Analysis of scaled robotic arm manipulators under microgravity conditions

This paper reports the results of a drop-tower experiment series with reduced-scaled robotic arm manipulators, performed under the United Nations Human Space Technology Initiative (UN-HSTI) Drop Tower Experiment Series (DropTES), at the Center for Applied Space Technology and Microgravity (ZARM), in Bremen, Germany. The tested prototype consists of two articulated arm manipulators with three degrees of freedom (DoF), about 30 cm long, installed on a rotating plate in the drop capsule. The forces on the structure, with a predefined movement sequence, were monitored during the fall through four load cell sensors per arm, located on the base, and an inertial measurement unit (IMU) sensor at the end effector of one arm. The results were compared to the case of Earth gravity conditions and correlated with analytical model predictions. A clear behaviour of the forces on load cells with different gravity conditions could be identified, in consistency with the expected behaviour, where the magnitude of oscillations in the microgravity environment are notably lower. Although substantial improvements to the experiment setup could be made in the future. With this experiment was shown that the analysis of electromechanical or robotic structures is feasible with drop tower facilities through a carefully planning of sensor setup and movement sequences.