A variable stiffness mechanism for improving energy efficiency of a planar single-legged hopping robot

Recently, variable stiffness actuators (VSAs) have been considered as actuation approaches to improve energy efficiency of legged locomotion robots. In this paper, we present the design and implementation of a variable stiffness actuator, named L-MESTRAN, which allows for improving energy efficiency of a planar single-legged robot over different stride frequencies. The leg in our setup consists of an actuated hip joint and a passive knee joint equipped with the L-MESTRAN. This mechanism is capable of varying stiffness in a large range, maintaining stiffness with almost no energy, and offers a linear joint stiffness. We empirically demonstrate that the L-MESTRAN actuator can increase energy efficiency for hopping locomotion for various stride frequencies. Furthermore, we also demonstrate the capability of the L-MESTRAN to adjust stiffness to improve energy efficiency during locomotion.