Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

Geometric Considerations
for the Design of Rigid Origami Structures
Tomohiro TACHI1*
1*

The University of Tokyo
3-8-1 Komaba, Meguro-Ku, Tokyo 153-8092, Japan
Abstract
Transformable polyhedral surfaces with rigid facets, i.e., rigid origami, areuseful for designing kinetic and deployable structures. In order to apply rigid origami tovarious architectural and other engineering design purposes, it is essential to consider
the geometry of origami in kinetic motion and provide sufficiently generalized methods
to produce controlled variations of shapes that suit the given design conditions. In thispaper, we introduce the author’s recent studies and their extensions on the geometry of
rigid origami for designing transformable and deployable structures.
Keywords: origami, deployable structure, transformable polyhedron, kinematics, form-finding

1 Introduction
Rigid-foldable origami, or rigid origami, is a piecewise linear developable surface thatcan realize a deployment mechanism if its facets and foldlines are substituted with rigid
panels and hinges, respectively. Designing such a deployment mechanism has asignificant meaning in an engineering context, particularly in architecture in thefollowing reasons:
1. The structure based on a watertight surface is suitable for constructing anenvelope of a space, a roof, or a facade.
2. Purely geometric mechanism that does not rely on the elasticity of materials canrealize robust kinetic structure in a larger scale under gravity.
3. The transformation of the configuration is controlled by smaller number ofdegrees of freedom. This enables a semi-automatic deployment of the structure.
Several designs of rigid-origami structures have been proposed from around 1970’s. For
example, the developable double corrugation surface, or Miura-ori [1], is a well-known
rigid origami structure utilized in the packaging of deployable solar panels for use inspace or in the folding of maps (Figure 1). This provides a one-DOF mechanism from adeveloped state to a flat-folded state. Resch and Christiansen [2] have proposed akinetic plate mechanism that forms a three-dimensional dome that is folded out of asheet of a panel and folds into another three-dimensional state without curvature (Figure2). Hoberman proposed several rigid-foldable surfaces based on symmetric operations,e.g., [3], although he does clearly distinguish rigid and non-rigid foldable patterns.
In spite of these proposals, freely applying rigid origami to actual designs ofarchitectural space has been unachieved thus far, the reason of which includes the lackof designability in the existing methods. Since rigid origami transforms in aProceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

synchronized motion based on multiple non-linear constraints, the design of rigid
origami is not a trivial problem given by an arbitrary design approach without geometricconsiderations. However, starting from a known pattern of origami and just applying
them to architectural purposes does not work either because the model cannot
sufficiently adapt functional and environmental conditions required by an actual designcontext. Therefore it is important to show a general geometric methods to find forms
based on the kinetic properties of origami, while enabling flexible design variations that
preserve that properties, rather than relying on trial-and-error based approach. The
objective of this study is to show basic considerations on the geometry of rigid origami
and introduce novel methods to obtain the design variations based on them. In this paper,
we will show the kinematics of rigid origami, the design methods to allow folding
motion, and the design examples. Note that we limit our considerations to geometricones and do not intend to analyze elastic and plastic behavior of the structure withspecific materials.

Figure 1: Miura-ori.

Figure 2: Ron Resch’s pattern.

2 Kinematics of Rigid Origami
2.1 Model
The kinematics of origami can be represented by the unstable truss model or therotational hinges model. The former represents the configuration of the structure by the
positions of vertices. The change in the configuration is constrained by length
preserving rigid bars along edges (creases and foldlines) and diagonals of facets (2(k −3) bars for a planar k-gonal facet); this model is used by Resch and Christiansen [2], and
it is suitable for directly using the points positions in a non-singular state. The latter
represents the configuration by the rotational angles of edges and asserts the constraints
so that closed loops cannot separate; this model gives comparatively robust simulation
method such as Rigid Origami Simulator [4].
Here, we use the latter model for understanding the concept of rigid foldability. As
described, the configuration is represented by their folding angles ρ, which areconstrained by any closed strip of facets being not separated by the folding motion. If
we assume that a surface is a disk, the closure of any loop can be reduced to the
combination of local constraints around interior vertices. For each interior vertex, we
can use an (altered) form of the rotational matrix condition introduced by Belcastro andHull [5]. For each interior vertex and its incident foldlines of fold angles ρ1, …, ρn,
R 1 ,,  n   1   n 1  n  I(1)Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

where 3×3 matrices χ1, …, χn represent rotation by fold lines; each of them isrepresented as00  cos i  sin  i 0
1
(2)
 i  0 cos  i  sin  i   sin  i cos i 0,0 sin  i cos  i   001
where θi is the sector angle between the foldlines i and i + 1 (Figure 3 Left). Since i
is a rotational matrix, this fundamentally reduces to 3 scalar equations by using
elements
R(2, 3), R(3, 1), R(1, 2). The constraints for the global model with NVi interior vertices
can be represented by a 3NVi-vector equation F = 0. Therefore, the infinitesimal motion
can be represented by the solution space of the Jacobian matrix, which is a 3NVi × NEi
matrix where NEi is the number of foldlines (or interior edges).
Note that in a general case of orientable manifold with (possibly multiple) boundary, we
can have different number of constraints. If the surface has NL hole(s), we obtain extra
NL loop constraints to preserve the connectivity of the loops. (We additionally suggestthat in the case of arbitrary manifold, these loops are the cycles that form a homology
basis of the manifold.) Each loop constraint is comprised of 6 equations derived from 3
equations of rotational matrix and 3 equations of transition along the rotated edges. The
additional 3 equations can be represented as, for a loop of n facets around the hole,
n
 k

(3)
   i d k  0 ,k 1  i 1where χi and di represent the rotation matrix of the i-th facet orientation and the vector
representing the difference of i-th and i+1-th origins in a local coordinates (Figure 3
Right). Therefore the number of constraints is 3NVi + 6NL.

ρi+1
di=0

χi

yi+1
θi

θi

xi+1
zi+1
di

ρi+1
yi zi
xi

Figure 3: Constraints around loops and vertices
2.2 Rigid Foldability
Infinitesimal Rigid Foldability: The kinetic property of origami can be consideredfrom the viewpoints of stability. By using the Jacobian matrix, we can investigate rigid
foldability based on numerically analyzing infinitesimal motion. If the matrix is not
singular, the constraint gives under-constrained system with NEi − 3NVi − 6NL
dimensional solution space. In general, if the number of redundant constraints is NS, theProceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

solution space has NEi −3NVi −6NL +NS dimensions. The kinetic motion is given bysolving the Jacobian as,F F ρ  I N Ei (4) ρ 0 ,ρ ρ where F ρ is the Moore-Penrose generalized inverse, or pseudo-inverse of
Jacobian matrix. Here, ∆ρ0 represents an arbitrary infinitesimal folding motion, and theequation solves the solution ∆ρ closest to ∆ρ0. In order to simulate the folding motion of
rigid origami, we can apply Euler integration of this infinitesimal motion whileeliminating the residuals using Newton-Raphson method.
As described, surface attains additional infinitesimal DOFs when the Jacobian matrix issingular. It is known that the constraint vector of one vertex is the direction cosines ofcrease line incident to the vertex [4, 6]. This indicates that the Jacobian matrix becomessingular when all the vectors are co-planar, which happens in flat states. In fact, every
vertex of origami can infinitesimally transform arbitrarily along the normal of thesurface in the developed state, although such a transformation is not valid in a finite
sense and cannot be applied for structural designs.
Finite Rigid Foldability: Here, in order to use the kinetic behavior for a transformation
mechanism, we require that the transformation is finite, i.e., not shaky. The finite
folding motion is ensured by keeping the degrees of freedom of the mechanism positive
throughout the transformation. If any part of panels is not touching each other, thedegrees of freedom is only given by the Jacobean matrix: DOF = NEi − 3NVi − 6NL + NS.
Here, note that in the discussion of finite foldability, the singularity must be
independent of folding configuration and be preserved through the transformation, thus
we cannot use singularity coming from co-planarity of edges. If we use Euler’s
polyhedral formula, this can be written as,
DOF  N Eo  3N L  3  N S   k  3num of k - gon facet,
(5)


k 4

where NEo is the number of edges on the boundary.
From this consideration, we can understand that the flexibility of rigid origami mainly
comes from the flexibility of the boundary of the surface. Therefore, a closed
triangulated polyhedron is normally not foldable, since its DOF is NS (its kinetic
behavior is equivalent to that of a disk of NEo = 3). Examples of rigid foldable closed
polyhedra [7, 8] are known to have volume preserving singularity as conjectured as thebellows conjecture by Connelly et al. [9].

3 Triangle Based Design
The most flexible design comes from a triangular mesh. If we assume no singularity, thedegrees of freedom is represented as
DOF  N Eo  3 N L  3 .
(6)
In this case, the kinetic motion of a mesh is totally controlled by the boundary
configuration. For example, a design of a triangular mesh shell with 6 boundary edges

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

and 3 pin hinged legs — let us call this structure triangulated tripod — can be useful.
The total number of degrees of freedom of the structure is 9 because the structure has 6
degrees of rigid body motion and 3 degrees of transformation mechanism. Since thestructure is pinned at their legs, it constrains 3 × 3 degrees of freedom, which makes theoverall structure statically determinate. Therefore the structure transforms according to
the positions of the legs as shown in Figure 4, and it becomes a static structure once thelegs are fixed.
We can design the variations of triangulated tripods in a comparatively easy way since
the basic property of the structure is ensured by the number of boundary elements(Figure 5). However, the global behavior such as the possible range of folding and theexistence of a path from a state to another is determined by the configuration space ofthe structure. This is only understood through examining the infinitesimal behavior at
every possible state of the specific model through exploring the configuration spacewith simulational methods. In order to simulate the kinematics of the structure with pin
constraints, we can use either the unstable truss model or rotational hinges model withinverse kinematics.

Figure 4: A triangulated tripod of different configurations.

(a)

(b)

(c)

(d)

Figure 5: Examples of triangulated tripods. Quadrilateralpanels are all triangulated.

4 Quadrilateral Based Design
Another approach for designing a rigid-foldable structure is to use a quadrilateral meshsuch as Miura-ori. A quadrilateral mesh origami is normally not rigid-foldable since thedegrees of freedom is given as
DOF  N Eo  3N L  N facets  3  N S ,(7)

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

Here, the number of facets Nfacets basically increases proportional to the square of NEo
for a normal two dimensional mesh. Therefore, a rigid-foldable quadrilateral meshorigami must rely on the singularity. Such a structure has an engineering advantage asfollows:
1. The mechanism has exactly 1 degree of freedom; thus the transformation can becontrolled by one actuator independent of the complexity of the overall surface.
2. The structure is redundant; this enables a robust mechanism that works evenwhen we remove several elements from the surface.
Finding the singularity that works throughout the finite transformation is not a trivial
problem, especially when designing a freeform. A general condition for this singularity
is not yet been revealed so far. Therefore, we propose a design approach to generalize apattern known to rigid fold while keeping its intrinsic symmetry. Typical examples ofrigid-foldable quadrilateral mesh surfaces are Miura-ori and the “eggbox” pattern [10].
These patterns are known to be generalizable to some extent: the rigid-foldability of thegeneralized form of the former is investigated by Tachi [11] as a flat-foldable 4-valentmesh origami and the latter by Schief et al. [12] as a discrete Voss surface. The
mechanisms of the vertices of these rigid-foldable structures are essentially identical,
and we can produce a hybrid rigid-foldable surface that is general enough to produce afreeform.

4-Valent Mesh Origami: The condition for the rigid-foldability of quadrilateral meshflat-foldable origami is investigated [11]. This is written in a general way: a polyhedralsurface homeomorphic to a disk composed of planar facets connected by 4-valency
developable and flat-foldable vertices is rigid-foldable if and only if there exists a valid
state where every foldline is semi-folded (not 0 or ±π). In other words, in this type ofstructure, the existence of a10ρ1
continuoustransformationisθ0
equivalent to the existence of an
θ3intermediate state. This leads to the
3
ρ0
ρ3
θ
design method based on obtaining
θ2
1
one valid intermediate state thatρ2
satisfies the following:2
1. Every vertex is developable.
Figure 6: Single vertex of origami.
2. Every vertex is flat-foldable
3. Every facet is planar.
The former two conditions can be represented as: 0     2 and 1     3 ,(8)where θi (i = 0, 1, 2, 3) are the sector angles incident to the vertex. If we obtain one
valid configuration represented by folding angles { ρi0 }, the continuous transformationis represented by, i t     i 0  tan t 2,(9)  tantan
2  
2  tan t 0 2

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

where t (0 ≤ t ≤ π ) is the parameter that defines the folding amount (t = 0, t = t0, and t =π indicate developed, the intermediate, and flat-folded states, respectively).
Discrete Voss Surface: Discrete Voss surface is a planar quadrilateral mesh surface
composed of degree-4 vertices each of which satisfies

 0   2 and 1   3 .
The rigid-foldability of the discrete Voss surface is proved by Schief et al. [12]. Here,notice the similarity to Eq. (8). In fact, discrete Voss vertex and flat-foldable vertex are
essentially identical in a local sense,
θ0
and we can construct rigid-foldable ρ11
0
hybrid surfaces by combining them.
ρ3
θ3
Figure 8 shows an example design
3of hybrid surface obtained by θ
θ21
ρ0solving the combined conditions of
ρ2
discrete Voss and flat-foldable
2
origamiverticesvia
theperturbation-based method as used Figure 7: Single vertex of discrete Voss surface.
in [11].

Figure 8: Rigid folding motion of a generalized hybrid of Miura-ori and eggbox pattern.
4.1 Cylindrical Structure: Topological Extension
The rigid-folding motion of a disk surface is ensured by the existence of angle
configuration that satisfies the local conditions around each vertex. However, a non-disk
surface, such as a cylinder, cannot always rigid fold because of the conditions along theloop around each hole. The exact condition for rigid-foldable loop is not yet revealed ina general way. We thus start from obtaining a valid rigid-foldable cylinder based onsymmetry, and then generalize them using the symmetry operations as proposed in [13].
In this proposition of rigid-foldable cylinders, repeating symmetry is used to construct acylinder from a modular loop. However, we have recently found that a more generalized
rigid-foldable cylindrical form can be created using the fact that the rigid folding
condition is represented by the combination of local conditions and the loop conditions[14] (Figure 9). The design process is as follows: first, we produce a repeating form ofcylinder using the isotropic type proposed in [13], which is composed of flat-foldable
origami and discrete Voss vertices; then we fix one of the modules to construct a valid(10)Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, Chinaloop; finally, we transform the other part of the pattern under the constraints used tobuild the rigid-foldable quadrilateral mesh disk.

Figure 9: Rigid foldable cylinder.

5 Design Example
The objective of our study is to generalize the16mgeometric conditions required for kinetic structures,
thereby enabling a system that a designer can findheight: 4.0m
forms that sufficiently adapt the design context andheight: 3.6m
required functionalities at the same time. We show ahypothetical design example of kinetic architectural
space based on generalized degree-4 vertex origami todemonstrate how our approach can potentially useful
Figure 10: Layout.
for architectural design.
Consider building a foldable space by connecting the openings of existing two separatebuildings having different sizes and orientations as in Figure 10. Also, the distance
between two buildings and the height of the openings are too large for the foldable
structure to be made of flexible materials. Therefore, the static form of the structure
must flexibly adapt the existing environment (the openings and the ground) while thestructure must follow a rigid mechanism (rigid-foldable and flat-foldable).
We solve this problem using the generalized rigid-foldable 4-valent origami. In thismethod, the problem is translated to a problem of obtaining a valid mesh represented byvertex coordinates x that satisfies
1.
2.
3.
4.

developable: for each interior vertex,  0  1   2   3  2flat-foldable: for each interior vertex,  0  1   2   3  0planar: for each non-foldline edge,   0
fixed boundary: for each vertex on the openings,  x, y, z   x target , y target , z target 

5. ground: for each vertex on the boundary, z  0
Let us represent these conditions as a non-linear vector equation c(x) = 0. We start froma known regular form of origami vault with 68 vertices as shown in Figure 11 (a), which
is not a valid form (c ≠ 0). Then we modify this shape so that it satisfies the above
conditions by optimization based approach (Newton-Raphson method) (Figure 11 (b)).
From this valid solution, we can modify the form based on perturbation along the kernelof the Jacobian matrix. The method for obtaining an infinitesimal transformation is theProceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

same as the simulation method; however we allow the pattern itself to be changed inthis case.
c c (11)
x  I 3 N v  x 0x x In this design example, the configuration is represented by 68 × 3 = 204 variables, while
the developability, flat-foldability, and planarity conditions give 30 + 30 + 48 = 108
equations, and the fixed boundary and ground conditions give 24 + 30 = 54 equations.
Therefore, the design space is 42-dimensional, and we can explore the design variations
within this space. By specifying ∆x0 via a graphical user interface, we obtained
variational shapes that follow the designer’s preference, in this example we have chosen
design (c).
(a)

(b)

(c)

Figure 11: Design Process. (a) Initial regular pattern that does not connect the openingsof two buildings shown in red. (b) Transformed pattern that fit the the openings. The
boundary points shown in blue are placed on xy-plane. (c) Variational design thatsatisfies the conditions.
The structure can be manufactured from double layered
panels of constant thickness by sufficiently offsetting theboundary shape such that the panels do not collide eachother by the folding motion (Figure 12) as presented in[15]. The cutting pattern of the panels is shown in Figure
13. The perspective view of folding motion of theresulting structure is as shown in Figures 14 and 15.

Figure 13: Panel layouts

Figure 12: Thickening.

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

Figure 14: Folding motion of the structure.

Figure 15: Perspective view.

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2010, Shanghai
Spatial Structures – Permanent and Temporary
November 8-12 2010, Shanghai, China

6 Conclusion and Future Works
In this paper, we presented geometric problems and their solutions for freely designing
rigid-foldable structures. Based on the consideration on rigid-foldability, we presented
two basic approaches: using triangles and quadrilaterals mesh.
1. Triangular patterns produce kinetic structures whose degrees of freedom aredetermined by the number of elements on the boundary; using this fact we
proposed the design concept of triangulated tripod.
2. Quadrilateral patterns can produce one-DOF kinetic motion based on redundantconstraints. Design of such a structure take advantage of the singularity of thepattern. We have shown an approach based on flat-foldable origami and discrete
Voss vertices, which can sufficiently generalize flat-foldable disk andcylindrical surfaces.
3. A design example using quadrilateral-based rigid origami is shown todemonstrate the high flexibility of the design method.
At the same time, our study indicates many future studies necessary for making rigid
origami structures more designable and realizable. The following shows some of theexamples of such studies.
1. The global kinetic behavior of the structures is not fully investigated. In
particular, understanding the transformability from one state to the other is very
important when applying rigid origami to engineering purposes.
2. Classifying every rigid-foldable quadrilateral mesh is expected to improve thedesignabilty of rigid origami. This is still an open problem and theoreticalstudies in this direction can be seen in [15].
3. Investigating rigid-foldability condition around a loop can topologically extend
the concept of origami.
4. Enabling kinetic constraints to work with rigid origami structures can contributeto the design of rigid origami combined with different mechanical systems.
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[3] Charles Hoberman. Curved pleated sheet structures. United States Patent No.
5,234,727, 1993.
[4] Tomohiro Tachi. Simulation of rigid origami. In Origami4: The FourthInternational Conference on Origami in Science, Mathematics, and Education,
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November 8-12 2010, Shanghai, China[5] Sarah-Marie Belcastro and Thomas Hull. A mathematical model for non-flatorigami. In Origami3: Proceedings of the 3rd International Meeting of Origami
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[12] W. K. Schief, A. I. Bobenko, and T. Hoffmann. On the integrability of infinitesimaland finite deformations of polyhedral surfaces. In Discrete Differntial Geometry(Oberwolfach Proceedings), pages 67–93, 2007.
[13] Tomohiro Tachi. One-DOF cylindrical deployable structures with rigid
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[14] Tomohiro Tachi. Freeform rigid-foldable cylinder using bidirectionally flatfoldable surfaces, In Proceedings of the Conference Advances in Architectural
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