The Motion Suspension System – MSS: A Cable-Driven System for On-Ground Tests of Space Robots

Abstract

Robotic manipulators play an important role in space exploration and pave the way for satellite lifetime extensions, orbital asset inspections, and deorbiting. However, space robots are tested in Earth’s gravity although they are designed for zero gravity. The joints are limited in the torque which might be below of what is necessary to move on ground. To address this challenge, the paper presents the Motion Suspension System (MSS), a novel suspension system for on-ground tests of space robots which allows functional tests in the full, three-dimensional workspace. It is based on a cable-driven parallel robot controlled in admittance mode. The mechanical interface and the optimal gravity compensation strategy are optimized for maximum joint torque reduction. The cables are actuated using direct-drive motors. For demonstrating the feasibility of the MSS, we provide experimental results using the compliant CAESAR (CAESAR: Compliant Assistance and Exploration SpAce Robot) space robot arm by the German Aerospace Center (DLR).