Modal analysis method for tensegrity structures via stiffness transformation from node space to task space

A tensegrity structure is a type of hybrid soft-rigid system, whose high compliance is prone to induce an oscillatory motion. The oscillatory characteristics can be exploited to control a tensegrity structure efficiently, and modal analysis is beneficial in guiding the exploration of the oscillatory characteristics of this type of structures. We derive node-based modes of tensegrity structures using the finite element method. By freezing the substructures as a rigid body, the node-based stiffness is converted into a task-space stiffness, during which the elasticity within the substructures is filtered out from the final modal analysis results. Compared with the node-based modal analysis results, the transformation method proposed in this paper significantly reduces the mode dimension. Concurrently, the low-order modes almost remain unchanged when the stiffness of the substructures is much higher than that of the interconnecting cables. We select two tensegrity structures as examples to demonstrate our method.