Deployable Space Frames
pantographs | dynamic & | kinematic simulation | finite element method | force method | geometry | linkages | mechanisms | prestress | retractable roofs | sensitivities | single degree of freedom system | topology
Deployable Space Frames are pantographic structures, which are assemblies of cables and pairs of rods with intermediate connections (see figures below). The simplicity and reliability of pantographic structures make them competitive again st more common structures, such as trusses, which can be folded only after introducing complex hinges or troublesome sliding elements. I have explored several concepts for pantographic structures, both straight and curved, and have made several working models.
The first pantographic structure I developed was a three-dimensional mast whose only internal degree of freedom is controlled by a single, continuous cable which runs over pulleys connected to the joints of the pantograph. One end of this cable is connected to a drum driven by an electric motor, and its route through the structure is such that winding the cable onto the drum causes the structure to deploy. A series of short cables linking neighbouring joints of the pantograph become taut when the pantograph is fully deployed, and in this configuration, the continuous cable imparts a global state of prestress onto the whole structure. Thus all cables are pre-tensioned, joint backlash is removed, and no latching devices are required anywhere in the structure. These are major advantages over conventional deployable structures. Figure 2 shows a 1.5 m tall mast based on a three-dimensional pantograph with triangular cross-section.
I moved on to develop a family of deployable ring structures. A geometrical study of rings made from straight pantographic elements identified three structures which have one mechanism and can be deployed synchronously without inducing any strain in the rods. A 3.5 m diameter ring based on one of these solutions has been built and tested. Its deployment is controlled by a long 'active' cable, similar to that of the mast, whose overall length is controlled by an electrical motor. By choosing an optimal route for the active cable, I can ensure that a series of shorter cables linking neighbouring joints of the ring become pretensioned after the structure is fully deployed, and before it goes into service. These cables considerably enhance the stiffness of the rod assembly.
A reflector whose mesh surface is connected to a deployable ring truss based on this concept is currently being considered by Matra Marconi UK Ltd. for a mission requiring a 12 m reflector dish. Comparing it with other structures for this type of applications, my concept is much simpler and easier to manufacture.
Further work on geometric solution for nested ring structures that can be folded without member deformation has resulted in the discovery of a new type of pantographic foldable domes [4,5]. These structures have only one internal degree of freedom and, for the first time, can be produced in any shape of revolution, including parabolic shape that is required for most antenna reflectors. The units of this structure can be triangulated, which increases their overall structural stiffness.
This page is created by Zhong You, who is a university lecturer in the Department of Engineering Science of Oxford University. This is a link to his current address. You may e-mail email@example.com for further infomation.
Zhong was an EPSRC advanced fellow based at Cambridge University before moving to Oxford.