Engineering,
Yale University,
New Haven, CT 06511
e-mail: zhe.xu@yale.edu

Connor McCann

Department of Mechanical Engineering,
Yale University,
New Haven, CT 06511
e-mail: connor.mccann@yale.edu

Aaron M. Dollar

Department of Mechanical Engineering,
Yale University,
New Haven, CT 06511
e-mail: aaron.dollar@yale.edu

Manuscript received October 7, 2016; final manuscript received January 13, 2017; published online March 9, 2017. Assoc. Editor: Hai-Jun Su.

J. Mechanisms Robotics 9(2), 025002 (Mar 09, 2017) (11 pages) Paper No: JMR-16-1298; doi: 10.1115/1.4035863 History: Received October 07, 2016; Revised January 13, 2017

A wide range of engineering applications, ranging from civil to space structures, could benefit from the ability to construct material-efficient lattices that are easily reconfigurable. The challenge preventing modular robots from being applied at large scales is mainly the high level of complexity involved in duplicating a large number of highly integrated module units. We believe that reconfigurability can be more effectively achieved at larger scales by separating the structural design from the rest of the functional components. To this end, we propose a modular chainlike structure of links and connector nodes that can be used to fold a wide range of two-dimensional (2D) or three-dimensional (3D) structural lattices that can be easily disassembled and reconfigured when desired. The node geometry consists of a diamondlike shape that is one-twelfth of a rhombic dodecahedron, with magnets embedded on the faces to allow a forceful and self-aligning connection with neighboring links. After describing the concept and design, we demonstrate a prototype consisting of 350 links and experimentally show that objects with different shapes can be successfully approximated by our proposed chain design.

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Fig. 1

Pictures of our proof-of-concept design: (a) 293 links are used in the folding of the pyramid shape and (b) a spool of the modular chain

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Fig. 2

Top views of the tiling patterns in 2D and 3D situations: (a) using regular triangle-lattices to construct 2D shapes and (b) using cube-lattices to construct 3D shapes

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Fig. 3

Tessellation of 3D space with regular octahedra and tetrahedra

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Fig. 4

Schematic drawing showing the lattice structure (left) and its unit cell after the solid-to-lattice conversion of a cube (right). Note: the arrows illustrate the loading orientations of the compressive and shear forces that act on the shaded top and bottom planes.

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Fig. 5

Schematic drawing showing the different components at the busiest connection joint inside a large three-dimensional lattice structure (an antenna frame)

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Fig. 6

The formation of the basic node geometry. Top row: a smaller rhombic dodecahedron is first fit into the center of the busiest connection joint. Bottom row: after a series of cutting processes, the rhombic pyramid shape is selected to form basic geometry of node design.

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Fig. 7

The important dimensions of our node design: (a) the rhombic pyramid with four symmetrically identical faces and (b) schematic drawing of the node design showing the critical assembly angles

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Fig. 8

Two different types of magnetic coupling used in our prototype: (a) type-I—embedding paired magnets directly at the contacting sites and (b) type-II—transmitting magnetic forces through the node made of ferrous materials. Note: the central hole is for anchoring connecting strings.

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Fig. 9

Possible connection joints supported by type-I coupling method. Note: except for the start and the end, all the other connection joints have even number of nodes inside any folded lattice structure. Rods were removed for better visibility of the nodes.

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Fig. 10

Two-dimensional simulation of the magnetic fields by using type-II coupling method: (a) alternating the poles at the two ends of each rod and (b) 2D simulation of the magnetic fields at different connection joints in a 3D reconfigurable lattice structure

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Fig. 11

The prototyping process of nodes via 3D printing: (a) a tray of 110 3D-printed nodes, (b) example of a separate link, and (c)–(j) variations of 2D and 3D structures folded by a 14-link chain

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Fig. 12

Prototyping process of nodes by using cold-casting method: (a) 3D-printed positives and the silicone rubber mold, (b) and (c) cold-casted parts made from the mixture of fine iron powder and resins, and (d) comparison of magnetic forces with nodes made of different materials. Note: each steel ball weights 8.4 g. The rod is the off-the-shelf Geomag part.

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Fig. 13

Example of the folding process: (a) the separate folding paths for constructing different layers of a pyramid and (b) snapshots showing the demonstration of planned folding process

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Fig. 14

Variations of folded shapes both in 2D and 3D (329-link)

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Fig. 15

Potential applications of our proposed chain design in space exploration. Note: the frames of the antenna and solar panel are all folded by the same chain with 1554 links.



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