Free-flying robot 3d simulator validation by means of air-bearings table 2d tests – test-bed design

Space robotics has nowadays an important role in space operations and is expected to increase its importance in Space Servicing missions and in Extra Vehicular Activities (EVA). Free-flying robots, which are characterized by a floating base controlled by means of thrusters, could be profitably used for surveillance, inspection, and handling operations. In EVA robots can substitute astronauts avoiding them to be injured by charged particles, solar flares or debris. The reproduction of the space microgravity environment for the effective on-ground testing of a 3D free-flying robot before employing it in a space mission is a real challenge. Such a challenging issue can be tackled by means of three kind of test-beds: active or passive tethered suspension systems, parabolic flight tests and underwater environment experiments. In this paper a different approach is proposed. First the robot has to be tested in a planar manoeuvre by means of an air-bearings table test-bed and then the data are going to be used to validate a fully 3D software dynamic simulator. The validation of the dynamic simulator is going to be performed comparing forces and torques transmitted to ground to those which come from the software simulator. The measurements are going to be performed by means of a custom built dynamometer. Other issues which can be assessed by means of the planar tests are the estimate of robot inertial parameters, the accuracy and repeatability of the end effector movements, and the verification of the concept that it is possible to minimize the base reactions by using a redundant manipulator and a special control which takes advantage of it. This paper presents the design of the test-bed necessary to perform the aforementioned tests. The robot taken into consideration is a 3D free-flying robot which has been tested on ESA parabolic flights. This 3D robot has been converted in a 2D robot by simply rotating one link, taking advantage of the robot modularity. An air-bearings table facility is going to be used to perform the planar tests. After that the simulator has been fully validated, simulations of any 3D manoeuvre in a microgravity environment can be performed. The data retrieved from ESA parabolic flight experiments can be compared to those of the validated simulator in order to verify its functionality in a 3D manoeuvre.