NOVEL REACTION CONTROL OF SPACE MANIPULATORS WITH INCREASED ROBUSTNESS AGAINST SINGULARITIES AND PHYSICAL JOINT LIMITS

Redundant space manipulators can perform robotic operations while minimizing the reactions transferred to the base spacecraft. In this way the load on the Attitude Control System can be reduced thus increasing its operating life. In this context, a robust reaction control solution should at least take into account the robot physical joint limits, the robot joint velocity and acceleration limits, and the avoidance of algorithmic and dynamic singularities. In this paper, the least squares reaction control solution recently developed by some of the authors, which can take into account the joint acceleration limits in the realtime solution, has been modified in order to take into account also the joint and the joint velocity limits. In this way a robust solution is obtained, which can take into account the physical limits of the manipulator joints and can be used to avoid the manipulator dynamic and algorithmic singularities, thanks to the imposed change of the history in the joint space. Then, the possibility of time scaling the desired end-effector trajectories, which allows to perform the given task with reduced joint velocities and accelerations has been analyzed. An additional advantage of this method is that reduced joint torques are necessary and, therefore, the error in the control due to joint flexibility is reduced or, from another point of view, lighter robot structures can be used. In addition, the time scaling of the desired end-effector trajectory can be used to perform accelerated tests of the operations of a space robot. Finally, the proposed robust reaction control solution and the method of time scaling have been combined in order to enhance their performance. The proposed robust reaction control method, the time scaling method, and their combination have been analyzed in order to evaluate their pros and cons and have been validated by means of software simulations.