Design and control of a robotic wrist with two collocated axes of compliant actuation

It has been a challenge to design robots that possess intrinsic compliance, especially for robots that are required to achieve multi-DOF manipulation. Inspired by human limbs, robotic manipulators with internal compliance can perform high-quality force/torque control and better human-robot interaction. This paper presents a robotic wrist whose size, range, and torque output are comparable to those of a human wrist. To achieve two collocated and perpendicular axes of compliant actuation, two linear 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 both axes without increasing size and complexity. Static and dynamic models of the compliant wrist are developed to analyze the motion. Through experiments of a prototype, the wrist is shown to achieve accurate and fast force/torque control. We expect this novel compliant wrist to serve as an alternative for applications involving human-robot interaction.