Kinematic synthesis of deployable cable-stiffened truss structures

Abstract

A technique is introduced for the kinematic synthesis of deployable cable-stiffened truss structures. This technique, which is an extension of a prior procedure [l-21 for generating deployable truss structures, can be applied to generate all concepts of cable-stiffened truss structures as well as all their deployable derivatives. Examples illustrating the implementation of this new technique, along with a discussion of the results achieved. are included in this article. The primary function of a deployable structure is to maintain a stable configuration in its deployed state. This is reflected in current design practices of trading off decreased deployment or retraction performance for increased structural performance. As a result, various designs of deployable truss structures (with, and without cables) have been introduced that are over-constrained during deployment/retraction, i.e. deployment/retraction of these structures can only be achieved through the deformation of individual links or by exploiting symmetric features of the structure. The number of different conceptual designs of deployable structures that are based on a given structural configuration is unlimited, if deployable structures are permitted to be overconstrained during deploymenthetraction. For this reason, researchers in the area of deployable structures have given little attention to the systematic design of deployable truss structures and have instead devoted much of their attention to the introduction and discussion of novel concepts of deployable truss structures [3-171. If, on the other hand, it is assumed that the primary function of a deployable structure is to serve as a mechanism with a minimum number (i.e. at least one) of degrees-of-freedom, then the number of different conceptual designs that are based on a given structural configuration is finite. Hence, it is then possible to generate all possible designs for a given structural configuration. The assumption that a deployable structure is not constrained during deployment/retraction has enabled the development of a technique for the generation of all conceptual designs of deployable truss structures that can be used as building blocks (modules) of much larger structures [I-21. It should be noted that this technique, referred to as kinematic synthesis of * Sr. Mechanical Engineer, Member AIAA deployable structures, does not assume that the structural configuration is known but instead uses the characteristics of a given class of structures (i.e. truss modules) to generate all possible configurations of structures in this class. The limitation of this technique to truss modules has been avoided in the Explosion-Implosion technique [19], developed by the same authors, for the generation of allconceptual designs of deployable truss structures of which the locations of the nodes are known. Both techniques have been shown to result in the generation of an enormous, yet finite, number of novel conceptual designs as well as those that have been reported in the literature. Furthermore, by limiting the degrees-of-freedom available at individual joints, conceptual designs can be generated of deployable structures that are overconstrained during deployment/retraction. Although the kinematic synthesis technique and the explosionimplosion technique result in the generation of an enormous number of conceptual designs of deployable truss structures, they are not applicable to truss structures with cables. Yet, cable-stiffened truss structures have important advantages such as the reduction in mass and/or reduction in joints that can be achieved by replacing links in truss structures with cables. The objective of this article is to modify the technique introduced in [I-21 such that the new technique is also applicable to cablestiffened truss structures. This new approach can then be applied to generate novel concepts of deployablecable-stiffened truss structures as well as those that have been reported in the literature.