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A Humanoid Robotic Wrist With Two-Dimensional Series Elastic Actuation for Accurate Force/Torque Interaction

It has been a challenge to design humanoid robots that possess intrinsic compliant actuation, especially for robots that are required to be manipulated multidimensionally. Adapting from human limbs, robotic manipulators with internal mechanical compliance can perform high-quality force/torque control and more safely interact with humans. This paper presents a humanoid robotic wrist whose size, range-of-motion, and torque density are comparable to those of a human wrist. To achieve 2-D series elastic actuation, two internal compliant couplers are proposed. Through slider crank and spherical mechanisms, the linear elasticity is converted to rotary elasticity to control the pitch and yaw torques at the same time. This new compact design realizes series elastic actuation in two perpendicular axes without increasing size or complexity relative to that without series elastic actuation. Experiments using a prototype demonstrate that the wrist can achieve accurate and fast force/torque control. We expect this novel compliant wrist to serve as an alternative for applications involving human-robot interaction.