An implementation of muscle-like passive noise rejection (pnr) in variable stiffness actuators (VSA): the pnrVSA solution

In the last years Variable Stiffness Actuators gathered the interest of the robotic community for their heightening role in new robot design. In particular, many solutions have been proposed to accomplish mechanical robustness, safe interaction and energy storage. In this paper we propose a novel mechanical solution that improves the passive capabilities of VSA. The new property we introduce is called “passive noise rejection” and it refers to the ability of the system to cancel out the effects of noise in a pure passive way. The idea behind this choice is that digital controllers are always band limited and this limitation reflects in the disturbance rejection property of the actuator. Starting from this observation through the use of non-linear springs in agonist and antagonist configuration we mechanically implemented an important characteristic of human muscles, which resides in the ability of open loop reject disturbances by means of muscle co-activation.