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| 1. | One Sonobe module | |
|---|---|---|
| 3. | Opened (left) and completed (right) Toshie's Jewel(triangular bipyramid) | |
| 6. | Cube (triakis tetrahedron) | |
| 12. | Triakis octahedron | |
| 30. | Triakis icosahedron |
The Sonobe module is one of the many units used to build modular origami. The popularity of Sonobe modular origami models derives from the simplicity of folding the modules, the sturdy and easy assembly, and the flexibility of the system.
The origin of the Sonobe module is unknown. Two possible creators are Toshie Takahama and Mitsunobu Sonobe, who published several books together and both members of Sōsaku Origami Gurūpu '67. The earliest appearance of a Sonobe module was in a cube attributed to Mitsunobu Sonobe in a Sosaku the Sōsaku Origami Gurūpu '67's magazine Origami in Issue 2 (1968). [2] It does not reveal whether he invented the module or used an earlier design; the phrase "finished model by Mitsunobu Sonobe" is ambiguous. The diagram from Issue 2 reappears in 1970 in the group's book Atarashii origami nyūmon (新しい折り紙入門 ). [3] [4] Another 1970s appearance was in the model "Toshie's Jewel", from Toshie Takahama's book Creative Life With Creative Origami Vol 1. [5] [6] However neither folder took advantage of the full potential of the module. This potential was discovered in the 1970s by other folders – particularly Steve Krimball, who created the 30-unit ball – as part of a sudden period of development in modular origami. Despite the module's importance and continued popularity, its designer remains uncertain. [7]
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Each individual unit is folded from a square sheet of paper, of which only one face is visible in the finished module; many ornamented variants of the plain Sonobe unit that expose both sides of the paper have been designed.
The Sonobe unit has the shape of a parallelogram with 45 and 135 degrees angles, divided by creases into two diagonal tabs at the ends and two corresponding pockets within the inscribed center square. The system can build a wide range of three-dimensional geometric forms by docking these tabs into the pockets of adjacent units. Three interconnected Sonobe units will form an open-bottomed triangular pyramid with an equilateral triangle for the open bottom, and isosceles right triangles as the other three faces. It will have a right-angle apex (equivalent to the corner of a cube) and three tab/pocket flaps protruding from the base. This particularly suits polyhedra that have equilateral triangular faces: Sonobe modules can replace each notional edge of the original deltahedron by the central diagonal fold of one unit and each equilateral triangle with a right-angle pyramid consisting of one half each of three units, without dangling flaps. The pyramids can be made to point inwards; assembly is more difficult but some cases of encroaching can be obviously prevented.
The simplest shape made of these pyramids, often called "Toshie's Jewel" (shown above), is named after origami artist Toshie Takahama, who first printed a diagram of this in her 1974 book Creative Life with Creative Origami [5] . It is a three-unit hexahedron built around the notional scaffold of a flat equilateral triangle (two "faces", three edges); the protruding tab/pocket flaps are simply reconnected on the underside, resulting in two triangular pyramids joined at the base, a triangular bipyramid.
The most popular intermediate model is the triakis icosahedron, shown below. It requires 30 units to build.
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The table below shows the correlation between three basic characteristics – faces, edges, and vertices – of polygons (composed of Toshie's Jewel sub-units) of varying size and the number of Sonobe units used:
| Number of Sonobe Units | Faces | Edges | Vertices |
|---|---|---|---|
| s | 2s | 3s | s + 2 |
| 3 | 6 | 9 | 5 |
| 6 | 12 | 18 | 8 |
| 12 | 24 | 36 | 14 |
| 30 | 60 | 90 | 32 |
| 90 | 180 | 270 | 92 |
| 120 | 240 | 360 | 122 |
| 270 | 540 | 810 | 272 |
The model made of three units results in a triangular bipyramid. Building a pyramid on each face of a regular tetrahedron, using six units, results in a cube (the central fold of each module lays flat, creating square faces instead of isosceles right triangular faces, and changing the formula for the number of faces, edges, and vertices), or triakis tetrahedron. Building a pyramid on each face of a regular octahedron, using twelve Sonobe units, results in a triakis octahedron. Building a pyramid on each face of a regular icosahedron requires 30 units, and results in a triakis icosahedron.
Uniform polyhedra can be adapted to Sonobe modules by replacing non-triangular faces with pyramids having equilateral faces; for example by adding pentagonal pyramids pointing inwards to the faces of a dodecahedron a 90-module ball can be obtained.
The 270-module ball looks like a very complicated shape, but it is just an icosahedron with each triangular face divided into 9 small triangles. Each small triangle is made of 3 sonobe units.
Arbitrary shapes, beyond symmetrical polyhedra, can also be constructed; a deltahedron with 2N faces and 3N edges requires 3N Sonobe modules. A popular class of arbitrary shapes consists of assemblies of equal size cubes in a regular cubic grid, which can be easily derived from the six unit cube by joining multiple ones at faces or edges.
There are two popular variants of the main assembly style of three modules in triangular pyramids, both using the same flaps and pockets and compatible with it:
{{cite book}}: CS1 maint: numeric names: authors list (link) CS1 maint: unrecognized language (link)In geometry, a dodecahedron or duodecahedron is any polyhedron with twelve flat faces. The most familiar dodecahedron is the regular dodecahedron with regular pentagons as faces, which is a Platonic solid. There are also three regular star dodecahedra, which are constructed as stellations of the convex form. All of these have icosahedral symmetry, order 120.
In geometry, the regular icosahedron is a convex polyhedron that can be constructed from pentagonal antiprism by attaching two pentagonal pyramids with regular faces to each of its pentagonal faces, or by putting points onto the cube. The resulting polyhedron has 20 equilateral triangles as its faces, 30 edges, and 12 vertices. It is an example of a Platonic solid and of a deltahedron. The icosahedral graph represents the skeleton of a regular icosahedron.
In geometry, a Johnson solid, sometimes also known as a Johnson–Zalgaller solid, is a strictly convex polyhedron whose faces are regular polygons. They are sometimes defined to exclude the uniform polyhedrons. There are ninety-two solids with such a property: the first solids are the pyramids, cupolas. and a rotunda; some of the solids may be constructed by attaching with those previous solids, whereas others may not. These solids are named after mathematicians Norman Johnson and Victor Zalgaller.
In geometry, an octahedron is a polyhedron with eight faces. An octahedron can be considered as a square bipyramid. When the edges of a square bipyramid are all equal in length, it produces a regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex. It is also an example of a deltahedron. An octahedron is the three-dimensional case of the more general concept of a cross polytope.
Modular origami or unit origami is a multi-stage paper folding technique in which several, or sometimes many, sheets of paper are first folded into individual modules or units and then assembled into an integrated flat shape or three-dimensional structure, usually by inserting flaps into pockets created by the folding process. These insertions create tension or friction that holds the model together. Some assemblies can be somewhat unstable because adhesives or string are not used.
In geometry, a deltahedron is a polyhedron whose faces are all (congruent) equilateral triangles. The name is taken from the Greek upper case delta letter (Δ), which has the shape of an equilateral triangle. There are infinitely many deltahedra. By the handshaking lemma, each deltahedron has an even number of faces. Only eight deltahedra are strictly convex; these have 4, 6, 8, 10, 12, 14, 16, and 20 faces. These eight deltahedra, with their respective numbers of faces, edges, and vertices, are listed below.
In geometry, a triakis tetrahedron is a Catalan solid with 12 faces. Each Catalan solid is the dual of an Archimedean solid. The dual of the triakis tetrahedron is the truncated tetrahedron.
In geometry, the triakis icosahedron is an Archimedean dual solid, or a Catalan solid, with 60 isosceles triangle faces. Its dual is the truncated dodecahedron. It has also been called the kisicosahedron. It was first depicted, in a non-convex form with equilateral triangle faces, by Leonardo da Vinci in Luca Pacioli's Divina proportione, where it was named the icosahedron elevatum. The capsid of the Hepatitis A virus has the shape of a triakis icosahedron.
The triaugmented triangular prism, in geometry, is a convex polyhedron with 14 equilateral triangles as its faces. It can be constructed from a triangular prism by attaching equilateral square pyramids to each of its three square faces. The same shape is also called the tetrakis triangular prism, tricapped trigonal prism, tetracaidecadeltahedron, or tetrakaidecadeltahedron; these last names mean a polyhedron with 14 triangular faces. It is an example of a deltahedron and of a Johnson solid.
The Tamatebako (玉手箱) is an origami model named after the tamatebako of Japanese folk tale. It is a modular cube design that can be opened from any side. If more than one face of the model is opened, the cube falls apart and cannot easily be reconstructed. The model, and the directions for creating it, had been lost for centuries and only recently rediscovered.
In geometry, the elongated square pyramid is a convex polyhedron constructed from a cube by attaching an equilateral square pyramid onto one of its faces. It is an example of Johnson solid. It is topologically self-dual.
In geometry, the elongated square bipyramid is the polyhedron constructed by attaching two equilateral square pyramids onto a cube's faces that are opposite each other. It can also be seen as 4 lunes linked together with squares to squares and triangles to triangles. It is also been named the pencil cube or 12-faced pencil cube due to its shape.
Kunihiko Kasahara is a Japanese origami master. He has made more than a hundred origami models, from simple lion masks to complex modular origami, such as a small stellated dodecahedron. He does not specialize in what is known as "super complex origami", but rather he likes making simple, elegant animals, and modular designs such as polyhedra, as well as exploring the mathematics and geometry of origami. A book expressing both approaches is Origami for the Connoisseur, which gathers modern innovations in polyhedral construction, featuring moderately difficult but accessible methods for producing the Platonic solids from single sheets, and much more.
In geometry, a compound of two tetrahedra is constructed by two overlapping tetrahedra, usually implied as regular tetrahedra.
In geometry, the truncated triakis tetrahedron, or more precisely an order-6 truncated triakis tetrahedron, is a convex polyhedron with 16 faces: 4 sets of 3 pentagons arranged in a tetrahedral arrangement, with 4 hexagons in the gaps.
In geometry, a simplicial polytope is a polytope whose facets are all simplices. For example, a simplicial polyhedron in three dimensions contains only triangular faces and corresponds via Steinitz's theorem to a maximal planar graph.
In geometry, chamfering or edge-truncation is a topological operator that modifies one polyhedron into another. It is similar to expansion: it moves the faces apart (outward), and adds a new face between each two adjacent faces; but contrary to expansion, it maintains the original vertices. For a polyhedron, this operation adds a new hexagonal face in place of each original edge.
In geometry, an icosahedron is a polyhedron with 20 faces. The name comes from Ancient Greek εἴκοσι (eíkosi) 'twenty', and ἕδρα (hédra) 'seat'. The plural can be either "icosahedra" or "icosahedrons".