A Cable Based Active Variable Stiffness Module With Decoupled Tension

Variable stiffness modules add significant robustness to mechanical systems during forceful interactions with uncertain environments. Most existing variable stiffness modules tend to be bulky—by virtue of their use of solid components—making them less suitable for mobile applications. In recent times, pretensioned cable-based variable stiffness modules have been proposed to reduce weight. While passive, these modules depend on significant internal tension to provide the desired stiffness—as a consequence, their stiffness modulation capability tends to be limited. In this paper, we present design, analysis, and testing of a cable-based active-variable stiffness module which can achieve large stiffness modulation range with low tension. Controlled changes in structural parameters (independent of cable length actuation) now permit independent modulation of both the desired tension and the perceived stiffness. This capability is now systematically evaluated via simulation as well as on a hardware-in-the-loop experimental setup.