Compliant antagonistic joint tuning for gravitational load cancellation and improved efficient mobility

This paper introduces the design tuning of a recently introduced compliant actuation scheme that was developed to provide large energy storage capacity and demonstrate energetic efficient operation. The joint is based on an asymmetric compliant antagonistic actuation scheme where torques from two motors are transmitted to the joint through two elastic elements of different stiffness level and energy storage capacity. The paper presents the method used to tune the joint compliance and shows how this can be used to select the passive elasticity of a single degree of freedom (DOF) hopping leg for improving its energetic efficiency. The design and modeling of the hopping leg are discussed and experimental results are presented to verify the improved efficiency of the leg, particularly the power and torque reduction benefits obtained under static postures or cyclic motions.