From modeling to control of a variable stiffness device based on a cable-driven tensegrity mechanism

Abstract : Cable-driven tensegrity mechanisms are now considered for various applications in which their reconfiguration capacities are required together with their inherent lightness. Moreover, they can exhibit interesting variable stiffness capacities through the modification of their level of prestress when composed of deformable cables. Control schemes that deal with both reconfiguration and stiffness variation have however not been developed in the literature yet.
This paper presents two control strategies for that purpose to transform a cable-driven tensegrity mechanism into a variable stiffness device. The mechanism is a planar tensegrity mechanism allowing us to control an angular position and the associated stiffness. Relying on the properties of the mechanism models, the proposed control strategies allow a modulation of the stiffness or of its first time derivative. The interest of both propositions is outlined and an experimental investigation of their characteristics is performed. Encouraging results are obtained in terms of reconfiguration capabilities and stiffness variation.