TRACKING OF A BASE REACTION PROFILE FOR A SPACE MANIPULATOR

A manipulator that is performing a manoeuvre generates reaction forces and torques that dynamically load the supporting base. A special interest in the control of the base reactions arises for robots mounted on a moving base, due to the interaction between the motion of the manipulator and the motion of the base itself, which in many cases needs to be controlled at the same time. In this paper the problem of tracking an arbitrary base reaction profile is considered. The present work gives a contribution to the subject of the kinematic control of spacecraft mounted manipulators and their dynamical effects in terms of reaction forces and torques, and can be used for the development of centralized control systems aimed at controlling multiple robots mounted on the same spacecraft, where a non-operating manipulator can cooperate to compensate the disturbances generated by a second operating robot, together with the reaction control system actuators. The solution to the problem is given in the form of a kinematic law for the joint variables of the manipulator, and the joint acceleration trajectories related to the desired base reaction profile are obtained. Furthermore, the influence of the degree of redundancy of the robot is analyzed, with respect both to the kinematic and the dynamic tasks. The availability of the redundancy can be exploited in order to prescribe a desired trajectory to the end-effector, and specifically the problem of realizing a defined base reaction profile and in the meantime achieve the best approximation of an end-effector trajectory is considered. The proposed solutions are developed in terms of pseudoinverse formulations, and the reaction control problems are set in local optimization form, leading to the definition of constrained least squares problems. The implementation of the proposed kinematic schemes in a robot simulator allowed to test the capabilities of the proposed concepts.