Shape control for self-stress following deployment of a tensegrity footbridge

Shape control is a combination of control commands with measurements to achieve a desired form. Tensegrity structures are pin-jointed assemblies of struts and cables, held together in a stable state of stress. Applying shape control to a near-full-scale deployable tensegrity structure presents a unique opportunity to study and control the effects of large shape changes on a closely coupled multi-element system. Simulated cable-length changes provide an initial activation plan to reach an effective sequence for self-stress. Controlling internal forces is more sensitive than controlling movements through cable-length changes; internal forces are thus a better objective for small adjustments to the structure. Due to modeling simplifications and eccentricities in joints, cable-length changes that have been determined only through simulation may not be effective. This paper compares two algorithms for implementing self-stress according to two goals. The first goal is to create sufficient stabilizing axial forces in elements. The second goal is to improve the position of nodes so that they are as close as possible to the design configuration. Applying these algorithms to full-scale structures such as tension-cable structures, tents, and domes, can change shape and stiffness properties in service.