Robot-Assisted Gravity Offloading Testing of Aerospace Structures

Abstract

The demand for testing aerospace structures on Earth before they are launched into space has led to the development of equipment that is able to simulate orbit conditions, namely zero gravity. Several passive solutions have been proposed to perform offloading testing on Earth. However, they present limitations and lack the flexibility normally required by the complexity of the pathways. Active zero gravity emulation systems have been developed to mitigate the difficulties of the passive ones. Moreover, the emergence of robotic arms with the ability to perform complex and easily reprogrammable motion and force-controlled trajectories has opened the possibility of creating robot-based gravity compensation systems. This paper proposes and evaluates a solution for the gravity offloading testing of space devices based on currently available industrial robots. This solution takes advantage of the functionalities of collaborative robots, namely built-in force controllers, together with custom auxiliary subsystems. A setup was arranged to allow the communication between the robot controller and a computer running an internet of things (IoT) platform based on Node-RED so as to connect and control all components of the offloading system. Multiple robot control techniques were designed and tested based on several approaches employing impedance control functionalities and sensing data to create a closed-loop system. The results obtained are within the validation criteria, creating conditions to affirm for the application in question that the gravity compensation was achieved with success using the robot.