Deployable structure

Abstract: This paper looks at a class of mechanisms that change structure when erected or folded. The class includes a variety of artefacts and decorative gifts and boxes comprised of flat card creased to enable the folding or unfolding of a structure. Such a structure admits kinematic study in keeping with theory of mechanisms when the creases are treated as hinges joining card and paper panels treated as links. New horizons have been brought up in the use and mechanised manufacture of mechanisms of this kind. Here typical types are described in terms of their fundamental parts and their equivalent mechanisms. Screw sy.'item theory is brought into the analysis of mechanisms of these kinds, particularly those containing multiple loops. Different geometry and system combinations are used for the study of mobility and kinematics making use of the result from the equivalent screw systems. Introduction A mechanism is most commonly characterised by its function as part of a machine or mechanical arrangement that transforms an input motion or a force into another. If, alternatively, a mechanism has the ability to have its structure transformed from one kind to another then another class of mechanism emerges, one whose primary function may be just to change structure. Amongst these new developments is a group of devices or arrangements that can be described as mechanisms whose number, the total of all effective links, changes as they move from one configuration to another or a singular condition in geometry occurs that makes it behave differently. We refer to this group of mech­anisms as metamorphic. The mechanism may start as an open chain or in a folded (plicated) chain loop to be subsequently erected as a structure. New interest areas around such mechanisms are growing. For example the study of deployable mechanisms has applications in space technology that requires a highly collapsible and portable mechanism to be carried in a spacecraft and expandable for use either for large antenna structures (Costabile et al., 1996), for ramp assembly (Spence and Sword, 1996) or for the solar array paddle (Kuramasu et al., 1995). New deployable structure has been found in the study of truss structures (Takamatsu and Onoda, 1991). A so called smart fractal structure and mechanisms are recommended in robot manipulators (Shahnipoor, 1993), and sequential logic (Chew and Ho, 1996) was used for the analysis of the mechanisms. A recent study by Pellegrino (1996) focused on one combination of mechanisms and presented a potential application of this kind of mechanisms. Less obviously related to the above examples is another class typically found in artefacts and fancy gift packs. A list of this kind of application can readily be drawn, including, for example Chi­nese lanterns, paper folding in Christmas decorations, and card boxes for used in packaging a various of products. Some exotic and innovative forms of the latter represent a technological chal­lenge in producing them by machine. This sets up the need to describe the process in quantifiable kinematic terms. This would also open an avenue for mechanism study leading to innovation in the design of artefacts and packaging. We usually conceive of mechanisms to be made of ostensibly