Maximum Stiffness of Impact-Robust Actuators in Highly Dynamic Robotics Tasks: Application to Series Elastic Actuator Design

Kurzfassung

Highly dynamic motions such as running expose legged robot actuators to substantial impact torques, necessitating impact-resilient or impact-robust designs. Accordingly, actuator design must explicitly account for these impact robustness requirements. We present solutions for the impact-induced peak torque at the gearbox, where we analyze applicable contact time and parameter sensitivity. From these, we derive algebraic inequalities to determine the maximum stiffness of series elastic actuators that exhibit impact robustness. Derived from a timedomain solution of the post-impact dynamics, the proposed closed-form inequalities incorporate gearbox peak torque, reduction ratio, motor and link inertia, operational torque acting before and during impact, as well as impact impulse. We demonstrate this method by designing a humanoid actuator featuring both a novel 14 J hollow-shaft spring with 546 Nm/rad, and a conceptual axial torque-overload breakaway disk for added safety. Experimental evaluation of the impact response validates our impact-torque prediction for two different contact-time regimes, three different link inertia settings and two different stiffness settings.