Deployable mechanisms

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Among the many deployable mechanisms currently available on the market, the most famous one is the Hoberman sphere. This mechanism which is mainly used as a toy, can be deployed from 24 to 75 cm (9.5 to 30 inches), thus increasing its volume by more than 30 times.

Fig. 1: A Hoberman Sphere used as a toy.

1. the mechanisms have only 1 DOF;
2. the mechanisms always keep the same gemometric shape;
3. the mechanisms always have an empty centre;
4. the mechanisms are based on the five Platonic solids.

Fig. 2: The five Platonic solids: tetrahedron (pyramid), hexahedron (cube), octahedron, dodecahedron and icosahedron. The name of each figure is derived from its number of faces: respectively 4, 6, 8, 12 and 20.

The design was achieved in paying special attention to mechanical interferences, which were eliminated, and to the optimization of the mechanism as a function of its expansion ratio.

An example of a tetrahedron deployable mechanism is given below. As shown, the centre of the mechanism is always empty, no matter what position of elongation the mechanism takes on. Moreover, the geometric shape of each of its faces, which are triangles in this case, is always maintained, if for example the face is clearly illustrated by connecting a cloth to the three vertices. In addition, the mechanism requires only one single motor to allow it to expand or contract. Only a single mobile polygon located on each face has to be actuated. The other faces automatically follow the movement as a result of the architecture of the system.

Fig. 3: CAD Model and simulation of the deployable tetrahedron.

Prototypes were also built using rapid prototyping. The figure below shows the cube, whose expansion ratio of 2.8 increases its volume by almost 22 times. Moreover, the expansion ratio can easily be increased by adding one or more additional parallelograms on each face.

Fig. 4: Prototype of the deployable cube.

Deployable mechanisms can be used in several applications, such as antennas of space systems, dome structures, portable temporary shelters and exhibition stands.

Poster

A poster on deployable mechanisms was prepared in 2002 and can be downloaded with the PDF file below.

1 DOF Deployable Mechanisms (5.1 Mb)

Selected Photos

Several photos of deployable mechanisms are provided below. The images can be enlarged by clicking directly on the photos.

         

         

Video Clips

The following video segments show deployable mechanisms in motion.

Triangular face Sequence illustrating the deployment of a triangular face. Format: mpg    Length: 0:19    Size: 3.5 Mb

Cubic face Sequence illustrating the deployment of a cubic face. Format: mpg    Length: 0:19    Size: 3.5 Mb

Pentagonal face Sequence illustrating the deployment of a pentagonal face. Format: mpg    Length: 0:19    Size: 3.5 Mb

Tetrahedron (pyramid) Sequence illustrating the deployment of a tetrahedron (pyramid). Format: mpg    Length: 0:20    Size: 3.7 Mb

Hexahedron (cube) Sequence illustrating the deployment of a hexahedron (cube). Format: mpg    Length: 0:15    Size: 2.8 Mb

Triangular prism Sequence illustrating the deployment of a triangular prism. Format: mpg    Length: 0:10    Size: 2.4 Mb

Pentagonal prism Sequence illustrating the deployment of a pentagonal prism. Format: mpg    Length: 0:10    Size: 2.5 Mb