OPTIMAL KINEMATIC CONTROL OF REDUNDANT SPACE ROBOTIC SYSTEMS FOR ORBITAL MAINTENANCE: SIMULATED MICROGRAVITY TESTS

摘要

This paper presents the theoretical formulation and the experimental validation of an innovative algorithm for the kinematic inversion of redundant space robotic systems aimed at minimizing the torque transferred to the spacecraft due to the robotic arm movement. The differential kinematics has been formulated at the acceleration level and an additional constraint has been imposed in order to minimize the torque transferred to the spacecraft center of mass. This problem results to be a constrained linear least squares problem and a closed form solution has been proposed for non singular trajectories. An extension of this algorithm has been presented for singular trajectories, or for non singular trajectories in which joint accelerations exceed their limits, in order to limit the joint accelerations under acceptable values. In this case the problem results to be a constrained linear least squares problem with both equality and inequality constraints, and need iterative or recursive calculations to be solved. The proposed algorithm has been experimentally tested using a 3D free-flying robot previously tested in an ESA Parabolic Flight Campaign. In this test campaign the 3D robot has been converted in a 2D robot taking advantage of its modular structure, and it has been suspended by means of air-bearings on a granite plane. In this way it is possible to perform simulated microgravity tests without time constraints. The base of the robot has been fixed on ground by means of a custom design dynamometer, which measures the torque transferred to the ground to be minimized. The experimental results validated the proposed algorithm and confirmed its good performance.