Tendon-Driven Finger, Wrist, and Thumb Actuation System

Lyndon B. Johnson Space Center, Houston, Texas

The Robonaut 2 (R2) Dexterous Robot is the result of an effort to build a two-armed, ten-fingered humanoid robot torso capable of assembly work. This invention concerns a multi-fingered hand, and is composed of several parts. One is a tendon-driven, four-link, four-degree-of-freedom robotic thumb. Another is an extrinsic actuation system for tendon-driven fingers. The final part is a wrist mechanism with a large range of motion capable of high strength and speed while maintaining human wrist range of motion. The wrist provides pass-through capability for extrinsic hand actuation.

Improved tendon routing in the robotic thumb provides control of four degrees of freedom with only five tendons. One of the five degrees of freedom of a human thumb is replaced in the robotic thumb with a permanent twist in the shape of a phalange.

For the fingers, this actuation system consists of a motor/ball-screw linear actuator that provides tension to a thin, braided polymer tendon used to actuate finger and thumb mechanisms of a multi-finger hand of a dexterous robotic manipulator. The actuation system is further comprised of a flexible conduit that transmits tendon tension from the actuator to the finger across a multi-axis robotic wrist, through a tension sensor, and to a terminator that anchors the tendon in the robotic finger.

The actuation system includes an actuator assembly, a tendon extending from the actuator assembly, and a tendon terminator mounted to the tendon at an opposing end from the actuator assembly. The actuator assembly is spaced apart from the tendon terminator to remotely actuate movement of the tendon terminator. The humanoid robot includes a robotic hand having at least one finger. The finger actuator assembly is supported by the robot and spaced apart from the robotic hand. A tendon extends from the finger actuator assembly to the finger. The finger actuator assembly is operable to actuate the tendon to move the finger.

For the wrist, the mechanism uses two push-pull links to provide two-degree-offreedom actuation of a robot wrist. Contrary to existing designs, it uses all possible geometric parameters of this kinematic arrangement to obtain a large workspace. An asymmetric arrangement customizes the working region to match the needs of a humanoid robot.

The wrist offers a large workspace with 140° travel in pitch; 60° travel in yaw facilitates dexterity. Open wrist structure allows pass-through of tendon conduits and facilitates a strong grasp in a compact hand by allowing finger actuators to be located in the forearm. Compact design enables working in tight areas, similar to humans. Special ball joint design enables higher wrist actuation forces for tasks requiring strength.

This work was done by Lyndon B. J. Bridgwater, Scott Askew, Myron A. Diftler, Robert Platt, Joshua S. Mehling, and Vienny Nguyen of Johnson Space Center; David M. Reich, Brian Hargrave, Michael C. Valvo, Michael Goza, and Frank N. Permenter of Oceaneering Space Systems; Chris A. Ihrke, Douglas Martin Linn, and Muhammad E. Abdallah of General Motors; and Charles W. Wampler II of GM Global Technology Operations, Inc. For further information, contact the JSC Innovation Partnerships Office at (281) 483-3809. MSC-24734-1/5-1/45-1