Deployable and Reconfigurable Liinkage Structures

Abstract

In a dynamic and evolving world, where terms of reducing, reusing and recycling are of great importance, specific aspects, such as structural flexibility, modularity, efficiency and transformability gain significance towards a sustainable future of the built environment. Deployable and reconfigurable structures that are able to be easily erected in different locations and respond to varying functional, environmental, or loading conditions through shape transformations facilitate new research directions in achieving a corresponding interactive and optimized behavior. The capability of adaptation by natural organisms is based not only on the ability of transformation, but is related to a process of evolution, efficiency and optimization with regard to time-variable environmental conditions. Along the field of biomimetics and specifically biomechanics, there is an investigation of the kinematic analysis of natural organisms, that is decoded and transferred to the application of linkage systems based on the effective crank–slider approach. In contrast to static and fixed-shaped systems, such adaptable systems build upon flexibility and controllability through modularity, reduced self-weight and simple actuation requirements. Reflecting upon the aforementioned aspects, this thesis refers to the investigation of different typologies of modular linkage structures. The control sequence implemented consists of stepwise system reconfigurations that involve the selective releasing of one intermediate joint in each closed-loop linkage, effectively reducing it to a 1-DOF “effective crank–slider” (ECS) mechanism with minimum actuation components. The approach enables minimum self-weight, structural simplicity and reduced energy consumption. A kinematics and a comparative Finite-Element Analysis of linkage aluminum systems in all reconfiguration steps of a sequence have been conducted for different typologies and geometrical characteristics of the members (i.e., simple and hybrid typologies). The systems have an overall length of 9.0, 12.0 and 15.0 m in their initial, almost flat configuration and a respective span of half their initial length in their symmetric arch-like target configurations. They are supported on a pivot joint on one end and a linear sliding block on the other end, which is associated to the external actuation. In addition, each intermediate joint is equipped with brakes. Special criteria serve the kinematics behavior evaluation of the systems, such as bending moments and axial forces in the members, relative cable length variation, sliding block displacement etc. Through the analysis results, general understandings of the structural behavior and explicit information with regard to the interdependencies of the inner stress state of the members and their load-bearing capacity are provided. The kinematics concept has been demonstrated experimentally on prototypes of small scale 1:10. The study provides necessary information of the influence of various structural typological and geometrical parameters on the systems behavior. It also demonstrates its feasibility and highlights practical implementation issues. An overview of the analysis results obtained with regard to design aspects and desirable features are presented at the end of the thesis and show the potential of the proposed ECS approach, as well as the efficiency of the hybridization concept for actuation purposes.