Easy-to-actuate multi-compatible truss structures with prescribed reconfiguration

Abstract

Abstract Multi-stable structures attract great interest because they possess special energy landscapes with domains of attraction around the stable states. This feature might allow the structure to reconfigure from one stable state to another with fewer and less accurate actuators, and it does not need constant actuation to be locked at a stable state. Consequently, multi-stable structures have the potential to achieve prescribed reconfiguration with only a few lightweight actuators (such as SMA springs). However, most existing multi-stability designs are based on assembling bi-stable unit cells, which contain multitudes of additional and distractive stable states, diminishing the feasibility of reconfiguration actuation. To help address this challenge, we first introduce the constraints that a truss structure is simultaneously compatible at multiple (more than two) prescribed states. Then, we solve for the design of a new type of multi-stable truss structure, named multi-compatible structures in this paper, where redundant stable states are very limited. Secondly, we explore minimum energy paths connecting the designed stable states. Then, we compute for a simple and inaccurate pulling actuation guiding the truss structure to transform along the computed minimum energy paths. Finally, we fabricated four prototypes to demonstrate that prescribed reconfigurations with easy-actuation have been achieved. Altogether, our full-cycle design approach contains multi-stability design, stiffness design, minimum-energy-path finding, and pulling actuation design, which highlights the potential for designing morphing structures with lightweight actuation for practical applications.