Shape Control of Adaptive Funicular Structures

Abstract

Funicular structures transfer their loads through axial forces. This feature makes them more efficient than structures subject to shear and bending, but in turn, the loads determine the structural shape and vice versa. Nevertheless, structures are often subjected to loads varying in time and funicularity requires adaptation of shape. Flexible tensile structures e.g. cables and textiles adapt their forms to loads spontaneously. In contrast, the bending stiffness of compression structures does not allow spontaneous change of shape, thus more structural material is needed to prevent bending-induced mechanical failure. At the same time pure compression or mixed structures offer better solutions in some structural applicationsThe purpose of this study is to use sensory feedback about a structure's deformations to guide the structure to a funicular shape which is time-dependent and unknown to the controller. We consider a discrete model of a cantilever structure composed of rigid bars and elastic joints equipped with sensors measuring bending moments and rotary actuators. We aim to guide the structure towards different funicular configurations when the external load is unpredictable and not directly observable. The efficiency of the system under different control policies is studied with emphasis on stability under constant load and ability of the controller to react to rapidly changing loads.