Underactuated four-fingered hand with five electro hydrostatic actuators in cluster

Abstract

For heavy duty tasks which are needed in field or rough terrain, we developed a hydrostatically actuated anthropomorphic hand. The hand is specifically designed for the humanoid robot HYDRA, whose 40 joints are driven by back-drivable electro-hydrostatic actuators (EHA). Each designed hand has four fingers with a total of five DOF. Each finger has three joints underactuated by one tendon. Opposition/reposition of the thumb joint is also driven by one tendon. The five tendons are pulled by a miniature linear cluster EHA mounted in the forearm. The cluster EHA consists of a light weight tie-rod cylinder cluster with five pistons, and five low friction trochoid pumps with a crescent separator. Its 300 N nominal tension generates 1.5 Nm joint torque on each of the finger joints. Design of the cylinder and pump, with results of evaluation experiments is shown in this paper. Forearm structure with a mechanism to measure the tendon tension, low friction tendon routing in the forearm, low friction wire guiding link for the wrist, and parallel link wrist driving mechanism with two EHAs are also described.