CONTROL OF FREE-FLYING UNDERACTUATED SPACE MANIPULATORS TO EQUILIBRIUM MANIFOLDS

Underactuated mechanisms will provide low cost automation and will easily overcome actuator failures. These mechanisms will be particularly useful for space applications because of their reduced mass and lower power consumption. In space underactuation can be effectively introduced in robot manipulators. Such mechanisms will however be difficult to control because of the fewer number of actuators in the system. Of theoretical interest to us, is the problem where the unactuated joints do not have brakes. It is shown that in such a situation it is possible to bring the system to a complete rest and converge the actuated joints to their desired values, provided the system maintains zero momentum and none of the unactuated joints are cyclic coordinates. Our main interest is to converge both the actuated and the unactuated joints to their desired set of values. For this purpose, we assume that the number of actuated joints are more than the number of unactuated joints, and the unactuated joints have brakes. It is shown that if there exists sufficient dynamical coupling between the set of actuated and unactuated joints it is possible to converge all the manipulator joints to their desired values. In the paper, the orientation of the space vehicle is not controlled because this task can be accomplished after the manipulator has been reconfigured, using methods already developed.