Experimental Verification of Vibration Control of a Flexible Arm for REX-J Robotic Demonstration on JEM

Abstract

This paper discusses the dynamics and control of an extendable arm for tether-based mobile robots on the International Space Station (ISS). The Japan Aerospace Exploration Agency (JAXA) is developing the robotic system which has an extendable arm and several tethers to support extravehicular activities (EVAs) by astronauts. The robotic experiment, called REX-J, will be conducted on the Japanese Experiment Module (JEM) of the ISS in 2012.The robot used in REX-J has an extendable and retractable arm that deploys tethered-grippers and attaches them to holding points. The arm is highly flexible due to its light-weight design and slender structure. This flexibility causes vibrations that make operation inefficient and difficult. To cope with this issue, we propose a dynamic model and a vibration control method for the arm, and verify their effectiveness by numerical simulation and experiment. The dynamic model of the arm is introduced as a planar two link model with a virtual passive joint. The proposed control method is capable of suppressing the vibrations of the arm using the inertial coupling between the arm and the wrist attached to the arm tip. The results of the simulation and experiment show the validity of the proposed model and control method.