A Novel Robotic Hand-SARAH For Operations on the International Space Station

Abstract

This paper presents the performance capabilities and possible applications of a novel design of a robotic hand for space applications that is self-adaptive and reconfigurable. In particular the Self-Adapting Robotic Auxiliary Hand (SARAH) was developed as a potential tool for Special Purpose Dextrous Manipulator (SPDM) on the International Space Station to support increasingly complex dextrous robotic operations on the International Space Station (ISS). SARAH's simple actuation and ability to grasp a large range of geometrical shapes, makes it an ideal multi-purpose tool used for unstructured and unrehearsed ISS operations. SARAH is being developed as a collaborative effort between MD Robotics Limited and Laval University. It consists of three underactuated fingers mounted on a common structure. The fingers can envelop various shapes including cylindrical and spherical geometries. SARAH has 10 DOF and is actuated only by the two drive systems of the SPDM End Effector or the ORU Tool Change Out Mechanism (OTCM). The key novelty of SARAH's design is that it is a completely self-contained, passive mechanism requiring only the existing SPDM-OTCM drives mechanism to actuate its fingers. The opening/closing of the fingers and the finger orientation are performed by the OTCM-Torque Drive Mechanism, while the switching between the two modes of operations are done by the Advance Mechanism of the OTCM. A reduced size version of SARAH developed for CSA is actuated by only two motors. One of the motors provides the opening/closing of the fingers while the second one is used for the orientation of the fingers. The overall envelope of SARAH is similar to an astronaut glove. However, SARAH's force capabilities are twice as large as applied by an astronaut in any EVA activities. SARAH has three fingers and each of the fingers has three phalanges. The self-adaptability of the hand is obtained using underactuation within and among the fingers of the robotic hand. The underactuation between the phalanges of a finger is obtained by using linkages and springs while the underactuation among the fingers is implemented by a special one-input/three-output differential. This paper presents a number of operational applications of SARAH on ISS. Experimentation results will be presented to illustrate the various application of SARAH. Possible Extra Vehicular Robotics (EVR) operations for SARAH include: SPDM stabilization when operating on the end of the Space Station Remote Manipulator System (SSRMS) in an unplanned environment, thermal blanket manipulation, temporary ORU storage location, auxiliary ORU manipulation. Ideally, this tool would provide increased SPDM functionality for unplanned operations and emergency situations.