A Variable Stiffness Joint with Electrospun P(VDF-TrFE-CTFE) Variable Stiffness Springs

This letter presents a novel rotational variable stiffness joint that relies on one motor and a set of variable stiffness springs. The variable stiffness springs are leaf springs with a layered design, i.e., an electro-active layer of electrospun aligned nanofibers of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] surrounded by two electrodes of aluminum and held together by inactive material. To achieve a variable stiffness, different voltages and, therefore, different electric fields, are applied to the springs. The variable stiffness springs are electromechanically analyzed to highlight the voltage-deflection and force-deflection characteristics. Finally, the springs are used in the design of a proof-of-concept variable stiffness joint prototype. Experimental results on the variable stiffness joint confirm the viability of the proposed solution.