Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia
Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures
28 September - 2 October 2009, Universidad Politecnica de Valencia, Spain
Alberto DOMINGO and Carlos LAZARO (eds.)

Generalization of Rigid Foldable Quadrilateral MeshOrigamiTomohiro TACHI** The University of Tokyo
7-3-1 Hongo , Bunkyo-ku, Tokyo 113-8656, Japanttachi@siggraph.org

Abstract
In general, a quadrilateral mesh surface does not enable a continuous rigid motion because anoverconstrained system, in which the number of constraints around degree-4 vertices (threefor each vertex) exceeds the number of variables (the number of hinges), is constructed. However, it is known that the developable double corrugation surface, called Miura-ori, produces arigid deployment mechanism. The rigid-foldability of Miura-ori is due to the singularity in its
pattern, where a single vertex is repeated. We generalize the geometric condition for enabling
rigid motion in general quadrilateral mesh origami without the trivial repeating symmetry. Toensure the existence of a finite motion, we derive the identity of functions from the formulafor degree-4 single-vertex origami. This yields a variety of unexplored generalized shapes ofquadrilateral mesh origami that preserve finite rigid-foldability in addition to developability
and flat-foldability.
Keywords: origami, rigid-foldability, isometric transformation, form finding

1 Introduction
Rigid-foldable origami is a piecewise linear developable surface that can realize a deployment
mechanism if its facets and foldlines are substituted with rigid panels and hinges, respectively.
Designing such a deployment mechanism is very important in an engineering context, particularly in architecture in the following reasons: 1) its structure based on watertight single
surface is suitable for constructing an envelope of a space; 2) its purely geometric mechanismthat does not rely on the elasticity of materials can contribute to a design of robust, repeatedly
usable deployable structure.
The developable double corrugation surface, or Miura-ori [7], utilized in the packaging of
deployable solar panels for use in space or in the folding of maps, is known to be rigidfoldable as well as developable and flat-foldable (Figure 1). Our objective is to investigate
this type of quadrilateral mesh origami and generalize it so that we can obtain a design offreeform surface that is developable, flat-foldable, and rigid-foldable (Figure 6).

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia
Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures

The developability and the flat-foldability of a piecewise linear surface are relatively easy tobe generalized. The developability is represented by the gauss area (2π minus the sum ofthe sector angles) around each vertex to be 0. The flat-foldability is satisfied if the alternating sum of the sector angles around each vertex is 0 and the overlapping ordering can bedetermined, as shown by Bern and Hayes [3]. There have also been studies that analyze avalid intermediate state of origami: Huffman [5] used the gauss map to represent the valid
states of an infinitesimal origami surface in three-dimensional spaces; Belcastro and Hull [2]introduced a matrix representation of the validity conditions.
On the other hand, rigid motion, i.e., the existence of a continuous path in the configuration
space, has not been generalized very well. Only numerical methods have been proposed forgeneral origami models: Watanabe and Kawaguchi [12] introduced the conditions for infinitesimal rigid-foldabilty by calculating the derivative (Jacobian) and the second derivativeof the matrix introduced by Belcastro and Hull [2]; the author [11, 10] developed a system
to calculate the folding motion of a given origami model by solving the Jacobian. However, these numerical methods cannot be used to estimate the singular finite rigid motion ofMiura-ori; the reason for this is described below.
A rigid origami constructs a constrained mechanism, where the configuration is represented
by the fold angle of each foldline, which is constrained by 3 equations for each inner vertex.
Therefore, the infinitesimal motion can be represented by the solution space of the 3M × N
Jacobian matrix, where N is the number of foldlines and M is the number of the innervertices. In this sense, a quadrilateral mesh origami constructs an overconstrained system
in general because N < 3M . However, a Miura-ori constructs a singular 3M × N matrix
whose rank is N − 1 in every possible state, resulting in one-DOF finite rigid motion.
In this paper, we investigate this singularity and find out a method that enables it. In Section
2, we focus on a flat-foldable degree-4 origami vertex, which is known to have a special
relationship between the fold angles. Then, in Section 3, we obtain the global condition thatenables rigid motion and show that this is equivalent to the existence of a non-trivial valid
state. Finally, a design method based on the condition is proposed in Section 4.

Figure 1: Rigid folding motion of Miura-ori

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia
Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures

2 Geometry of Degree-4 Flat-foldable Vertex
The configuration of a flat-foldable degree-4 vertex can be represented by four sector angles— θA , θB , θC , and θD — and four folding angles —ρAB , ρBC , ρCD , and ρDA — between
the sector angles, as shown in Figure 2. Note that ρCD is negative (mountain fold), while theother three folding angles are positive (valley fold). The crease pattern of a single vertex thatsatisfies the developability and the flat-foldability conditions can be represented in terms oftwo parameters, θA and θB (0 < θA < π, 0 < θB < π, π ≤ θA + θB ), as θC = π − θAand θD = π − θB , as shown by Murata [8] and Fushimi [4]. A degree-4 single vertex rigidorigami is known to have one degree of freedom. The relation between the folding angles isderived as follows using spherical trigonometry, as shown by Huffman [5] and Hull [6].
ρCD = −ρAB

ρDA = ρBCand(1)This means that the folding angles can be represented by the two angles ρAB and ρBC , which
are dependent on each other. According to Hull [6], the relationship between these two angles
was derived by Robert Lang as follows:cos (π − ρAB ) = cos (π − ρBC ) −sin2 (π − ρBC ) sin θA sin θB,
1 − cos ξ(2)where ξ is the angle between ℓAB and ℓCD and is given bycos ξ = − cos θA cos θB + sin θA sin θB cos (π − ρBC ) .
Here, we assumed that ξ ̸= 0 to enable a one-to-one correspondence, and we will continue tomake this assumption in the following sections.
Equation (2) gives a one-to-one map f : cos ρBC → cos ρAB as follows:cos ρAB = f (cos ρBC ) = K +1 − K2,cos ρBC + K

where(3)

1 + cos θA cos θB.
(4)sin θA sin θBNote that map f is only dependent on a one-dimensional parameter K (K > 1), which is
K = K(θA , θB ) =ℓABℓDAθAθDθBθCℓBCℓCD

ρAB

ρCD

ρDA
ρBCFigure 2: A flat-foldable degree-4 vertex.

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia
Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures

determined with respect to the crease pattern. We shall call K the conversion coefficient ofthe vertex.

3 Global Condition
3.1 Valid Loop Condition
A general condition can be derived from Equation (3). The map f represents the conversion
from the rotation of the lateral foldlines to the rotation of the longitudinal foldlines. Hence,
its inverse f −1 : cos ρAB → cos ρBC represents the conversion from the longitudinal to thelateral foldlines. f −1 can be calculated from Equation (3) as follows.
cos ρBC = f −1 (cos ρAB ) = −K +1 − K2cos ρAB − K(5)According to Equations (1), the configuration of a regular quadrilateral mesh origami is rep↕
resented by the cosine of the lateral and longitudinal fold angles, cos ρ↔
i (t) and cos ρj (t)(i = 0, 1, · · · , m − 1 and j = 0, 1, · · · , n − 1), each of which is a one-dimensional functionof a parameter t (0 ≤ t ≤ π) representing the folding motion of the entire model; m andn are the number of rows and columns of the array of inner vertices, respectively (Figure3). The configuration is constrained at each inner vertex vi,j whose conversion function andcoefficient are denoted by fi,j and Ki,j , respectively.
nρվjρվ

j+1

cos ρtiKi, jmρti
ρti+1Ki, j+1
cos ρվj+1
Ki+1, j+1

cos ρվj
Ki+1, jcos ρti+1

Figure 3: A quadrilateral mesh origami.
↕

The model is rigid-foldable if and only if we can obtain cos ρ↔
i (t) and cos ρj (t) that areconsistent with Equation (3) for all inner vertices. An inconsistency can arise for the loop
around an inner facet, i.e., facet whose incident vertices are not on the boundary. The foldangle of a segment determines the fold angle of the next segment, which in turn determinesthat of the following segment; this procedure is repeated until the fold angle of the original
segment is once again determined (Figure 3 Right). Therefore, the necessary and sufficientcondition for the rigid-foldability is represented as follows. For any x = cos ρ (−π ≤ ρ ≤ π),
and for every inner facet surrounded by vi,j , vi+1,j , vi+1,j+1 , and vi,j+1 ,( −1(( −1)))
fi,j+1 fi+1,j+1fi+1,j fi,j(x)≡ Identity,Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia
Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures

or

( −1)
( −1)
fi+1,j fi,j(x) ≡ fi+1,j+1 fi,j+1(x) .

(6)This can be calculated as,
Bj x + Aj
Bj+1 x + Aj+1≡,
Aj x + Bj
Aj+1 x + Bj+1

(7)

where, for j ′ = j, j + 1,
Aj ′Bj ′= −Ki,j ′ + Ki+1,j ′= 1 − Ki,j ′ Ki+1,j ′ .

This gives the following necessary and sufficient condition:(Aj Bj+1 − Aj+1 Bj ) x2 − (Aj Bj+1 − Aj+1 Bj ) ≡ 0,(8)

which can be satisfied if and only if
Aj Bj+1 − Aj+1 Bj = 0(9)Theorem 1 A quadrilateral mesh origami is finitely rigid-foldable if and only if Equation (9)is satisfied for every inner facet.
3.2 Existence of State and Existence of Motion
While the existence of a rigid motion is represented by identities, the existence of a single,
static state can be represented by equalities. From the identical Equation (8), we obtain thefollowing specific equation: For every inner quadrilateral,()(Aj Bj+1 − Aj+1 Bj ) cos2 ρ − 1 = 0.
(10)This equation indicates that if there exists no rigid motion, i.e., if Equation (9) is not satisfied,a valid state can exist only if cos ρ = ±1 (i.e., ρ = 0, π, −π). Here, we can conclude that theexistence of rigid motion and the existence of a non-trivial state are equivalent.
Theorem 2 A flat-foldable planar-quad mesh origami has rigid-folding motion if and only ifthere exists a non-trivial valid state, i.e., every foldline is folded (ρ ̸= 0) but not completelyfolded (ρ ̸= π, −π).

4 Design
4.1 Trivial Model
It is obvious from Theorem 1 that the pattern is rigid-foldable if the conversion coefficient Kof every inner vertex is constant (Ki,j = K 0 ). Miura-ori (Figure 1) and “MARS” (a modelby Paulo Taborda Barreto [1]) (Figure 4(a)) satisfy this condition. Furthermore, if the K ofevery inner vertex is constant in each row or in each column (Ki,j = Ki0 or Ki,j = Kj0 ),the pattern is rigid-foldable. The single-curved Miura-ori form (Figure 4(b)) satisfies thissufficient condition.

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia
Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures

(a)

(b)

Figure 4: Rigid foldable models with trivial symmetry. (a)MARS (b)Single-curved Miuraori.
4.2 General Model
Theorem 2 indicates that we can design a rigid-foldable origami pattern by finding a valid
three-dimensional state. Here, we denote by nvert , ninner-vert , and nquad , the numbers of all thevertices, the inner vertices, and the quadrilaterals, respectively. We assume that the surface
is a triangular mesh so that it is represented in terms of 3nvert × 1 vector x representing thevertex
coordinates.)We can numerically find a valid shape by solving the following nonlinear( inner-vert
2n+ nquad × 1 vector equation with respect to x:][∑4 dev θ
2π−k,ik=1c
inner-vert×1 [∑]n = 0,4kc (x) =  cflat  = (11)(−1)θk,ik=1
inner-vert
planarn×1c]nquad ×1[ρcreasei
where θk,i is the angle between k-th pair of adjacent foldlines around i-th inner vertex, andis the angle between the normals of two triangles consisting i-th quadrilateral. Note that
ρcreaseicdev = 0 and cflat = 0 represent developability and flat-foldability of the surface, respectively,and cplanar = 0 indicates that the quadrilaterals are planar.
Equation (11) yields an underdetermined system, by exploring the solution space of which
we can obtain variations in the shape. We find valid shapes by starting from a trivial solution,e.g., a regular Miura-ori, and perturbing the vertex coordinatesaccording to) the null space of(∂cthe Jacobian ∂x, as shown in Figure 5. The Jacobian is a 2ninner-vert + nquad ×(3nvert ) matrix[ ∂c ]+and the solution is calculated using the pseudoinverse ∂xof the Jacobian as follows:)([ ]+ [ ]∂c∂c∆x = I −
∆x0 ,
(12)
∂x
∂x
where ∆x0 represents the initial perturbation determined by an arbitrary user input. Equation(12) finds the valid perturbation closest to ∆x0 by orthogonal projection to the solution space.
For each step, the residual c is eliminated by the Newton-Raphson method.
This method is implemented as an interactive design system in which a user can intuitively
manipulate a freeform valid surface just by dragging it via a standard pointing device. Figure
6 shows the actual rigid motion of the resulting structure, animated using the rigid origami

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia
Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures

simulator [10]. We have also observed that freeform patterns that do not satisfy our condition
cannot fold without the triangulation of the quadrilateral panels.

Figure 5: A perturbation within the solution space. Each form is rigid-foldable.

Figure 6: Freeform Miura-ori with a rigid motion.

5 Conclusion and Future Works
We have derived the necessary and sufficient condition for the existence of finite rigid motionof general flat-foldable quadrilateral mesh origami. The condition was expressed with respect
to the angles in the crease pattern. We have also shown that the condition is equivalent to theexistence of any non-trivial valid state. Using the condition, we have shown the method toexplore freeform variations of generalized Miura-ori.
A recent study in the field of discrete differential geometry by Schief et al. [9] reveals thefinite rigid-foldability of a quadrilateral mesh called discrete Voss surface. The singularity
investigated in our study is closely related to that of discrete Voss surface. There are also otherspecific quadrilateral meshes known to be rigid-foldable. In the future, we intend to study
on the rigid-foldability of a general quadrilateral mesh surface to unify these independently
derived singular surfaces.

Acknowledgement
This research is supported by a Grant-in-Aid for JSPS Fellows funded by Japan Society for
the Promotion of Science.

Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2009, Valencia
Evolution and Trends in Design, Analysis and Construction of Shell and Spatial Structures

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